Carbon-Based Metal-Free Catalysts E-Book

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 1361

Veröffentlichungsjahr: 2018

Beschreibung

Offering comprehensive coverage of this hot topic, this two-volume handbook and ready reference treats a wide range of important aspects, from synthesis and catalytic properties of carbon materials to their applications as metal-free catalysts in various important reactions and industrial processes.
Following a look at recent advances in the development of carbon materials as carbon-based metal-free catalysts, subsequent sections deal with a mechanistic understanding for the molecular design of efficient carbon-based metal-free catalysts, with a special emphasis on heteroatom-doped carbon nanotubes, graphene, and graphite. Examples of important catalytic processes covered include clean energy conversion and storage, environmental protection, and synthetic chemistry.
With contributions from world-leading scientists, this is an indispensable source of information for academic and industrial researchers in catalysis, green chemistry, electrochemistry, materials science, nanotechnology, energy technology, and chemical engineering, as well as graduates and scientists entering the field.

Leseprobe

Table of Contents

Cover

Preface

Volume I

1 Design Principles for Heteroatom‐Doped Carbon Materials as Metal‐Free Catalysts

1.1 Introduction

1.2 Basic Approaches for Catalyst Design

1.3 Design Principles for Electrocatalysis of Oxygen

1.4 Design Principles for Catalysis of Hydrogen Production

Acknowledgments

References

2 Design of Carbon‐Based Metal‐Free Electrocatalysts

2.1 Introduction

2.2 C‐MFECs for ORR

2.3 C‐MFECs for OER

2.4 C‐MFECs for HER

2.5 Bifunctional ORR/OER Electrocatalysts for Rechargeable Metal–Air Battery

2.6 Bifunctional HER/OER C‐MFECs for Full Water Splitting

2.7 C‐MFECs for CDR

2.8 Carbon‐Based Electrocatalysts for Dye‐Sensitized Solar Cells (DSSCs)

2.9 Conclusions and Perspectives

Acknowledgments

References

3 Defective Carbons for Electrocatalytic Oxygen Reduction

3.1 Introduction

3.2 Defect‐Driven ORR Catalysts

3.3 Summary

References

4 Designing Porous Structures and Active Sites in Carbon‐Based Electrocatalysts

4.1 Introduction

4.2 Porous Carbon as ORR Electrocatalysts

4.3 Porous Carbon for HER Applications

4.4 Summary and Conclusions

Acknowledgments

References

5 Porous Organic Polymers as a Molecular Platform for Designing Porous Carbons

5.1 Introduction

5.2 Porous Carbons Derived from Porous Aromatic Frameworks

5.3 Porous Carbons Derived from Conjugated Microporous Polymers

5.4 Porous Carbons Derived from Hyper‐Cross‐Linked Polymers

5.5 Porous Carbons Derived from Covalent Triazine Frameworks

5.6 Porous Carbons Derived from Covalent Organic Frameworks

5.7 Summary and Perspectives

References

6 Nanocarbons from Synthetic Polymer Precursors and Their Catalytic Properties

6.1 Introduction

6.2 Carbon Catalysts Derived from Non‐templated Synthetic Polymers

6.3 Hard Templating of Polymer‐Derived Carbons

6.4 Soft Templated Carbons

6.5 Templating by Carbon/Polymer Hybrids

6.6 Polymer‐Derived Carbons as Catalysts

6.7 Conclusions and Outlook

Acknowledgments

References

7 Heteroatom‐Doped, Three‐Dimensional, Carbon‐Based Catalysts for Energy Conversion and Storage by Metal‐Free Electrocatalysis

7.1 Introduction

7.2 3D Carbon Catalysts for Oxygen Reduction Reaction (ORR)

7.3 Carbon‐Based 3D Electrocatalysts for Oxygen Evolution Reaction (OER)

7.4 Carbon‐Based 3D Electrocatalysts for Hydrogen Evolutions Reaction (HER)

7.5 Carbon‐Based 3D Electrocatalysts for Carbon Dioxide Reduction Reaction (CO

2

RR)

7.6 Carbon‐Based 3D Electrocatalysts for H

2

O

2

Reduction (HPRR)

7.7 Conclusions and Perspectives

Acknowledgments

References

8 Active Sites in Nitrogen‐Doped Carbon Materials for Oxygen Reduction Reaction

8.1 Introduction

8.2 Debate for the Active Sites (Pyridinic‐N or Graphitic‐N?)

8.3 The Differences Between Pyridinic‐N and Graphitic‐N

8.4 Pyridinic‐N Creates the Active Sites for ORR

8.5 Role of Pyridinic‐N and Conjugation Size

8.6 Effect of the Local Structure Around Pyridinic‐N on ORR

8.7 ORR Selectivity in Acid and Basic Condition by DFT Study

8.8 Perspective and Future Directions for Nitrogen‐Doped Carbon Materials

References

9 Unraveling the Active Site on Metal‐Free, Carbon‐Based Catalysts for Multifunctional Applications

9.1 Introduction

9.2 Electrochemical Reduction Reaction: Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER)

9.3 Electrochemical Oxidation: Oxygen Evolution Reaction (OER)

9.4 Bifunctional ORR and OER Electrocatalyst

9.5 CO

2

Reduction Reaction (CO

2

RR)

9.6 Identification of Possible Active Site by Poisoning

9.7 Summary

References

10 Carbocatalysis: Analyzing the Sources of Organic Transformations

10.1 How to Identify Active Sites?

10.2 Oxygen Atoms in Carbon‐Driving Catalysis

10.3 Carbon–Carbon and Carbon–Nitrogen Coupling Catalyzed by Carbonaceous Materials

10.4 Acidic Sites at Nanocarbons for Carbocatalysis

10.5 Carbocatalysis with Carbon Holes and Edges

10.6 Frustrated Lewis Pairs in Nanocarbon Structures

10.7 Beyond Localized Chemical Functionality as the Active Site: Collective Solid‐State Effects in Catalysis

10.8 The Heterojunction and Dyad Concepts in Catalysis

10.9 Nitrogen, Sulfur, and Boron Doping to Construct Active Sites

10.10 Summary of the Current State of the Art of Carbocatalysis and Future Developments

Acknowledgements

References

Volume II

1 Carbon‐Based, Metal‐Free Electrocatalysts for Renewable Energy Technologies

1.1 Introduction

1.2 Oxygen Reduction Reaction

1.3 Electrochemical Water Splitting (HER and OER)

1.4 Carbon‐Based Electrocatalysts for All‐Vanadium Redox Flow Battery

References

2 Carbon‐Based, Metal‐Free Catalysts for Electrocatalysis of ORR

2.1 Introduction

2.2 Materials and Regulation Strategies

2.3 The Origin of the ORR Activity

2.4 Summary and Perspective

References

3 Hydrothermal Carbon Materials for the Oxygen Reduction Reaction

3.1 Introduction

3.2 Sustainable HTC Catalysts for the Oxygen Reduction Reaction

3.3 Carbon–Carbon Composites Based Electrocatalysts

3.4 Summary and Conclusions

References

4 Carbon‐Based Electrochemical Oxygen Reduction and Hydrogen Evolution Catalysts

4.1 Carbon Materials for Electrochemical Oxygen Reduction Catalysis

4.2 Carbon Materials for the Electrochemical Hydrogen Evolution Reaction

4.3 Conclusion, Summary, and Perspective

Acknowledgment

References

5 Carbon‐Based, Metal‐Free Catalysts for Photocatalysis

5.1 Introduction

5.2 Graphene‐Based, Metal‐Free Photocatalysis

5.3 Carbon‐quantum‐dot‐Based, Metal‐Free Photocatalysis

5.4 Graphitic Carbon‐Nitride‐Based, Metal‐Free Photocatalysis

5.5 Graphene/g‐C

3

N

4

Metal‐Free Catalysts for Photocatalysis

5.6 CQDs/g‐C

3

N

4

Metal‐Free Catalysts for Photocatalysis

5.7 Summary and Outlook

References

6 Metal‐Free Nanoporous Carbons in Photocatalysis

6.1 Introduction

6.2 Semiconductor‐Free Nanoporous Carbons as Photocatalysts

6.3 Pollutant Confinement on the Porosity of the Nanoporous Carbons

6.4 Postulated Mechanisms

6.5 Photocatalytic Cycles

6.6 Summary and Conclusions

Acknowledgments

References

7 Functionalized Graphene‐Based, Metal‐Free Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells

7.1 Introduction

7.2 Carbon Materials as ORR Electrocatalysts

7.3 Structurally Engineered Graphene as Metal‐Free Catalysts for ORR

7.4 Conclusions and Perspectives

Acknowledgements

References

8 Carbon‐Based, Metal‐Free Catalysts for Metal–Air Batteries

8.1 Introduction

8.2 Carbon‐Based, Metal‐Free Cathodes for Li–O

2

Batteries

8.3 Carbon‐Based, Metal‐Free Cathodes for Na–Air Batteries

8.4 Carbon‐Based, Metal‐Free Cathodes for Zn–Air Batteries

8.5 Carbon‐Based, Metal‐Free Cathodes for Other Metal–Air Batteries

8.6 Conclusions and Perspectives

Acknowledgments

References

9 Carbon‐Based, Metal‐Free Catalysts for Chemical Catalysis

9.1 Introduction

9.2 Dehydrogenation

9.3 Oxidation Reactions

9.4 Reduction Reactions

9.5 Carbon–Carbon Coupling

9.6 Perspective and Future Work

References

10 Carbon‐Based, Metal‐Free Catalysts for Chemical Productions

10.1 Introduction

10.2 Active Sites of Carbon‐Based, Metal‐Free Catalysts

10.3 Oxidation Reactions

10.4 Reduction Reactions

10.5 H

2

O

2

Synthesis

10.6 Vinyl Chloride Monomer Synthesis

10.7 Perspectives

References

11 Heteroatom‐Doped, Carbon‐Supported Metal Catalysts for Electrochemical Energy Conversions

11.1 Introduction

11.2 N‐Doped, Carbon‐Supported Metal Catalysts

11.3 B‐Doped, Carbon‐Supported Metal Catalysts

11.4 Conclusions and Perspective

References

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 Charge transfer, distance, and overpotential of typical carbon nanostructures [6, 8, 28].

Chapter 4

Table 4.1 ORR activities of various metal‐free porous carbons in 0.1 M KOH electrolytes.

Table 4.2 Elemental contents and pore surface areas of different electrocatalysts [44].

Table 4.3 Elemental contents and pore surface areas of various CNFe and CNCo catalysts [46].

Chapter 6

Table 6.1 Examples of precursors used for producing carbons with corresponding stabilization methods.

Chapter 7

Table 7.1 Nitrogen‐ or sulfur‐doped 3D carbon catalysts for oxygen reduction reaction (ORR).

Table 7.2 Co‐doped and tri‐doped carbon‐based 3D catalysts for oxygen reduction reaction.

Table 7.3 Heteroatom‐doped, carbon‐based 3D catalysts for oxygen evolution reaction (OER).

Table 7.4 Heteroatom‐doped, carbon‐based 3D catalysts for bifunctional activities toward oxygen reduction (ORR) and evolution reaction (OER).

Table 7.5 Heteroatom‐doped, carbon‐based 3D catalysts for hydrogen evolution reaction (HER).

Table 7.6 Heteroatom‐doped, carbon‐based 3D catalysts for trifunctional activities toward oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution reaction (HER).

Table 7.7 The electrode potentials for electrochemical CO

2

reduction half reactions in aqueous solution at standard experimental conditions.

Chapter 13

Table 3.1 Summary of best performing sample from each presented reference in Section 3.2, all potentials mentioned are versus Ag/AgCl.

Table 3.2 Summary of best performing sample from each presented reference in Section 3.3, all potentials mentioned are versus Ag/AgCl.

Chapter 14

Table 4.1 Summary of the properties of different carbon blacks.

Chapter 16

Table 6.1 Main physicochemical characteristics of the selected nanoporous carbons obtained from gas adsorption data (i.e. N

2

adsorption/desorption isotherms at −196 °C), elemental analysis (on dry ash‐free basis), and pH of the point of zero charge.

Chapter 18

Table 8.1 Summary of carbon material performance in Li/Na–air batteries.

Table 8.2 Summary of carbon materials performance in Zn–air and Al–air batteries.

Chapter 20

Table 10.1 Conversion of benzylic and aliphatic alcohols to their respective ketones or aldehyde products and conversion of aryl and aliphatic alkynes to their respective methyl ketone products by graphene oxide catalysts.

List of Illustrations

Chapter 1

Figure 1.1 Metal‐free, carbon‐based nanomaterials with the catalytic activities to ORR, OER, or HER. (a) Defects. (b) Heteroatom doping. (c) Adsorptions. (d) N‐doped graphene carbon nanotube hybrid. (e) Adsorption of ammonia borane at N‐doped carbon nanotube. (f) Adsorption of oxygen molecule at N‐doped carbon nanotube.

Figure 1.2 Electron transfer on different types of defective graphene: (a) Mulliken charge population on heteroatom‐doped graphene. (b) Spatial distribution of charge density on graphene with line defect‐558 grain boundary. (c) Electron transfer between the adsorbed organic molecule and graphene.

Figure 1.3 Flow chart for rational design of new catalysts using simulation method.

Figure 1.4 ORR and OER elementary reaction pathways in both acidic and alkaline media.

Figure 1.5 (a) Armchair and zigzag N‐doped graphene structures. The numbers denote substitutional sites and reaction sites. Symbols a, b, c, d, e, and f denote reaction sites apart from 1, 2, 3, 4, 5, and 6; (b) adsorption energies of OOH* versus adsorption energies of OH*; and (c) adsorption energies of OH* versus adsorption energies of O* on different sites of armchair and zigzag graphene nanoribbons.

Figure 1.6 (a) Schematic of the X‐doped graphene nanoribbons, showing the possible positions of dopants. (b) The lower limit of OER/ORR overpotentials for X‐doped graphene structures versus the descriptor

Φ

. (c) Measured limiting current density from the LSV curves, normalized by Pt/C electrode current density at 0.5 V (SCE, saturated calomel electrode) under the same conditions in the same experiment and the predictions.

Figure 1.7 (a) Schematic of the N–X co‐doped graphene nanoribbons (X = B, P, S, and Cl), showing the possible positions of dopants. (b) The lower limit of OER/ORR overpotentials for N‐ and X‐doped and N–X co‐doped graphene structures versus the descriptor Φ. (c) Average measured limiting current density from the linear scan voltammogram (LSV) curves, normalized by N‐doped carbon electrode current density under the same conditions, as a function of the descriptor Φ for N–B, N–P, N–F, N–S, and N–Cl co‐doped graphene, and for N–B, N–P, N–Si, and N–S co‐doped CNTs.

Figure 1.8 Differential charge density distributions (between doped and undoped graphene) of (a) boron‐, (b) nitrogen‐, and (c) fluorine‐doped graphene sheets. The active sites with the minimum overpotential are marked with values. Light and dark gray indicate the positive and negative values of electron quantities, respectively. The isosurface value is set to 0.0015. Black and white balls refer to carbon and hydrogen atoms, respectively.

Figure 1.9 Perfect and defective graphene clusters. (a) Perfect graphene cluster, (b) Stone–Wales defect (SW), (c) single vacancy (SV), (d) double vacancies (DV), (e) edge defect with pentagon ring at zigzag edge (PZ), octagon and fused pentagon carbon rings line defect with (f) odd number of octagon rings (GLD‐558‐01) and (g) even number of octagon rings (GLD‐558‐02), and pentagon–heptagon pairs line defects with (h) odd number of heptagon rings (GLD‐57‐01) and (i) even number of heptagon rings (GLD‐57‐02). The larger gray and smaller white balls denote carbon and hydrogen atoms, respectively.

Figure 1.10 (a) Configurations of TCNE‐adsorbed carbon nanoribbons without intermediate adsorption and with intermediates of pristine graphene. Green and blue atoms indicate carbon and nitrogen atoms of the TCNE molecules. Differential charge density distributions of TCNE‐attached graphene sheets with (b) defective armchair edge (top view) and (c) defective armchair edge (side view), Volcano plots of (d)

η

OER

versus , and (e)

η

ORR

versus , including TCNE‐absorbed defective and perfect graphene nanoribbons. For comparison, the data for N‐, P‐, and S‐doped graphene nanoribbons are also plotted in the graph.

Figure 1.11 Reaction mechanism for HER in (a) Volmer–Heyrovsky and (b) Volmer–Tafel of C

3

N

4

at nitrogen‐doped graphene. The activation barriers were represented as dashed lines for each reaction steps.

Figure 1.12 (a) Free energy diagram for the HER following the Volmer–Heyrovsky pathway and (b) the Volmer–Tafel pathway on various graphene models. (c) Tafel slopes obtained from theoretical computation (filled symbols) and experimental measurement (open symbols) on various graphene models/samples.

Figure 1.13 (a) Schematic summary of the heteroatom‐doping configurations: pr‐N, py‐N, g‐N, N‐O, B‐2C‐O, B‐3C, B‐C‐2O, P‐3C(‐O), and P‐2C(‐2O) (top row, from left to right); th‐S, S‐2O, py‐O, C–O–C, C–OH, C=O, g‐C, z‐C, and a‐C (bottom row, from left to right). (b) The computed lowest Δ

G

H*

for different models. The Δ

G

H*

values on graphitic-type doping models is labeled by solid bars, whereas those on edge doping models are labeled by shaded bars (except for th‐S, which is shown by shaded bars because the inability to construct a graphitic doping model).

Figure 1.14 (a) Six various nonmetallic heteroatoms of NBO population in graphene temple. gN and pN represent graphitic and pyridinic type of N, respectively. Inset figure shows that site 1 is edge, site 2 is center in‐plane sites, and site 3 is out‐of‐plane site in graphene. (b) The free energy diagram (Δ

G

H*

) at the equilibrium potential (

U

RHE

 = 0 V) in HER for whole possible N‐ or P‐doped graphene models. (c) Linear relationship between

E

diff

and Δ

G

H*

for various models.

Figure 1.15 DFT calculation of C

3

N

4

@NG as a HER catalyst. (a) Band structure of pure g‐C3N4 (left side) and C

3

N

4

@NG hybrid (right side). (b) Interfacial electron transfer in C

3

N

4

@NG. Yellow and cyan isosurfaces represent electron accumulation and electron depletion; the isosurface value is 0.005eÅ3. (c) The projected density of states (PDOS) on pure g‐C

3

N

4

(top‐blue) and C

3

N

4

@NG hybrid (down‐red). (d) The free energy diagram of HER in equilibrium potential for comparison of three various catalysts with Pt. (e) The free energy diagram for hydrogen evolution on g‐C

3

N

4

under coverages of 1/3 and 2/3. Atom color code: carbon (gray), nitrogen (blue), and hydrogen (white). The coverages are labeled by

θ

.

Figure 1.16 Volcano plot between

i

0

/

sitetheory

and Δ

G

H* with charge‐transfer coefficient

α

 = 0.125 (black solid line). The hollow symbols represent

i

0

/

siteexp

obtained from Tafel plots and DFT‐derived Δ

G

H*

for each graphene sample/model.

Chapter 2

Figure 2.1 (a) SEM and (b) TEM images of the vertically aligned nitrogen‐containing carbon nanotubes (VA‐NCNTs). (c) Liner sweep voltammograms at Pt‐C/GC (1), VA‐CCNT/GC (2), and VA‐NCNT/GC (3) electrodes in 0.1 M air‐saturated KOH solution. (d) Calculated charge density distribution for the NCNTs. (e) Schematic representations of possible adsorption modes of an oxygen molecule at the CCNTs (top) and NCNTs (bottom). CCNT represents nitrogen‐free carbon nanotubes; GC represents glassy carbon.

Figure 2.2 Schematic diagrams for preparation of N‐doped graphene with different N‐binding configurations.

Figure 2.3 Schematic diagrams for cracking of graphite by ball milling in the presence of corresponding gases and subsequently exposure to air moisture to result in the formation of edge‐selectively functionalized graphene nanoplatelets (EFGnPs).

Figure 2.4 (a) Oxygen evolution activities of the various electrodes in 0.1 M KOH electrolyte. (b) Relationship between the different elemental contents and OER activities of the N/C electrocatalyst.

Figure 2.5 Schematic diagram of surface‐oxidized CNTs and energy profiles of the four‐electron water oxidation mechanism. Water oxidation on the pre‐oxidized graphene cluster models with (a) both lactone and ketone groups, and (b and c) only ketone groups.

Figure 2.6 (a) Schematic diagram of g‐C

3

N

4

nanoribbon‐graphene (g‐C

3

N

4

nanoribbon‐G). (b) HER activities of g‐C

3

N

4

nanoribbon‐G compared with other catalysts. (c) The HER current density at 10 mA cm

−2

versus overpotential for various catalysts.

Figure 2.7 (a) Schematic illustration of the preparation process for the N‐ and P‐co‐doped porous carbon foams (NPMC). (b) Discharge/charge cycling curves of two‐electrode rechargeable Zn–air batteries by using the NPMC‐1000 air electrode. (c) Schematic diagrams of the basic configuration of a three‐electrode Zn–air battery by coupling the Zn electrode with two air electrodes to separate ORR and OER. (d) Charge and discharge polarization curves of three‐electrode Zn–air batteries. (e) Discharge/charge cycling curves of three‐electrode rechargeable Zn–air batteries by using the NPMC‐1000 air electrode.

Figure 2.8 (a) Free energy diagram of electrochemical reduction of CO

2

to CO on N‐doped graphene. (b) Schematic diagram of N configuration and CO

2

reduction pathway.

Figure 2.9 (a) Schematic diagram of EMIM‐carbon fiber for CO

2

reduction. (b) Schematic diagram of proposed mechanism for CO

2

reduction at PEI‐functionalized, N‐doped carbon nanomaterials.

Chapter 3

Figure 3.1 (a) Pictorial representation of the G585 defect in graphene and (b) calculated free energy diagram of perfect monolayer graphene (G), N‐doped graphene (N‐G), graphene with G585 defect (G585), and an ideal catalyst (Ideal) for the ORR at the equilibrium potentials.

Figure 3.2 (a, b) Defective graphene cluster with pentagon ring at the zigzag edge (PZ) and the corresponding calculated reaction free energy diagram for the four‐electron transfer ORR process. (c, d) Defective graphene cluster with odd number of octagon rings and fused pentagon rings line defect (GLD‐558‐01) and the corresponding calculated reaction free energy diagram for the four‐electron transfer ORR process.

Figure 3.3 (a) A schematic diagram showing the synthesis of DG and (b)

high‐angle annular dark‐field

(

HAADF

) image of DG. Hexagons, pentagons, heptagons, and octagons were labeled in orange, green, blue, and red, respectively; (c) ORR performance evaluations of the prepared samples under an oxygen‐saturated 0.1 M KOH solution; (d) calculated energy profiles for the ORR pathway on defective graphene in alkaline solution; (e) edge pentagon; (f) 5‐8‐5 defect; and (g) 7‐55‐7 defect.

Figure 3.4 (a) Raman spectra of the prepared samples H‐AC, N‐AC, and D‐AC and (b)

linear sweep voltammetry

(

LSV

) curves of the H‐AC, N‐AC, D‐AC, H‐AC‐1050, and Pt/C measured at the rotation speed of 1600 rpm in O

2

‐saturated 0.1 M KOH solution; (c) amperometric

i

–

t

curves of the D‐AC and Pt/C; and (d) methanol tolerance test for D‐AC.

Figure 3.5 (a) Schematic structural characters of the carbon nanocages. I, II, and III represent three typical defective locations (the corner, the broken fringe, and the hole, respectively); (b) Raman spectra of the prepared samples; (c) LSV curves of CNC700‐, CNC800‐, and CNC900‐tested in O

2

‐saturated 0.1 M KOH solution with the rotating speed of 2500 rpm; and (d) free energy diagrams derived from the DFT calculations for ORR activity of different defects.

Figure 3.6 (a) Raman mapping of the D band of the defective graphene patterns; (b) SECM images of the same defective graphene patterns with a tip potential of 0.4 V and a substrate potential of 0.11 V. The tip–substrate distance was kept constant at 8 μm (

d

/

a

 = 0.67); (c) SECM approach curves obtained on each defective graphene pattern, with a tip potential of 0.4 V and a substrate potential of 0.18 V. The microscopic model in different defect density ranges: (d) low defect density with

L

D

 > 6 nm; (e) moderate defect density with 2 nm ≤ 

L

D

 ≤ 6 nm; and (f) high defect density with

L

D

 < 2 nm. The area in red is the structurally disordered area with a radius of 1 nm, and the area in yellow is the electronically activated but structurally preserved area (1 nm < 

r

 < 3 nm). (g) The standard HET rate constant

k

0

as a function of defect density

n

D

(cm

−2

). (h) The mean distance between defects

L

D

(nm). The dashed lines in (g) and (h) are a guide for the eye only.

Chapter 4

Figure 4.1 (a) Synthesis procedure of the NOMGAs; (b)

rotating disk electrode

(

RDE

) polarization plots of electrocatalysts at the rotation rate of 1600 rpm; and (c) kinetics‐limiting current density (

J

k

) at −0.35 V and the electron transfer number of the electrocatalysts.

Figure 4.2 (a) High‐resolution XPS spectra of N 1s in model catalysts and (b) ORR polarization plots of model electrocatalysts. Nitrogen contents of the model catalysts are shown as an inset in (b).

Figure 4.3 (a) Preparation procedure of the N, P‐co‐doped porous carbon; (b) atomic contents of pyridinic‐N, pyrrolic‐N, graphitic‐N, and oxidized pyridinic nitrogen in various porous carbons; and (c) polarization curves of the electrocatalysts in O

2

‐saturated 0.1 M KOH electrolytes.

Figure 4.4 (a, d) TEM images of nitrogen‐doped carbon nanosheets and carbon nanospheres with a pore size of ∼22 nm, respectively; (b, e) pore size distribution of nitrogen‐doped carbon nanosheets and carbon nanospheres, respectively; and (c, f) polarization curves of electrocatalysts in 0.1 M KOH aqueous solution.

Figure 4.5 Synthesis procedure of meso/micro‐P

o

PD electrocatalyst; (a) polymerization of

o

PD in the presence of colloidal silica; (b) calcination of P

o

PD/SiO

2

composite in N

2

atmosphere and then etching of the SiO

2

template; and (c) activation of the meso‐P

o

PD electrocatalyst.

Figure 4.6 TEM images of (a) meso‐P

o

PD and (b) meso/micro‐P

o

PD; (c) N

2

adsorption/desorption isotherms; (d) related pore size distribution plots of meso‐P

o

PD and meso/micro‐P

o

PD; (e) ORR polarization plots and H

2

O

2

yield plots of various electrocatalysts. Scale bars, 30 nm.

Figure 4.7 (a) Polarization plots of fuel cells using various catalysts as the cathode: (i) PANI‐C, (ii) PANI‐Co‐C, (iii) PANI‐FeCo‐C(1), (iv) PANI‐FeCo‐C(2), and (v) PANI‐Fe‐C and (b) long‐term durability evaluation of the PANI‐FeCo‐C(1) electrocatalyst at a cell voltage of 0.40 V.

Figure 4.8 (a) Polarization plots of

membrane electrode assemblies

(

MEA

s) using 1/20/80‐Z8‐1050 °C‐15 min (stars), 1/50/50‐BP‐1050 °C‐60 min (circles), and Pt‐based (squares) as the cathode, respectively and (b) corresponding power density plots of electrocatalysts.

Figure 4.9 TEM and SEM images of achieved CNCo electrocatalysts: (a) VB12/colloidal silica; (b) VB12/SBA‐15; and (c) VB12/MMT. Insets in (a−c) are the structural illustrations of the electrocatalysts; (d−f) N

2

sorption isotherms of CNCo electrocatalysts; (g) ORR polarization curves of the CNCo electrocatalysts; (h) H

2

O

2

yield of the CNCo electrocatalysts and Pt/C catalyst; and (i) ORR polarization curves of VB12/colloidal silica before and after 10 000 potential cycles in O

2

‐saturated electrolyte. Insets show the corresponding pore size distribution [46].

Figure 4.10 (a) Preparation process of nanoporous NS‐doped graphene; (b) polarization plots of various electrocatalysts; and (c) calculated HER free energy diagram of a Pt catalyst, pyridinic (pN‐G), graphitic (gN‐G), sulfur‐doped (S‐G), and nitrogen/sulfur‐co‐doped (NS‐G) graphene catalysts.

Figure 4.11 (a) Free energy diagram of the pure, single‐, and dual‐doped graphene models and (b) polarization plots of different graphene‐based electrocatalysts in 0.5 M H

2

SO

4

aqueous solution. Source: Jiao et al. 2016 [49]. Reproduced with permission from Springer Nature.

Figure 4.12 (a) polarization curves of different electrocatalysts in 0.5 M H

2

SO

4

solution; (b) polarization plots of the CoNPs/CoN

x

/C and CoN

x

/C electrocatalysts before and after acid leaching; (c) polarization curves of the CoN

x

/C before and after the addition of KSCN; and (d) comparison of the TOF of CoN

x

/C with reported electrocatalysts. Insets in (b) are TEM images of the CoNPs/CoN

x

/C and CoN

x

/C after acid leaching.

Figure 4.13 (a) Preparation process of the Co/N‐doped carbon; (b) polarization plots of PPANI750, PANICo550‐950A, and Pt/C in 0.5 M H

2

SO

4

solution; and (c) free energy diagram of the electrocatalysts. Inset shows the model structure of the Co‐3C1N catalyst.

Chapter 5

Figure 5.1 Schematic of the synthesis of PAF‐1 and the pyrolysis of PAF‐1 at different temperatures into porous carbons PAF‐1‐350, PAF‐1‐380, PAF‐1‐400, and PAF‐1‐450.

Figure 5.2 Schematic of the synthesis of PAF‐Carbons and N‐doping PAF‐Carbon from PAF‐1 at different temperatures.

Figure 5.3 Schematic of the synthesis of N‐rich COP precursors using nickel‐catalyzed Yamamoto‐type Ullmann cross‐coupling reaction.

Figure 5.4 The incorporation of non‐precious metals (Fe, Co, and Mn) into C‐COP. Owing to the poor solubility of the synthesized COP materials in most common solvents, it is difficult to introduce metals into the COP‐P.

Figure 5.5 (a) Schematic of the synthesis of CoP‐CMP by Yamamoto coupling reaction and (b) schematic of the synthesis of 3D CoPOP.

Figure 5.6 Schematic diagram of the synthesis of PCN‐MM from TIPP‐M and TEPP‐M monomers (M = Fe and Co).

Figure 5.7 Schematic of the synthesis and structure of Fe/Co‐CMP via Suzuki polycondensation.

Figure 5.8 Schematic of GMPs and related graphene‐based microporous carbons (GMCs).

Figure 5.9 Schematic of the synthesis of the B,N‐contained CMP that is pyrolyzed into dimension‐controlled carbons.

Figure 5.10 Schematic of the synthesis of M‐CMPs‐

T

from MoS

2

and N‐rich CMPs.

Figure 5.11 Schematic of the synthesis of polycarbazole networks and their derived carbons.

Figure 5.12 Schematic of the synthesis of HCPs from benzene, thiophene, and pyrrole.

Figure 5.13 Schematic of the synthesis of TNNs‐T using ionothermal method (

T

is the reaction temperatures of 400, 450, 500, 550, 600, 650, and 700 °C).

Figure 5.14 Schematic of the synthesis of heteroatom‐doped carbons from 2D CTF.

Figure 5.15 Schematic of the synthesis of G‐PPFs from RGO.

Figure 5.16 Schematic of the synthesis of (a) Co‐COF and (b) 2DPPV.

Figure 5.17 Schematic of the synthesis of B‐doped carbons upon pyrolysis of COF‐5.

Figure 5.18 Schematic of synthesis of N‐doped graphene from RT‐COF‐1 by metal‐functionalization approach.

Figure 5.19 Schematic of (a) synthesis of LZU‐1 and (b) the fabrication of Pd@NHCS.

Chapter 6

Figure 6.1 Organic synthesis of graphene nanoribbons by Suzuki–Miyaura coupling polymerization, followed by the Scholl reaction. The resulting nanoribbons have precisely defined widths because of the use of organic synthesis approach.

Figure 6.2 Carbon fibers comprised graphitic stacks oriented mostly in the direction of the fiber axis. With an increased orientation being more desirable, a well‐chosen precursor, such as PAN , and polymer fiber processing can help produce more aligned, higher quality carbon fiber.

Figure 6.3 Geochemical degradation of polymeric biomaterial forms new bonds, resulting in char, or cleaves bonds via depolymerization or fragmentation (a). The heavier, insoluble portion that results from this initial degradation process can be characterized as labile, inert, or refractory depending on its composition and final state (b).

Figure 6.4 Biomass conversion into products including carbons, fuels, and energy, based on the conversion method chosen (a), and fraction of products based on the conversion method (b).

Figure 6.5 Steps in the graphitization for lignin and cellulose. (a) Lignin's aromatic rings cross‐link through substituents intermolecularly consolidating into a small molecule, like methanol. (b) Cellulose undergoes a similar process, but often starts with desaturation of the carbons.

Figure 6.6 Oxidative stabilization of PAN self‐cross‐links the polymer, after which the formed ladder polymers under pyrolytic conditions fuse together through a variety of eliminations [7c].

Figure 6.7 Methods for infiltration of a polymer into a hard template. Limitations for each method are based on template feature sizes, tortuosity, and solution/melt properties. This can also apply to monomer infiltration but is generally easier.

Figure 6.8 TEM images taken at different angles of carbon templated by SBA‐15. The carbon was synthesized by grafting polyacrylonitrile from SBA‐15 using surface‐initiated controlled polymerization, followed by thermal treatment.

Figure 6.9 Poly(4‐cyanostyrene)‐grafted silica nanoparticles using SI‐ATRP. Grafting the polymer from silica nanoparticles provides control over the resulting structure based on the diameter of the grafted nanoparticles.

Figure 6.10 Template confinement by anodic aluminum oxide (a) resulted in increased crystallinity for

carbon nitride nanorod

s (

CNR

s) as compared with its bulk g‐C

3

N

4

counterpart, as shown by

X‐ray diffraction

(

XRD

) (b).

Figure 6.11 PAN grafted from silica nanoparticles to produce carbons with precisely sized mesopores (a). This method is directly comparable with synthesizing carbon from PAN grafted from cross‐linked PMMA spheres (b).

Figure 6.12 Soft templating induces structure dynamically and thereby can be used to create a feature gradient. In this example, a concentration gradient was induced by evaporation of the solvent, which was then converted into a structural gradient by submerging in deionized water.

Figure 6.13 Multi‐beam interference lithography was used to 3D pattern a SU8 photoresist. The large surface area polymer pattern without a support or sufficient cross‐linking can collapse during the thermal treatment necessary to produce carbons. Liquid immersion reduces the surface energy of the polymer, so the resulting heat‐treated polymer does not collapse.

Figure 6.14

Atomic force microscopy

(

AFM

) images of (AN)

45

‐(BA)

530

‐(AN)

45

ultrathin films spin‐coated onto silicon at different stages of treatment, all showing retained morphology: (a) thermal annealing under vacuum, (b) pyrolysis at 600 °C, and (c) pyrolysis at 1200 °C.

Figure 6.15 The morphology of carbon produced from block copolymer templating is directly resulted from microphase separation between the blocks. This method is a conceptually simple way to produce carbons with structures varying from spheres to sheets.

Figure 6.16 Block copolymers can be used to drive the formation of a nanostructure without being the source of carbon themselves. The carbon precursor, dopamine, preferentially occupies space within the PEO phase, resulting in a carbon with pores produced by degradation of the PS phase.

Figure 6.17 By synthesizing BCPs with longer or shorter overall DPs (while maintaining block ratios), morphology remains consistent but produces different feature sizes that translate to pore sizes of resulting carbons. At lower DP, reduced strength in microphase separation causes less sharp boundaries between block phases, rendering some carbon pores inaccessible due to collapse.

Figure 6.18 Surfaces of PAN‐

b

‐PBA films of varying thickness were measured by AFM before and after thermal stabilization/pyrolysis and image‐processed to group interconnected segments. The AFM images and an overlay of interconnected domains differentiated by color are shown to the left for the thickest and thinnest films. The pixel sizes of the largest interconnected segment for all BCPs and subsequently pyrolyzed films are shown to the right.

Figure 6.19 Bottlebrush polymers can be used to form carbons from either an interior carbon source block (a) or exterior (b). The bottlebrush architecture causes strong steric repulsion, preventing partial miscibility that can limit the formation of high surface area carbons from low‐DP BCPs.

Figure 6.20 A block copolymer and hydrophobic small‐molecule carbon source in water will spontaneously form vesicles with the carbon source occupying space within the more hydrophobic polymer block. Wall thickness can be tuned by changing the length of blocks within the BCP, and diameter can be modified by changing concentrations.

Figure 6.21 Water‐in‐oil emulsion with a hydrophobic carbon source can be used to produce spherical polymeric precursors, and by controlling the amount of emulsifier compared with precursor, size can be controlled.

Figure 6.22 Pluronic P123 (PEG‐

b

‐PPG‐

b

‐PEG) (

poly(ethylene glycol)

,

PEG

;

poly(propylene glycol)

,

PPG

) can be used to stabilize microemulsion polymerization to produce nanoparticles. The nanoparticles are then hyper‐cross‐linked to form a 3D network that is maintained through pyrolysis, resulting in a carbon aerogel.

Figure 6.23 Carbons produced from polyHIPEs can exhibit very open pore structures with as much as 91% open volume. The extent of hyper‐cross‐linking can be used to further control the resulting carbon, depending on the desired final structure. (A) A scheme showing polyHIPEs (a), which is hyper‐cross‐linked (b), or simply pyrolyzed (c). Pyrolyzing hyper‐cross‐linked polyHIPEs (d) will contain granularity that is not present when not hyper‐cross‐linked. (B) Experimental SEM of polyHIPEs with letters corresponding to the state described by the scheme.

Figure 6.24 Polystyrene grafted from carbon nanotubes by SI‐ATRP was hyper‐cross‐linked and pyrolyzed to produce a carbon with a mesoporosity arising from the organization of nanotubes, and with microporosity from the cross‐linked PS.

Figure 6.25 The effect of pyrolysis temperature on N:C ratio and conductivity for carbons from PAN‐

b

‐PBA (a). The nanostructure of the resulting carbons remained consistent across pyrolysis temperatures, as shown by radial profiles of azimuthally averaged small‐angle X‐ray‐scattering patterns (b). Tested as binder‐free catalysts for ORR, all carbons showed activity, but those produced by pyrolysis at 800 °C exhibited optimal performance.

Figure 6.26 A plot showing the effect of catalyst loading on onset/half‐wave overpotential (

η

os

:

η

hw

) for

copolymer‐templated nitrogen‐enriched carbon

s (

CTNC

s) pyrolyzed at 700 °C (a). Numbers below individual points correspond to measured average number of electrons transferred. Comparison of estimated film densities with bulk CTNCs (b), indicating low loadings resulted in collapse of nanostructure.

Figure 6.27 Hydrogen evolution by a metal‐free catalyst was dramatically enhanced by the use of a Pt counter electrode (a). X‐ray photoelectron spectroscopy revealed a shift in the distribution of N‐binding energies, whose density functional theory confirmed to be due to Pt coordinating to pyridinic nitrogen in the carbon (b).

Chapter 7

Figure 7.1 The polarization curves of various electrochemical reactions.

Figure 7.2 Schematic plots for (a) Butler–Volmer equation and (b) Tafel plots with Tafel slopes and exchange current density.

Figure 7.3 Evolution of carbon‐based, metal‐free catalysts since its discovery in 2009.

Figure 7.4 (a) Schematic and experimentally visualized structural details of different carbon materials, STM image of C

60

. (b) SWCNT. (c) Graphene. . (d) SEM image of 3D CNT‐graphene architectures obtained by intercalated growth of VACNTs into thermally expanded HOPG.

Figure 7.5 (a) Illustration of the synthetic route for N‐GNRs‐A. (b) Photographs of as‐prepared 3D graphene nanoribbon aerogels derived from Py‐free (left) and 5 vol.% Py‐containing (middle) GONRs suspension (10 mg ml

−1

) after hydrothermal treatment. (c) A monolith of ultra‐light N‐GNRs‐A standing on a dandelion. (d) Photograph of N‐GNRs‐A in a hot flame of an alcohol burner. (e) XRD patterns of (1) pristine MWCNTs, (2) GONRs, (3) GNRs‐A, and (4) N‐GNRs‐A. (f) SEM image of the resulting N‐GNRs‐A. (g, h) Typical TEM and high‐resolution TEM images of the as‐prepared N‐GNRs‐A. Inset in (g) shows three interwoven curly nanoribbons. Inset in (h) is the selected area electron diffraction (SAED) pattern of the aerogel.

Figure 7.6 Synthesis and morphologies of N‐CNF aerogels. (a) Schematic diagram of the synthetic steps. (1) A large‐sized BC pellicle (200 × 230 × 5 mm

3

, water content ∼99 vol.%) produced by an industry‐scaled microbial fermentation. (2) Photograph, scanning electron microscopy (SEM) image, and schematic illustration of BC aerogels after cutting and freeze‐drying of wet BC pellicles. (3) Black N‐CNF aerogels were obtained finally by heat treatments of BC aerogels two times under N

2

and NH

3

atmospheres, respectively. The fibrous networks survived after pyrolysis and various types of nitrogen were doped into carbon matrix successfully after NH

3

treatment. (b, c) SEM and TEM images of N‐CNF aerogels, respectively, showing the nanofibrous network structure. (d) HRTEM image of an individual N‐CNF. (e) ORR polarization plots of CNF aerogel, N‐CNF aerogel, and Pt/C catalyst. (f) ORR polarization plots for N‐CNF aerogel in O

2

‐saturated 0.1 M KOH with different speeds. (g) Negative shift of the half‐wave potential (

E

1/2

) of N‐CNF aerogel and Pt/C catalyst with the number of potential cycles under O

2

.

Figure 7.7 (a) The route for stepwise structural evolution from raw materials to LHNHPC. Electrocatalytic ORR results in O

2

‐saturated 0.1 mol l

−1

KOH: (a) RDE polarization curves of LNHPC, LHNHPC, and Pt/C at 10 mV s

−1

and 1600 rpm; (b) RDE polarization curves of LHNHPC at different rotating speeds; (c) The Koutecky–Levich plots for LHNHPC obtained from the RDE results.

Figure 7.8 (a) Schematic illustration of the preparation of N/S‐hcs, (b) LSVs of N,S‐hcs treated at various temperatures, and (c) various samples at a rotation speed of 1600 rpm and a scan rate of 5 mV s

−1

. (d) LSVs of N,S‐hcs‐900 °C at different rotating speeds and (e) the Koutecky–Levich plots at different potentials.

Figure 7.9 Illustration of the growth mechanism of 3D‐HPG: (a) phase evolution process and (b) illustration of gas exfoliation and K intercalation.

Figure 7.10 (a) Schematic illustration of direct growth of N‐ and P‐doped carbon nanofibers on carbon paper, (b,c) SEM, and (d,e) TEM images of NPC‐CP, inset in panel (d) shows the corresponding SAED pattern. (f) OER curves and (g) Tafel plots of NPC‐CP, NC‐CP, IrO

2

, and pristine CP in O

2

‐satuated 1 M KOH (scan rate: 2 mV s

−1

). (h) Calculated free energy diagrams for the OER pathway on N,P‐doped carbon at three different potentials: 0 V, 0.402 V (equilibrium potential), and 0.907 V. (i) Volcano plots of OER overpotential versus the difference between the adsorption energy of O* and OH*, that is Δ

G

(O*) − Δ

G

(OH*), for the simulated carbon structures.

Figure 7.11 (a) Schematic representation of the thermal conversion of [Ni2(EDTA)] into 3D mesoporous graphene, 3D mesoG. The processes indicated by red arrows occurred during the one‐step heat treatment of [Ni

2

(EDTA)]. (b) Electrocatalytic polarization curves showing ORR and OER activities of 3D mesoG, Ir/C, and Pt/C catalysts. (c) Bar graph showing the potential differences to drive 10 mA cm

−2

for the OER and 3 mA cm

−2

for the ORR. (d) Changes in relative current densities of 3D mesoG, Ir/C, and Pt/C catalysts for the OER before and after cycling tests. TEM image of (e) mesoG/Ni during the thermal conversion at 400 °C, (f) mesoG/Ni after heat treatment at 1000 °C, and (g–i) 3D mesoG at various magnifications.

Figure 7.12 (a) Schematic for the synthesis of N‐MCN/CNTs and the corresponding structural model. (b) CVs of N‐MCN/CNTs at a scan rate of 50 mV s

−1

in N

2

‐ or O

2

‐saturated 0.1 M KOH solution. (c) LSVs of N‐MCN/CNTs at the rotation rate of 300–2000 rpm. (d) Koutecky–Levich plots of N‐MCN/CNTs at the potentials of 0.20, 0.30, 0.40, 0.50, 0.60, and 0.70 V. (e) LSV comparison of N‐MCN/CNTs and Pt/C in an O

2

‐saturated 0.1 M KOH solution at a rotation rate of 1600 rpm. (f) LSVs for GCE and N‐MCN/CNTs at different mass loadings in O

2

‐saturated 0.1 M KOH solution. (g) LSVs of all catalysts. (h) Comparison of the overpotentials at 10 mA cm

−2

of the catalysts. (i) Tafel plots of the above catalysts. (j) CP and CA plots of the N‐MCN/CNTs in O

2

‐saturated 0.1 M KOH solution. (k) LSVs of the N‐MCN/CNTs before and after 2000 cycles (inset (k) TEM of N‐MCN/CNTs after the stability test). (l) CP and CA plots of mixed N‐MCN + CNTs in O

2

‐saturated 0.1 M KOH solution. (m) CP and CA plots of IrO

2

in O

2

‐saturated 0.1 M KOH solution.

Figure 7.13 (a1) Schematics showing the synthesis of P,S‐CNS catalysts and (a2) the reaction mechanism for the formation of the C–N polymeric complex. (b) Photographs of as‐synthesized cylindrical sponge‐like P,S‐CNS structure. (c, d) SEM, (e) TEM, and (f) HRTEM images of P,SCNS catalyst (inset show enlarged view). (g) Corresponding FFT pattern of the crystallite in the inset of (f). (h) TEM and the elemental maps of C, N, P, and S of P,S‐CNS (scale, 300 nm).

Figure 7.14 (a) LSV plots of ORR in O

2

‐saturated 0.1 M KOH electrolyte at 1600 rpm for different catalysts. (b) LSV curves of P,S‐CNS of ORR on various rotation speeds; the inset shows corresponding K–L plots on various voltages. (c) The HO

2

‐yield generated by ORR and calculated electron transfer number for P,S‐CNS catalysts. (d) LSV plots of the OER in 0.1 M KOH at 1600 rpm for different catalysts. (e) Tafel slopes for the ORR and OER. (f) LSV plots of the ORR and OER for different catalysts (scan rate, 5 mV s

−1

; electrolyte in 0.1 M KOH; rotation speed, 1600 rpm). Volcano plots of (g) OER and (h) ORR for P‐CNS, S‐CNS, and P,S‐CNS catalysts (overpotential

η

against difference between the adsorption energy of O* and OH* and adsorption energy of OH*). Standard free energy diagrams of P,S‐CNS for (i) OER pathway and (j) ORR pathway at equilibrium and different overpotentials.

Figure 7.15 (a) g‐C

3

N

4

nanoribbon‐G and a possible structural model of the g‐C

3

N

4

nanoribbon. (b,c) SEM images of the prepared g‐C3N4 nanoribbon‐G. The inset of (b) is a photo of the as‐prepared g‐C

3

N

4

nanoribbon‐G. (d) TEM images of the prepared g‐C

3

N

4

nanoribbon‐G and (e) a typical high‐resolution TEM image of the g‐C

3

N

4

nanoribbon. (f) The HER polarization curves and (g) the corresponding Tafel plots of various catalysts (g‐C

3

N

4

nanoribbon‐G, Pt wire, N‐G, and g‐C

3

N

4

, respectively) with a scan rate of 50 mV s

−1

in 0.5 M H

2

SO

4

. (h) The polarization curves of g‐C

3

N

4

nanoribbon‐G with a scan rate from 5 to 100 mV s

−1

. (i) The HER current density at 10 mA cm

−2

versus overpotential for various catalysts. (j) Plot showing the extraction of the double‐layer capacitance (

C

dl

) for g‐C

3

N

4

nanoribbon‐G at 0.2 V. (k) Time dependence of the current density at 200 mV versus RHE. (l) Schematic illustration of the preparation process of PCN@N‐graphene film. (m) Polarization curves (inset shows polarization curves with current density below 10 mA cm

−2

). (n) Tafel plots at low potentials. (o) Overpotential at 10 mA cm

−2

versus RHE (left) and exchange current density (right). (p) Electrochemical impedance spectra at −0.2 V versus RHE of PCN@graphene, PCN@N‐graphene, and PCN@N‐graphene‐750 films.

Figure 7.16 (a) Schematic illustration of the synthesis process of the self‐supported, C

3

N

4

‐based, metal‐free electrolyzer, (b) digital photograph, (c, d) SEM images, and (e and f) HRTEM images of the C

3

N

4

‐CNT‐CF electrode, (g) LSV and (h) Tafel curves of CNT‐CF, C

3

N

4

‐CF, C

3

N

4

‐CNT‐CF, S‐C

3

N

4

‐CNT‐CF, and Pt in 0.5 M H

2

SO

4

at 5 mV s

−1

; (i) chronopotentiometric response of S‐C

3

N

4

‐CNT‐CF in 0.5 M H

2

SO

4

; (j) LSV curve of S‐C

3

N

4

‐CNT‐CF in 1 M KOH at 5 mV s

−1

(inset: the corresponding Tafel slope); (k) LSV curves and (l) corresponding Tafel plots of C

3

N

4

, CNT‐CF, and C

3

N

4

‐CNT‐CF in 1 M KOH aqueous solution at 5 mV s

−1

, (m) Nyquist plots of CNT‐CF and C

3

N

4

‐CNT‐CF in 1 M KOH with a bias of 1.63 V, inset: the equivalent circuit diagram and (n) the duration test of the C

3

N

4

‐CNT‐CF electrode at a potential of 1.63 V.

Figure 7.17 Publications per year on photocatalytic and electrochemical reduction of CO

2

.·The data were extracted from the ISI Web of Science (search: Topic = electrochemical reduction of CO

2

, photoelectrochemical reduction of CO

2

).

Figure 7.18 (a) Schematic illustration of mechanism and (b) relative energy levels of photocatalytic reduction of CO

2

on a semiconductor photocatalyst.

Figure 7.19 (a) Digital image of CNF mat used as catalyst, (b) SEM image of the CNF mat displaying entangled fibers (scale bar, 5 mm), and (c) high‐resolution SEM image on individual fibers (scale bar, 200 nm). Random corrugations are visible at the fiber surface. Catalytic performance of CNFs for CO

2

reduction: (d) CVs for CO

2

reduction in the Ar‐saturated (black curve) and CO2‐saturated pure EMIM‐BF

4

on carbon film electrode (blue curve) and CNFs electrode (red curve), respectively (10 mV s

−1

). (e) Absolute current density for CO

2

RR at different electrodes in pure EMIM‐BF

4

electrolyte, (f) current density (at the highest CO

2

RR) for CNFs catalyst with respect to water mole fraction (%) in EMIM‐BF

4

, (g) chronoamperogram for CNFs catalyst at potential 0.573 V versus SHE in pure EMIM‐BF

4

(10 mV s

−1

). HR‐TEM images of (h, i) S‐doped and (j, k) S,N‐doped polymer‐derived carbons and (l, m) wood‐based activated carbon. (n) Stationary CO

2

reduction current densities and (o) LSV of CO

2

reduction on CPS and CPSN (conditions: CO

2

‐saturated 0.1 m KHCO

3

, 2.5 mg cm

−2

catalyst loading).

Figure 7.20 SEM images of (a) rGO and (b) and NS‐rGO. (c) CV curves of 5.0 mM H

2

O

2

obtained at GCE, rGO/GCE, and NS‐rGO/GCE in N

2

‐saturated 0.1 M PBS (pH 7.0) with a scan rate of 50 mV s

−1

(scale bar, 5 mm), (d) CV curves of 5 mM H

2

O

2

in 0.1 M PBS (pH 7.0) solution for different volumes of the dropped suspension (5, 7.5, 10, and 11.25 μl). (e) Plot of cathodic peak current of H

2

O

2

versus volume of the dropped suspension. (f) Illustration of the relative energy and configurations for the reaction intermediates (showing only part of the N graphene) in reaction paths I and II of the H

2

O

2

reduction process on the pyridinic‐N‐doped graphene surface. The indicated values are the relative energies for each step of the reaction system.

Chapter 8

Figure 8.1 Nitrogen species in nitrogen‐doped carbon materials.

Figure 8.2 Graphitic nitrogen (graphitic‐N) and pyridinic nitrogen (pyridinic‐N) in nitrogen‐doped carbon materials. XPS can distinguish that these species. N 1s peak at 401.2 eV corresponds to the graphitic‐N species while peak at 398.5 eV corresponds to pyridinic‐N species.

Figure 8.3 STM and STS of pyridinic‐N [26]. (a) STM topographic image (scan size: 4.81 × 4.61 nm

2

,

I

t

 = 96.9 pA,

V

s

 = −108 mV). The simulated STM image (

V

 = −0.1 V) is also shown for comparison. (b) STS spectrum measured at the position indicated by the arrow in (a). (c) The geometry of pyridinic‐N defect calculated by DFT. (d) Simulated STS spectrum of pyridinic‐N.

Figure 8.4 STM and STS of graphitic‐N [26]. (a) STM topographic image (scan size: 5.09 × 5.08 nm

2

,

I

t

 = 39.0 pA,

V

s

 = 500 mV). The simulated STM image (

V

 = +0.5 V) is also shown for comparison. (b) STS spectrum measured at the position indicated by the arrow in (a). (c) The geometry of graphitic‐N defect calculated by DFT. (d) Simulated STS spectrum of graphitic‐N.

Figure 8.5 Structural characterization of edge‐patterned HOPG [23]. (a) Optical image of patterned

edge

‐N

+

‐HOPG. (b) The AFM image obtained for the region indicated by the rectangle in (a). (c) Three‐dimensional representation of (b). (d) Line profile of the AFM image obtained along the line in (b).

Figure 8.6 XPS and ORR results of N‐HOPG model catalysts [23]. (a) N 1s XPS spectra of model catalysts. (b) ORR results for model catalysts corresponding to (a). Nitrogen contents of the model catalysts are shown as the inset in (b).

Figure 8.7 Catalytic performance of N‐HOPG model catalysts [23]. (a) ORR results obtained for the model catalysts with different N concentrations. (b) Correlation between current densities of ORR at 0.2, 0.3, and 0.4 V versus RHE and the pyridinic‐N concentrations. (c) Correlation between onset potentials at 1 μA cm

−2

and the pyridinic‐N concentrations. Different markers indicate different sample preparation methods. Nitrogen contents of the HOPG model catalysts are shown as the inset in (a).

Figure 8.8 Post‐ORR XPS analysis and CO

2

‐TPD of the N‐HOPG model catalysts [23]. (a) N 1s XPS spectra of the N‐HOPG model catalyst before and after ORR, respectively. (b) Schematic images of the formation of pyridonic‐N by the attachment of OH to the carbon atom next to pyridinic‐N. (c) CO

2

‐TPD results for the HOPG model catalysts.

Figure 8.9 N 1s XPS spectra and ORR performance of N‐GNS powder catalysts [23]. (a, b) N 1s XPS spectra of N‐GNS powder catalysts with different nitrogen concentrations and the corresponding ORR results. (c) Correlation between current densities of ORR at 0.5, 0.6, and 0.7 V versus RHE and pyridinic‐N concentrations.

Figure 8.10 Schematic pathway for oxygen reduction reaction on nitrogen‐doped carbon materials.

Figure 8.11 Molecular structure of pyridinic‐N‐doped graphene quantum dot (N‐GQD

1

).

Figure 8.12 pH‐dependent electrochemical reduction of N‐GQD

1

[36]. (a) Reduction curves of N‐GQD

1

at various pH values measured with

differential pulse voltammetry

(

DPV

). (b) Pourbaix diagram of N‐GQD

1

at 25 °C constructed with the data in (a). The data points are marked with crosses, and the grey lines are the best linear fit for the data point. Also shown are the proposed structures for the most stable species in each region of the diagram. (c) Resonance structures of

4

.

Figure 8.13 Geometry around the nitrogen atoms corresponding to the lowest calculated Gibbs free energy before and after oxygen activation (spin inversion of oxygen from triplet to singlet) by

4

[36]. Oxygen activation occurs at a carbon atom next to the protonated nitrogen atoms.

Figure 8.14 (a) Chemical structure for oxidized flavin, neutrally reduced flavin, and fully reduced flavin. (b) Resonance structure of fully reduced flavin (c) Reaction process for hydroperoxyflavin.

Figure 8.15

Linear sweep voltammetry

(

LSV

) curves (10 mV s

−1

) for 5–7 and Pt/C on a

rotating‐disk electrode

(

RDE

) (1600 rpm) in an O

2

‐saturated 0.1 M KOH solution.

Figure 8.16 Preparation of three different types of graphite‐conjugated pyrazine (GCP) moieties having different functional groups. Condensation of

ortho

‐phenylenediamine derivatives with

ortho

‐quinone edge sites of graphene sheets to generate GCPs.

Figure 8.17 Structure of N‐doped graphene quantum dot (

1

) (upper) and its space‐filling model (lower), showing the enclosing nature of solubilizing alkyl chains [40].

Figure 8.18 Proposed mechanism of oxygen activation by

1

[40].

1

is first reduced with two electrons and one proton to form carbanion in the resonance structure (including the reactive anion intermediate

2

).

2

activates oxygen to form peroxygraphene anion

3

. The structures of the species involved are truncated for clarity. Transition state for OO bond cleavage,

4

, and the resultant intermediate,

5

. In

4

, the arrows indicate the displacement vectors of the normal mode leading to OO bond cleavage.

Figure 8.19 (a) Free energy diagram of branching point for 2e and 4e selectivity of ORR at pH = 13 in

3

solvated with implicit water with a dielectric constant

ε

of 8 (solid lines), 4 (dashed lines), and 2 (dotted lines) [40]. The thick grey line represents oxygen activation, the light grey line represents OO bond cleavage, and the black line represents CO bond cleavage. All energies are relative to

2

 + O

2

(gas 1 atm). (b) Free energy diagram of branching point for 2e and 4e selectivity of ORR in

3

with implicit solvation with a dielectric constant of 4 at pH = 1 [40]. The black line represents oxygen activation, the light grey line represents the OO bond cleavage for the 4e pathway, and the thick grey line represents the CO bond cleavage for the 2e pathway at pH = 1. All energies are relative to pure solid 6. Labels in bold text refer to molecule labels that appear in Figure 8.18.

Chapter 9

Figure 9.1 Different forms of doped nitrogen and oxygen in nitrogen/oxygen‐functionalized carbon materials. Four featured nitrogen‐containing groups (pyrrolic‐N, pyridinic‐N, graphitic‐N, and pyridinic oxide), which are generally discussed as the active sites on nitrogen‐functionalized carbon materials, are particularly marked in the carbon matrix.

Figure 9.2 XPS spectra of G‐NH

3

·H

2

O. Oxygen 1s XPS spectra (a) before and (b) after ORR. The fitted peaks are C



O at 530.8 eV, C(aliphatic)OH/C(aliphatic)OC(aliphatic) at 532.0 eV, C(aromatic)OH at 533.3 eV, and chemisorbed water molecules at 535.7 eV. Carbon 1s XPS spectra (c) before and (d) after ORR. The fitted peaks are CC/C



C at 284.6 eV, COH at 285.4 eV, COC at 286.5 eV, C



O at 288.1 eV, and COOH at 290.8 eV. The contribution from Nafion to the carbon 1s XPS spectrum has been subtracted. (e) Nitrogen 1s XPS spectra before and after ORR. The least‐squares fitted peaks are pyridinic‐N at 398.5 eV, pyrrolic‐N at 399.8 eV, graphitic‐N at 401.2 eV, and nitrogen oxide at 403 eV. (f) Diagram of the chemical structure of OH attached to the carbon‐neighboring pyridinic nitrogen, leading to a bonding energy upshift of the pyridinic nitrogen in XPS.

Figure 9.3 Post‐ORR XPS analysis and CO

2

‐TPD of the N‐HOPG model catalysts. (a) N 1s XPS spectra of the N‐HOPG model catalyst before and after ORR, respectively. (b) Schematic images of the formation of pyridonic‐N by the attachment of OH to the carbon atom next to pyridinic‐N. (c) CO

2

‐TPD results for the HOPG model catalysts.

Figure 9.4 Hydrogen adsorption and reaction mechanism on various graphene models. (a) Δ

G

H*

for different models. The values of Δ

G

H*

on graphitic‐type doping models are labeled by solid bars, whereas those on edge‐doping models are labeled by shaded bars (except for th‐S, which is represented by shaded bars due to the inability to construct a graphitic doping model). (b) Reaction pathways on edge (marked by dark grey circle) and non‐edge carbons (marked by light circle) within the py‐N model. The edge carbon possesses a Δ

G

H*

of −0.45 eV, which should lead to a higher activity as compared with the non‐edge carbon in the same model (0.97 eV). However, the free energy change toward the next H

2

recombination step of the reaction on the edge carbon is 2.92 eV, indicating that it is difficult for this step to proceed and therefore that the overall reaction pathway on the edge carbon is unfavorable. For the non‐edge site, such a recombination step is limited by the Heyrovsky route and is, therefore, not shown. Free energy diagram for HER follows the Volmer–Heyrovsky pathway (c) and the Volmer–Tafel pathway (d) on various graphene models. (e) Tafel slopes obtained from theoretical computation (filled symbols) and experimental measurements (open symbols) on various graphene models/samples.

Figure 9.5 Identification of the catalytic active site in echo‐MWCNTs. (a) High‐resolution XPS O 1s spectra obtained from raw MWCNTs, oxidized MWCNTs (o‐MWCNTs),

hydrothermally treated o‐MWCNT

s (

ho‐MWCNT

s), and electrochemically activated MWCNTs (echo‐MWCNTs), respectively. (b–d) Energy profiles of the four‐electron water oxidation mechanism. The energy corrections due to the working voltage potential of 1.53 V and the pH of 13 were taken into account. Water oxidation on preoxidized graphene cluster model with (b) both lactone and ketone groups and (c,d) ketone groups only.

Figure 9.6 Ex situ XPS and in situ EIS measurements. (a) Deconvolution of the XPS O 1s spectra after different treatments, where P‐CNTs, R‐CNTs, and O‐CNTs represent raw CNTs, thermally reduced CNTs, and plasma O‐CNTs, respectively. (b) Ex situ C 1s XPS spectra of O‐CNTs acquired after applying different anodic potential for 15 min. (c) Nyquist plots of O‐CNTs, P‐CNTs, and R‐CNTs obtained at 1.625 V versus RHE (inset shows the electrical equivalent circuit) and (d) variation in the surface coverage of intermediates on CNTs.

Proposed OER pathway on O‐CNTs.

Figure 9.7 Mechanistic study of bifunctionality for ORR and OER. (a) ORR and (b) OER volcano plots of overpotential

η

versus adsorption energy of O* and the difference between the adsorption energy of O* and OH*, respectively, for N‐doped, P‐doped, and N,P‐doped graphene. (c) Initial structure and structures after the adsorption of (d) hydroxyl OH*, (e) oxyl O*, and (f) peroxyl OOH* intermediates on N‐ and P‐coupled graphene. O*, OH*, and OOH* are adsorbed intermediates. The overpotentials of the best catalysts predicted theoretically for ORR (Pt) [60] and OER (RuO

2

) [61] are also plotted in (a) and (b), respectively. Inset in (b) shows the details of the volcano top in the main panel. Schematic energy profiles for the (g) OER pathway and the (h) ORR pathway on N,P‐co‐doped graphene in alkaline media.

Figure 9.8 Electronic characteristics and ORR/OER active sites of N‐doped graphene catalysts. (a,b) Carbon and nitrogen K‐edge XANES spectra of N‐GRW catalyst, acquired under ultrahigh‐vacuum, pristine (black line), after ORR (light grey line), and after OER (thick grey line). In carbon K‐edge XANES spectra, A: defects, B: π*

C



C

, C: π*

COH

, D: π*

COC, CN

, E: π*

C



O, COOH

, F: σ*

CC

. (c) Schematic diagram of ORR and OER occurring at different active sites on the n‐ and p‐type domain of the N‐GRW catalyst.

Figure 9.9 Evolution of nitrogen atomic structure in CNFs. (a) Deconvoluted N 1s spectra for CNFs before and (b) after electrochemical CO

2

RR. (c,d) show the corresponding atomic structure deduced from the XPS analysis.

Figure 9.10 The active N site for CO

2

adsorption. (a) Post‐CO

2

reduction XPS analysis showing the change of N configuration concentration. (b) A schematic of CO

2

adsorption onto the pyridinic‐N site.

Figure 9.11 (a) Deconvoluted N 1s spectrum for N‐doped CNTs, which elucidates the existence of four main nitrogen species: pyridinic N (B.E. ∼ 398.9 eV), pyrrolic N (B.E. ∼ 400.1 eV), quaternary N (B.E. ∼ 401.5 eV), and nitrogen oxide (B.E. ∼ 402.2 eV). (b) Proposed mechanism for CO

2

reduction at the PEI‐functionalized, nitrogen‐doped CNTs.

Figure 9.12 (a) ORR polarization curves of CNx catalyst in 0.1 M H

3

PO

4

and 0.1 M HClO

4

before and after exposing the catalyst‐coated electrode to 0.1 M H

3

PO

4

. (O

2

‐saturated 0.1 M HClO

4

, 1600 rpm, 10 mV s

−1

, and 800 μg catalyst cm

−2

). (b) ORR polarization curves of CNx catalyst before and after soaking in 0.1 M H

3

PO

4

.

Figure 9.13 P 2p, O 1s, and N 1s XPS spectra for CNx catalyst before and after soaking in 0.1 M H

3

PO

4

.

Chapter 10

Figure 10.1 Temporal profiles of phenol degradation (a) and consumed H

2

O

2

(b) using G‐based catalysts. Legend: G (□), rGO (▾), and GO (○). Reaction conditions: catalyst (200 mg l

−1

), phenol (100 mg l

−1

, 1.06 mM), H

2

O

2

(200 mg l

−1

, 5.88 mM), pH 3, room temperature.

Scheme 10.1 Graphene‐oxide‐catalyzed alkylation of arenes.

Scheme 10.2 Synthesis of quinazolin‐4(3

H

)‐one derivatives.

Scheme 10.3 Ring opening of styrene oxide catalyzed by GO.

Scheme 10.4 Acetalization of benzaldehyde with methanol using GO as catalyst.

Scheme 10.5 GO‐catalyzed dehydration of fructose to HMF.

Figure 10.2 Proposed mechanism of ba‐GO‐catalyzed oxidative coupling of primary amines.

Scheme 10.6 Mukaiyama–Michael addition between TMSOF and β‐nitrostyrene with graphite‐based catalyst.

Figure 10.3 Geometry of the anti‐ and syn‐transition states for the CC bond‐forming step in the presence of G (a,b). Distances are in angstroms. The CC bond is represented in yellow color. (c) Energy profile up to the intermediate corresponding to the complete formation of the CC bond.

Figure 10.4 (a) Phenol degradation by PMS using different catalysts. (b) Stability and recyclability of NG‐700 [76]. Reaction conditions: catalyst (0.1 g l

−1

), PMS (6.5 mM), phenol (20 mg l

−1

, 0.21 mM), 25 °C, pH not indicated.

Figure 10.5 (A) Temporal profile of phenol disappearance by PMS activation promoted by a series of doped G catalyst as indicated in the plot; (B) model of co‐doped G used for theoretical calculations; (C) electrostatic potential mapping from charge density matrix for (a) undoped model G, (b) S‐G, (c) N‐G, (d) S‐N‐G, and (e) S‐S‐N‐G.

Chapter 11

Figure 1.1 (a) Hydrogen and oxygen cycles for energy storage and conversion. HER and OER can realize energy storage in chemical form. For energy conversion, ORR and HOR (MOR) are two half‐cell reactions of fuel cell. (b) Scheme of the overpotentials associated with HER, OER, ORR , and HOR. (c) Scheme of the anion‐exchange membrane electrolyzer. (d) Scheme of a fuel cell in alkaline electrolytes.

Figure 1.2 (a) Calculated charge density distribution for the NCNTs and the schematic representations of possible adsorption modes of an oxygen molecule at the CCNTs (top) and NCNTs (bottom) [5]. (b) Illustration of charge transfer process and oxygen reduction reaction on PDDA‐CNT [6]. (c) The air‐saturated droplet was deposited on the basal plane of the HOPG electrode [7]. (d) HAADF image of DG, hexagons, pentagons, heptagons, and octagons was labeled in orange, green, blue, and red, respectively [8].

Figure 1.3 (A) Charge distribution on the two representative graphene sheets of C72H24. (B) (a) Micro apparatus for the ORR electrochemical experiment. (b, c) Optical photograph of the HOPG surface as the working electrode with the air‐saturated droplet deposited on the edge and basal plane of the HOPG surface. (d) LSV curves of the ORR tested for a droplet located either on the edge or on the basal plane of the HOPG surface [7].

Figure 1.4 (A) Illustration of the preparation of the edge‐rich and dopant‐free graphene by the Ar plasma etching. (B) SEM and TEM images of pristine graphene (a, c) and Ar‐ plasma‐treated graphene (b, d). (C) CV curves of G and P‐G at a scan rate of 50 mV s

−1

in N

2

‐saturated and O

2

‐saturated 0.1 M KOH. (D) RDE voltammograms of G and P‐G in an O

2

‐saturated 0.1 M KOH with a scan rate of 10 mV s

−1

[20].

Figure 1.5 (a) NBO population analysis of six different nonmetallic heteroatoms in graphene matrix. pN and gN represent pyridinic and graphitic type of N, respectively. Inset shows the proposed doping sites for different elements, sites 1 and 2 are the edge and center in‐plane sites, respectively, and site 3 is an out‐of‐plane center site in graphene. (b) The calculated free energy (Δ

G

H*

) diagram for HER at the equilibrium potential (URHE = 0 V) for N‐ and/or P‐doped graphene models. (c) Relationship between Δ

G

H*

and

E

diff

for various models [33a].

Figure 1.6 (a) Schematic illustration of the preparation process for the NPMC foams. An aniline (i)–phytic acid (ii) complex (iii) is formed (for clarity, only one of the complexed anilines is shown for an individual phytic acid), followed by oxidative polymerization into a three‐dimensional PANi hydrogel cross‐linked with phytic acids. As each phytic acid molecule can complex with up to six aniline monomers, phytic acid can be used as the cross‐linker and protonic dopant to directly form the three‐dimensional PANi hydrogel network; for clarity, only a piece of the two‐dimensional network building block is shown in the enlarged view under the three‐dimensional PANi hydrogel. The PANi hydrogel is freeze‐dried into an aerogel and pyrolyzed in Ar to produce the NPMC (for clarity, only a piece of the two‐dimensional NPMC network building block is shown in the enlarged view under the three‐dimensional NPMC). (b, c) SEM images of PANi aerogel (b) and NPMC‐1000 (c). Inset in (c): digital photo images of PANi aerogel before (left) and after (right) pyrolysis at 1000 °C. (d, e) High‐resolution TEM image (d) and TEM image (e, left), with corresponding element‐mapping images of NPMC‐1000 (e). The TEM image shows a piece of interconnected network‐like scaffold. The element‐mapping images for C, N, and P show a uniform distribution of the elements [39].

Chapter 12

Figure 2.1 (a) Doping of graphitic carbon structure with heteroatoms (e.g. N, B, and P). (b) Doping of graphitic carbon structure with heteroatoms (e.g. N) by posttreatment. (c) Periodic table and the corresponding electronegativity of elements.

Figure 2.2 Nitrogen‐doped carbon nanotube arrays are efficient ORR electrocatalysts.

Rotating ring disk electrode

(

RRDE

) voltammograms for oxygen reduction in air‐saturated 0.1 M KOH at the electrodes of Pt/C (curve 1), VA‐CNTs (curve 2), and VA‐NCNT (curve 3) (a). Calculated charge density distribution for the NCNT (b). Schematic representations of possible adsorption modes of an oxygen molecule at the CNTs (top) and NCNT (bottom) (c).

Figure 2.3 Typical nitrogen species in N‐doped sp

2

carbon.

Figure 2.4 The ORR activities and the important molecular orbitals of BCNT. (a)

Rotating disk electrode

(

RDE

) voltammetries of the catalysts for ORR in O

2

‐saturated 1 M NaOH electrolyte at a scan rate of 50 mV s

−1

and a rotation speed of 2500 rpm. (b) The second

highest occupied molecular orbital

(

HOMO‐1

) of BCNT(5,5). (c) Methanol crossover tests by introducing 1.5 ml methanol into the electrolyte at 1200 s. (d) CO poisoning tests by introducing additional CO with the same flow of O

2

into the electrolyte at 520 s. B

x

CNTs (

x

 = 1,2,3) denote the BCNTs with an increased B content. For comparison, corresponding examinations for CNTs and commercial Pt/C catalysts (20 and 40 wt% Pt loading) were also carried out.

Figure 2.5 The schematic pictures of two types of B/N‐co‐doped CNTs and their ORR activities. (a) Separated B/N‐co‐doped CNTs with high ORR activity. (b) Bonded B/N‐co‐doped ones with low ORR activity.

Figure 2.6 Schematic representation of the physical cracking of graphite flake in a ball mill crusher in the presence of nitrogen and subsequent exposure to air moisture to produce N‐doped graphene nanoplatelets (a). Schematic representation for the edge expansions of graphene nanoplatelets caused by the edge halogens (b).

Figure 2.7 Scheme for the full exposure of “active sites” on the surface: NCNTs with bulk doping of nitrogen atoms, whereas CNT@NCNT coaxial nanocables with surface‐enriched nitrogen.

Figure 2.8 (a) Illustration of the charge transfer process and ORR on PDDA‐CNT. (b) Polyelectrolyte‐functionalized graphene as metal‐free electrocatalyst for oxygen reduction.

Figure 2.9 3D‐architectured carbon nanostructures. (a) Carbon nanocages. (b) 3D porous carbon. (c) 3D‐pillared CNT−graphene network.

Figure 2.10 Electronegativity of elements increases along the

y

‐axis.

Figure 2.11 Contour plots of the spin up (a) and spin down (b) HOMO of a physisorbed O

2

‐CNT system, and the potential energy profiles for triplet (black) and singlet (grey) O

2

approaching CNT (c).

Figure 2.12 The possible active sites in acid: C neighboring to pyridinic‐N.

Figure 2.13 Correlation of ORR activity (a) and four‐electron selectivity (b) of the doped OMCs with their work function values.

Figure 2.14 The schematic N‐doping configurations and the corresponding electronic structures.

Pristine graphene

(

PG

), nitrile‐like (N1), pyridinic (N2), and graphitic‐N (N3).