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- Herausgeber: Wiley-VCH GmbH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Electrocatalysis in Balancing the Natural Carbon Cycle
Explore the potential of electrocatalysis to balance an off-kilter natural carbon cycle
In Electrocatalysis in Balancing the Natural Carbon Cycle, accomplished researcher and author, Yaobing Wang, delivers a focused examination of why and how to solve the unbalance of the natural carbon cycle with electrocatalysis. The book introduces the natural carbon cycle and analyzes current bottlenecks being caused by human activities. It then examines fundamental topics, including CO2 reduction, water splitting, and small molecule (alcohols and acid) oxidation to prove the feasibility and advantages of using electrocatalysis to tune the unbalanced carbon cycle.
You’ll realize modern aspects of electrocatalysis through the operando diagnostic and predictable mechanistic investigations. Further, you will be able to evaluate and manage the efficiency of the electrocatalytic reactions. The distinguished author presents a holistic view of solving an unbalanced natural carbon cycle with electrocatalysis.
Readers will also benefit from the inclusion of:
- A thorough introduction to the natural carbon cycle and the anthropogenic carbon cycle, including inorganic carbon to organic carbon and vice versa
- An exploration of electrochemical catalysis processes, including water splitting and the electrochemistry CO2 reduction reaction (ECO2RR)
- A practical discussion of water and fuel basic redox parameters, including electrocatalytic materials and their performance evaluation in different electrocatalytic cells
- A perspective of the operando approaches and computational fundamentals and advances of different electrocatalytic redox reactions
Perfect for electrochemists, catalytic chemists, environmental and physical chemists, and inorganic chemists, Electrocatalysis in Balancing the Natural Carbon Cycle will also earn a place in the libraries of solid state and theoretical chemists seeking a one-stop reference for all aspects of electrocatalysis in carbon cycle-related reactions.
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Seitenzahl: 977
Veröffentlichungsjahr: 2021
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Table of Contents
Cover
Title Page
Copyright
Preface
Acknowledgments
Part I: Introduction
1 Introduction
References
Part II: Natural Carbon Cycle
2 Natural Carbon Cycle and Anthropogenic Carbon Cycle
2.1 Definition and General Process
2.2 From Inorganic Carbon to Organic Carbon
2.3 From Organic Carbon to Inorganic Carbon
2.4 Anthropogenic Carbon Cycle
References
Part III: Electrochemical Catalysis Process
3 Electrochemical Catalysis Processes
3.1 Water Splitting
3.2 Electrochemistry CO2 Reduction Reaction (ECDRR)
3.3 Small Organic Molecules Oxidation
References
Part IV: Water Splitting and Devices
4 Water Splitting Basic Parameter/Others
4.1 Composition and Exact Reactions in Different pH Solution
4.2 Evaluation of the Catalytic Activity
References
5 H
2
O Oxidation
5.1 Regular H
2
O Oxidation
5.2 Photo‐Assisted H2O Oxidation
References
6 H
2
O Reduction and Water Splitting Electrocatalytic Cell
6.1 Noble‐Metal‐Based HER Catalysts
6.2 Non‐Noble Metal Catalysts
6.3 Water Splitting Electrocatalytic Cell
References
Part V: H
2
Oxidation/O
2
Reduction and Device
7 Introduction
7.1 Electrocatalytic Reaction Parameters
References
8 Hydrogen Oxidation Reaction (HOR)
8.1 Mechanism for HOR
8.2 Catalysts for HOR
References
9 Oxygen Reduction Reaction (ORR)
9.1 Mechanism for ORR
9.2 Catalysts in ORR
9.3 Hydrogen Peroxide Synthesis
References
10 Fuel Cell and Metal‐Air Battery
10.1 H
2
Fuel Cell
10.2 Metal‐Air Battery
References
Part VI: Small Organic Molecules Oxidation and Device
11 Introduction
11.1 Primary Measurement Methods and Parameters
References
12 C1 Molecule Oxidation
12.1 Methane Oxidation
12.2 Methanol Oxidation
12.3 Formic Acid Oxidation
References
13 C
2+
Molecule Oxidation
13.1 Ethanol Oxidation
13.2 Glucose Oxidase
13.3 Ethylene Glycol Oxidation
13.4 Glycerol Oxidation
References
14 Fuel Cell Devices
14.1 Introduction
14.2 Types of Direct Liquid Fuel Cells
References
Part VII: CO
2
Reduction and Device
15 Introduction
15.1 Basic Parameters of the CO
2
Reduction Reaction
References
16 Electrocatalysts‐1
16.1 Heterogeneous Electrochemical CO2 Reduction Reaction
16.2 Thermodynamic and Kinetic Parameters of Heterogeneous CO2 Reduction in Liquid Phase
References
17 Electrocatalysts‐2
17.1 Single‐Atom Metal‐Doped Carbon Catalysts (SACs)
17.2 Metal Nanoparticles‐Doped Carbon Catalysts
17.3 Porous Organic Material
17.4 Metal‐Free Carbon‐Based Catalyst
17.5 Electrochemical CO Reduction Reaction
References
18 Devices
18.1 H‐Cell
18.2 Flow Cell
18.3 Requirements and Challenges for Next‐Generation CO2 Reduction Cell
References
Part VIII: Computations‐Guided Electrocatalysis
19 Insights into the Catalytic Process
19.1 Electric Double Layer
19.2 Kinetics and Thermodynamics
19.3 Electrode Potential Effects
References
20 Computational Electrocatalysis
20.1 Computational Screening Toward Calculation Theories
20.2 Reactivity Descriptors
20.3 Scaling Relationships: Applications of Descriptors
20.4 The Activity Principles and the Volcano Curve
20.5 DFT Modeling
References
21 Theory‐Guided Rational Design
21.1 Descriptors‐Guided Screening
21.2 Scaling Relationship‐Guided Trends
21.3 DOS‐Guided Models and Active Sites
References
22 DFT Applications in Selected Electrocatalytic Systems
22.1 Unveiling the Electrocatalytic Mechanism
22.2 Understanding the Electrocatalytic Environment
22.3 Analyzing the Electrochemical Kinetics
22.4 Perspectives, Challenges, and Future Direction of DFT Computation in Electrocatalysis
References
Part IX: Potential of In Situ Characterizations for Electrocatalysis
23 In Situ Characterization Techniques
23.1 Optical Characterization Techniques
23.2 X‐Ray Characterization Techniques
23.3 Mass Spectrometric Characterization Techniques
23.4 Electron‐Based Characterization Techniques
References
24 In Situ Characterizations in Electrocatalytic Cycle
24.1 Investigating the Real Active Centers
24.2 Investigating the Reaction Mechanism
24.3 Evaluating the Catalyst Stability/Decay
24.4 Revealing the Interfacial‐Related Insights
24.5 Conclusion
References
Part X: Electrochemical Catalytic Carbon Cycle
25 Electrochemical CO
2
Reduction to Fuels
References
26 Electrochemical Fuel Oxidation
References
27 Evaluation and Management of ECC
27.1 Basic Performance Index
27.2 CO
2
Capture and Fuel Transport
27.3 External Management
27.4 General Outlook
References
Index
End User License Agreement
List of Tables
Chapter 7
Table 7.1 Summary of test conditions for ECSAs of HOR electrocatalysts in var...
Chapter 8
Table 8.1 Computed Pt electrochemical surface areas calculated from the HUPD ...
Table 8.2 Summary of alkaline HOR activity of noble metal‐based electrocataly...
Table 8.3 Alkaline HOR activity of PGM‐free electrocatalysts.
Table 8.4 Electrochemical stability data for the Ni
3
M/C electrocatalysts.
Chapter 9
Table 9.1 Electrode materials for the electrosynthesis of H
2
O
2
.
Chapter 12
Table 12.1 Some reactions may be related to the electrocatalytic conversion o...
Chapter 13
Table 13.1 Summary of performance of single direct ethanol fuel cell tests ad...
Chapter 14
Table 14.1 General reactions of DLFC with different fuels.
Chapter 16
Table 16.1 CO
2
electrolysis products at different standard redox potentials....
Table 16.2 Summary of ECDRR performances on different nanocatalysts in aqueou...
Table 16.3 Summary of ECDRR performances on different bimetallic/alloy cataly...
Chapter 17
Table 17.1 Summary of ECDRR performances on different SACs in aqueous solutio...
Chapter 18
Table 18.1 Summary of ECDRR performance on various catalyst materials in the ...
Chapter 21
Table 21.1 An overview of descriptors sets found in different electrocatalyti...
Chapter 22
Table 22.1 Equilibrium potentials of different ECR possibilities.
Chapter 25
Table 25.1 The theoretical reduction potential of aqueous ECDRR to several ch...
Table 25.2 Typical catalysts for ECDRR to CO.
Table 25.3 Typical catalysts for ECDRR to HCOOH/HCOO
−
.
Table 25.4 Typical catalysts for ECDRR to CH
4
.
Table 25.5 Typical catalysts for ECDRR to CH
3
OH.
Table 25.6 Typical catalysts for ECDRR to CH
3
CH
2
OH.
Chapter 26
Table 26.1 Typical catalysts for CO/CH
4
electrooxidation to CO
2
.
Table 26.2 Typical catalysts for HCOOH oxidation to CO
2
.
Table 26.3 Typical catalysts for CH
3
OH oxidation.
Table 26.4 Typical catalysts for CH
3
CH
2
OH oxidation.
List of Illustrations
Chapter 2
Figure 2.1 Light and dark reactions of photosynthesis.
Figure 2.2 Sustainable anthropogenic recycling of atmospheric CO
2
to fuels a...
Figure 2.3 Schematic representation of the general concept of artificial pho...
Figure 2.4 Schematic diagram of the clean energy supply of electricity to el...
Chapter 3
Figure 3.1 The OER mechanism for acid (blue line) and alkaline (red line) co...
Scheme 3.1 Possible reaction pathways for the electrocatalytic reduction of ...
Scheme 3.2 Possible reaction pathways for the electrocatalytic reduction of ...
Scheme 3.3 Possible reaction paths for electrocatalytic CO
2
reduction to pro...
Scheme 3.4 Possible reaction paths for electrocatalytic CO
2
reduction to pro...
Scheme 3.5 Possible reaction paths for electrocatalytic CO
2
reduction to pro...
Scheme 3.6 Possible reaction paths for electrocatalytic CO
2
reduction to pro...
Chapter 4
Figure 4.1 Schematic diagram of the reaction rate associated with a water‐sp...
Chapter 5
Figure 5.1 (a) TEM image and model (insert); (b) TOF value of IrM alloy; (c)...
Figure 5.2 (a) TEM image of as synthesized IrW nanodendrites (NDs); (b) prop...
Figure 5.3 (a) Cyclic voltammogram of a RuO
2
(110) single‐crystal surface in...
Figure 5.4 (a) Schematic illustration of the formation process of Co‐doped I...
Figure 5.5 (a) Schematic diagram of HCM@Ni–N production process; (b) TEM ima...
Figure 5.6 (a) Manufacturing process summary of A‐CoS
4.6
O
0.6
PNC. (b) A‐CoS
4
...
Figure 5.7 (a) Schematic diagram of the preparation of Fe
1
Co
1
‐ONS and (b) Fe
Figure 5.8 Schematic illustration of the photo‐coupled electrochemical OER m...
Figure 5.9 Polarization curves; comparison plots; corresponding Tafel slopes...
Figure 5.10 (a) LSV curve scanned from −0.2 to 1.4 V vs. Ag/AgCl for BVO and...
Chapter 6
Figure 6.1 (a) Schematic diagram for WO
x
@C/C. (b) Polarization curve. (c) Ca...
Figure 6.2 The combination of a perovskite tandem cell with a Ni‐Fe‐LDH/Ni f...
Figure 6.3 (a) Schematic representation of solar water decomposition with tw...
Figure 6.4 (a) Neutral pH photolysis of seawater, a schematic diagram of a p...
Chapter 7
Figure 7.1 Experimentally measured HER/HOR exchange current densities (marke...
Figure 7.2 RDE voltammograms of Ru/C, Ir/C, and Ir
10–
x
Ru
x
/C in 0.1 M K...
Chapter 8
Figure 8.1 Hydrogen oxidation reaction curves obtained in a hydrogen‐saturat...
Figure 8.2 Upper part: HOR/HER Tafel plots of the specific current densities...
Figure 8.3 Schematic of (a) Pt/Cu NWs, (b) Pt
NT
s (
nanotube
s) (Cu), (c) 5% M...
Figure 8.4 Current–voltage behavior was compared vs.
standard hydrogen elect
...
Figure 8.5 HOR performances. (a) Polarization curves of Ni/N‐CNT, Ni/CNT, Ni...
Figure 8.6 Comparison of the experimental (solid line) and simulated (dashed...
Figure 8.7 (a) Cyclic voltammograms obtained for NiMo/KB with various loadin...
Figure 8.8 Online dissolution data during the potentiodynamic cycling protoc...
Figure 8.9
X‐ray powder diffraction
(
XRD
) patterns (a) and electrochem...
Chapter 9
Figure 9.1 Oxygen reduction reaction polarization curves on single‐atom Pt: ...
Figure 9.2 ORR polarization curves for 20‐nm Pt multioctahedrons and Pt/C ca...
Figure 9.3 Structural and compositional characterizations of PtGa alloy NWs....
Figure 9.4 Electrocatalytic performance of Pt
4.31
Ga NWs/C, Pt NWs/C, and com...
Figure 9.5 Electrocatalytic performance of different catalysts. (a) CV curve...
Figure 9.6 (a) Cyclic voltammograms recorded at room temperature in Ar‐satur...
Figure 9.7 (a) ORR polarization curves of the catalysts in O
2
‐saturated 0.1 ...
Figure 9.8 Electrochemical properties of Pt
3
Fe surfaces. (a) Cyclic voltammo...
Figure 9.9 CV curves for the electro‐oxidation of methanol by the as‐prepare...
Figure 9.10 Structural and compositional analyses of the Pd@Pt core–shell co...
Figure 9.11 Evaluation of the electrocatalytic performance of Fe–NC SAC for ...
Figure 9.12 (a) ORR polarization plots for Fe‐ZIF‐derived catalysts in 0.5 M...
Figure 9.13 RRDE voltammograms for oxygen reduction in air‐saturated 0.1 M K...
Figure 9.14 Rotating disk electrode (RDE) voltammograms of a glassy carbon e...
Figure 9.15 Electrocatalytic activity for ORR and
oxygen evolution reaction
...
Figure 9.16 Schematic illustrations of different types of electrochemical ce...
Chapter 10
Figure 10.1 Hydrogen and oxygen cycle for energy storage and energy conversi...
Figure 10.2 (a) Schematic illustration of a Zn–air battery. Adapted with per...
Figure 10.3 Schematic polarization curves of zinc‐air cell. The equilibrium ...
Figure 10.4 Scheme of the modified electrode using polysufonium.
Figure 10.5 (a) Illustration of reaction products in 3DOm carbons with diffe...
Figure 10.6 (a) SEM image of a freestanding hG electrode made by hydraulic c...
Chapter 11
Figure 11.1 Typical cyclic voltammogram for a reversible
O + ne− ↔ R
...
Figure 11.2 Tafel plots for cathodic and anodic branches of the current–pote...
Figure 11.3 CV (a) and CO stripping (b) for the 1 nm catalyst for Pt loading...
Figure 11.4 Using CO bulk oxidation (CO
b
) correct the capacity caused by the...
Chapter 12
Figure 12.1 Schematic diagram of a typical electrocatalytic cell for methane...
Figure 12.2 (a) Simplified catalytic cycle for electrophilic methane oxidati...
Figure 12.3 Schematic illustration of alkaline fuel cell reactor using alkal...
Figure 12.4 (a) Schematic illustration of the electrocatalytic cell using ga...
Figure 12.5 Schematic diagram of different reaction steps in the methanol ox...
Figure 12.6 (a) Cyclic voltammograms methanol oxidation on the heat‐treated ...
Figure 12.7 (a) LSV curves of methanol oxidation on the Pd/C, Pd–CeO
2
/C, Pd–...
Figure 12.8 SEM images of (a) Pt and (b) W gauzes prior to Pt NW growth, wit...
Figure 12.9 (a) SEM image of Ag NWs, (b) Transmission electron microscope (T...
Figure 12.10 Typical SEM images of Sn NT (a, b), Sn–Pt bimetallic NT (d). Ty...
Figure 12.11 SEM images of Pt nanostructures (a) 25 seconds, (b) 400 seconds...
Figure 12.12 Representative (a) SEM, (b, c) TEM and elemental analysis, and ...
Figure 12.13 (a) TEM image and selected area electron diffraction pattern an...
Figure 12.14 TEM images of Pt hollow nanocubes at (a) low and (b) high magni...
Figure 12.15 (a) Low‐magnification TEM image of the overall morphology of Pt...
Figure 12.16 (a) Stable cyclic voltammograms obtained for the Pt–Pd NCs and ...
Scheme 12.1 Shape‐selective synthesis of Pt–Pd NTHs and NCs.
Figure 12.17 Current density vs. time profiles of Pd (a) under a constant po...
Figure 12.18 Cyclic voltammograms of formic acid oxidation on Pt/CNT, Pt
1
Pd
1
Figure 12.19 FTIR spectra of the formic acid oxidation (a) Pd, (b) PdCd, (c)...
Figure 12.20 Normalized activity decay for Pt films deposited on Au‐poly aft...
Chapter 13
Figure 13.1 Proposed mechanism for the selective conversion of ethanol into ...
Figure 13.2 In situ FTIR spectra obtained under potential step polarization ...
Figure 13.3 (a)
In situ infrared reflection‐absorption spectroscopy
(
I
...
Figure 13.4 Ratio of the current densities of ethanol oxidation recorded on ...
Figure 13.5 Dependence of the maximum power density of DEFCs with Pt/C, Pt–R...
Figure 13.6 Polarization curves and power density curves in single DEFC with...
Figure 13.7 Cyclic voltammetry of Pt–Sn/C and Pt–Sn–Ni/C electrocatalysts in...
Figure 13.8 Polarization curves and power density curves in single DEFC.
Figure 13.9 Voltammograms of Pt–metal alloy electrodes in 0.5 mol dm
−3
Figure 13.10 Polarization curves and power density curves in single DEFC....
Figure 13.11 The glycerol oxidation.
Figure 13.12 Working principles of (a) AEM fuel cell, (b) AEM electrolysis, ...
Scheme 13.1 Mechanism of glycerol oxidation on platinum and gold electrodes ...
Chapter 14
Figure 14.1 General operating principle of DLFCs.
Chapter 15
Figure 15.1 Schematic of different mechanisms for ECDRR. (a) Homogeneous ele...
Figure 15.2 Homogeneous Ir catalysts mechanism for the conversion of CO
2
int...
Chapter 16
Figure 16.1 Various products formed by electrochemical reduction of carbon d...
Figure 16.2 Overall mechanistic pathways in ECDRR. (a) 2e
−
(C
1
) produc...
Figure 16.3 Catalysts and electrolytes acting as cocatalysts can lower the e...
Figure 16.4 Schematic correlation between metal size and specific activity. ...
Figure 16.5 (a) Proposed mechanisms for CO
2
reduction to CO and (b) FEs for ...
Figure 16.6 (a) Summary of hydrocarbon selectivity of plasma‐treated Cu foil...
Figure 16.7 (a) Schematic and (b) CO FE.(c) Schematic and (d) C
2
H
4
FE....
Chapter 17
Figure 17.1 (a) Atomic structure of M–N
4
–C
10
and M–N
2+2
–C
8
(M = Fe or Co...
Figure 17.2 (a) FE
CO
and
on different amounts of Cu doping. (b) Cu atom pa...
Figure 17.3 (a) Optimized atomic structures of CuSAs/TCNFs and proposed reac...
Figure 17.4 The molecular reaction pathway diagram of the ECORR. H
2+
rep...
Chapter 18
Figure 18.1 (a) A schematic of the conventional H‐type electrochemical cell....
Figure 18.2 A schematic diagram of various configurations for electrochemica...
Figure 18.3 (a) A conventional schematic diagram of a gas diffusion electrod...
Chapter 19
Figure 19.1 Double‐layer models, according to (a) Helmholtz, (b) Gouy–Chapma...
Figure 19.2 Schematic representation of catalyzed and non‐catalyzed chemical...
Figure 19.3 A hypothetical free energy relationship illustrating the reactio...
Figure 19.4 Typical time length scales in catalysis.
Chapter 20
Figure 20.1 A timeframe of the development of reactivity descriptors and sca...
Figure 20.2 (a) The
local density of state
s (
LDOS
s) change where an adsorbat...
Figure 20.3 Calculated generalized coordination numbers describing the adsor...
Figure 20.4 (a) Adsorption scaling relationships for adopted adsorbates on n...
Figure 20.5 (a) Representative illustration of Sabatier principle.(b) Th...
Figure 20.6 (A) A representation of a catalyst surface‐involved processes: m...
Figure 20.7 The
Δ
G
GCHE
energy as a function of work function and
eU
RHE
,...
Figure 20.8 Schematic representation of reaction field concept (a),, and...
Figure 20.9 Water/Cu simulation with hydrogen bonds and Na
+
ion's inclus...
Figure 20.10 Water shuttling simulation for proton–electron transfer to *CO ...
Figure 20.11 (a) Schematic simulation of hydrogen adsorption on Cu(111) (A →...
Chapter 21
Figure 21.1 (a) The adsorption scaling of metal classification according to ...
Figure 21.2 Illustration for breaking the scaling relationships by (a)
Nitro
...
Figure 21.3 (A) ORR volcano plot for metals.(B) Scaling relations betwee...
Figure 21.4 OER volcano plots according to various descriptors, such as (a) ...
Figure 21.5 (a) Theoretical volcano–activity curve of HER where
α
is th...
Figure 21.6 (a) Representation of DOS plot (top) and a qualitative indicatio...
Figure 21.7 Calculated DOS over different surfaces, such as (a and b) CO pro...
Chapter 22
Figure 22.1 Schematic presentation for DFT output; such as catalyst represen...
Figure 22.2 (a) Overview of possible pathways for ECR toward various product...
Figure 22.3 Schematic representation of two possible OER mechanisms; AEM (a)...
Scheme 22.1 Elementary steps of OER half‐reaction.
Scheme 22.2 ORR processes with thermodynamic potentials and elementary steps...
Figure 22.4 Free energies diagram for four‐electrons (a) and two‐electrons (...
Figure 22.5 (a) Schematic illustration of HER mechanism possibilities in aci...
Figure 22.6 (a) Schematic representation of HER mechanism possibilities....
Scheme 22.3 The elementary steps of HOR possible mechanisms.
Scheme 22.4 Elementary steps of several mechanisms for CO oxidation.
Figure 22.7 Free energies diagrams of CO oxidation via different possible (a...
Figure 22.8 (a) Schematic diagram of possible FAOR mechanisms.(b) Illust...
Figure 22.9 Solvation profiles of Langmuir–Hinshelwood (a) and Eley–Rideal (...
Figure 22.10 (a) Schematic diagram for MOR under CH and OH cleavage pathways...
Scheme 22.5 Calculated reaction network and reaction barriers (units, eV) fo...
Figure 22.11 Free energy surfaces as (a) a function of the position
d
2
of th...
Figure 22.12 (a) Representation of global minima structures of ECR possible ...
Figure 22.13 Computed HER/HOR polarization plots using the DFT incorporation...
Figure 22.14 (a) Trends in ORR activity plotted as a function of the O and t...
Figure 22.15 (a) Corresponding theoretical limiting potentials for HER and E...
Chapter 23
Figure 23.1 Illustration of electromagnetic radiation range expressing its i...
Figure 23.2 Schematic designs of different in situ IR configurations and cel...
Figure 23.3 Different adjustments of Raman spectroscopy setup for in situ el...
Figure 23.4 UV–vis spectroscopy for in situ electrochemical measurements. (a...
Figure 23.5 In situ X‐ray techniques. (a) Schematic illustration of the cust...
Figure 23.6 Different designs of electrochemical MS cells for in situ analys...
Figure 23.7 In situ electron‐based characterization techniques. (a) A schema...
Chapter 24
Figure 24.1 Exploring the electronic changes by XAS characterization: (a, b;...
Figure 24.2 Monitoring the electronic change using sXAS and Raman in situ te...
Figure 24.3 The electronic reversibility of CoAl
2
O
4
by DRUV spectroelectroch...
Figure 24.4 Capturing the atomic structure evaluations: fitted first shell o...
Figure 24.5 Tracking the atomic structure of HKUST‐1‐derived Cu clusters in ...
Figure 24.6 Detecting phase changes by in situ XAS measurements on Pd cataly...
Figure 24.7 Phase evaluation by in situ grazing‐angle X‐ray diffraction: (a)...
Figure 24.8
Electrochemical scanning tunneling microscopy
(
ECSTM
) and EC‐AFM...
Figure 24.9 Molecular adsorption and activation by in situ XAS and XPS inves...
Figure 24.10 Probing ECR intermediate species using in situ FTIR: (a) Predic...
Figure 24.11 Intermediate detection by in situ Raman: Raman shift on Pt(111)...
Figure 24.12 Schematic representations of the detection of carbonate (a) and...
Figure 24.13 Product detection using in situ MS measurements: (a) mormalized...
Figure 24.14 In situ ECR product quantification: (a and b) Comparison of the...
Figure 24.15 Phase stability evaluated by in situ XAX of 1
T
′ MoS
2
. The norma...
Figure 24.16 M–N–C‐like materials stability interpreted by in situ XAS chara...
Figure 24.17 In situ probing catalyst decay using ICP‐MS measurement: (a) ra...
Figure 24.18 (a) Representative scheme of buffer reactions, pH gradient, and...
Figure 24.19 (a and b; right) Voltage‐dependent Raman spectra of MOR and ORR...
Chapter 25
Figure 25.1 (a) Distribution of FE with corresponding overpotential. (b) Max...
Guide
Cover Page
Table of Contents
Begin Reading
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Electrocatalysis in Balancing the Natural Carbon Cycle
Yaobing Wang
Author
Prof. Yaobing Wang
Fujian Institute of Research on the Structure of Matter CAS
155#, YangQiao West Road
Gulou District
350002 Fuzhou
China
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Preface
In recent years, sustaining the carbon cycle and producing valuable fuels that may considerably reduce dependence on fossil fuels using electrocatalysis has grown. A great deal of interest has arisen, leading to an increase in young researchers entering this area. This book focuses on the aspects of efficient redox catalysis, such as water and carbon dioxide electrolysis toward hydrogen and fuel‐based energy systems, respectively, and remarkable energy technologies such as fuel cells and metal–air batteries. An introduction and recent progress are provided, emphasizing reaction conversions developments over various types of electrocatalysts. In addition, the book includes chapters that attract not only experimentalists but also theoretical chemists who have interest in the electrocatalyst design.
The book comprises 10 parts. The first three parts provide a solid introduction for the electrocatalytic carbon cycle addressing water splitting, carbon dioxide reduction, and its counterpart, the oxidation of small organic molecules, followed by detailing each related reaction in separated part: (i) part IV presents water‐splitting devices after describing the key fundamental research developments of water oxidation and reduction reactions, (ii) part V includes hydrogen and oxygen‐related electrocatalytic aspects with well‐defined fuel cell and batteries models, (iii) part VI illustrates the oxidation of C1 and C2+ molecules as up‐and‐coming advanced power systems, and (iv) part VII reviews the fundamentals in carbon dioxide reduction reaction including well‐defined catalytic electrodes as well as the current and next generation of its devices. From the experimentation developments to the theoretical approaches, part VIII focuses on the kinetics and thermodynamics of the reactions aforementioned. For the most popular current motifs, the fundamentals of computational screening, descriptors, and modeling are outlined, as well as their application toward catalyst design direction instead of trial‐and‐error approach. While emerging the advanced characterizations addressing the in situ techniques become shining, part IX includes modern analytical methods to uncover the surface evolution/reconstruction of a given catalyst under the electrocatalytic conditions, which drive the electrochemical surface science research toward confirming the real active sites of a desired catalytic performance. The book ends with part X evaluating the electrocatalytic carbon cycles and its involved redox reactions. The parts are detailed as follows:
In Chapter 1, Prof. Yaobing Wang discusses the motivation for writing this book introducing the natural carbon cycle (NCC) and the emergence of its challenges in multiple environmental and ecological systems due to the overuse of fossil fuels and the increasingly severe energy crisis. Prof. Yaobing Wang highlights the electrochemical carbon cycle (ECC) as an endorsed solution for such concerns. In Chapter 2, Mr. Wei Wang and Dr. Jiafang Xie explain the various aspects in NCC from organic to inorganic cycle and vice versa, as well as anthropogenic carbon standpoint. In Chapter 3, Miss Zhen Peng and Dr. Jiafang Xie present the possible involved reaction in the ECC including oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), electrochemical carbon dioxide reduction reaction (ECDRR), and small molecule oxidation reaction (MOR) from mechanistic viewpoint and their evaluation parameters such as Faradic efficiency (FE), Tafel slope, current density, and onset potential. In Chapter 4, Miss Rui Yang and Dr. Yiyin Huang go through water‐splitting reactions in various pH media and evaluation of their catalytic parameters such as turnover frequency (TOF), stability, and FE. In Chapter 5, Miss Rui Yang and Dr. Yiyin Huang specify the regular OER over various electrocatalytic materials and further consider the photo‐assisted OER. As HER is involved in water splitting, Miss Rui Yang and Dr. Yiyin Huang explore it in Chapter 6 over noble and non‐noble catalysts, in addition to the overall device. In Chapter 7, Mr. Zipeng Zeng, Dr. Parameswaram Ganji, and Dr. Yiyin Huang cover the basic parameters for hydrogen oxidation reaction (HOR) and ORR. In addition, they review the catalytic materials, the possible pathways, and the final products of HOR and ORR in Chapters 8 and 9, respectively. In Chapter 10, the focus of Mr. Zipeng Zeng, Dr. Parameswaram Ganji, and Dr. Yiyin Huang goes to H2 fuel cell and metal–air batteries as promising devices in which these reactions undergo. Moving to small MOR, Miss Xueyuan Wang and Dr. Yiyin Huang outline the measurement conditions in Chapter 11. MOR could be classified into C1 and C2+ reactants; thus, Miss Xueyuan Wang and Dr. Yiyin Huang describe C1 (including methane, methanol, and formic acid) and C2+ (including ethanol, glucose, ethylene glycol, and glycerol) reactions and their advances in Chapter 12 and 13, respectively. Miss Xueyuan Wang and Dr. Yiyin Huang give a general model and the advantage of the related typical device, the direct liquid fuel cell (DLFC) in Chapter 14. Parallel with schematic content, Mr. Rahul Anil Borse and Dr. Jiafang Xie elaborate the experimentation fundamentals (Chapter 15), the electrocatalytic advances of the ECDRR on various catalytic materials (Chapters 16 and 17); in addition, the available fabricated devices and their aspects (Chapter 18). Transferring from the experimentations into theoretical approach, Mrs. Aya Gomaa Abdelkader Mohamed provides more fundamental insights into the catalytic process addressing the electric double layer, the thermodynamics and kinetics, and the electrode potential effects in Chapter 19. In Chapter 20, Mrs. Aya Gomaa Abdelkader Mohamed covers the computational theories (such as DFT) and their principles such as reactivity descriptors and scaling relationships, which are related into the electrocatalytic process. Mrs. Aya Gomaa Abdelkader Mohamed explores how these principles can guide the rational design toward high‐performance and desired catalyst in Chapter 21. Moreover, Mrs. Aya Gomaa Abdelkader Mohamed reveals the computational applications to get deep understanding of the electrocatalytic mechanism for ORR, OER, HER, HOR, ECO2RR, and various MOR, as well as the electrocatalytic environment, and analyze their kinetics in Chapter 22. Recently, the in situ characterizations have become potential to identify the real active sites. Therefore, Mr. Mostafa Ragab Hassan and Mrs. Aya Gomaa Abdelkader Mohamed cooperate to give a basic background for the most reported in situ characterizations, which are classified into optical, X‐ray, mass, electron‐based techniques in Chapter 23. The investigation of a given catalyst in several electrocatalytic reactions by the in situ analysis is addressed in Chapter 24 by Mrs. Aya Gomaa Abdelkader Mohamed and Mr. Mostafa Ragab Hassan in different aspects such as probing the real active sites, determining the reaction mechanism, evaluating the catalyst stability/decay, and providing interfacial‐related insights. Finally, Dr. Jiafang Xie proposes the anthropogenic ECC solution to supplement unbalanced NCC from a global viewpoint in which the advances in critical electrocatalysts and performance for ECDRR (Chapter 25) and electrochemical fuel oxidation (Chapter 26) are presented. Then, several key indexes, external managements, and general principles are proposed to evaluate, support, guide the overall efficiency of ECC in Chapter 27.
This multidisciplinary work is not just a reference for the electrochemistry researchers, but also a handy book for advanced graduate‐level students in surface science‐, engineering‐, and theoretical‐related courses, especially those with interest in developing novel catalysts for efficient energy conversions, as well as the experienced researchers seeking to expand their scope.
19 November 2020
Yaobing Wang
Fujian Institute of Research
on the Structure of Matter
Chinese Academy of Sciences
Fuzhou, Fujian
China
Acknowledgments
I much acknowledge the dedication of all the authors who worked on this work. Without their effort, the book could not have been finished. My appreciation also goes to Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, my family, my wife, and two daughters, as well as Wiley Publishing, specially Lifen Yang, Katherine Wong, etc.
Part IIntroduction
Electrocatalysis is considered a core technique for sustaining the carbon cycle and producing valuable fuels as an additional benefit. In recent years, a great deal of interest has arisen in efficient redox catalysis, such as water and carbon dioxide electrolysis toward hydrogen and fuel‐based energy systems, respectively, and remarkable energy technologies such as fuel cells and metal–air batteries. Understanding the fundamental aspects and the catalytic behavior of such reactions plays a considerable role in further commercializing electrocatalytic energy devices, helping to close the carbon cycle. In this part, we are going to discuss the motivation for writing this book and presenting a preface to its contents. Our hope is that this book will prove useful to researchers already familiar with electrocatalysis but interested in acquiring more insights and in‐depth digestion of state of the art of their catalysis research.
1Introduction
Carbon cycle is the basic cycle on earth to maintain all the life forms. In the earth, there are four primary carbon pools [1]. Among them, the natural carbon cycle (NCC) mainly refers to the cyclic change of carbon in the three‐carbon pools of atmospheric carbon pool, marine carbon pool, and terrestrial ecosystem carbon pool [1–4]. The atmospheric carbon has a direct influence on human life; therefore, it attracts great attention from researchers. The carbon in the atmospheric carbon pool mainly exists in the form of CO2 gas. The basic process of the NCC can be expressed as follows [1,5]: CO2 in the atmosphere is solidified into organic carbon through photosynthesis of plants and stored in plants. Part of the organic carbon in plants releases CO2 into the atmosphere through the plant's respiration (i.e. autotrophic respiration), the consumption of organic carbon by animals, and the decomposition of organic matter by microorganisms (i.e. heterotrophic respiration), forming a terrestrial ecology system carbon cycle process.
Since the industrial revolution and with the rapid world population/economic expansion, people utilized more and more fossil fuels for providing raw materials and electrical power, etc. [6]. Challenges in multiple environmental and ecological are emerging due to the overuse of fossil fuels and the increasingly severe energy crisis [7]. The results are that the NCC has been increasingly broken, leading to unavoidable sustainability in energy and environment, threatening the survival of human society. Thus, various strategies and various renewable energy technologies have been developed from all aspects to solve the broken NCC and maintain the sustainability of human society and the economy [8,9]. These techniques include fuel cells, CO2 electrolysis, metal‐air batteries, water splitting, and so on. All of these techniques consist of the kernel and/or secondary components in artificial nature carbon cycle (ACC) to supplement for the NCC with synergistic effects [5,7]. These techniques are mainly powered by solar‐derived electricity, which were also defined as the artificial electrochemical carbon cycle (ECC). The ECC mainly involves electrochemical oxidation of chemicals and fuels into CO2 (CO2 liberation) and electrochemical reduction of CO2 into value‐added chemicals/fuels (CO2 fixation), and also other fuel storage and transport, and other secondary reactions for supporting the carbon‐based electrochemical reactions.
For the realization of ECC, the extensive fundamental and utilitarian electrochemical processes, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), small organic molecule oxidation reaction, hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), and electrochemistry carbon dioxide reduction reaction (ECDRR), were involved. In the water splitting processes [10], water oxidation (OER) occurs on the anode, and four‐electron transfer is needed for a complete OER. At the same time, the generated electron and proton will be combined on the cathode and releasing H2 from the cathode. In various fuel cells [11,12], HOR via the two‐electron transfer process and various small organic fuel (ethanol, formic acid, methanol, glucose oxidase, ethylene, glycerol, glycol, etc.) oxidation occur on the anode, while ORR takes place on the cathode. The cathode of metal‐air batteries [13] also employs ORR processes. For the CO2 electrolysis [14], CO2 was electrochemically transformed into various fuels, as mentioned earlier, via different electron‐transfer processes.
The generally sluggish reaction kinetics is always a bottleneck that limits the overall performance of the new energy devices, hindering their progress of commercialization [15,16]. To drive these electrochemical processes, electrocatalysts are required. Noble metal catalysts are widely used in these electrocatalytic processes due to their high activity and stability. On the other hand, the high cost hinders their commercialization. Various non‐noble metal catalysts were also developed, such as carbon materials, polymer, transition metal materials, and metal‐organic materials [15]. With the development of nanotechnology and nanoscience over the past decades, the research mode for developing electrocatalysts has shifted gradually from the traditional trial‐and‐error methods to the accurate design and fabrication of nanocatalysts at atomic and molecular levels [15,17,18]. Besides, other factors in the electrochemical devices, such as the device structure, electrolyte, electrode configuration, and operation temperate, should be considered toward the high performance of the devices. Among these controllable factors, the electrocatalyst design is still among the core factor. To achieve the rational design of electrocatalyst for highly efficient electrocatalytic reaction processes, studies on the active sites' recognition, reaction mechanism, and kinetic and thermodynamic processes should be conducted. In this sense, computational methods combined with in situ characterization techniques allowed the researcher to realize an in‐depth and comprehensive understanding of realistic reaction conditions into the nature of the active sites and its interaction with reactants, intermediates, and products and the final overall catalytic processes.
In this book, we will discuss the reaction mechanism and core reaction parameters (e.g. turnover frequency [TOF], onset potential or overpotential, stability, Faradaic efficiency, partial current density) of these electrochemical reactions strongly to the ECC and summarize the advances of various catalysts in terms of the categories to gain an overview on the design principles for electrocatalysts toward various electrochemical reactions. The device categories and advances will also be summarized, with respect to the electrolyte, device structure, electrode, and external environment controls. Then, theoretical calculations for these electrocatalytic reactions were introduced in terms of background, concepts, processes, and applications. Besides, an overview of the common and the most crucial in situ characterization techniques was summarized to assist the theoretical calculations study and help the electrocatalyst design. Further, we have summarized the advances on electrochemical reactions highly related to the ECC, that is, ECDRR, and fuel oxidation for the chemical conversions including CO2/CO, CO2/HCOOH, CO2/CH3OH, and CO2/CH3CH2OH, along with presenting the mechanistic understanding and proposed key indexes, general principles, and external managements for evaluating and optimizing the overall ECC efficiency. Finally, current challenges and future perspectives for promoting ECC to supplement NCC were concluded. It is believed that this book will provide a comprehensive, deep‐going, and cutting‐edge introduction on the ECC and related electrocatalysis.
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Part IINatural Carbon Cycle
Nature's photosynthesis uses green plants to absorb carbon dioxide (CO2) from the atmosphere, convert it into glucose and release oxygen with the participation of water, and organisms reuse glucose to synthesize other organic compounds. Only when enough geological time is given can new fossil fuels be formed naturally. Due to the continuous massive consumption of fossil fuels by human beings, a large amount of CO2 is produced. These anthropogenic CO2 emissions exceed the recovery capacity of natural CO2, causing serious damage to the environment. In order to supplement the natural carbon cycle, the researchers proposed and developed a feasible chemical cycle of anthropogenic CO2. Carbon dioxide can be captured from the atmosphere or industrial production through absorption technology. Then it can be converted into fuel through feasible chemical conversion. For example, by electrochemical reduction method, CO2 can be efficiently converted into reusable chemical products under normal temperature and pressure, such as carbon monoxide (CO), formic acid (HCOOH), methane (CH4), ethylene (C2H4), ethanol (CH3CH2OH), etc. The required renewable raw materials, water, and CO2 can be used anywhere on earth. The energy required for the synthetic carbon cycle can come from any alternative sustainable clean energy, such as solar energy, wind energy, geothermal energy, and even safe nuclear energy. When fossil fuels become scarce, the anthropogenic CO2 cycle provides a way to ensure a sustainable future for humanity.
2Natural Carbon Cycle and Anthropogenic Carbon Cycle
2.1 Definition and General Process
Carbon is an essential part of all life forms on Earth. There are four main carbon pools in the earth system: atmospheric carbon pool, marine carbon pool, terrestrial ecosystem carbon pool, and lithosphere carbon pool. Among them, the lithospheric carbon pool mainly exists in the earth's rocks and its cycle period is the geological age scale, which is up to millions of years. It can be considered that the lithospheric carbon pool is fixed on the scale of hundreds of years, so the natural carbon cycle mainly refers to the cyclic change of carbon in the three‐carbon pools of atmospheric carbon pool, marine carbon pool, and terrestrial ecosystem carbon pool. The size of the atmospheric carbon pool is about 700 GtC, which is the smallest carbon pool among the three‐carbon pools, but because the atmosphere directly affects human life, the atmospheric carbon pool was the first to attract people's attention. The carbon in the atmospheric carbon pool mainly exists in the form of CO2 gas. The ocean, which accounts for 71% of the earth's surface, is a huge carbon pool with carbon storage of about 38 000 Gt. It is more than 50 times the atmospheric carbon pool and 20 times the terrestrial carbon pool, the largest of the three‐carbon pools. The primary forms of carbon in the ocean are dissolved inorganic carbon, dissolved organic carbon, carbonate, particulate organic carbon, etc., of which more than 97% is dissolved in the form of inorganic carbon. The carbon storage of terrestrial ecosystems is about 2000 Gt, of which the carbon storage of living organisms is 600–1000 Gt and the storage of soil organic carbon such as biological residues is about 1200 Gt. The basic process of the terrestrial ecosystem carbon cycle is: CO2 in the atmosphere is solidified into organic carbon through photosynthesis of plants and stored in plants [1,2]. The chemical expression of photosynthesis is formula (Figure 2.1). Part of the organic carbon in plants releases CO2 into the atmosphere through the plant's own respiration (i.e. autotrophic respiration), the consumption of organic carbon by animals, and the decomposition of organic matter by microorganisms (i.e. heterotrophic respiration), forming a terrestrial ecology system carbon cycle process. In short, the natural carbon cycle includes carbon chemical and biological processes and is a comprehensive and complex system. In this article, we focus on the chemical processes of the carbon cycle.
Figure 2.1 Light and dark reactions of photosynthesis.
Source: Dogutan and Nocera [3]. © 2019, American Chemical Society.
2.2 From Inorganic Carbon to Organic Carbon
In the natural carbon cycle, the energy of the sun is used by vegetation, plankton, algae through photosynthesis, along with the recovery of carbon dioxide from the natural environment. In this process, water serves as a source of hydrogen and green chlorophyll as a catalyst, which ultimately creates new plant life. It will eventually be converted into fossil fuels over millions of years [4].
Photosynthesis occurs in the chloroplasts of plant cells and is divided into two stages: the light reaction stage and the dark reaction stage [3]. Under the catalysis of the photosynthetic system II (Photosystem II), water is broken down into electrons, oxygen, and protons (photoreaction, Figure 2.1). Among them, electrons are transported along the electron transfer chain to Photosystem I (Photosystem I) through a series of electron transport substances and participate in the generation of reduced coenzyme II (triphosphopyridine nucleotide, nicotinamide adenine dinucleotide phosphate [NADPH]), which is used to fix carbon dioxide in the subsequent dark cycle (dark reaction, Figure 2.1). The whole process involves not only the synthesis and decomposition of various substances but also various energy conversions: from light energy to electrical energy, to biological energy, and finally to chemical energy. This series of processes achieves energy conversion and cleverly fixes solar energy into green plants.
The hydrogen evolution reaction (HER) is a simple 2e−/2H+ process, which is kinetically easier than reducing the multi‐electron/multi‐proton of carbon dioxide to biomass. Therefore, systems that directly reduce carbon dioxide in water face the challenge of suppressing HER with greater kinetic advantages and competitiveness. Photosynthesis does not use H2O but uses H2 equivalent (NADPH/H+) to reduce CO2, thereby avoiding the HER during CO2 reduction. However, photosynthesis is relatively inefficient in converting solar energy in the form of sugar, cellulose, lignin, etc. into chemical energy. In spite of some green plants enable about 8% of solar energy to be converted into biomass, the photosynthetic efficiency of most crops is usually limited to 0.5–2%. Substances produced by photosynthesis can eventually be transformed into fossil fuels under anaerobic conditions through the decay of animals and plants. Therefore, fossil fuels are also often regarded as stored fossil solar energy. However, the natural circulation of regenerated fossil fuels requires certain special conditions to proceed, and this process is prolonged.
Carbon dioxide can be used as the only carbon source for many microorganisms found in the microbial world. There are several ways and solutions for organisms to reduce carbon dioxide to organic carbon. The most important one is Calvin reducing the pentose phosphate pathway. Throughout the evolutionary process, the immobilization, reduction, and reconstruction of CO2 receptor molecules will be involved. Therefore, some autotrophic bacteria, almost all photosynthetic bacteria, eukaryotic algae, and some prokaryotes and green plants absorb carbon dioxide through the Calvin cycle. Reactions unique to this pathway are catalyzed by ribulose 1,5‐bisphosphate (RuBP) carboxylase/oxygenase, and phosphoribulokinase (PRK). In some cases, there is a distinct sedoheptulose 1,7‐bisphosphatase, separate from fructose 1,6‐bisphosphatase, that may be considered unique to the Calvin cycle [5]. Although the Calvin reductive pentose phosphate pathway is the major assimilatory path used in the biosphere, many autotrophic species fix CO2 by different routes. In particular, the acetogenic bacteria and the methanogens reduce CO2 to acetate (and other short‐chain fatty acids) or methane, respectively. The green photosynthetic bacteria appear to be unusual among photosynthetic organisms in not using the Calvin cycle to reduce CO2.
2.3 From Organic Carbon to Inorganic Carbon
Carbon dioxide gas is part of the atmosphere (about 0.03% of the total volume of the atmosphere) and is abundant in nature. The main ways of producing carbon dioxide in nature are: the respiration of plants and animals converts part of the organic carbon taken into the body into carbon dioxide and releases it into the atmosphere, and the other part constitutes the organism's body or is stored in the body. After the death of animals and plants, the organic carbon in the debris is also converted into carbon dioxide by the decomposition of microorganisms and finally discharged into the atmosphere. The cycle of carbon dioxide in the atmosphere takes about 20 years.
2.4 Anthropogenic Carbon Cycle
By imitating the natural carbon cycle, humans have developed an artificial model to utilize CO2 present in the atmosphere and water (Figure 2.2) [6]. The anthropogenic carbon cycle is based on the capture, and where needed, temporary storage of CO2 followed by its chemical/physical recycling (carbon capture and recycling) into products. Compared with the natural carbon cycle, the anthropogenic carbon cycle can be industrially scaled to produce sustainable, renewable, and environmentally friendly carbon sources. At the same time, human‐made carbon dioxide recycling can reduce the harmful effects of excess carbon dioxide in the atmosphere in the global environment [7]. Therefore, carbon dioxide should be regarded as a valuable industrial C1 raw material, not just a greenhouse gas that harms the global environment.
Figure 2.2 Sustainable anthropogenic recycling of atmospheric CO2 to fuels and materials. CCR, carbon capture and recycling; CCS, carbon capture and storage; DME, dimethoxyethane.
Source: Goeppert et al. [6]. © 2013, Newslands Press Ltd.
2.4.1 Anthropogenic Carbon Emissions
Anthropogenic carbon emissions refer to various forms of carbon emissions (mainly carbon dioxide) resulted from human activities. Human activities that increase net emissions include but are not limited to the burning of fossil fuels, logging of forests, changes in land‐use patterns, livestock, and fertilizers. The concentration of CO2 in the atmosphere has kept steadily increasing in the last 60 years, rising to 416 ppm from 315 ppm [8]. Global CO2 emissions from fossil fuel combustion and industrial activities have increased every 10 years, from an average of 11.4 Gt CO2 per year in the 1960s to an average of 34.7 ± 2 Gt CO2 per year from 2009 to 2018. Emissions in 2018 reached a record 36.6 ± 2 Gt CO2; the emissions from the burning of coal, oil, natural gas, cement, and natural gas account for 40%, 34%, 20%, 4%, and 1% of the total global emissions, respectively [8]. The anthropogenic CO2 emissions mainly come from scattered small emission sources, such as heating and cooling of houses and offices, agricultural production, and the most important transportation industry. Now, it is generally believed that the excessive release of carbon dioxide along with other greenhouse gases is caused by human activities and is the main factor leading to global warming. They also caused other serious environmental damage, including ocean acidification, sea‐level rise, more frequent extreme climate events, and unpredictable changes in biodiversity. Therefore, many efforts have been made worldwide to reduce carbon dioxide emissions of carbon dioxide in the atmosphere, including the famous Paris Agreement in the United Nations Framework Convention on Climate Change. Governments have promulgated laws to limit carbon dioxide emissions in industrial production. At the same time, individuals are encouraged to use clean energy and purchase clean energy vehicles that use non‐gasoline fuel. In addition, scientists are actively studying the industrial application of CO2.
2.4.2 Capture and Recycle of CO2 from the Atmosphere
The bulk of carbon dioxide emissions comes from scattered, small‐scale sources. It would be difficult and expensive to collect CO2 from millions of or even billions of small fossil‐fuel combustion plants [4]. For example, the cooling or heating of homes and offices produces a widely dispersed and limited amount of carbon dioxide. The capture and transportation of these CO2 will require a large amount of expensive infrastructure, which is obviously impractical. Therefore, in order to deal with small‐scale CO2 emission sources and to avoid the development and construction of huge CO2 collection infrastructure, capturing CO2 from the air is an ideal strategy [9,10]. The atmosphere can be considered a medium that transmits CO2 emissions to its capture location; it is like a free “natural carbon dioxide conveyor belt.” Since the concentration of CO2 in the air in the world is in equilibrium, this will make the collection site of CO2 not affected by the source of CO2 emissions and can capture CO2 from a variety of sources.
Alkaline absorbents (such as NaOH or KOH) can be used to capture CO2 from the atmosphere. These absorbents react with CO2 to form Na2CO3 and K2CO3, respectively. The absorption of CO2 is an exothermic reaction and can be easily implemented by mixing CO2 with an appropriate alkali. However, desorption, as the opposite step, is an endothermic process, so additional energy is required to regenerate the alkali and recover the CO2. Both CaCO3 and Na2CO3 require a lot of energy to recycle alkali, so they are not suitable for capturing and releasing CO2. KOH is considered to be a promising absorbent. Electrolysis of K2CO3 in water can effectively produce CO2, accompanied by H2 production.
The physical absorption of carbon dioxide by solids is accomplished by the reversible adsorption of certain substances in the mixture on the solid surface. Solids with good physical adsorption properties include silica gel, zeolite, alumina, activated carbon, and other materials with large pore size distribution and specific surface area. Among them, some zeolite adsorbents show high CO2 absorption capacity at room temperature (13X zeolite, 160 mg CO2 g−1 zeolite, and 4A zeolite, 135 mg CO2 g−1 zeolite) [11]. However, these adsorbents all have the problem that as the increase of temperature, the adsorption property weakens speedily. In addition, since the gas is fixed on the adsorbent by physical adsorption, the separation coefficient between the gas of different components is very low. This makes it impractical to capture CO2 from a mixed gas source containing low CO2 content. Therefore, in practical use, the adsorbent is often required to have high adsorption capacity and easy regeneration and high selectivity for CO2. Currently, the metal–organic framework (MOF) has also been found to have high CO2 storage capacity. For example, MOF‐177 consists of zinc clusters and 3,5‐triphenyltricarboxylic acid triphenyl ester units. Its surface area is up to 4500 m2 g−1. At 30 atm, the CO2 storage per gram of MOF is about 1.47 g [12,13]. However, under lower pressure and mixed gas conditions, the absorption capacity of MOF is more restricted.
2.4.3 Fixation and Conversion of CO2
Much of the CO2 used today is obtained not only as a byproduct of industrial processes such as ammonia production, oil and gas refineries, ethanol production, and chemical manufacturing but also natural sources such as geological formations. However, any CO2 source, including CO2 captured from fossil fuel‐burning power plants and the atmosphere, could be used. The products for which CO2 can be used as a feedstock are by no means limited to the ones obtained presently from CO2. Essentially, all the fuels and materials currently derived from fossil fuels could potentially be made from CO2 through various synthetic pathways. The utilization and recycling of CO2 through chemical, electrochemical, photochemical, and other routes have been extensively covered and reviewed in light of the increasing concerns about climate change [14–19].
