Electrochemical Engineering E-Book

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Wissenschaft und neue Technologien
• Serie: Advances in Electrochemical Sciences and Engineering
• Sprache: Englisch

Seitenzahl: 658

Veröffentlichungsjahr: 2018

Beschreibung

This volume in the "Advances in Electrochemical Sciences and Engineering" series focuses on problem-solving, illustrating how to translate basic science into engineering solutions.

The book's concept is to bring together engineering solutions across the range of nano-bio-photo-micro applications, with each chapter co-authored by an academic and an industrial expert whose collaboration led to reusable methods that are relevant beyond their initial use.

Examples of experimental and/or computational methods are used throughout to facilitate the task of moving atomistic-scale discoveries and understanding toward well-engineered products and processes based on electrochemical phenomena.

Leseprobe

Table of Contents

Cover

Series Preface

Preface

Chapter 1: Introductory Perspectives

References

Chapter 2: The Joint Center for Energy Storage Research: A New Paradigm of Research, Development, and Demonstration

2.1 Background and Motivation

2.2 Lithium‐ion Batteries: Current State of the Art

2.3 Beyond Li‐Ion Batteries

2.4 JCESR Legacies and a New Paradigm for Research

2.5 The JCESR Team

2.6 JCESR Operational Tools

2.7 Intellectual Property Management

2.8 Communication Tools

2.9 JCESR Change Decision Process

2.10 Safety in JCESR

2.11 Battery Technology Readiness Level

2.12 JCESR Deliverables

2.13 Scientific Tools in JCESR

2.14 Techno‐economic Modeling

2.15 The Electrochemical Discovery Laboratory

2.16 Electrolyte Genome

2.17 Combining the Electrolyte Genome with Techno‐economic Modeling

2.18 Prototype Development

2.19 Legacy of JCESR

2.20 Conclusion

Acknowledgments

References

Chapter 3: Determination of Redox Reaction Mechanisms in Lithium–Sulfur Batteries

3.1 Basics of Lithium–Sulfur Chemistry

3.2 End Products of Electrochemical Reactions in the Sulfur Cathode sulfur cathode"?> sulfur cathode!end-products"?>

3.3 Intermediate Products of Electrochemical Reactions in the Sulfur Cathode

3.4 Fingerprinting Lithium Polysulfide Intermediates

3.5 In Situ Spectroscopic Studies of Li–S Batteries

3.6 Practical Considerations

3.7 Concluding Remarks

Acknowledgment

References

Chapter 4: From the Lab to Scaling‐up Thin Film Solar Absorbers

4.1 Introduction

4.2 State‐of‐the‐art Electrodeposition for Photovoltaics

4.3 Electrodeposited Cu

2

ZnSn(Se,S)

4

(CZTS) and Emerging Materials

4.4 From the Rotating Disk to the Paddle Cell as a Scale‐up Platform

4.5 Scaling‐up to 60 cm × 120 cm from Tiny Electrodes to Meters

4.6 Conclusions

Acknowledgments

References

Chapter 5: Thin‐film Head and the Innovator's Dilemma

5.1 Introduction

5.2 Thin‐film Head Technology

5.3 Data Storage Business in Japan

5.4 The Innovator's Dilemma

5.5 TMR Head

5.6 Discussion

Acknowledgments

References

Chapter 6: Development of Fully‐Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions

6.1 Introduction

6.2 Current Methods

6.3 Development of Dewatering Technologies for Phosphatic Clays

6.4 Economic Assessment for On‐site Implementation

6.5 Our Next Prototype: Dual‐zone Continuous Operation

6.6 Conclusions

Acknowledgments

References

Chapter 7: Breaking the Chemical Paradigm in Electrochemical Engineering: Case Studies and Lessons Learned from Plating to Polishing

7.1 Introduction

7.2 A Brief Overview of Pulse Reverse Current Plating

7.3 Early Developments in Pulse Plating

7.4 Transition of Pulse Current Plating Concepts to Surface Finishing

7.5 Concluding Thoughts

Acknowledgments

References

Chapter 8: The Interaction Between a Proton and the Atomic Network in Amorphous Silica Glass Made a Highly Sensitive Trace Moisture Sensor

8.1 Unexpected Long Propagation of Surface Acoustic Waves Around a Sphere

8.2 Invention of a Ball SAW Device and Application to Gas Sensors

8.3 Unexpected Fluctuations in the Output Signal of the Gas Sensor Leading to the Development of Trace Moisture Sensors

8.4 Sol–Gel Silica Film for the Trace Moisture Sensors

8.5 A Thermodynamic Model of Interaction of Water Vapor with Amorphous Silica Glass

8.6 Concluding Remarks

References

Chapter 9: From Sensors to Low‐cost Instruments to Networks: Semiconducting Oxides as Gas‐Sensitive Resistors

9.1 Overview

9.2 Basic Science of Semiconducting Oxides as Gas‐Sensitive Resistors

9.3 Commercial Development of Sensors and Instruments

9.4 Conclusion and Prospects

Acknowledgment

References

Index

End User License Agreement

List of Tables

Chapter 2

Table 2.1 Goal performance metrics for JCESR prototypes when projected to battery packs, as written in the JCESR proposal.

Table 2.2 JCESR collaboration mechanisms.

Chapter 3

Table 3.1 UV–Vis absorption peak assignments in nonaqueous solvents in the literature; method A, 2Li +

S

8

→ Li

2

S

x

; B, Li

2

S +

S

8

→ Li

2

S

x

; C, electrochemical reduction of S

8

.

Chapter 4

Table 4.1 List of parameters to be monitored in a copper plating chemistry for thin film PV applications.

Chapter 6

Table 6.1 Results of power and energy calculations for dewatering of simulated one‐square‐mile clay‐settling area.

Table 6.2 Summary of prototype performance scaled to the output of the Four Corners phosphate mine.

List of Illustrations

Chapter 1

Figure 1.1 Annual electricity‐generating capacity additions and retirements. Most of the wind capacity is expected to be built before the scheduled expiration of the production tax credit in 2023, although wind is likely to remain competitive without the credits. Substantial cost reductions and performance improvements strongly support continuous solar generation growth.

Chapter 2

Figure 2.1 JCESR's new paradigm for battery research and development.

Figure 2.2 JCESR is pursuing three scientific thrusts beyond lithium‐ion: multivalent intercalation, chemical transformation, and nonaqueous redox flow.

Figure 2.3 The JCESR team consists of 5 national laboratories, 5 industrial partners, and 10 universities (5 partners and 5 collaborators).

Figure 2.4 Organizational chart of JCESR from July 2015 to April 2016.

Figure 2.5 The JCESR sprint process answers a specific scientific question to provide guidance to management in choosing the direction of scientific thrusts.

Figure 2.6 All activity in JCESR can be placed into a battery technology readiness level. The results from BTRL‐4 are fed into techno‐economic models as well as new directions for fundamental science (BTRL‐1).

Figure 2.7 JCESR science engineering initiatives drawn to show the ownership and integration of scientific tools.

Figure 2.8 Calculated systems‐level energy density and specific energy for both Li‐ion and beyond Li‐ion systems.

Figure 2.9 Chart showing modeled “design space” for aqueous and nonaqueous flow batteries that may meet cost targets.

Figure 2.10 Picture of the Electrochemical Discovery Laboratory showing ultra‐high vacuum, multi‐module synthesis, and characterization system.

Figure 2.11 Depiction of how the Electrolyte Genome is utilized to down‐select redox‐active materials for flow batteries and the feedback loop that improves future predictions.

Figure 2.12 JCESR nonaqueous redox flow cell prototype designs optimized for various cell chemistries. The cells on the left and right of the photograph are variants of the GEN 2 cell design with the cell on the right being the most current version. The cell in the middle is the first JCESR prototype, the GEN 1 cell, which enabled preliminary materials screening albeit at low power due to high cell resistance. The GEN 2 cell design replaced the GEN 1 cell design.

Chapter 3

Figure 3.1 Schematic of a charged and discharged balanced Li–S cell. The cathode comprises 50 vol.% S. The relative thicknesses of the electrodes are indicated.

Figure 3.2 X‐ray diffraction patterns for elemental sulfur, lithium metal, and lithium sulfide.

Figure 3.3 Proposed sulfur K‐edge XAS spectral standards for Li

2

S

4

in the literature 37], 50]–52]. There is no agreement on either the locations or the heights of the main spectral features.

Figure 3.4 First‐principles simulation of sulfur K‐edge XAS spectra of lithium polysulfide dianion species dissolved in tetraethylene glycol dimethyl ether,

x

 = 2–8.

Figure 3.5 Ratio of main edge peak area to pre‐edge peak area vs

x

, chain length of polysulfide dianion (Li

2

S

x

). Areas determined from Gaussian fits through the theoretical X‐ray absorption spectra obtained from first‐principles calculations (see Figure 3.4).

Figure 3.6 First‐principles simulation of sulfur K‐edge XAS spectra of lithium polysulfide radical anion species dissolved in tetraethylene glycol dimethyl ether,

x

 = 3–5, obtained by Pascal and coworkers.

Figure 3.7 Sulfur K‐edge XAS standards for elemental sulfur (S

8

) and lithium sulfide (Li

2

S), obtained experimentally.

Figure 3.8 UV–Vis peak area (617 nm) vs the double integral of the EPR spectra for TEGDME and PEO solutions. Peak areas obtained from UV–Vis and the EPR double integrals are proportional, indicating a direct relationship between the 617 nm UV–Vis feature and the presence of radical anions.

Figure 3.9 In situ EPR of a Li–S cell during cyclic voltammetry. (Top) Cell voltage as a function of time. (Bottom) Amplitude of obtained EPR spectrum. Based on the data presented in Ref. [27].

Figure 3.10 Hypothetical reaction “pocket” and ideal cathode for Li–S cells that enable long cycle life and studies of Li–S redox reactions that are void of the issues invoked by polysulfide dissolution.

Figure 3.11 Discharge profile of three Li–S cells: the red trace (“Conventional”), adopted from Jeong et al. [100], is the first discharge profile of a conventional Li–S cell with a liquid‐like electrolyte. The black traces (“solid‐state”), adopted from Nagao et al. [101], show the 1st and 10th discharges of a fully solid Li–S cell, in the solid and dotted lines, respectively. The blue trace (“sub‐nano confined”), adopted from Fu et al. [99], shows the first discharge of a Li–S cell with a liquid electrolyte and a “sub‐nano‐confined” cathode.

Chapter 4

Figure 4.1 Chart of record efficiencies of laboratory solar cells for all PV technologies.

Figure 4.2 Structure of silicon solar cells with record efficiencies.

Figure 4.3 Typical structure of a CIGS thin film solar cells.

Figure 4.4 Picture of electrodeposited CIGS modules from NEXCIS.

Figure 4.5 Chemical formula of bis‐(sodium‐sulfopropyl) disulfide (SPS).

Figure 4.6 Chemical formula of second oxidized or breakdown by‐product during bath aging.

Figure 4.7 Cyclic voltammogram of indium sulfate solution on 30 nm Cu seed and insert is chronoamperometry of indium deposition on Cu seed at −1.2 V vs SMSE [31].

Figure 4.8 X‐ray diffraction spectra of 150 nm Cu/200 nm In thin film structure [31].

Figure 4.9 Top‐down and cross‐sectional SEM images of 200 nm indium plated from the indium sulfate solution on 150 nm Cu (a, b) at 0.5 mA cm

−2

and (c, d) at 5 mA cm

−2

.

Figure 4.10 Top‐down SEM and cross‐sectional STEM images of indium plated from the In sulfate solution on 300 nm Cu plated from a damascene copper chemistry. The copper was (a, b) as plated and (c, d) 100 °C one hour annealed in N

2

before the indium plating.

Figure 4.11 Cyclic voltammogram of a polished gold substrate in a Ga bath consisting of 0.25 M Ga

3+

and 0.5 M sodium citrate with pH ≥ 10 at a scan rate 0.05 V s

−1

from+0.5 to −2.0 V (SCE). The scaled‐up

I

–

V

in the inset clearly shows the onset of cathodic reduction at −0.8 V vs SCE [55].

Figure 4.12 A scanning electron micrograph of a cross‐sectional view of a metallic precursor stack. Gallium was electrodeposited onto an indium layer and subsequently annealed to form an indium‐rich gallium eutectic layer [57].

Figure 4.13 SEM image shows a surface topography of glass/Mo/Cu/In/Ga sample after annealing up to 150 °C.

Figure 4.14 Bright and dark‐field TEM micrograph of a typical CIS electro‐deposited precursor. Crevices are observed and average grain sizes can be estimated.

Figure 4.15 Raman spectra for a slightly Cu‐rich CIS electrodeposited precursor.

Figure 4.16 Picture of 30 × 30 cm

2

CuInSe

2

co‐electrodeposited film on glass/molybdenum substrate.

Figure 4.17 Composition of the precursor film as a function of CuCl

2

.

Figure 4.18 SEM cross‐sectional and top view of one step electrodeposited Cu(In,Ga)Se

2

film.

Figure 4.19 Schematic of the two‐step approach – metallic precursor and annealing under Se and/or S atmosphere – for the synthesis of the CIGS absorber.

Figure 4.20 Photographs of NEXCIS 60 × 120 cm

2

RTP equipment (a) and CIGSSe absorber layer (b).

Figure 4.21 General process flow for the synthesis of 60 × 120 cm

2

CIGS modules.

Figure 4.22 60 × 120 cm

2

CIGS module developed at NEXCIS.

Figure 4.23 Certified IV curve of 60 × 120 cm

2

NEXCIS plate with 17.3% efficiency.

Figure 4.24 Certified IV curve of 60 × 120 cm

2

NEXIS module with 14.0% aperture area efficiency.

Figure 4.25 Surface scanning microscopy images of electrodeposited layers: (a) Cu layer deposited on SLG/Mo, (b) Sn layer on SLG/Mo/Cu, (c) Zn layer on SLG/Mo/Cu/Sn, (d) surface, and (e) cross section of the full stack precursor after alloying at 200 °C.

Figure 4.26 The

I

–

V

curve (a) and photographic image (b) of best efficiency cells (9.1%) from NEXCIS precursors with a deposited grid and without antireflective coating.

Figure 4.27 Paddle agitation mechanism [84].

Figure 4.28 Paddle cell as described in the US Patent 3,652,442 [84].

Figure 4.29 Schematic cross section of paddle cell 85], 86].

Figure 4.30 Indium plated in paddle cell with four pin contacts at current densities (a) 20 mA /cm

−2

, (b) 10 mA cm

−2

, and (c) 5 mA cm

−2

.

Figure 4.31 Contact methods for 15 × 15 cm

2

substrates, (a) sketch and (b) the plated samples with copper tapes and with 12 contact pins and (c) sketch of ring sealed continuous pin contacts.

Figure 4.32 (a) Teflon‐coated continuous pin contact where electrical connection to the wafer is made from the back side. (b) A cathode holder after assembly.

Figure 4.33 The microstructure of a 300 nm gallium film plated in a paddle cell using an alkaline gallium chemistry at room temperature and using 30 mA cm

−2

current density for 36 seconds and 1 Hz paddle speed.

Figure 4.34 Thickness uniformity achieved on 30 cm × 60 cm after the optimization of the paddle cell parameters.

Figure 4.35 General and detailed view of the NEXCIS 60 × 120 cm

2

plating line.

Figure 4.36 Top‐down view of an electrolytic cell (CU) with a plurality of paddles AG1, …, AGN 86], 89].

Figure 4.37 View of the Cu, In, and Ga electrodeposited layers and typical XRF mapping for each element.

Figure 4.38 Capability analysis of (a) Cu/(In + Ga), (b) Ga/(In + Ga), and (c) CuInGa precursor total thickness after electrodeposition.

Figure 4.39 Capability analysis of the Se/(Cu + In + Ga) XRF ratio measured on CIGSSe absorbers after annealing.

Figure 4.40 Capability analysis of the 60 × 120 cm

2

modules efficiency.

Figure 4.41 HPLC chromatograph showing a fresh bath with SPS only (peak at 10.5 minutes) and an aged bath with SPS, first (peak at 3 and 3.5 minutes), second (peak at 5.5 minutes), and third (peak at 7.5 minutes) oxidation by‐products [25].

Figure 4.42 Voltammogram of Heliofab IN‐390 chemistry with the addition of different amounts of Cu

2+

.

Figure 4.43 Process flow for analysis, monitoring, and control of the metallic contamination in the Enthone indium chemistry.

Chapter 5

Figure 5.1 Domain configuration model for thin‐film head core.

Figure 5.2 Domain configurations before and after slicing the head wafers [18]. The domain wall in the core with positive magnetostriction after slicing is a 180° wall as the magnetization directions on either side of the wall have opposite directions, up and down along the vertical direction of the paper. Domain changes in the dummy core are expected to reflect the domain changes in Al

2

O

3

, which cannot be observed by using the powder‐pattern method.

Figure 5.3 The “Electroplated Head” developed in the Peripherals Development Division at NEC (1974). The head core material was electroplated Ni

45

Fe

55

. The 1‐turn Cu coils were electrodeposited from a pyrophosphate bath.

Figure 5.4 Calculated time response of write magnetic field for a magnetic spacing of 40 nm (at the recording medium) for core lengths of 10 and 30 μm in response to changing the write current from −40 mA to 40 mA in 1 ns. The resistivity of the core and the saturation magnetization is 0.2 μΩm and 2.0 T [58]. The rise time of the write field was shortened to <1.0 ns by focusing the magnetic flux.

Figure 5.5 Cross‐sectional view of thin‐film heads with different core lengths: (a) 120 μm, (b) 50 μm, and (c) 10 μm. It significantly reduced the eddy current loss at high frequency. (a) Thirty‐six turn coil thin‐film head (1991). (b) Ten turn coil GMR head (1999). (c) Nine turn coil TMR head (2000).

Figure 5.6 Read output voltage of heads vs relative velocity between head and disk.

Figure 5.7 Inductive read lost decisively by increasing the read output voltage by the evolution of MR technology from AMR to GMR and then to TMR.

Figure 5.8 Photographs of the first practical TMR head. Left: Spin‐valve‐type TMR head element immediately after the last process of the read head had finished. Right: Combined head structure of a Co–Ni–Fe write head on a TMR element [79].

Figure 5.9 TMR head assembly (left) and read signal of a hard disk from the TMR head (right) [79].

Chapter 6

Figure 6.1 Phosphate production in major counties from 1994 to 2016. All data from U.S. Geological Survey, Mineral Commodity Summaries, Phosphate Rock 3], 5], 25].

Figure 6.2 Scanning electron microscope image of phosphatic clay suspension before dewatering.

Figure 6.3 Photographs of the bench‐top batch dewatering system: (a) charged initially with a 9 wt% solids suspension and (b) after a duration of nine hours under an 4 V

applied electric field. The layer of clarified water was decanted, leaving the thickened lump of a thickened lump of clay consisting of 33.5 wt% solids.

Figure 6.4 Final solids content as a function of the product of electric field and elapsed time with applied electric field as a parameter. The initial solids content was 10 wt%. The solid lines are taken from Eq. (6.1) .

Figure 6.5 Schematic representation of the semi‐continuous prototype used to recover clear supernatant water.

Figure 6.6 Turbidity of supernatant liquid as a function of scaled elapsed time for an electric field of 3 V

(

) and a feed flow rate of 40 ml

(

,

h):

measured immediately after the sample was collected and

measured 24 hours after the sample was collected. The electric field and flow were discontinued overnight.

Figure 6.7 Representative images showing the supernatant samples 24 hours after collection.

Figure 6.8 pH of supernatant liquid as a function of scaled elapsed time corresponding to the results presented in Figure 6.6.

Figure 6.9 A schematic representation of the semi‐continuous prototype for solids recovery.

Figure 6.10 A thickened clay cake with an average solids content of 24.4 wt% was produced under the electric field of 8 V

. The electrode separation was 3.2 cm, and the residence time was 3.3 hours.

Figure 6.11 Photographs illustrating the operation of the semi‐continuous prototype for solids removal: (a) Initial operation before introduction of feed showed that a layer of supernatant water was formed; (b) pseudo‐steady‐state operation showed turbidity above the cathode due to introduction of the feed and mixing by gases produced by the electrochemical reactions; and (c) a clear supernatant was formed after the feed and electrical current was stopped.

Figure 6.12 A schematic representation of the fully continuous prototype 76]. The horizontal electrode configuration (on the left) represents the cake formation zone, whereas the inclined section represents the cake dewatering zone.

Figure 6.13 Final solids content as a function of

under an electric field of 4 V

. The scatter plot represents the experimental result, and the solid line represents the simulation result obtained from Eq. (6.1)

Figure 6.14 Final solids content as a function of

with electric field as a parameter.

Figure 6.15 Energy consumption as a function of applied electric field. The batch experiments and CP3D simulation results were reported by McKinney and Orazem 71], 73], and the semi‐continuous and continuous results were presented by Kong 76].

Figure 6.16 Relationship between final solids content and energy consumption for the fully continuous prototype: (a) The energy consumption was normalized by mass of water removed, and (b) the energy consumption was normalized by mass of dry clay produced.

Figure 6.17 Operation cost as a function of dry clay production rate with applied electric field as a parameter.

Figure 6.18 Final solids content obtained as a function of dry clay production rate with applied electric field as a parameter.

Figure 6.19 Capital cost as a function of dry clay production rate with estimated equipment construction cost as a parameter.

Figure 6.20 A schematic representation of the thickening zone of the dual‐zone fully continuous prototype.

Figure 6.21 A schematic representation of the sludge dewatering zone of the dual‐zone fully continuous prototype.

Chapter 7

Figure 7.1 Schematic illustration of a generalized pulse reverse current waveform.

Figure 7.2 Schematic representation delineating the pulsating vs stationary diffusion layer for (a) a cathodic (metal deposition) process and (b) an anodic (metal removal) process.

Figure 7.3 Schematic representation of the change in pulsating diffusion layer thickness as a function of the relationship between

t

on

and the transition time,

τ

.

Figure 7.4 Schematic illustration of “bump” plating under (a) DC and (b) PC conditions at the same average current density.

Figure 7.5 Schematic illustration of (a) macroprofile and (b) microprofile.

Figure 7.6 Guidelines for designing pulse parameters as a function of macroprofile/microprofile and need for more uniformity or more non‐uniformity.

Figure 7.7 Illustration of two methodologies for studying the impact of increasing pulse peak current density on grain size while maintaining the same average current density, (a) cathodic charge per pulse and off time increase and (b) cathodic charge per pulse and off time are constant.

Figure 7.8 Illustration of (a) macroprofile waveform and (b) microprofile waveform.

Figure 7.9 Plating of a 100 μm feature under microprofile boundary layer conditions from a copper bath without brightener (a) DC plating, (b) PC plating, (c) PRC plating with a macroprofile waveform, (d) PRC plating with the macroprofile waveform at higher frequency, (e) PRC plating with a microprofile waveform, and (f) PRC plating with the microprofile waveform for a longer period of time.

Figure 7.10 Stress–strain data for copper tensile specimens plated with (a) DC from a bath‐containing brighteners and (b) PRC from a bath without brighteners.

Figure 7.11 Schematic illustration of electrochemical deburring with a highly resistive electrolyte.

Figure 7.12 Picture of (a) planetary gear and cathode tool and (b) oil‐groove before and after deburring.

Figure 7.13 Schematic illustration of the region of the polarization curve purported by Jacquet to enable electropolishing [3].

Figure 7.14 Schematic illustration of the Jacquet paradigm of mass transport.

Figure 7.15 Schematic illustration of PRC approaches to mitigate (a) adverse effect of hydrogen evolution during plating and (b) adverse effect of oxide layer formation during surface finishing.

Figure 7.16 Model geometry used for theoretical and experimental studies of DC electropolishing.

Figure 7.17 Schematic representation of the sequenced waveform used to electropolish the stainless valves.

Figure 7.18 Sample part before (left) and after (right) electropolishing in an aqueous salt solution.

Figure 7.19 Image of niobium coupon electropolished in 5% sulfuric acid by weight using pulse reverse voltage.

Figure 7.20 Anodic current transition observed for effective electropolishing of niobium. Applied waveform: anodic pulse of 3 V for 2.5 ms, off time of 1 ms, cathodic pulse of 9 V for 2.5 ms.

Figure 7.21 Elimination/minimization of heat buildup during pulse reverse voltage electropolishing by inserting longer pulse off times.

Figure 7.22 Niobium SRF cavity geometry gaps and area ratios for the beam tube and equator regions.

Figure 7.23 SRF cavity processing apparatus with rotating horizontal cavity orientation and partially filled with electrolyte.

Figure 7.24 SRF cavity processing apparatus operation in the “dump” mode oriented vertically without rotation and completely filled with electrolyte.

Figure 7.25 SRF developmental cavity processing sequence. Shaded areas on the cathode indicate masking. (a) 1 beam tube, (b) equator, (c) 1 beam tube + equator, and (d) 2 beam tubes + equator (unmasked).

Figure 7.26 Anodic current transitions for the SRF developmental cavity per the experiments shown in Figure 7.25: (a) beam tube only, (b) equator only, and (c) 2 beam tubes + equator. Note, for clarity, the anodic and cathodic voltage pulses and cathodic current responses are not shown.

Figure 7.27 Anodic current transition times for SRF developmental cavity processing sequence described in Figure 7.25. Note, for clarity, the anodic and cathodic voltage pulses and cathodic current responses are not shown.

Chapter 8

Figure 8.1 Apparatus for generating and detecting SAW on a bearing ball by scanning interference fringes method.

Figure 8.2 Detected signal of SAW with a large number of monotonically decaying periodic pulses.

Figure 8.3 Expended waveforms of SAW at (a) the first and (b) the twelfth turn.

Figure 8.4 Schematics of Rayleigh wave propagation on a spherical solid: (a) point source excitation, (b) line source excitation.

Figure 8.5 Waveform received by the same transducer used as a transmitter.

Figure 8.6 Waveforms obtained by a pin transducer at positions 90° from the transmitter. Lateral positions measured from the center of the beam for W1–W9 are +20, +15, +10, +5, 0, −5, −10, −15, and −20 mm.

Figure 8.7 Waveforms obtained by a pin transducer at positions 180° from the transmitter. Lateral positions measured from the center of the beam for W1–W9 are +20, +15, +10, +5, 0, −5, −10, −15, and – 20 mm [4].

Figure 8.8 Ball SAW sensor: (a) the adsorption of gas molecules to the sensitive film causes a change in delay time and amplitude of SAW propagating around the piezoelectric ball, (b) A φ = 1 mm quartz ball SAW H

2

gas sensor with 40‐nm‐thick Pd30% Ni film installed in package [5].

Figure 8.9 Waveform of ball SAW sensor. (a) Forty‐five megahertz SAW signal observed on

Z

‐axis cylinder of φ = 10 mm quartz ball, (b) effect of 3% H

2

in Ar gas producing significant difference in delay time at 51st turn [5].

Figure 8.10 Delay time responses for hydrogen concentration from 0.01% to 100% [5].

Figure 8.11 Ball SAW sensor with 1 mm diameter: (a) entire body of the sensor, (b) enlarged photograph of IDT.

Figure 8.12 Appearance of the ball SAW hygrometer: (a) sensor head, (b) detection circuit box.

Figure 8.13 Typical output wave form of amplitude from the ball SAW hygrometer.

Figure 8.14 Diffusion method of generating gases including 1 μmol mol

−1

moisture.

Figure 8.15 Change in delay time measured by the phase shift during the alternative injection of 1 μmol mol

−1

moisture into N

2

carrier gas.

Figure 8.16 Phase shift versus moisture concentration in various carrier gases. The dashed line indicates the square root dependence of the phase shift on the moisture.

Figure 8.17 Delay time of ball SAW sensor when the frost point was changed from −95 to 0 °C: (a) with 80 MHz, (b) with 240 MHz, and (c) the difference between (a) and (b) [7].

Figure 8.18 Phase velocity change vs temperature at a constant moisture density, 1 μmol mol

−1

. The

x

‐coordinate is

T

−1

(K) and the

y

‐coordinate is log (change in the delay time) in parts per million. The change in the delay time is proportional to the phase velocity change when it is small enough.

Chapter 9

Figure 9.1 Gas‐sensitive resistors based on semiconducting oxides. A Pt heater is printed on one side of an alumina ceramic tile and an interdigitated electrode on the other side. A porous layer of oxide is printed over the electrodes. Sensors are mounted suspended on their connecting wires and protected by a suitable housing. In other forms, sensors with low power consumption and fast thermal response are prepared using micro‐hotplates by deposition of heater, electrodes, and sensing material onto a thin membrane of Si

3

N

4

prepared by microfabrication on a Si wafer.

Figure 9.2 Schematic of an electronic band structure near the gas–solid interface of a semiconducting oxide. The basic concepts used to describe the response are listed on the right, including a phenomenological reaction scheme.

Figure 9.3 Screening of oxides for gas sensor behavior. Oxides show regular patterns of behavior. Gases in air may be classified as reducing or oxidizing toward the surface and oxides as “n” or “p” type. Behavior may switch with change of temperature or gas concentration.

Figure 9.4 Effective medium model; surface trap‐limited conductivity. Dependence of relative response,

S

r

on the ratio of surface trap state concentration,

N

S

, to bulk donor,

N

D

, and acceptor,

N

A

state concentration, for different values of

α

 = 

μ

e

K

1

/

μ

p

K

2

(legend). The inset defines the equilibrium constants,

K

1

and

K

2

, of electrons between the surface states and the conduction and valence bands of the solid.

S

r

positive corresponds to “n”‐type response to a reducing gas and

S

r

negative to “p”‐type response. Here

μ

e

and

μ

p

respectively denote the electron and hole mobility.

Figure 9.5 Sensitivity Δ

σ/σ

0

of conductivity of sintered pellets of compounds in the solid solution series (MWO

4

)

1−

x

(M′O

2

)

x

to 1% carbon monoxide in dry air, measured at 400 °C M = Mn, Fe, Co, Ni, Cu, Zn; M′ = Sn, Ti.

Figure 9.6 (a) Two model geometries; porous oxide thickness

h

on impervious substrate: semi‐infinite coplanar spacing 2

a

, and hemispherical electrodes radius

b

and center distance 2

a

; (b) current density through the layer against position,

X

, along the symmetry plane between the electrodes, coplanar electrodes, two spacing with (1) no gas; (2) gas with no concentration profile and

K

p

 = 1; (3) gas with concentration profile for first‐order combustion,

K

T

 = 10,

K

P

= 1; (c) electric field ratio for planar/hemispherical electrodes against position,

X

, along the symmetry plane between the electrodes; (d) response coefficient against rate constant for first‐order decomposition, illustrating the effect of electrode geometry.

Figure 9.7 Dependence of gas response on electrode geometry: cylindrical pellet of SnO

2

with gas access from the circumference only. Response of inner ring (open circles) and outer disc (closed circles) to CO in air at 430 °C.

Figure 9.8 Methane response of multi‐gap SnO

2

sensor operating at 625 °C. Printed SnO

2

on an impervious alumina substrate with gold electrodes. SnO

2

thickness 100 μm. Three different electrode gaps. Inset shows a multi‐gap electrode arrangement.

Figure 9.9 (a) Variation of signal,

R

0

/

R

 = 

σ

/

σ

0

to 0.25 vol.% CH

4

in dry air. (b) Derived surface combustion rate constant,

K

T

 = 

kh

2

/

D

−

k

, is the first‐order rate constant for surface catalyzed combustion,

h

the porous oxide layer thickness, and

D

the gas diffusivity within the oxide layer – and conductivity response constant,

K

P

, as a function of total time of previous exposure to 25 ppm hexamethyldisiloxane in air,

t

p

. The arrows mark the titration of two different types of surface site: one mediating surface‐catalyzed combustion and one mediating the electrical response.

Figure 9.10 Illustration of operating line principle using multi‐gap electrodes and CTO as the sensing material: signal on the narrow gap against that on the wide gap. The operating line slope is smaller in the presence of ethanol than in the presence of CO because the surface‐catalyzed combustion rate constant for ethanol on CTO is significantly larger than that for CO. Labels: gas concentration in air/ppm.

Figure 9.11 Sensor microstructure at different scales (chromium‐titanium oxide). (a) Cross section showing micrometer scale voids. (b) Surface view showing microstructure within each agglomerate. (c) Focussed‐ion beam section through the surface, showing very fine‐scale porosity on the immediate outside surface of the sensor.

Figure 9.12 Crystallite size effects on conductivity and gas response. Resistance (A) and sensitivity

S

 = 

σ/σ

0

to 1% methane in air (B) of pressed pellets of Sn(Sb)O

2

(from Dusastre [89]). (C) Three models for conductance limited by intergrain constrictions: open neck, closed neck, and Schottky barrier.

Figure 9.13 Equivalent circuit approximation for microstructure effects on conduction and gas response. (A) “Agglomerates” and “connections” represented as resistors,

R

or conductances,

σ

. A series–parallel circuit represents the agglomerates as a parallel combination of “surface” and “bulk” elements, connected by a series element representing the inter‐agglomerate connection. (B) Results of simulation appropriate to an “n”‐type (surface depletion layer) material, using a reduced two‐element network, of gas‐sensitive “connection” and gas‐insensitive “bulk”: (a) conductance response of the network; (b) correlation of pre‐factor and exponent in Eq. 9.12. Symbols are defined in the text.

Figure 9.14 Effects of microstructure variation on response parameters of SnO

2

sensors explained by microstructure models. (a) Correlation of log(

α

g

) with

β

, for different gases. (b,c) Example of microstructure variation obtained by altering processing parameters. Scale bar: (b) 750 nm; (c) 3 μm.

Figure 9.15 Response to carbon monoxide in air,

R

g

/

R

0

, for CTO sensors fired at different temperature to achieve different microstructure. The average particle size, determined by measurement on scanning electron micrographs, increased from 0.4 to 0.6 μm with increasing firing temperature. The solid line is the fit to the equivalent circuit model shown in Figure 9.13, using Eq. 9.16 for the “surface” and “connection” conductances (linear response law). The dotted line is an empirical fit to Eq. 9.12 with

β

= 0.5.

Figure 9.16 Model microstructure and effect of current percolation on power law response order,

β

, for conductance‐increasing response. The inset shows a typical model microstructure of spheres with randomly placed centers and a Poisson distribution of radius, constructed from elementary cubes. Dependence of

β

on mean radius of the spheres for structures of porosity ≈0.54.

Figure 9.17 Effects of Ti substitution in chromium titanium oxide. (a) X‐ray photo electron spectroscopy, valence band edge: shift of Cr‐d states,

x

= 0.2 compared with

x

= 0; (b) diminution in Cr(VI) – 2p signal in XPS with Ti substitution: Cr(VI)/(Cr(total) + Ti) against

x

; (c) surface segregation of Ti:

x

surface

determined by XPS against

x

bulk

; (d) Resistance change in response to CO in air of a screen‐printed Cr

1.8

Ti

0.2

O

3

sensor at 400 °C, showing the effects of change of relative humidity: 1 is 50%, 2 is 25%, 3 is 10% RH at 20 °C. (e) Resistance response to 400 ppm CO in air increases sharply with increase of

x

from zero to 0.01, after which the variation is quite small: screen printed sensors at 400 °C in air at 100% RH at 20 °C. Each measurement is on a different sensor.

Figure 9.18 Model for the (110) face of SnO

2

.

Figure 9.19 Resistance response to trace ozone in air of a printed WO

3

sensor at 500 °C; rapid air flow.

Figure 9.20 Early prototype ozone measurement module, with measurement cycle alternating fan speed and sensor temperature, and sensor resistance variation in response to the temperature and fan speed steps.

Figure 9.21 Hand‐held instrument for measurement of ozone at part‐per‐billion levels in the atmosphere. The base unit has power, display, and communications. The detachable head unit holds the sensor ID, the sensor calibration, and the measurement result computation. Heads are calibrated as complete units. The arrow points to the sensor, mounted on its heater control, and resistance measurement circuitry, in front of the fan.

Figure 9.22 Compact air quality measurement station utilizing low‐cost sensors. The station is configured simply by choosing modules for the parameter of interest. The housing is temperature controlled. The unit can be remotely operated.

Figure 9.23 Low‐cost ozone measurement instrument configured to operate in an air quality measurement network.

Figure 9.24 Resistance transients of a screen‐printed WO

3

sensor in response to temperature steps, in the presence and absence of ozone in air.

Figure 9.25 Variation of WO

3

sensor resistance with ozone concentration, measured for a large number of sensors of two different microstructures (mean ± 1SD). The resistance is measured 5 s and 35 s after the step from high to low temperature.

Figure 9.26 Response of two different WO

3

‐based ozone instruments in the atmosphere (unit similar to that shown in Figure 9.22) correlated with the measurement result of a reference analyzer with which they were co‐located. The measurements are hourly averaged for 48‐h periods at the beginning and end of each month, with a total measurement time of four months. The line is for one set of 48 h measurements at the beginning of the trial.

Figure 9.27 Performance of WO

3

sensor for NO

2

in the atmosphere, using a simple thermal scrubber to remove ozone interference. (a) High sensitivity to ppb levels of NO

2

in air and lack of sensitivity to NO. (b) Illustration of the efficiency of the ozone scrubber (a heated length of stainless steel tube). (c) Sensor resistance against signal from co‐located NO

2

reference analyzer, 1 week of measurements every minute. The square symbols and dashed line are the laboratory calibration. (d) Mean daily difference of NO

2

concentration derived from the sensor resistance calibration in (c) from the analyzer measurement, for measurements every minute, for 1500 h.

Figure 9.28 Demonstration of application of Eqs. 9.28, 9.32, and 9.33 to detect drift of low‐cost instruments at three different locations with respect to reference stations as proxies. Three different proxies are shown: reference station with which the low‐cost instrument was co‐located, remote reference station in the same land use in the same air‐shed, and remote reference station in the same air shed but different land use. The vertical line shows when drift of the instrument at Maple Ridge was detected by manual inspection of the data.

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E1

Edited byRichard C. Alkire, Philip N. Bartlett,andMarc T. Koper

Advances in Electrochemical Science and Engineering

Volume 18Electrochemical Engineering: The Path fromDiscovery to Product

Advances in Electrochemical Science and Engineering

Advisory Board:

Philippe Allongue, Ecole Polytechnique, Palaiseau, France

Robert Hillman, University of Leicester, Leicester, UK

Tetsuya Osaka, Waseda University, Tokyo, Japan

Laurence Peter, University of Bath, Bath, UK

Lubomyr Romankiw, IBM T. J.Watson Research Center, Yorktown Heights, NY, USA

Shi-Gang Sun, Xiamen University, Xiamen, China

Esther Takeuchi, State University of New York, Stony Brook, USA; and Brookhaven

National Laboratory, Brookhaven, NY, USA

Mark Verbrugge, GeneralMotors Research and Development,Warren,MI, USA

Clare Grey, University of Cambridge, Cambridge, UK

Edited by

Richard C. Alkire, Philip N. Bartlett, and Marc T. Koper

Advances in Electrochemical Science and Engineering

Volume 18

Electrochemical Engineering: The Path from Discovery to Product

Copyright

The Editors

Prof. Richard C. Alkire

University of Illinois

Department of Chemical & Molecular

Engineering

600 S. Mathews Avenue

Urbana, IL 61801

USA

Prof. Philip N. Bartlett

University of Southampton

Department of Chemistry

Highfield

SO17 1BJ Southampton

United Kingdom

Prof. Dr. Marc T. Koper

Leiden University

Leiden Institute of Chemistry

Einsteinweg 55

2333 CC Leiden

The Netherlands

All books published by Wiley‐VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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Cover Design Schulz Grafik‐Design, Fußgönheim, Germany

Series Preface

It is with sincere gratitude that we express appreciation to our co‐editor and good friend, Professor Jacek Lipkowski, who has indicated his desire to bring more than two decades of editorial leadership to closure with his 2017 publication of Volume 17 of this series, entitled “Nanopatterned and Nanoparticle‐Modified Electrodes.” His deep technical knowledge and gracious personal manner have made it a genuine pleasure to work with him through the years.

With this volume, we are pleased to welcome Professor Marc Koper as co‐editor. Professor Koper studied chemistry at the University of Utrecht (the Netherlands) and the Université Libre de Bruxelles and received his PhD from the University of Utrecht in 1994. After a postdoctoral stay at the University of Ulm (Germany), he first became research fellow and then Associate Professor at the Eindhoven University of Technology. In 2005, he moved to Leiden University (the Netherlands) where he is currently a professor of fundamental surface science. His research interests focus on electrocatalysis, electrochemical surface science, and theoretical and computational electrochemistry. Marc Koper is a member of the Royal Netherlands Academy of Arts and Sciences, fellow of the International Society of Electrochemistry, and has received awards from the Royal Society of Chemistry, the International Society of Electrochemistry, and The Electrochemical Society.

The purpose of this series is to provide high‐quality advanced reviews of topics of both fundamental and practical importance for the experienced reader.

Preface

The path from scientific discovery to impact on society has many steps. Today, new science and engineering approaches are being developed to facilitate that task of moving atomistic‐scale discoveries and understanding into well‐engineered products and processes based on electrochemical phenomena. However, people working on one particular application often find it difficult to recognize highly relevant new methods that were developed for entirely different applications. That is, especially at the atomistic scale, routine science and engineering methodologies are still in an early phase of development for use in assessing emerging business opportunities.

Therefore, the focus for each chapter in this volume includes not only the overarching science and engineering roadblocks that were faced, but also the reusable approaches that were developed to inform the technological/business applications with the underlying atomistic science. Many such reusable methods could be relevant beyond their initial use. Bringing together such approaches for diverse applications that span the nano–bio–photo–micro landscape will facilitate recognition and cross‐fertilization between seemingly different applications and will lessen the need to “reinvent the wheel” for each.

Alivisatos and Osowiecki, in their Introductory Perspective, emphasize the central importance of the value to society of new candidate technologies. Whether a proposed breakthrough is valuable enough depends in large part on its theoretical performance limits as compared to the current state of the art. Also important for electrochemical applications are selectivity and control of the desired reaction. They illustrate these points with the example of quantum dots, once unusual materials that are today produced at the ton scale and used in commercial display technologies. They comment on several electrochemical applications where considerations based on limits‐selectivity‐control could provide guideposts on the path from discovery to product.

Brushett describes a new paradigm for battery research: tight integration of discovery science, battery design, research prototyping, and manufacturing collaboration within a single highly interactive organization. This new paradigm, pursued at the Joint Center for Energy Storage Research (JCESR), seeks transformational change in transportation and the electric grid driven by next‐generation, high‐performance, low‐cost electrochemical energy storage. Although JCESR focuses exclusively on “beyond lithium‐ion batteries,” the overall systems approach is portable and can be applied to other applications in order to accelerate the pace of discovery and innovation, while reducing the time from conceptualization to commercialization. To this end, the chapter presents JCESR's motivation, vision, mission, as well as outcomes and lessons learned in the development, execution, and refinement of this mode of operation.

Balsara and colleagues review the redox pathways that have been proposed for the cathode of a Li–S cell as it is charged and discharged. The use of various in situ spectral methods to identify the fingerprints of reaction intermediates is discussed. The electrode design required of such methods should guarantee unimpeded access to the species of interest and avoid transport bottlenecks. The basis for understanding the role of the electrolyte for achieving high specific energy is described. The general approach, based on in situ spectroelectrochemical methods, is reusable for other electrochemical systems where intermediate steps in the overall reaction are not yet resolved, such as in alkaline fuel cells and carbonate‐ or ether‐based electrolytes.

Deligianni and coworkers describe the scientific and technological path from laboratory research to early industrial development of electrodeposition for inorganic solar cells. An overarching consideration is to design earth‐abundant materials whose elements are amenable to massive‐scale application. The chapter describes initial investigations on copper–indium–gallium–diselenide (CIGS) solar cells, before turning to fabrication approaches used for electrodeposited precursor materials, associated fundamentals of electrodeposition, and development of solution chemistries for copper‐based earth‐abundant electrodeposited kesterite precursor materials such as Cu2ZnSn (Se,S). A comprehensive description of scale‐up procedures is described from the laboratory scale of a rotating disk, to 15 × 15 cm glass plates, to 30 × 60 cm modules, and full‐size 60–120 cm module, leading up to an industrial‐scale production line for producing solar cells at the rate of 1 m2 min−1.

Ohashi describes the perspectives in Japan that guided evolution of the thin film head technology within the hard disk drive business sector. The technical issues included understanding the properties of candidate magnetic materials and their suitability for use in thin film heads, such as stress, thermal decay, and noise emanating from domain walls of finite thickness. The business issues included recognizing trade‐offs between different candidate technologies whose suitability depended on the application. The fluid state of new technologies and new business opportunities creates “The Innovator's Dilemma,” which occurs when a new technology brings a value proposition that is different from any ever proposed by existing customers, that is, choosing between sustaining a proven path forward and investing in a potentially disruptive technology.

Orazem and colleagues address the problem of separating water from clay suspensions generated as a waste stream in beneficiation of phosphate ores. The sequential development of a continuous electrokinetic separation process was accomplished with experimental and computational methods that moved atomistic‐scale discoveries and understanding toward a well‐engineered process. The approach involved empiricism guided by understanding how solids content depended on applied electric field and elapsed time. While electron microscopy and surface analyses provided insight into the structure of the clay, the design of successive prototypes relied on intuition, insights gained from previous prototypes and informed engineering judgment.

Taylor and coworkers investigate pulse reverse‐current electroplating and surface‐finishing operations. While there are well‐establish traditional paradigms for such processes, the authors report various research and development activities carried out with a balance between current fundamental understandings combined with a willingness to pursue non‐conforming observations that lead them to paradigm‐breaking conclusions. Examples include copper electrodeposition with pulse‐reverse cathodic current and decreased used of chemical additives, deburring of non‐passive metals with use of forward‐only anodic pulses, deburring of passive metals with reverse‐pulse anodic and decreased hydrogen evolution, and pulse reverse voltage electropolishing of niobium that uses low concentration acid devoid of HF.

Tsukuhara describes development of a trace moisture sensor that was developed via a series of investigations, spanning several decades, of puzzling phenomena and blind alleys in their pursuit. The tortuous path from discovery to product included non‐intuitive results, failed hypotheses, unexpected phenomena, and the need to rethink past observations. All of these roadblocks served to seed fresh ideas guided by background knowledge of laser ultrasonics, surface acoustic waves, propagation of waves in elastic spheres, hydrogen interaction with Pd/Ni films, deposition of amorphous silica, and chemical interaction of water with silica glass, among others. The guiding strategies that emerged from this project include the following: find the thermodynamic limit, do not dismiss something that is apparently wrong, think about observations many times over and be prepared to change you previous opinions, test experiments with numerical simulation, and look broadly into cumulative knowledge available in other fields.

Williams reports on development of low‐cost sensors based on gas‐sensitive semiconducting oxides. A key concept illustrated in this case is to focus on what limits the path forward. For example, the central technical requirement involved correct control of the sensor and sample, while the economic barriers included the cost of calibration, maintenance, and the cost of an erroneous or unreliable reading. These constraints, along with the knowledge of fundamental science aspects of high sensitivity and low selectivity, led to innovative design of catalyst layers and T‐programmed desorption routines. The scientific and engineering threads brought together in this work included understanding surface reactions on semiconducting oxide, sensor development, instrument development, and big data associated with the application. These illustrate how deep scientific understanding led to well‐engineered products and markets for them, which, in turn, generated questions that further stimulated the quest for knowledge in fields that were never in view at the start.

In the long run, the reduction to routine use of such methods as described in this volume will provide the foundation for next‐generation science and engineering at the molecular scale. In this spirit, we take inspiration from Carl Wagner,1 who wrote in an earlier volume of this series:

… molecular engineering may be important in the future development of industrial electrochemical processes.

June, 2018

Richard Alkire

Urbana

Note

1

Wagner C. (1962). The scope of electrochemical engineering. In:

Advances in Electrochemistry and Electrochemical Engineering

, vol.

2

(ed. C.W. Tobias), 2.

1Introductory Perspectives

A. Paul Alivisatos1,2,3,4 and Wojciech T. Osowiecki2

1Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, CA, 94720, USA

2University of California, Department of Chemistry, D43 Hildebrand Hall, Berkeley, CA, 94720, USA

3University of California, Department of Materials Science and Engineering, Berkeley, CA, 94720, USA

4Kavli Energy NanoScience Institute, Berkeley, CA, 94720, USA

The path from a scientific discovery to a commercial product is a long one, with many twists and turns. It is easy to list many examples of potential breakthroughs that never crystallized into real‐life solutions. Instead, this book takes the approach of finding the best examples of discoveries that either have already been able to deliver products or are on their way to accomplish this goal. Each chapter discusses a different field, as we believe that there exist certain themes that unite all these success stories.

In order to create a viable product, one has to be brutally honest about what is actually likely to be of genuine value to society, represented by real markets. Many projects and companies struggle if they cannot realize what is fundamentally distinctive about their technology and whether the proposed breakthrough is valuable enough. This conceptualization of what makes a technology distinctive almost necessarily has to be in reference to its theoretical performance limits as compared to the current state of the art.

This comparison between limits and current performance informs the researcher of not only how long the path forward is, but also whether the new technology has any chance of supplanting others or of creating a new market. Research is very complex and unpredictable, and often, we see a clear progression of discoveries that “tell a story” only after the fact. Nevertheless, the question regarding maximum theoretical limits should never leave our minds. Only then can we focus on putting our efforts into the most promising endeavors.

In the case of electrochemical transformations, the most important issues to address after the theoretical limits are selectivity and control of the desired reaction. For example, how do we make sure that the bonds that break and form are ones that we intended and that the desired products are obtained? Sometimes, the inspiration can come from nature and other scientific fields. Enzymes control reactions with an awe‐inspiring degree of precision, forming exactly the compounds organisms need, and reminding us how sophisticated and optimized chemical environments can be. Although scientists did not have billions of years of evolution to perfect their processes, this book is also intended as a reminder to look beyond one's area of expertise for encouragement and fresh ideas.

So how can the ideas of theoretical limits and control be applied in electrochemical engineering? The challenges of the current world dictate opportunities for researchers, especially those interested in seeing their work incorporated in crucial technological innovations of the future. In the twenty‐first century, supplying energy to the ever‐growing global population in a sustainable manner is, without doubt, one of the most important such challenges.

Each year, the U.S. Energy Information Administration forecasts changes in energy generation for the next few decades and we expect to see significant shifts in the fuel mix; as market forces oblige coal plants to retire, they will be successively replaced by renewable sources and oil and gas (Figure 1.1). Among the renewable sources, solar and wind energy are particularly enticing to the electrochemical community, as they promise a growing supply of cheaper electrons, decoupled from environmentally costly fossil fuel combustion.

Figure 1.1 Annual electricity‐generating capacity additions and retirements. Most of the wind capacity is expected to be built before the scheduled expiration of the production tax credit in 2023, although wind is likely to remain competitive without the credits. Substantial cost reductions and performance improvements strongly support continuous solar generation growth.

In this new economy, scientists should be encouraged to think of electrons as crucial and readily available chemical reagents. Just like fossil fuel industry turned oil into a ubiquitous precursor to many compounds and products, now electrons will be involved in crucial processes such as fuel generation and energy storage. Indeed, the ability to store energy in chemical bonds solves one of the greatest challenges for renewables, namely their transience. Energy storage brings opportunities for a distinctive set of technologies to emerge.

We believe that in order to use electrons properly, the issues, highlighted above, of (i) theoretical efficiency limits and (ii) control must be addressed. To start, let us consider a field that the authors of this foreword are particularly familiar with: quantum dots (QDs). QDs are small semiconducting nanoparticles that possess bound, discrete electronic states [1]. The optoelectronic properties of these dots depend on the size and shape: the larger the particles are, the longer the wavelength of the emitted light is. After a long period of discovery and development, these once unusual materials are produced today at the ton scale and used in commercial display technologies. Their most distinctive edge comes from the color purity of their emission, which creates displays that realize a broader color gamut than previous technologies did.

For current commercial quantum dot display devices, such as televisions, the efficiency of light emission following absorption of a higher energy blue pump photon is crucial for the success of the product. Energy from every absorbed blue photon must be emitted as a green or red photon to form the full color image. The desired radiative rate competes with non‐radiative processes that emit phonons instead of photons. Phonon emission not only decreases energy efficiency but also causes unwanted heating that may lead to device failure. This competition is measured by the quantum yield (QY