Electrocatalytic CO2 reduction reaction on copper : designs toward product selectivity optimization

다국어 초록 (Multilingual Abstract)

Encountering an environmental crisis from an atmospheric CO2 surge, the research demand on the electrochemical carbon dioxide reduction reaction (CO2RR) has increased. Foremost, research on carbon dioxide reduction reaction (CO2RR) at Cu has been considered especially promising for its capability of CO2 conversion into valuable chemical fuels without emitting pollutants. However, two hurdles are still unsolved in the selective production of desired chemical fuels, even for a promising copper-based carbon dioxide reduction reaction (CO2RR). One is a competitive hydrogen evolution reaction (HER) that proceeds at a potential range-reducing carbon dioxide, and another is a unveiled reaction mechanism stemming from byproducts accompanying complex reaction steps. To overcome these hurdles and improve the selectivity of desired products, I’ve developed three research projects to control electrode surface-adsorbed carbon monoxide (COads) and electrode surface-adsorbed hydrogen (Hads).
Firstly, I found that electrodeposited-Cu10Ag14Hg0.6 multimetallic films displayed an improved selectivity of C2 chemicals production in carbon dioxide reduction reaction (CO2RR), with highly suppressed hydrogen evolution reaction (HER). To elucidate the improved reaction mechanism at electrodeposited-Cu10Ag14Hg0.6 multimetallic films, surface-interrogation scanning electrochemical microscope (SI-SECM) and in-situ IR spectroscopy was used. These surface analysis methods revealed that electrode surface-adsorbed hydrogen (Hads) was suppressed and electrode surface-adsorbed carbon monoxide (COads) was increased at the developed catalyst. These results supported that Ag and Hg metal incorporation led to C2 selectivity enhancement by surface dynamics changes.
Secondly, I designed a Cu-Ag Bipotentiostatic reaction system and measured CO efficiency in CO2-CO-C2 production made between two working electrodes (Cu and Ag). Through the unique capability of this system, I applied CO efficiency calculation that had been limited in the precedent literature. By applying the potential insufficient to produce C2 from CO2 reduction on Cu, I tried to minimize interference of C2 from Cu sole operation (CO2 to C2). Through the optimization process of various reaction factors (distance between Cu and Ag, applied potential at Ag (EAg), applied potential at Cu (ECu), and cation composition in the electrolyte), the selectivity of C2+ could be vastly improved (67% including 6.5% 1-PrOH).
For last, I developed the reactor to modulate electrode surface temperature and investigated the reactivity of carbon dioxide reduction reaction (CO2RR). The COMSOL-based simulation revealed that electrode surface temperature could be depressed up to -4.0℃ when the thermoelectric module was set at -40℃ temperature. Combined with the potential-pulse program, surface chilling at subzero (-40℃ thermoelectric module temperature and -4.0℃ copper foil) improved the reactivity of CH4 at large amounts (80%). Compared to the bath cooling reactor (5℃), the selectivity of CH4 in surface chilling was 9% higher even without additional overpotential consumption (cathodic potential at surface chilling and bath cooling was -1.2 V and -1.5 V vs. RHE). By in-situ spectroscopic analysis and COMSOL-based simulation result, this reactivity improvement is presumably due to increased residence time of electrode surface-adsorbed carbon monoxide (COads) and increased CO2 concentration at electrode peripheral.
Toward the dream of the carbon-neutral strategy to complete, many problems were still left unsolved in the carbon dioxide reduction reaction (CO2RR). However, I believe these pieces of novel research keep going will bring the dream come to reality finally.

목차 (Table of Contents)

• Contents ................................................................................................................... i
• List of Figures ......................................................................................................... v
• List of Tables ........................................................................................................ xvi
• Abbreviations .................................................................................................... xxii
• ABSTRACT ........................................................................................................ xxx
• Chapter 1: Introduction ........................................................................................ 1
• Chapter 2: Electrodeposited CuAgHg Multimetallic Thin Films for Improved
• CO2 Conversion ...................................................................................................... 5
• 2.1 Introduction ................................................................................................ 5
• 2.2 Results & Discussion .................................................................................. 7
• 2.2.1. Characterization of Cu10Ag14Hg0.6 ............................................................ 7
• 2.2.2. Electrochemical CO2 Reduction Reaction at Cu10Ag14Hg0.6 ................... 10
• 2.2.3. SI-SECM Investigation on Cu10Ag14Hg0.6 .............................................. 14
• 2.2.4. In-situ IR Spectroscopic Analysis on Cu10Ag14Hg0.6 ............................... 18
• 2.3 Conclusion ................................................................................................ 22
• 2.4 Experimental Section ................................................................................ 23
• 2.4.1. General .................................................................................................... 23
• 2.4.2. Synthesis of Catalysts ............................................................................. 23
• 2.4.3. Multimetallic Thin-Film Characterization .............................................. 24
• 2.4.4. Gaseous Product Quantification .............................................................. 24
• 2.4.5. Liquid Product Quantification ................................................................. 26
• 2.4.6. SI-SECM Experimental Details .............................................................. 26
• 2.4.7. Double Layer Capacitances of Thin Film Catalysts ................................ 28
• 2.4.8. In-situ Attenuated Total Reflection/Fourier Transform Infrared
• Measurements ................................................................................................... 29
• 2.5 Appendix ................................................................................................... 30
• 2.5.1. Supplementary Figures ............................................................................ 30
• 2.5.2. Supplementary Tables ............................................................................. 38
• Chapter 3: Bipotentiostatic Tandem Electrocatalysis of the CO2 Reduction
• Reaction Yielding C2+ Fuels ................................................................................ 40
• 3.1 Introduction .............................................................................................. 40
• 3.2 Results & Discussion ................................................................................ 43
• 3.2.1 Bipotentiostatic Reactor Design and COMSOL-based Simulation ......... 43
• 3.2.2 Electrochemical CO2 Reduction Reaction in Tandem System at Varying
• Distances ........................................................................................................... 46
• 3.2.3 Electrochemical CO2 Reduction Reaction in Tandem System at Various
• Applied Potentials ............................................................................................. 50
• 3.2.4 Electrochemical CO2 Reduction Reaction in Gas-flow Tandem System . 53
• 3.3 Conclusion ................................................................................................ 55
• 3.4 Experimental Section ................................................................................ 56
• 3.4.1 General ..................................................................................................... 56
• 3.4.2 Electrode Preparation ............................................................................... 56
• 3.4.3 Electrochemical Measurement ................................................................. 56
• 3.4.4 Product Analysis for Bipotentiostatic Tandem Reaction .......................... 58
• 3.4.5 COMSOL Multiphysics Simulation Details ............................................. 64
• 3.4.6 Double Layer Capacitances Evaluation of Cu Substrates ........................ 67
• 3.4.7 CO Conversion Efficiency Calculations .................................................. 68
• 3.4.8 Quantification of Dissolved Cu Species................................................... 70
• 3.4.9 Turnover Frequency of the C-C Bond Formation Reaction on a Surface
• Copper Atom ..................................................................................................... 71
• 3.4.10 Partial Current Analysis on Cu-Ag Tandem Reaction ............................ 73
• 3.5 Appendix ................................................................................................... 74
• 3.5.1 Supplementary Figures ............................................................................. 74
• 3.5.2 Supplementary Tables .............................................................................. 86
• Chapter 4: Highly Selective Reduction of CO2 to Methane Induced by Subzero
• Depression of the Electrode Surface Temperature ......................................... 104
• 4.1 Introduction ............................................................................................ 104
• 4.2 Results & Discussion .............................................................................. 106
• 4.2.1 Surface Chilling Reactor Design and COMSOL-based Simulation ...... 106
• 4.2.2 Electrochemical CO2 Reduction Reaction at Various Bath Temperatures
• ......................................................................................................................... 109
• 4.2.3 Electrochemical CO2 Reduction Reaction at Various Electrode Surface
• Temperatures ................................................................................................... 111
• 4.2.4 In-situ IR Spectroscopic Analysis on CO2 Reduction Reaction at Varying
• Temperatures ................................................................................................... 114
• 4.3 Conclusion .............................................................................................. 116
• 4.4 Experimental Section .............................................................................. 117
• 4.4.1 General ................................................................................................... 117
• 4.4.2 Electrode Preparation ............................................................................. 117
• 4.4.3 Temperature Control .............................................................................. 118
• 4.4.4 COMSOL Multiphysics Simulation Details ........................................... 119
• 4.4.5 Electrochemical Measurement ............................................................... 127
• 4.4.6 Product Analysis for Bipotentiostatic Tandem Reaction ........................ 127
• 4.4.7 In-situ ATR/FTIR Experimental ............................................................. 131
• 4.5 Appendix ................................................................................................. 132
• 4.5.1 Supplementary Figures ........................................................................... 132
• 4.5.2 Supplementary Tables ............................................................................ 146
• Reference ............................................................................................................ 154
• Publication List .................................................................................................. 170
• Abstract in Korean ............................................................................................ 171

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