Fundamental Electrocatalysis Design for Glucose Upgrading
Open Access
- Author:
- Ostervold, Lars
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 01, 2023
- Committee Members:
- Seong Kim, Professor in Charge/Director of Graduate Studies
Simon Bare, Special Member
Ezra Clark, Co-Chair & Dissertation Advisor
Lauren Greenlee, Major Field Member
Michael Janik, Co-Chair & Dissertation Advisor
Michael Hickner, Outside Unit & Field Member - Keywords:
- Electrocatalysis
Operando Raman Spectroscopy
X-ray Absorption Spectroscopy
Density Functional Theory
Biomass Upgrading - Abstract:
- The chemical industry currently accounts for 10% of the global energy demand, is responsible for 7% of greenhouse gas emissions, and is on pace to be the largest global oil consumer by 2030. The chemical industry requires a transition to environmentally-friendly processes for a sustainable future. This dissertation explores decarbonization of the conversion of glucose to lactic acid by using green electrocatalysis. The first study (Chapter 2) confirms the an electrocatalytic system can improve performance for this reaction, and achieved a lactic acid yield of a 23.3±1.2%. This improvement in an electrocatalytic configuration occurs despite the overall glucose to lactic acid reaction not being a redox process. The electrocatalytic system was designed based on mechanistic studies from thermocatalytic literature that identified the 3+3 retro-aldol reaction of fructose as the rate-limiting step and showed copper catalysts could obtain high yields of lactic acid. Using polycrystalline copper foil as a catalyst, this initial evaluation served as a proof-of-concept; however, this yield was not competitive with the thermocatalytic studies (which achieved >75% yield). Since intrinsic activity improvements outweigh site-density-based improvements by several orders of magnitude, the rest of this work focused on gaining a fundamental understanding of the system to pursue rational catalyst design. The second study (Chapter 3), coupled operando Raman spectroscopy with density functional theory (DFT) simulated Raman spectra to identify the active form of copper under reaction conditions as CuOOH. This CuOOH species likely takes the form of a surface-adsorbed hydroxide on a CuO surface (CuO-OH*). With the active form of the catalyst identified, the next study (Chapter 4) leveraged these fundamental insights (i.e., understanding of the active form of the catalyst) to increase lactic acid yield by 277%. This system achieved the highest yield to date for the conversion of glucose to lactic acid in an open-to-atmosphere, room temperature reaction, while employing an earth-abundant catalyst. This study utilized DFT calculations to determine the most favorable adsorption configuration for reactants was fructose adsorbed through O1 and O3. Because the retro-aldol reaction is driven by weakening the C3-C4 bond, we hypothesized a divalent cation could interact with the exposed oxygens (O2 and O4) to further weaken the C3-C4 bond and increase catalyst activity or selectivity. To test the hypothesis, Ba2+ was added to the system and reaction yields increased by 277% to 64.6 ± 2.8%. In Chapter 5, we sought to understand the interaction of the catalyst with Ba(OH)2 electrolyte as the operando Raman experiments in Chapter 3 suggest a direct interaction of the Ba2+ cation with the electrode. Using X-ray absorption spectroscopy (XAS) data of copper in KOH and Ba(OH)2 we were able to identify the formation of a BaCuO2 phase. The data in Chapter 5 suggest that Ba2+ significantly changes the catalyst structure, which likely has considerable effects on the glucose to lactic acid reaction. This effect is in addition to the suggested interaction between Ba2+ and O2,4 of fructose, but the details of the interaction of BaxCuyOz with glucose were not studied in this work. Lastly, to assist future researchers in performing operando XAS electrochemistry, we presented a versatile operando XAS cell in Chapter 6. This new cell has the capabilities for liquid flow, gas flow, pH monitoring, temperature monitoring, and can be used with a wide variety of catalyst types. Our aim is to lower the barrier for researchers looking to perform operando XAS measurements and allow researchers to convert time typically spent on cell design to time spent on breakthroughs in electrocatalysis. The final chapter contains a summary of the findings in this work along with a path forward to continue the pursuit of rational design of this system, which begins with characterizing the interaction between BaCuO2 and glucose.