Advanced Material Engineering Strategies for Electrocatalytic Carbon Dioxide Reduction Reaction
Date
2025
Authors
Jiang, Yunling
Editors
Advisors
Zheng, Yao
Qiao, Shizhang
Qiao, Shizhang
Journal Title
Journal ISSN
Volume Title
Type:
Thesis
Citation
Statement of Responsibility
Conference Name
Abstract
The electrocatalytic CO2 reduction reaction (CO2RR), powered by renewable electricity, offers an efficient and sustainable technology to convert CO2, the major greenhouse gas, into valuable chemicals, contributing to the advancement of carbon neutrality and the zero emissions concept. In the development of CO2RR, alkaline and neutral media have dominated the main advancements due to their high CO2 solubility and enhanced CO2 activation ability. However, despite significant progress in the related device technologies, achieving superior CO2RR Faradaic efficiency (FE) under high current densities (> 200 mA cm−2) is still challenging. Additionally, CO2RR processes in alkaline and neutral media encounter a severe carbonate generation issue, causing carbon crossover to the anodic sides and sacrificing carbon conversion efficiency. Moreover, the generated carbonate salts precipitate on the electrode, blocking gas transport channels and disrupting the long-term operation of the whole system. To address this issue, acidic CO2RR shows its advantages in avoiding carbonate formation and crystallization. Nevertheless, acidic CO2RR processes suffer from intense competition with the hydrogen evolution reaction, largely reducing the selectivity of CO2RR products. Introducing alkali metal salts into acidic electrolytes has emerged as a potential strategy to promote acidic CO2RR performance. However, this approach is accompanied by a similar carbonate generation issue as that in the alkaline and neutral media. Aimed to address the above challenges in CO2RR development, this thesis is dedicated to investigating feasible strategies, including catalyst modification, electrolyte engineering, and interface optimization, to achieve high-performance CO2RR. Firstly, in terms of the low CO2RR FE in high current density at alkaline media, we proposed an atom doping strategy to induce defect effects in SnO2 lattices, facilitating the maintenance of Sn in high-valence state during alkaline CO2RR processes and the adsorption of formate-related *OCHO intermediates. A series of SnO2 catalysts doped by Cu, Bi, and Pt atoms at different ratios was prepared, in which Cu-substituted SnO2 with a doping ratio of 2 atom% exhibited the best CO2RR performance with an excellent formate FE of over 80% and a single-cell energy efficiency exceeding 50% at 100 ~ 500 mA cm−2. In-situ spectroscopy measurement results revealed that the improved performance of atom-doping SnO2 originated from enhanced CO2 activation and promoted SnO2 stability after doping. Simultaneously, the exposure of oxygen vacancy induced by atom substitution enhanced the adsorption of *OCHO intermediate. Consequently, the CO2-to-formate conversion efficiency was highly boosted by this atomic doping strategy. Furthermore, to address the issues of carbonate generation and ensure a high FE of multicarbon products, we introduced an electrolyte engineering strategy by adding iodine into the acidic electrolyte to protect the oxidation state of Cu and construct a dynamic Cu0/Cu+ interface during the acidic CO2RR process. With an excessive amount of I2 introduced into the electrolyte, a high multi-carbon product FE of above 70% was achieved over a broad current density range of 0.4 ~ 0.6 A cm−2, along with a good SPCE of 54 % at a CO2 flow rate of 2.5 sccm under a low K+ concentration of 0.3 M. This acidic CO2RR performance is comparable to reported studies with over ten times higher K+ concentrations. Thus, this I2-added strategy can effectively alleviate carbonate generation and gas transport channel blockage issues that occur in high K+ concentration cases. Combining experimental and theoretical calculation results, it confirms that I2 addition induced the formation of CuI on the electrode interface, subsequently, the generated CuI was reduced back into Cu under reduction currents. This Cu- CuI-Cu cycle ensured the continuous construction of Cu0/Cu+ interface, which is conducive to the *CO intermediate adsorption and the further C-C coupling process. As a result, these facilitating effects drive the high-performance acidic CO2RR under a low K+ concentration. Lastly, we proposed an interface engineering strategy to build a cation-enriched interface on the Ag nanoparticles, driving the suppression of proton diffusion and the enhancement of the CO2RR intermediate adsorption, even under a low KCl concentration. Thereby, the modified Ag catalyst exhibits a higher CO selectivity of over 70% and a longer operational stability in acidic electrolyte with 0.3 M KCl, which surpasses the performance of pure Ag. Further, in-situ characterizations provide in-depth mechanistic analyses into the role of interfacial cations in tuning intermediate adsorption. Overall, this thesis integrates strategies including catalyst modification, electrolyte engineering, and interface optimization to advance CO2RR processes. These efforts collectively offer new insights into enhancing the selectivity and stability of CO2RR operations and lay a solid foundation for the future development of practical CO2RR systems targeting sustainable carbon conversion.
School/Discipline
School of Chemical Engineering
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2025
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