Interfacial pH and Product Selectivity Measurements during CO2 Reduction on a Rotating Ring-Disk Electrode

Despiteits increased relevance for the ongoing energy transition,the CO2-reduction reaction (CO2RR) continuesto be poorly understood, particularly in the context of how its kineticsand product outcome are affected by surface-specific parameters suchas the interfacial pH. The latter has received increased attentionlately, with numerous studies reporting its impact on the productdistribution of the CO2-electroreduction reaction but failingto quantify it reliably due to the poorly defined mass transport propertiesof the electrochemical cells in which most of those studies were performed.With this motivation, herein we investigate the CO2RR onpolycrystalline Au and a Au aerogel in a rotating ring-disk electrode(RRDE) setup characterized by its well-defined hydrodynamic propertiesand quantify these surfaces' CO2-to-CO conversionperformance and interfacial pH using a Au or an IrO (x) ring, respectively. The experimental ring pH was found tobe in close agreement with the values computed from a mathematicalmodel, from which we estimated disk surface pH maxima of & SIM;9.2vs & SIM;9.0 for Au-AG vs Au-PC. The subsequentquantification of CO-specific kinetic currents made possible by theuse of this RRDE approach unveiled that the polycrystalline surfacefeatures an & SIM;2-fold larger Au-surface-specific current thanthe aerogel, thus hinting at the existence of a roughness factor effecton this key performance metric.

Automated summary

Despite increased relevance in energy transition, understanding of CO2 reduction reaction (CO2RR) is still limited, especially regarding the impact of surface-specific parameters such as interfacial pH on its kinetics and product outcome. In this study, CO2RR on polycrystalline Au and Au aerogel was investigated using a rotating ring-disk electrode (RRDE) setup, with the quantification of interfacial pH through measuring the pH value of the gold ring electrode. The results showed that the polycrystalline Au surface had approximately twice the current efficiency compared to the aerogel surface, suggesting a roughness factor effect on this key performance metric.