Editors' Choice-Rapid Deactivation Convolutes Electrochemical CO2 Reduction Selectivity Measurements on Gold Rotating Ring Disk Electrodes: Article No. 046503

Voltammetric measurements of electrochemical CO2 reduction reaction (CO2RR) selectivity on rotating ring disk electrodes (RRDE) are a rapid and sensitive method for quantifying an electrocatalyst's selectivity, i.e. faradaic efficiency (FE). This method has been applied to polycrystalline Au electrocatalysts where a Au disk electrode catalyzes both the CO2RR and hydrogen evolution reaction while the concentric Au ring electrode selectively senses CO by oxidizing CO back to CO2. Such measurements enabled fundamental mechanistic studies but suffer from poor inter-laboratory reproducibility. This work identifies causes of variability in RRDE selectivity measurements by comparing protocols with different electrochemical methods, reagent purities, and glassware cleaning procedures. We observed FECO decrease by 56% during 5 min chronoamperometry measurements, a phenomenon that is not readily apparent in voltammetric scans due to their dynamic nature. Electroplating of electrolyte impurities onto the disk and ring surfaces were identified as a major contributor to Au deactivation. Additionally, the oxygen reduction reaction may lead to higher disk currents in inadequately purged electrolytes, causing an apparent underestimation of FECO at low overpotentials. Lastly, we propose operational bounds for CO2RR selectivity measurements on Au using the RRDE method and provide suggestions on steps for improving the accuracy of this technique.