pH Matters When Reducing CO2 in an Electrochemical Flow Cell

The pH at the electrocatalyst surface plays a key role in defining the activity and selectivity of the CO2 reduction reaction (CO2RR). We report here operando Raman measurements of the catalyst surface in a customized CO2RR flow cell that enable the measure of pH. Using this flow cell, we were able to measure surface pH as a function of time, current density, and proximity to the catalyst surface during the electrolysis of bicarbonate solutions. We observed that increasing the current density from 0 to 200 mA cm(-2) increased the surface pH from 8.5 to 10.3. We also show here that operation at elevated temperatures (70 degrees C) results in an increased surface pH and serves to suppress the competing and undesirable hydrogen evolution reaction.