(62d) Surface pH Measurement on Aqueous CO2 Reduction Electrocatalysts Using a Rotating Ring Disk Electrode
AIChE Annual Meeting
2020
2020 Virtual AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Electrochemical CO2 Conversion I
Monday, November 16, 2020 - 8:45am to 9:00am
Understanding pH changes at a CO2 electroreduction catalyst surface is vital to optimization of activity and selectivity. The pH influences concentration of reactant CO2, reaction mechanism, and the electrochemical potential to which experiments are referenced. Determination of near surface pH is complicated by the buffering ability of reactant CO2, itself, and by the fact that CO2 reduction and hydrogen evolution both consume protons, thus changing the pH. Previous attempts to model and measure surface pH gradients under reaction conditions have suffered from neglected or poorly defined convection of CO2 to the electrode surface. Here we utilize a rotating ring disk electrode (RRDE) to control reaction and convection conditions at the CO2 electroreduction disk, while directly measuring pH in real-time with a potentiometric pH-sensing iridium oxide ring. The well-defined transport within the boundary layer of the RRDE enables accurate determination of electrocatalyst surface pH by solving the convection-diffusion-reaction equations. The effects of buffer strength and of cation size on the pH gradient are evaluated. Interchangeable disks reveal pH differences between planar metals and high-surface area electrocatalysts.