Probing the Boundary Layer of Electrochemical CO2 Reduction with Electrochemical Mass Spectroscopy

Abstract

Research into the aqueous electrochemical reduction of CO2 to fuels and commodity chemicals has grown quickly in conjunction with increasing concerns of greenhouse gas emissions and wider availability of “clean” electrons coming from solar and wind power. Reduction of CO2 to valuable multi-carbon products, such as ethylene or ethanol, has been observed on copper-based electrocatalysts, but many fundamental questions remain about such processes. Specifically, the nature of the active site under reaction conditions is unclear, due to possibilities for surface copper rearrangement,1 subsurface reactant species,2,3 and changes in local pH,4 among others. Here we attempt to deconvolute these process to gain a more fundamental understanding of this electrocatalytic reaction. We utilize a newly designed thin layer electrochemical mass spectrometer with 100% collection efficiency at fast time-scales5,6 to probe the product species in the boundary layer during electrochemical reduction of CO2 on copper-based electrocatalysts. We employ a range of electrode sizes to enable product sensitivity at low overpotentials and at high current densities. We combine these measurements with an analysis of pH at the surface to better understand the local pH changes as a function of reaction potential. These insights into boundary layer phenomena should guide future design of both selective catalysts and efficient device configuration for CO2 electroreduction.