Electrochemical Cell with Electrolyte Flow Enables Operando ATR-IR Spectroscopy of Electrocatalytic CO2 Reduction through Control of Mass Transport

Abstract

The efficient electrocatalytic conversion of abundant species such as water, carbon dioxide, and nitrogen to fuels and chemicals with renewable energy could provide a sustainable alternative to fossil fuels and thus mitigate climate change. To develop better electrocatalysts for reactions such as electrochemical CO2 reduction (CO2R), it is desirable to probe the electrode-electrolyte interface spectroscopically while also measuring intrinsic reaction rates that are not affected by concentration polarization. Infrared absorption spectroscopy in the Kretschmann attenuated total reflection mode (ATR-IR) provides such interfacial sensitivity, especially when the working electrode’s morphology and thickness are optimized to maximize surface-enhanced IR absorption (ATR-SEIRAS). Here, we address a persistent challenge – i.e., collecting operando vibrational spectra while measuring intrinsic electrochemical reaction rates – by designing and evaluating a new electrochemical cell for ATR-IR studies. The parallel orientation of the electrodes in the cell yields a more uniform current distribution, and the convective flow of electrolyte both removes bubbles and provides the control over mass transport that is essential to avoid concentration polarization. The membrane between the working and counter electrodes allows for quantitative product detection. We evaluated the cell’s transport properties with a reversible redox reaction, and we used it to collect operando vibrational spectra during CO2R with Au working electrodes. We found that electrolyte flow both determined the boundary layer thickness and effectively removed bubbles, and that the measured current densities and product selectivity were consistent with the known CO2R activity of Au. In light of these results, this new cell design for operando electrochemical ATR-IR spectroscopy should improve the link between vibrational spectra and intrinsic reaction rates and thereby provide valuable mechanistic insights for CO2R and other reactions in electrocatalysis.