A Novel Experimental Method for Measuring CO Binding on Catalyst Surfaces Using a Gas Diffusion Electrode

The electrocatalytic reduction of carbon dioxide (CO₂) into various fuels, such as ethylene, ethanol, and propanol, represents a promising technology to address global warming. For commercial viability, numerous studies have focused on enhancing selectivity and activity of catalyst through both catalyst design and device engineering. In the CO₂ reduction, initial intermediates, *CO, play a crucial role, particularly regarding their binding and surface coverage. A deeper understanding of *CO on the catalyst surface is essential for optimizing catalyst behavior and guiding catalyst design. However, direct observation of intermediates during reaction kinetics has been challenging, leading many studies to rely on theoretical simulations to explore adsorption and desorption on catalyst.
In this work, we introduce a novel experimental methodology to measure adsorption strength, desorption rates, and intermediate coverage in real-time. Unlike conventional H-cells, a gas diffusion electrode enables rapid modification of the gas environment at the catalyst surface due to its separated gas and electrolyte phases. Our approach involves alternating the supply of CO and inert gas to non-CO-reductive catalysts such as Ag, Pt, and Pd. Under inert gas conditions, the hydrogen evolution reaction (HER) occurs, resulting in H* as the primary adsorbate, which is monitored through current measurements. When CO is introduced, it adsorbs onto the catalyst surface, blocking HER-active sites and thus decreasing the current. Reintroducing inert gas allows CO desorption based on adsorption strength, with real-time tracking achieved by monitoring current variations. We developed a gas-switching system capable of alternating between CO and inert gas within milliseconds while applying a potential for the reaction. Using this method, we successfully observed CO adsorption and desorption on various catalysts, influenced by factors such as applied potential, electrolyte composition, and pH.