Electrochemical Reduction of CO2 on Au Electrocatalysts in a Zero-Gap, Half-Cell Gas Diffusion Electrode Setup: a Systematic Performance Evaluation and Comparison to a H-cell Setup

Abstract

Much research effort has been devoted to the development of effective catalysts for the electrochemical reduction of CO2 (CO2RR). For CO2RR, the most common catalyst screening method is performed in a H-cell configuration where the reactant CO2 gas is usually dissolved in an aqueous bicarbonate-based electrolyte. However, the low solubility of CO2 in aqueous solutions (∼35 mM at 298 K and 1 atm pressure) causes mass transport limitations in such setups. Based on H-cell measurements gold (Au) is one of the most selective catalysts for the CO2RR to CO. The preparation of small Au nanoparticles (NPs) based on conventional synthesis methods often requires the use of surfactants and capping agents such as polyvinylpyrrolidone (PVP). Here, we present a systematic evaluation of the performance of Au NPs for the CO2RR in our recently developed gas diffusion electrode (GDE) setup and compare the results to investigations in a conventional H-cell configuration. The GDE setup can be characterized as a zero gap, half-cell setup and supplies a continuous CO2 stream at the electrode−membrane electrolyte interface to circumvent CO2 mass transport limitations encountered in conventional H-cells. We investigate the influence of the catalyst loading as well as the influence of PVP. The results comparing the two screening methods show that the performance of the same catalyst can be substantially different in the different setups, which highlights the importance of having commercially relevant conditions for catalyst screening. In both setups, it is found that the presence of PVP favours the hydrogen evolution reaction (HER), however, in the GDE setup PVP is more detrimental for the performance than in conventional H-cells.