Probing the Catalytically Active Region in a Nanoporous Gold Gas Diffusion Electrode for Highly Selective Carbon Dioxide Reduction

We report the use of a nanoporous gold (np-Au) catalyst for CO₂ reduction in a gas diffusion electrode (GDE) and characterize the role of wetting in electrochemical performance. The np-Au catalyst has pores on the order of 20 nm and is cross-sectionally isotropic, enabling Faradaic efficiencies for CO of greater than 95% across a wide range of potentials and a maximum partial current density for CO of 168 mA/cm². Secondary ion mass spectroscopy and in situ copper underpotential deposition were employed to provide insights into catalyst wetting. At a typical CO₂ flow rate of 50 SCCM, approximately half of the catalyst is in contact with the electrolyte during operation, and the dry region exists in the bottom half of the nanoporous catalyst. We discuss implications of the nanoporous GDE wetting characteristics for catalyst performance and the design of improved GDE architectures that can maximize the catalytically active area.