Probing the Catalytically Active Region in a Nanoporous Gold and Copper Gas Diffusion Electrode to Enhance 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 crosssectionally 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. An analogous nanoporous copper (Np-Cu) catalyst was prepared by electron beam vapor deposition of Cu/Al followed by selective chemical etching of the Al. The morphology and catalyst stability under applied potential were studied before and after electrolysis.