In the future, biomass, plastic waste, water and carbon dioxide could replace crude oil, coal and natural gas as the major feedstocks for a circular and sustainable production of fuels and chemicals.¹ Techno-economic studies already indicate that it could also become profitable to use renewable power to electrochemically convert carbon dioxide directly or using cascade routes into ethylene, ethanol and propanol - from which a broad range of value added products could be produced.²

Over the past years we have studied films of soft-landed copper (oxide) nanocrystals as cathode catalyst layers for both the direct and cascade CO₂ and CO electroreduction routes, exploring their behavior from the particle-level to the device-level.^3-4 The electrochemical performance of these catalysts has been evaluated in H-cells, flow-by and more recently in membrane electrode assembly cells, yielding valuable insights with respect to the interplay between loading, surface area and operating conditions on performance and product distribution (multicarbon products such as ethylene and ethanol being the major ones).

While the majority of the work has been applied in nature, we also carried out in-situ synchrotron X-ray absorption spectroscopy experiments in diluted bicarbonate (CO₂ reduction) and potassium hydroxide (CO reduction) to better understand the dynamic behavior of the nanoporous catalyst layers under bias. These experiments were combined with porosity and surface area information from electron tomography and Pb underpotential deposition to establish the link between electrochemically active surface area, in-situ electronic structure and faradaic efficiency ratio of the most important products (methane/ethylene and C₂₊/acetate, respectively). For example, the data indicate that the oxide CLs reduce to metallic Cu under alkaline conditions without significant compaction of the film. In addition, the analysis shed light on the extent and significance of catalyst reconstruction in the case of <50 and 200 nm-thick nanoporous CLs, which helped us explain the observation of irreversible and reversible methane formation in membrane electrode assembly cells under CO₂ reduction conditions. Together, this work establishes a baseline understanding and framework for operating ionomer-free porous catalyst layers in these applications.