Steering Hydrocarbon Selectivity in CO 2 Electroreduction over Soft-Landed CuO x Nanoparticle-Functionalized Gas Diffusion Electrodes.

The use of physical vapor deposition methods in the fabrication of catalyst layers holds promise for enhancing the efficiency of future carbon capture and utilization processes such as the CO 2 reduction reaction (CO 2 RR). Following that line of research, we report in this work the application of a sputter gas aggregation source (SGAS) and a multiple ion cluster source type apparatus, for the controlled synthesis of CuO x nanoparticles (NPs) atop gas diffusion electrodes. By varying the mass loading, we achieve control over the balance between methanation and multicarbon formation in a gas-fed CO 2 electrolyzer and obtain peak CH 4 partial current densities of -143 mA cm -2 (mass activity of 7.2 kA/g) with a Faradaic efficiency (FE) of 48% and multicarbon partial current densities of -231 mA cm -2 at 76% FE (FE C 2 H 4 = 56%). Using atomic force microscopy, electron microscopy, and quasi in situ X-ray photoelectron spectroscopy, we trace back the divergence in hydrocarbon selectivity to differences in NP film morphology and rule out the influence of both the NP size (3-15 nm, >20 μg cm -2 ) and in situ oxidation state. We show that the combination of the O 2 flow rate to the aggregation zone during NP growth and deposition time, which affect the NP production rate and mass loading, respectively, gives rise to the formation of either densely packed CuO x NPs or rough three-dimensional networks made from CuO x NP building blocks, which in turn affects the governing CO 2 RR mechanism. This study highlights the potential held by SGAS-generated NP films for future CO 2 RR catalyst layer optimization and upscaling, where the NPs' tunable properties, homogeneity, and the complete absence of organic capping agents may prove invaluable.