Directed Assembly of Nanoparticle Catalysts on Nanowire Photoelectrodes for Photoelectrochemical CO<sub>2</sub> Reduction

Reducing carbon dioxide with a multicomponent artificial photosynthetic system, closely mimicking nature, represents a promising approach for energy storage. Previous works have focused on exploiting light-harvesting semiconductor nanowires (NW) for photoelectrochemical water splitting. With the newly developed CO<sub>2</sub> reduction nanoparticle (NP) catalysts, direct interfacing of these nanocatalysts with NW light absorbers for photoelectrochemical reduction of CO<sub>2</sub> becomes feasible. Here, we demonstrate a directed assembly of NP catalysts on vertical NW substrates for CO<sub>2</sub>-to-CO conversion under illumination. Guided by the one-dimensional geometry, well-dispersed assembly of Au<sub>3</sub>Cu NPs on the surface of Si NW arrays was achieved with facile coverage tunability. Such Au<sub>3</sub>Cu NP decorated Si NW arrays can readily serve as effective CO<sub>2</sub> reduction photoelectrodes, exhibiting high CO<sub>2</sub>-to-CO selectivity close to 80% at −0.20 V vs RHE with suppressed hydrogen evolution. A reduction of 120 mV overpotential compared to the planar (PL) counterpart was observed resulting from the optimized spatial arrangement of NP catalysts on the high surface area NW arrays. In addition, this system showed consistent photoelectrochemical CO<sub>2</sub> reduction capability up to 18 h. This simple photoelectrode assembly process will lead to further progress in artificial photosynthesis, by allowing the combination of developments in each subfield to create an efficient light-driven system generating carbon-based fuels.