Photoelectrochemical CO2 Reduction Toward Multicarbon Products with Silicon Nanowire Photocathodes Interfaced with Copper Nanoparticles

The development of photoelectrochemical systems for converting CO2 into chemical feedstocks offers an attractive strategy for clean energy storage by directly utilizing solar energy, but selectivity and stability for these systems have thus been limited. A promising approach is to use a multicomponent system in which each individual component is optimized for a different aspect of the photoelectrochemical process. Here, we fabricate high aspect ratio silicon nanowire (SiNW) arrays on a wafer scale to use as photocathodes for its favorable light absorption and charge separation properties and form a radial n⁺p junction for increased photovoltage and stability. We then interface these photocathodes with a copper nanoparticle (CuNP) ensemble through a facile dropcasting method to drive efficient photoelectrochemical CO2 conversion to multicarbon products. This integrated system enables CO2-to-C2H4 conversion with faradaic efficiency approaching 25% and partial current densities above 2.5 mA/cm² at −0.50 V vs RHE, while the nanowire photocathodes deliver 350 mV of photovoltage under 1 sun illumination. Under 50 h of continual bias and illumination, CuNP/SiNW can sustain stable photoelectrochemical CO2 reduction. These results demonstrate the nanowire/catalyst system as a powerful modular platform to achieve stable photoelectrochemical CO2 reduction and the feasibility to facilitate complex reactions toward multicarbons using generated photocarriers.