Harmonized Physical and Electrochemical Process Design for Densely Dispersed Cu Catalysts on Cu2O Absorbers for Efficient Photoelectrochemical CO2 Reduction Reaction

The photoelectrochemical CO₂ reduction reaction (photo-CO₂RR) is a promising technology to convert CO₂ into high-value-added carbon-based chemicals using a relatively low voltage, which can economically solve the problem of CO₂ emissions. Nevertheless, unlike the conventional electrochemical CO₂RR approach, photo-CO₂RR technology is in its initial development stage. Particularly, when sunlight is applied to photoelectrodes for photo-CO₂RR, severe photocorrosion is unavoidable, resulting in the deterioration of fundamental functions including device long-term stability and conversion performance. This study proposes an innovative two-step catalyst formation strategy to enable the efficient photo-CO₂RR with Cu catalysts prepared using intrinsic photocorrosion of the Cu₂O absorption layer. This approach is based on the harmonized process design of the i) growth of physically generated Cu nanoparticles and ii) construction of improved photoelectrochemical Cu cluster catalysts. The vacuum-evaporated Cu seeds are designed to induce an evenly dispersed electrical path on Cu₂O, and the selectively concentrated electrical field from the Cu seeds provides preferential sites for metallic Cu catalysts in subsequent photoelectrochemical reduction. This harmonized combination process of Cu catalysts on Cu₂O demonstrates a synergistic performance of −1.2 mA cm⁻² at 0 V_RHE with suppression of photocorrosion and produces ≈95% CO product gas (0.4 V_RHE).