Effect of Gold Nanoparticles as Co‐Catalyst on WO ₃ /Cu ₂ O Heterojunction Photoelectrodes to Enhance Light‐Driven CO ₂ Conversion Efficiency

Heterojunction electrodes based on tungsten trioxide (WO 3 ) and cuprous oxide (Cu 2 O), decorated with gold nanoparticles as co‐catalyst, were developed for use in the photoelectroreduction of CO 2 to generate value‐added products. Layer‐by‐layer addition of the materials was performed by consecutive electrodepositions on metallic Ti. The resulting electrode showed good performance during the conversion of CO 2 to methanol and CH 4 , identified by chromatographic methods, achieving 44.6 and 25.8 μmol L −1 cm −2 , respectively. The Au co‐catalyst enhanced the charge transfer efficiency, reducing the interfacial resistance from 5500 Ω (Ti/WO 3 ) to 450 Ω (Ti/WO 3 /Cu 2 O/Au). Experiments with controlled potential revealed optimal performance at intermediate biases, with extreme potentials causing electrode degradation (at −0.8 V vs. AgAgCl) or insufficient charge separation (at −0.1 V vs. Ag/AgCl). The uniform distribution of Au across the electrode surface facilitated charge carrier mobility, while maintaining structural integrity during operation.