Improvement of performance to form syngas utilizing water and CO2 over a particulate-Cu0.8Ag0.2GaS2-based photocathode by surface co-modification with ZnS and Ag†

Surface of a particulate-Cu_0.8Ag_0.2GaS₂-based photocathode was co-modified with ZnS and Ag, resulting in improvement in the performance of the Cu_0.8Ag_0.2GaS₂ photocathode for syngas (H₂ + CO) formation through photoelectrochemical H₂O and CO₂ reduction under visible light in an aqueous electrolyte. Bubbles of the syngas were visually observed over the developed Ag and ZnS-co-modified Cu_0.8Ag_0.2GaS₂ photocathode at 0 V vs. RHE at the applied potential using a 300 W Xe-arc lamp (λ > 420 nm). Based on various control experiments and characterization studies, the following two crucial factors have arisen: (1) formation of a (ZnS)–(Cu_0.8Ag_0.2GaS₂) solid-solution near the surface of Cu_0.8Ag_0.2GaS₂ particles was vital for enhancing the separation of the photogenerated carriers, (2) the Ag cocatalyst loaded on the solid-solution worked as an active site for photoelectrochemical CO₂ reduction. Moreover, artificial photosynthetic syngas formation using water as an electron donor under simulated sunlight without any external bias was demonstrated by combining the developed Ag/ZnS/Cu_0.8Ag_0.2GaS₂ photocathode with a CoO_x-loaded BiVO₄ photoanode.