Ink-Based CuIn_0.3Ga_0.7S₂ Nanocrystal Thin Films as Photocathodes for Photoelectrochemical CO₂ Reduction Reaction

One of the promising methods to solve the current energy and environment issues is photoelectrochemical (PEC) water splitting and CO 2 reduction reaction. Chalcopyrite copper indium gallium sulfide (CIGS) and CuIn 0.3 Ga 0.7 S 2 nanocrystal thin films have been considered photovoltaic materials, and here, we demonstrated their potential to reduce CO 2 into CO. A modified solution process affords to decrease the number of surface ligands, which triggers an increase in the crystal size and an improved reproducibility in performance and output current. After depositing gold nanoparticles on the surface of CIGS, the Faradic efficiency related to the CO 2 -to-CO conversion can reach 12.93% in aqueous electrolytes and 25% in nonaqueous electrolytes. Further investigation points out that in the range of applied potential between −0.1 and −0.2 V vs a reversible hydrogen electrode (RHE), the CIGS photocathode appears to display a stable photocurrent density for 1 h, but when applying a higher applied bias, such as of −0.3 V vs RHE, the degradation of the current is significant. Additionally, we found that coupling catalysts to the CIGS increases the selectivity toward CO and minimizes the competitive hydrogen evolution reaction.