Advanced CIGS-mesoporous TiO2 hybrid photocathode functionalized with cobalt quaterpyridine for solar-driven CO₂ reduction

Hybrid photocathodes that integrate inorganic semiconductors with molecular catalysts offer a promising strategy for photoelectrochemical CO2 reduction into value-added products. In this work, we present the design and characterization of a high-performance photocathode based on copper indium gallium sulfide (CIGSu), functionalized with a cobalt quaterpyridine (CoQPy) molecular catalyst. The device features a thin (5 nm) TiO2 protective layer deposited by atomic layer deposition (ALD) on CIGSu/CdS, followed by a mesoporous TiO2 layer formed under mild conditions using UV curing and low-temperature annealing (150°C). The mesoporous structure enables high CoQPy loading through chemisorption via phosphonic acid anchoring groups. Under simulated sunlight, the optimized photocathode delivers a photocurrent density of ca. 2 mA/cm² with 95% CO selectivity in carbonate buffer, double the performance of systems using low-porosity TiO2. This work marks progress toward efficient, molecularly functionalized photocathodes for aqueous CO2 reduction.