Conversion of CO2 to formic acid by integrated all-solar-driven artificial photosynthetic system

Abstract Sunlight-driven valorization of CO2 into fuels is a promising solution to renewable energy storage, but the design of an integrated and efficient solar-to-chemical conversion system remains challenging. Herein, an all-solar-driven artificial photosynthetic system (APS) by tailoring photovoltaic-photoelectrochemical cell which can efficiently produce formic acid fuel from CO2 and H2O with bias-free illumination is demonstrated. Guided by density functional theory (DFT) calculations, a BiOI–Bi (BOI–Bi) cathode catalyst is synthesized, which is highly selective for CO2 to HCOOH conversion, and coupled with a single crystalline argon-treated TiO2 (TiO2-Ar) photoanode, whose valence band edge is beneficial for the oxidation of H2O to O2. The APS exhibits high product selectivity, robust activity and good durability. A solar-to-HCOOH selectivity of 96.5% is obtained with a HCOOH yield of 108.2 mmol g−1 h−1 under bias-free illumination of AM1.5G. The device can operate stably for at least 12 h. In particular, an apparent photon quantum efficiency of 7.5% and a solar-to-chemical conversion efficiency (ηSCC) of 8.3% are recorded, rivaling all the incumbent precious-metal-free all-solar-driven components for CO2-to-HCOOH conversion. This study highlights the potential of BOI-Bi for CO2 to HCOOH conversion with high selectivity and its integration into APS system to realize carbon-negative solar-to-chemical conversion with industrial relevance.