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

Abstract

Sunlight-driven valorization of CO 2 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 CO 2 and H 2 O 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 CO 2 to HCOOH conversion, and coupled with a single crystalline argon-treated TiO 2 (TiO 2 -Ar) photoanode, whose valence band edge is beneficial for the oxidation of H 2 O to O 2 . 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 (η SCC ) of 8.3% are recorded, rivaling all the incumbent precious-metal-free all-solar-driven components for CO 2 -to-HCOOH conversion. This study highlights the potential of BOI-Bi for CO 2 to HCOOH conversion with high selectivity and its integration into APS system to realize carbon-negative solar-to-chemical conversion with industrial relevance. • The pathways of selectively converting H C O 3 – /CO 2 -to-HCOOH is simulated. • The gain effect of VBM for potential distribution in PEC system is clarified. • The cell voltage of optimized APS meets the highest selectivity for HCOOH. • The APS exhibits a highest η S C C of 8.3% in all the precious-metal-free devices.