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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. [ABSTRACT FROM AUTHOR]

Single‐atom metal‐insulator‐semiconductor (SMIS) heterojunctions based on Sn‐doped Fe2O3 nanorods (SF NRs) were designed by combining atomic deposition of an Al2O3 overlayer with chemical grafting of a RuOx hole‐collector for efficient CO2‐to‐syngas conversion. The RuOx‐Al2O3‐SF photoanode with a 3.0 nm thick Al2O3 overlayer gave a >5‐fold‐enhanced IPCE value of 52.0 % under 370 nm light irradiation at 1.2 V vs. Ag/AgCl, compared to the bare SF NRs. The dielectric field mediated the charge dynamics at the Al2O3/SF NRs interface. Accumulation of long‐lived holes on the surface of the SF NRs photoabsorber aids fast tunneling transfer of hot holes to single‐atom RuOx species, accelerating the O2‐evolving reaction kinetics. The maximal CO‐evolution rate of 265.3 mmol g−1 h−1 was achieved by integration of double SIMS‐3 photoanodes with a single‐atom Ni‐doped graphene CO2‐reduction‐catalyst cathode; an overall quantum efficiency of 5.7 % was recorded under 450 nm light irradiation. [ABSTRACT FROM AUTHOR]

Single‐atom metal‐insulator‐semiconductor (SMIS) heterojunctions based on Sn‐doped Fe2O3 nanorods (SF NRs) were designed by combining atomic deposition of an Al2O3 overlayer with chemical grafting of a RuOx hole‐collector for efficient CO2‐to‐syngas conversion. The RuOx‐Al2O3‐SF photoanode with a 3.0 nm thick Al2O3 overlayer gave a >5‐fold‐enhanced IPCE value of 52.0 % under 370 nm light irradiation at 1.2 V vs. Ag/AgCl, compared to the bare SF NRs. The dielectric field mediated the charge dynamics at the Al2O3/SF NRs interface. Accumulation of long‐lived holes on the surface of the SF NRs photoabsorber aids fast tunneling transfer of hot holes to single‐atom RuOx species, accelerating the O2‐evolving reaction kinetics. The maximal CO‐evolution rate of 265.3 mmol g−1 h−1 was achieved by integration of double SIMS‐3 photoanodes with a single‐atom Ni‐doped graphene CO2‐reduction‐catalyst cathode; an overall quantum efficiency of 5.7 % was recorded under 450 nm light irradiation. [ABSTRACT FROM AUTHOR]

An artificial photosynthetic (APS) system consisting of a photoanodic semiconductor that harvests solar photons to split H2O, a Ni‐SNG cathodic catalyst for the dark reaction of CO2 reduction in a CO2‐saturated NaHCO3 solution, and a proton‐conducting membrane enabled syngas production from CO2 and H2O with solar‐to‐syngas energy‐conversion efficiency of up to 13.6 %. The syngas CO/H2 ratio was tunable between 1:2 and 5:1. Integration of the APS system with photovoltaic cells led to an impressive overall quantum efficiency of 6.29 % for syngas production. The largest turnover frequency of 529.5 h−1 was recorded with a photoanodic N‐TiO2 nanorod array for highly stable CO production. The CO‐evolution rate reached a maximum of 154.9 mmol g−1 h−1 in the dark compartment of the APS cell. Scanning electrochemical–atomic force microscopy showed the localization of electrons on the single‐nickel‐atom sites of the Ni‐SNG catalyst, thus confirming that the multielectron reduction of CO2 to CO was kinetically favored. [ABSTRACT FROM AUTHOR]