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Selective CO2 reduction via photoelectrocatalysis is a creative approach to alleviating the energy crisis and environmental deterioration as well as to producing value-added chemicals. A considerable challenge is the development of electrocatalysts and photoelectrocatalytic systems to selectively and efficiently produce a target product. Here, we report an efficient and selective photocathode for converting CO2 to HCOOH in aqueous solution. A rational compositional screening strategy was first applied to pinpoint In0.4Bi0.6 from ternary In–Bi–Sn alloys as the most HCOOH-selective electrocatalyst composition among the electrocatalysts reported. A photocathode was then fabricated by coating the catalytic, protective, and conductive In0.4Bi0.6 alloy layer on a halide perovskite photovoltaic, effectively utilizing its low melting point eutectic molten state. The generated photovoltage assisted reduction of the overpotential by 680 mV while producing a stable current for nearly exclusive HCOOH production under simulated AM 1.5G irradiation. This work provides a promising approach to achieving efficient and selective solar–fuel conversion.

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Single-phase bismuth silver oxysulfide, BiAgOS, was prepared by a hydrothermal method. Its structural, morphological and optoelectronic properties were investigated and compared with bismuth copper oxysulfide (BiCuOS). Rietveld refinement of the powder X-ray diffraction (XRD) measurements revealed that the BiAgOS and BiCuOS crystals have the same structure as ZrSiCuAs: the tetragonal space group P4/nmm. X-ray photoelectron spectroscopy (XPS) analyses confirmed that the BiAgOS has a high purity, in contrast with BiCuOS, which tends to have Cu vacancies. The Ag has a monovalent oxidation state, whereas Cu is present in the oxidation states of +1 and +2 in the BiCuOS system. Combined with experimental measurements, density functional theory calculations employing the range-separated hybrid HSE06 exchange-correlation functional with spin-orbit coupling quantitatively elucidated photophysical properties such as absorption coefficients, effective masses and dielectric constants. BiCu-OS and BiAgOS were found to have indirect bandgaps of 1.1 and 1.5 eV, respectively. Both possess high dielectric constants and low electron and hole effective masses. Therefore, these materials are expected to have high exciton dissociation capabilities and excellent carrier diffusion properties. This study reveals that BiAgOS is a promising candidate for photoconversion applications.

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis.

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