Ternary metal sulfides (TMSs) have been widely documented as an important subgroup of semiconducting materials in solar water splitting into hydrogen (H2) fuel. Recently, interest has been rekindled in this specific branch of chalcogenide materials, particularly in the opportune integration of indium-based TMSs with emerging materials such as MXenes, metal–organic frameworks (MOFs), carbon quantum dots (CQDs), carbon nanofibers (CNFs), and metal-like Mo2C for various nanoscale heterojunction formations. In this mini review, recent outstanding advances of TMS-based heterostructures are concisely reviewed. Following an overview of the fundamental rationales of photocatalytic water splitting, a panorama of different indium-based TMSs (ZnIn2S4, CdIn2S4, and CaIn2S4) and their heterostructures (Z-scheme, conventional heterojunction, and Schottky junction) are outlined and discussed in terms of mechanistic insights and water splitting application prospects. On top of that, investigations of other burgeoning TMS-based heterostructures are carried out, followed by recommendations on future prospects of emerging TMS-based materials and the key challenges in practical water splitting. It is believed that this critical mini review is timely to bring new advances of TMS-based heterostructures and acts as a reference toward future endeavors in developing highly efficient and stable photocatalytic systems for H2 generation.

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ZnIn2S4 (ZIS) is an efficient photocatalyst for solar hydrogen (H2) generation from water splitting owing to its suitable band gap, excellent photocatalytic behaviour and high stability. Nevertheless, modifications are still necessary to further enhance the photocatalytic performance of ZIS for practical applications. This has led to our interest in exploring phosphorus doping on ZIS for photocatalytic water splitting, which has not been studied till date. Herein, phosphorus-doped ZnIn2S4 (P-ZIS) was modelled via Density Functional Theory to investigate the effects of doping phosphorus on the structural and electronics properties of ZIS as well as its performance toward photocatalytic water splitting. This work revealed that the replacement of S3 atom by substitutional phosphorus gave rise to the most stable P-ZIS structure. In addition, P-ZIS was observed to experience a reduction in band gap energy, an upshift of valence band maximum (VBM), an increase in electron density near VBM and a reduction of H* adsorption–desorption barrier, all of which are essential for the enhancement of the hydrogen evolution reaction. In overall, detailed theoretical analysis carried out in this work could provide critical insights towards the development of P-ZIS-based photocatalysts for efficient H2 generation via solar water splitting.

Photocatalytic conversion of carbon dioxide (CO2) into value‐added fuels is a vastly promising anthropogenic chemical carbon cycle to combat the greenhouse effect while meeting the ever‐increasing energy demand. Recently, lead‐based halide perovskites have demonstrated great potential in various applications including photochemical reduction of CO2. However, in view of lead toxicity, the exploration of a lead‐free alternative is crucial for long term application. Herein, a series of lead‐free mixed halide perovskites Cs3Sb2ClxBr9−x (0 ≤ x ≤ 9) is prepared via a facile antisolvent recrystallization technique, where the incorporation of a secondary halide enhances the charge transfer and separation while allowing precise tuning of bandgap between 2.59 and 2.90 eV. Theoretical calculations further reveal that the formation of mixed Cl/Br halides engenders favorable charge redistribution due to lower octahedral distortion, which in turn strengthens CO2 adsorption and activation. Under visible light illumination, the optimal dual halide perovskite, Cs3Sb2Cl4Br5 manifests substantial twofold and fourfold enhancements of CH4 yield over the single halide perovskite, Cs3Sb2Br9 and Cs3Sb2Cl9, respectively. In brief, this study provides a compelling demonstration of lead‐free mixed halide perovskites for photocatalytic CO2 reduction, and it is anticipated to drive further application of perovskite‐based photocatalysts toward a diverse range of artificial photoredox reactions.

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