Unravelling the role of built-in electric Fields in p-n SnS/NiFe-LDH heterojunctions for enhanced photocatalytic CO2 reduction

Carbon-dioxide (CO 2 ) photo-reduction reaction (CO 2 PR) offers a sustainable and cost-effective approach for transforming CO 2 into value-added fuels. Nickel iron double layered hydroxides (NiFe-LDH) are promising photocatalysts for CO 2 PR due to their earth-abundance, tunable band gaps (∼2.1–2.3 eV) and inherent CO 2 adsorption capacity. However, hasty recombination of photo-generated charge carriers confines their overall photocatalytic activity. Herein, a tin (II) sulphide (SnS)/NiFe-LDH heterojunction was engineered to enhance charge separation and catalytic efficiency. Structural analyses reveal that SnS incorporation beyond 15 wt% induces lattice strain and interfacial active sites, significantly improving the CO 2 adsorption. Among the synthesized compositions, NFTS20 (20 wt% SnS) exhibits superior activity by yielding carbon monoxide (CO) and methanol (CH 3 OH) at rates of 60.76 and 5.76 µmol g -1 h −1 , respectively. This enhanced performance is attributed to suppressed charge recombination, increased surface area, and efficient interfacial charge transport. Notably, the Scanning tunneling microscope imaging and the X-ray photoelectron spectroscopy identifies sulfur diffusion into the LDH lattice, while valence band and flat band potential measurements confirms the development of a p-n (SnS/NiFe-LDH) heterojunction and its role in promoting directional charge separation. The formation of p-n junction is further corroborated with in-situ EPR studies, which demonstrated a notable increment in superoxide and hydroxyl radicals in NFTS20 under illumination, signifying the suppressed recombination and accelerated interfacial charge transfer. These synergetic structural and electronic modifications in NFTS20 result in significantly improved CO 2 PR activity, highlighting the potential of heterojunction engineering for solar-to-fuel conversion.