Surface-State-Regulated Product Distribution in Photothermal CO₂ Hydrogenation Over MXene-Based S-Scheme Catalyst

The rational design of heterostructured photocatalysts that simultaneously enable efficient carrier separation, photothermal synergy, and controllable reaction pathways is crucial for advancing CO₂ conversion. Here, a Ni/Ti₃C₂Cl_x MXene heterojunction is synthesized via Lewis acid molten-salt etching, featuring ultrathin Ni platelets strongly anchored to the MXene substrate through interfacial TiNi₃ bonding. This architecture establishes an S-scheme charge transfer pathway, as evidenced by in situ irradiated X-ray photoelectron and X-ray absorption spectroscopy, which confirm efficient carrier transfer and separation, while femtosecond transient absorption spectroscopy reveals ultrafast interfacial dynamics. Under photothermal conditions, the cooperative interplay of metallic Ni, surface NiO_x, and the conductive MXene substrate couples directional charge migration with thermally assisted molecular activation and barrier lowering, thereby enabling regulated CO₂ hydrogenation product distribution between CH₄ and CH₃OH. Density functional theory demonstrates that surface-state evolution, rather than simple oxidation degree, modulates adsorption energetics and alters the relative barriers of CH₄ and CH₃OH pathways, such that moderately oxidized Ni-NiO_x interfacial ensembles favour methanol forming intermediates, whereas extensive oxidation suppresses CH₃OH formation. Collectively, these findings demonstrate a robust strategy for exploiting MXene-based heterojunction interfaces in photothermal catalysis and underscore the pivotal role of surface state regulated reaction pathways in steering product distribution during CO₂ hydrogenation.