Boosting photocatalytic hydrogen production in complex environments by confining trace MoBT(x) MBene.

Charge carrier recombination represents a fundamental constraint in semiconductor photocatalysis. Combining heterostructure design with deliberate defect engineering to facilitate hydrogen intermediate (*H) adsorption is a viable strategy for boosting photocatalytic hydrogen evolution reaction (HER). Herein, we design defective MBene via controlled etching and perform in situ hydrothermal assembly to develop a tailored MoBT/CdS heterostructure. Incorporating a mere 0.5 wt % two-dimensional MoBT MBene leads to a fourfold enhancement in HER activity over bare CdS. The established MoBT/CdS catalyst achieves a remarkable HER of 10.2 millimoles per gram per hour under ambient conditions with 23.2% apparent quantum yield and sustains 90.2% activity after 24 hours of continued operation. Outstanding environmental adaptability is demonstrated through a consistent HER value of 7.1 millimoles per gram per hour in tap water and 5.7 millimoles per gram per hour in seawater. The temperature-dependent performance demonstrates notable robustness, reaching 11.1 millimoles per gram per hour at 35°C while preserving 40% functionality at harsh 5°C. Integrated photoelectrochemical and computational analyses elucidate that Mo vacancies create band alignment-optimizing electron traps and reduced *H adsorption barriers, enhancing fast carrier separation. Concurrently, interfacial covalent Mo─S bonds establish atomic-level charge-transfer pathways and enable rapid electron migration. This work establishes a previously unidentified paradigm for advanced photocatalyst design through concerted defect-interface modulation.