Enhancing hydrogen production from photocatalytic water splitting over ZnIn₂S₄/Ni-MOF via magnetically induced spin polarization

Photocatalytic water splitting (PWS) for hydrogen production is a highly promising technology to address energy and environmental challenges and enable efficient solar energy conversion and storage. However, in light-driven PWS systems, rapid recombination of photogenerated electron–hole pairs due to low charge separation efficiency leads to unsatisfactory catalytic performance. Recently, introducing a magnetic field into PWS has proven effective in enhancing photocatalytic activity by suppressing charge recombination. Notably, nickel ions in Ni-MOF can act as magnetic response centers. Building on this, we report a dramatically enhanced PWS system using a ZnIn₂S₄/nickel-based metal–organic framework (ZnIn₂S₄/Ni-MOF) ferromagnetic heterojunction photocatalyst under a static magnetic field. A series of ZnIn₂S₄/Ni-MOF catalysts with varied Ni-MOF content was synthesized; the optimized sample achieved a hydrogen evolution rate of 71.91 mmol·g⁻¹·h⁻¹ under a 500 mT static magnetic field, 2.97 times higher than under visible-light irradiation alone. Systematic photoelectrochemical, magnetic, and DFT studies revealed that this enhancement stems from significantly prolonged carrier lifetimes due to spin-polarization effects of Ni ions under the magnetic field. This work offers new insights into designing high-efficiency heterojunction photocatalysts leveraging electron spin polarization. A magnetic field–induced spin polarization strategy was developed to enhance photocatalytic hydrogen evolution (PHE) from water splitting. A series of ZnIn₂S₄/Ni-MOF heterojunctions were synthesized via a facile low-temperature solvothermal method, with the optimal composite (20 wt% Ni-MOF, denoted NZ-20) exhibiting a Type II band alignment. Under visible light and a 500 mT static magnetic field, NZ-20 achieved a PHE rate of 71.91 mmol·g⁻¹·h⁻¹—2.97 times higher than under light alone—whereas ZnIn₂S₄ showed minimal magnetic response and pristine Ni-MOF displayed negligible activity. Combined photoelectrochemical, magnetic, and DFT analyses revealed that the enhancement originated from Ni²⁺-driven spin polarization, which significantly prolonged photogenerated carrier lifetimes by suppressing recombination. • Photo-magnetic catalytic of ZnIn 2 S 4 /Ni-MOF heterojunction was investigated. • Type-Ⅱ heterojunction enables effective carrier transportation and separation. • Spin polarization induced by magnetic field enhances charge separation. • A 500 mT magnetic field boosts photocatalytic H₂ evolution to 71.91 mmol·g⁻¹·h⁻¹. • Paramagnetic MOF/magnetic field coupling enables a new route to photocatalytic H₂ evolution.