Enhanced photoelectrochemical hydrogen production with Ni single-atom catalyst decorated NH2-MIL-125 (Ti) nanocomposites

Green hydrogen is becoming increasingly important for sustainable energy, and the development of Ni single-atom catalyst (Ni SAC )-derived photoelectrocatalysts for hydrogen evolution from water splitting is crucial. In this study, 1 – 5 wt% Ni SAC were prepared through a wet-chemical reduction process and then atomically anchored onto the NH 2 -modified MIL-125 (Ti) (Ni-Ti-MOF)as the support to form Ni SAC -MIL-125 photoelectrocatalysts for H 2 production. The pristine NH 2 -MIL-125 (Ti) framework retains its structural and morphological features after incorporation of Ni SAC , while HAADF-STEM and elemental mapping support the highly dispersed nature of the introduced Ni SAC . The K-edge XANES and EXAFS analyses of Ni SAC further indicate an oxidized, low-coordination Ni environment distinct from Ni foil and bulk nickel oxides, together with strongly suppressed Ni–Ni scattering, providing additional evidence for atomically dispersed Ni sites. The Ni SAC -anchored NH 2 -MIL-125 (Ti) exhibits an improved charge-carrier utilization, which is evidenced by suppressed photoluminescence, enhanced photocurrent response, and low interfacial charge-transfer resistance. Moreover, 4 wt% Ni SAC -NH₂-MIL-125(Ti) exhibits the highest H 2 evolution rate of 1.36 mmol g −1 h −1 , which is 8.5 times higher than that of pristine NH 2 -MIL-125. Moreover, the H 2 evolution rate of the 4 wt% Ni SAC -NH 2 -MIL-125(Ti) under irradiation is 2.2-fold higher than that in the dark, confirming the beneficial role of photoexcitation in H 2 evolution from water splitting. These results elaborate that the introduction of atomically dispersed Ni SAC sites into NH 2 -MIL-125(Ti) is an effective strategy for improving PEC hydrogen evolution by promoting more efficient electron extraction and utilization at the catalyst interface.