Size-matching encapsulation of a high-nuclearity Ni-containing polyoxometalate into a light-responsive MOF for robust photogeneration of hydrogen

The development of robust host-guest composite photocatalysts has been considered as an interesting research direction for efficient photo-driven hydrogen evolution. In this work, an interesting size-matching strategy was adopted to construct the Ni16As4P4@NU-1000 composite by encapsulating a high-nuclearity Ni-containing polyoxometalate, [{Ni₄(OH)₃AsO₄}₄(B-a-PW₉O₃₄)₄]²⁸⁻ (Ni16As4P4), guest into a mesoporous Zr-based MOF (NU-1000) host. Under optimized conditions, the resulting Ni16As4P4@NU-1000 composite photocatalyst shows outstanding long-term photo-driven hydrogen evolution activity, achieving a hydrogen evolution of 1120 mmol g⁻¹ and a TON of 28 600 after 120-hour Xe-lamp irradiation. The photocatalytic activity remains essentially unchanged for at least four successive recycling tests. Mechanistic insights revealed that the excellent and robust photocatalytic activity of the Ni16As4P4@NU-1000 composite could be attributed to the synergistic cooperation of good light-responsive ability of the NU-1000 host, reversible multi-electron-catalytic properties of the structurally intact Ni16As4P4 cluster, and the suitable host-guest size-matching effect.