Surface phosphating activation of PtMo₆-Ni-BDC nanosheets for an enhanced hydrogen evolution reaction

Polyoxometalate-based metal-organic frameworks (POMOFs) are promising electrocatalysts for electrochemical water splitting due to their controllable structures, stabilized polyoxometalate clusters, and reversible charge transfer. However, elemental leaching, structural collapse, and active site blocking are commonly observed under harsh electrolyte conditions. Herein, a surface phosphating strategy is applied to activate the POMOF of PtMo₆-Ni-BDC, enabling its enhanced electrocatalytic performance for the hydrogen evolution reaction (HER). Active species of Ni₂P and Pt are formed on the surface, while the nanosheet morphology of PtMo₆-Ni-BDC is preserved after phosphidation, thus optimizing electronic interactions and exposing abundant active sites. The P-PtMo₆-Ni-BDC composite achieves a current density of -100 mA cm^-2 at a low overpotential of 65 mV, a small Tafel slope of 21 mV dec^-1, and long-term stability in an alkaline medium. Due to the synergy among the surface-formed Ni₂P/Pt, the reconstructed Ni(OH)₂, and the dissolved Mo-based species after the HER, P-PtMo₆-Ni-BDC reduces the energy barrier for facilitating water adsorption and dissociation efficiently. This work offers insights into the surface modification of POMOFs for electrochemical water splitting applications.