Unveiling reactive origin through the in situ 2D core–shell formation, Ni(CN)₂@Ni₂P, derived from Hofmann-type MOF for water oxidation

The electrochemical water splitting into pure hydrogen (H₂) and oxygen (O₂) is considered the most promising green energy generation system. However, so far, the bottleneck of the oxygen evolution reaction (OER) has demanded kinetically and thermodynamically effective electrocatalysts, and simultaneously, replacement of the noble metal-based catalysts. In this work, 2D Ni Hofmann-type MOF is suggested as a new type of versatile template to obtain freestanding nanoplate and concurrently assert the intrinsic properties of 2D structure. This study reports the in situ core–shell formation upon 2D Ni H-MOF to design the topological 2D Ni(CN)₂@Ni₂P core–shell heterostructure, which retains the organic-linked structure as the core, and exposes reactive sites directly onto the shell. The synergistic effect of the 2D Ni(CN)₂@Ni₂P core–shell heterostructure exhibits remarkable OER activity with overpotential values of 356.8 and 442.8 mV to achieve current densities of 50 and 100 mA/cm², respectively, surpassing the single-phase catalysts and the benchmark RuO₂. In addition, the stability shows 97.8 and 94.8 % retention of the initial activity after 24 and 100 h electrolysis, respectively. Further, density functional theory provides deep insight into the heterointerface engineering by which the electronic modulation successfully optimizes the binding free energy of intermediate, thereby promoting the OER performances of the 2D Ni(CN)₂@Ni₂P core–shell heterostructure.