Hierarchical NiCoP thistles: a promising electrocatalyst for the alkaline oxygen evolution reaction

The rational development of efficient and durable electrocatalysts for the alkaline OER is indispensable for the advancement of next-generation energy-conversion and energy-storage technologies. Herein, a slow-growth kinetics favoured synthetic strategy sequenced by solid-state phosphorization was employed to fabricate a synergistically favourable bimetallic NiCoP electrocatalyst possessing a hierarchical thistle flower-like microarchitecture. The physicochemical characteristics of the resultant NiCoP exhibit significant mesoporosity, interconnected hierarchical mesopore channels, small crystallite dimensions, a specific surface area of 52.9 m² g^-1, multivalent Ni/Co redox centers and catalytically active phosphide nanodomains along with amorphous phosphate layers constituting phosphide/phosphate heterointerfaces on the surface of NiCoP thistles. The electrochemical investigations reveal highly reversible redox characteristics, elevated electrocatalytically active sites, a substantial electrochemically active surface area (357 cm², corresponding to a C_dl value of 14.3 mF or 72.9 mF cm^-2), a low onset potential and favourable interfacial charge-transfer kinetics toward the alkaline OER. Consequently, the NiCoP electrocatalyst displays remarkable OER activity with an overpotential of 285 ± 2.65 mV (at 10 mA cm^-2), a Tafel slope of 113 mV dec^-1, a low charge-transfer resistance of 4.6 Ω and an apparent turnover frequency of 6.72 s^-1, along with excellent operational durability over 18 h amperometric i-t and 24 h chronopotentiometric operations. The superior electrocatalytic efficacy is attributed to the electrochemical synergism between multivalent Ni and Co species, abundant catalytically accessible low-dimensional phosphide active sites, and hierarchically interconnected mesoporous channels that collectively facilitate electrolyte-ion diffusion, rapid charge transport, enhanced OH^- adsorption kinetics, and efficient release of evolved oxygen bubbles during prolonged OER operation. Furthermore, the robust mesoporous microstructural framework effectively mitigates electrochemical degradation and stabilizes the partially reconstructed catalytically active phase under anodic OER conditions. Overall, the present study establishes hierarchically architectured and synergistically favourable bimetallic phosphides as promising non-noble alternatives to conventional OER electrocatalysts for advanced alkaline oxygen electrochemistry and sustainable energy technologies.