Br-Doped Nickel-Cobalt Phosphide Nanoarrays on Engineered Porous NF for High-Efficiency Water Oxidation

ABSTRACT: The rational design of cost-effective electrocatalysts for the oxygen evolution reaction (OER) is pivotal for advancing green hydrogen production. This study presents a substrate-engineered Br-doped nickel-cobalt phosphide (NiCoP) electrocatalyst fabricated through a stepwise synthesis protocol. A porous and roughened nickel foam (NF) is initially constructed to provide a 3D conductive scaffold, followed by the hydrothermal growth of vertically aligned NiCo-layered double hydroxide (LDH) nanosheets. Subsequent controlled pyrolysis in the presence of a bromine source yields Br-doped NiCoP nanoarrays securely anchored on the NF/Ni substrate. Comprehensive structural characterization confirms the successful Br incorporation, which induces lattice distortion and optimizes the electronic configuration of NiCoP, while the interconnected porous architecture enhances electrolyte infiltration and gas release. Electrochemical evaluations reveal exceptional OER performance, achieving an ultralow overpotential of 220 mV at 10 mA·cm⁻² and a Tafel slope of 61.2 mV·dec⁻¹ in 1 M KOH, surpassing most reported NiCo-based phosphides. In-situ Raman spectroscopy and post-OER characterization uncover dynamic surface reconstruction into Br-enriched (oxy)hydroxide active species, elucidating the dual role of Br as both an electronic modulator and a stabilizer for reactive intermediates. This work demonstrates a substrate-guided heteroatom doping strategy to engineer high-performance bimetallic phosphide electrocatalysts, offering insights into interface engineering for sustainable energy technologies.