Synergistic electronic structure tuning of self-assembled hollow hierarchical Ni-Fe-Co-P nanowire arrays on carbon cloth for enhanced water splitting

The pursuit of efficient and durable catalysts utilizing non-noble metals is critical for sustainable energy conversion through electrochemical water splitting. Herein, we present a novel bifunctional electrocatalyst of Ni-FeCo-P nanowire arrays on carbon cloth for overall water splitting, which was synthesized via a facile ion-exchange reaction between Co-MOF nanowires array and Fe2+/Ni2+ ions, followed by NaH2PO2-assisted phosphorization. By carefully controlling the molar ratios of Ni2+/Fe2+, the solid Co-MOF nanowire were transformed into hollow hierarchical nanowires assembled by nanosheets, allowing for effective modulation of the atomic composition of the titled catalyst. Specifically, this self-supported architecture showcases various advantageous features, including substantial surface areas, elevated structural void porosity, and accessible inner surfaces. These attributes not only facilitate the exposure of abundant active sites but also bolster the structural integrity, consequently facilitating efficient mass diffusion and charge transport. Density functional theory (DFT) calculations revealed that the synergistic effect of Ni, Fe, and Co elements with phosphorus vacancies leads to an increased electron density around the Fermi level, thus optimizing the adsorption free energy of H* and improving its intrinsic catalytic activity. As expected, the optimized catalyst exhibits low overpotentials of 106 and 249 mV for achieving a current density of 10 mA cm-2 in the hydrogen and oxygen evolution reactions, in 1.0 M KOH electrolyte, respectively. Moreover, the electrocatalyst exhibits outstanding bifunctional catalytic activity, achieving a current density of 10 mA cm-2 at a low voltage of 1.62 V in a two-electrode electrolyzer system. These findings demonstrate a potential avenue for the development of efficient and cost-effective bifunctional electrocatalysts for water splitting.