A Multi‐Active Site Subnano Heterostructures Catalyst Grown In situ POM and Fe_0.2Ni_0.8Co₂O₄ onto Nickel Foam Toward Efficient Electrocatalytic Overall Water Splitting

Abstract Designing efficient, durable, and cheap bifunctional electrocatalysts is a challenging goal in water splitting. Herein, trivanadium‐substituted Keggin‐type polyoxometalate H₆PV₃Mo₉O₄₀ (POM) and Fe_0.2Ni_0.8Co₂O₄ (FNCO) are in situ grown onto nickel foam (NF) yielding a self‐supporting nanoflower‐like heterojunction via convenient hydrothermal reaction. The POM‐Fe_0.2Ni_0.8Co₂O₄/NF as HER and OER electrocatalyst, displays low overpotential (89 and 259 mV) and high electrode stability at 10 mA cm⁻². POM‐FNCO/NF as the cathode and anode requires a lower voltage (1.58 V) to provide 10 mA cm⁻² for overall water splitting (OWS), which is better than that of commercial catalysts. The electronic sponge characteristics of POM provide more active sites and fast reaction kinetics for HER and OER. The synergy of POM and FNCO optimizes the electron distribution at the interface and enhances the intrinsic activity of HER/OER. Density Functional Theory (DFT) calculations show that water molecules preferentially bind to Co sites on POM‐FNCO. Additionally, POM has proton‐coupled electron transfer properties and its modified FNCO exhibits thermodynamic advantages. The synergistic effect of these two factors enables the efficient overall water splitting of POM‐FNCO. This study offers a novel pathway for the construction of self‐supporting efficient catalysts by in situ growth of POM nanoclusters and spinel oxide sub‐nanometer heterojunctions on NF.