Construction of micro-nano hierarchical wing-like iron/molybdenum oxide heterojunction with synergistic effect for accelerated overall water splitting.

Designing heterojunction catalysts with high-energy interfacial effects, especially combining the geometrical advantages of hierarchical micro-nano structures with the advantages of bi- or multi-metal syergistically optimised electronic coordination environments, is crucial for achieving efficient and stable water splitting. In this study, a simple one-step hydrothermal method was used to construct a hierarchical wing-like iron/molybdenum oxide heterojunction with a porous structure on nickel foam (FMO/NF). The synergistic effect of Fe, Mo, and the heterostructures can enrich structural defects, overcome the disadvantages of the individual components, and improve material performance by optimising the structural configurations and electronic properties and exploiting the electronic interactions that occur between interfaces composed of different phases. In addition, owing to the high porosity of the hierarchical micro-nano structure and abundant active sites, the wing-like FMO/NF was utilised as an efficient bifunctional catalyst for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), presenting low overpotentials of 278.06 and 263.72 mV, respectively, at a current density of 100 mA·cm in 1 mol/L KOH. Furthermore, assembling FMO/NF as both the anode and cathode (FMO/NF || FMO/NF) required a cell voltage of 1.87 V to drive 100 mA·cm in 1 mol/L KOH, and it proceeded continuously for 110 h with negligible cell voltage decay. This work provides a rational synthetic route for the preparation of innovative double transition metal-based micro-nano hierarchical heterostructured electrocatalysts with a synergistic effect and further advances the development of energy-conversion technology.