Hierarchical 3D Fe-doped Bi ₂ MoO ₆ arrays supported on a Ni foam: an effective electrocatalyst for alkaline water splitting

Electrocatalytic water splitting is a viable route to sustainable hydrogen generation; however, designing high-performance, stable catalysts remains a considerable challenge. Bismuth-based materials have not yet been well studied for electrocatalytic alkaline water splitting, despite their favourable electronic structure and chemical stability. Here, iron-doped hierarchical three-dimensional (3D) Bi₂MoO₆ arrays have been grown in situ on a 3D conductive nickel foam (NF) substrate using a facile solvothermal method. The optimal Fe-doped Bi₂MoO₆/NF (Fe, 5 mol% substituting Bi) or BMOF-5 electrocatalyst exhibits excellent electrocatalytic activity towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media (pH ∼ 14.0) owing to abundant active sites in the hierarchical 3D framework, high electrical conductivity, and superhydrophilic nature. At a current density of 10 mA cm⁻², the BMOF-5 electrocatalyst requires 262 mV and 153 mV overpotentials for the OER and HER, respectively. In addition, a potential of 1.62 V is required by the BMOF-5/NF∥BMOF-5/NF cell at a current density of 10 mA cm⁻² for overall water splitting. The BMOF-5/NF electrocatalyst shows durability of 24 h and 22 h for the HER and OER in a 1 M KOH electrolyte at current densities of 100 and 10 mA cm⁻², respectively. In this study, a small amount of iron plays an important role in altering the electronic environment of Bi₂MoO₆, increasing the electrochemically active sites and reducing the charge-transfer resistance at the electrode-electrolyte interface. In addition, this work presents an easy and efficient approach to enhance the electrocatalytic performance of Bi₂MoO₆, which is of significant practical importance.