Heterostructure-enhanced performance of Mo-NiSe_x/CoFe layered double hydroxide bifunctional catalysts for efficient...

The development of bifunctional electrocatalysts with outstanding performance is crucial for overall water splitting but remains a major challenge. Interfacial engineering has emerged as a promising strategy for fabricationg low-cost and highly efficient bifunctional catalysts. Herein, we report a Mo-NiSe_x/CoFe layered double hydroxide (LDH) heterojunction bifunctional electrocatalyst that integrates the high conductivity of NiSe_x with the abundant active sites of CoFe LDH. The catalyst was synthesized by combining in-situ selenization of nickel‑molybdenum foam (NMF) and electrodeposition growth, resulting in three-dimensional heterostructures composed of Mo-NiSe_x nanoneedles and CoFe LDH nanosheets grown on NMF. Benefiting from the high specific surface area and excellent electrical conductivity of Mo-NiSe_x, the strong corrosion resistance of CoFe LDH, and the low reaction energy barrier at their interfaces, the Mo-NiSe_x/CoFe LDH catalyst simultaneously exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, with ultra-low overpotentials of 144 and 200 mV at a current density of 100 mA/cm², respectively, along with excellent stability. Furthermore, the dual-electrode water-splitting system assembled with Mo-NiSe_x/CoFe LDH achieves a current density of 100 mA/cm² at 1.732 V and operates continuously for 600 h at industrial-grade current densities of 500 and 1000 mA/cm². Anion exchange membrane water electrolyzer (AEMWE) constructed from Mo-NiSe_x/CoFe LDH attains a 1000 mA/cm² current density at merely 1.990 V at 80 °C. Density functional theory (DFT) calculations reveal that Mo-NiSe_x/CoFe LDH enables electron redistribution through the heterogeneous interface, thereby optimizing the adsorption energies of hydrogen- and oxygen-containing intermediates. This process brings the Gibbs free energy of H* (ΔG_H⁎) for the HER close to the optimal value and reduces the Gibbs free energy (ΔG) of the rate-determining step (RDS) for the OER. Furthermore, this synthesis method is environmentally friendly and easily scalable, and has been successfully applied to other systems, such as Mo-NiSe_x/NiFe LDH. Future work will focus on scaling up the preparation process and optimizing the parameters to prepare large-area, uniform electrodes, thereby advancing the practical application of this catalyst for efficient overall water electrolysis.