Architecting Hollow Spherical NiCo₂S₄@rGO Bifunctional Electrocatalyst-Loaded Quaternized Poly(2,6-dimethyl-1,4-phenylene Oxide)-Based Membrane Electrode Assembly for an Alkaline Water Electrolyzer

In alkaline media for overall water splitting with instantaneous oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), we urgently required a noble metal free bifunctional electrocatalyst. We report a simple protocol for the preparation of NiCo2S4@rGO spherical hollow spheres, as a bifunctional electrocatalyst. The N-methyl imidazole-grafted poly 2,6-dimethyl-1,4-phenylene oxide (PPO)-based alkaline membrane (QimPPO) was prepared as a substrate for direct electrocatalyst loading and construction of membrane electrode assembly (MEA). The reported electrocatalyst (NiCo2S4@rGO hollow spheres) exhibited a shape/morphology-dependent electrocatalytic activity for water splitting (simultaneous OER/HER) in an alkaline environment. The NiCo2S4@rGO hollow spheres exhibited a current density of 10 mA cm–2 at 1.61 and 0.22 V for the OER and HER, respectively. In an alkaline medium, the reported MEA showed superior performance in comparison with precious (Pt/Ir) or nonprecious metal-based electrocatalysts. The electrolyzer performance was assessed at an applied current density of 400 mA cm–2 for 70 h. An optimized MEA will mark a significant milestone for an advanced alkaline water electrolysis and corresponding HER/OER processes. The reported results will facilitate the advancement of research in designing a meticulously structured bifunctional electrocatalyst for eco-friendly H2/O2 production via water electrolysis.