Multi-chambered, carbon-coated Ni0.4Fe2.6O4 nanoparticle superlattice microspheres for boosting water oxidation reaction

Developing active and robust non-noble-metal-based electrocatalysts for the oxygen evolution reaction (OER) is of vital practical significance for accelerating the kinetics of water splitting. Here, a novel double emulsion template method is proposed to design and prepare hierarchically multichambered, carbon-coated Ni0.4Fe2.6O4 nanoparticle superlattice microspheres (M-NFO@C-NSMs) for the highly efficient oxygen evolution. The high-temperature calcination under inert gas enables an improved electrochemical property by rationally transforming the long-chain organic capping ligands into partially graphitized uniform carbon coatings. More importantly, benefiting from the unique hierarchical superstructure with macro-/meso-/microporosities and three-dimensional continuous conductive carbon frameworks, M-NFO@C-NSMs exhibit comprehensively enhanced OER activity in a dilute alkaline electrolyte as compared to their solid counterparts and most spinel-based electrocatalysts reported to date. Notably, the collective property of supraparticles endowed M-NFO@C-NSMs with superior long-term cyclic stability. This work sheds light on the sophisticated design of functionalized supraparticles for efficient water splitting.