Facile fabrication of a 3D network composed of N-doped carbon-coated core–shell metal oxides/phosphides for highly efficient water splitting

Development of robust, bifunctional, and non-precious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is a prerequisite to realizing the overall splitting of water. This, however, remains a great challenge. In this context, we fabricated a novel three-dimensional (3D) network comprising N-doped carbon-coated core–shell NiFeOx@NiFe–P (denoted as NC–NiFeOx@NiFe–P) by two-pot high-temperature phosphorization and surface oxidation of a NiFe-Prussian blue analogue/polyvinylpyrrolidone (denoted as NiFe–PBAs/PVP) hybrid precursor. The as-synthesized NC–NiFeOx@NiFe–P catalyst demonstrated exceptional performance for both OER and HER, offering a current density of 10 mA cm−2 (a metric related to solar fuel) at small overpotentials of 285 mV for the OER and 237 mV for the HER in 1 M KOH, respectively. As expected, a NC–NiFeOx@NiFe–P based alkaline electrolyzer with durability of 20 h was manufactured to achieve 10 mA cm−2 at a voltage of 1.59 V, outperforming most non-precious metal-based electrolyzers. The exceptional performance could be attributed to the unique 3D network composed of core–shell NiFeOx@NiFe–P and highly conductive N-doped carbon (NC), which provided a large amount of highly active sites for both OER and HER and favored fast electron transport during electrocatalytic processes.