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Designing efficient metal nitride electrocatalysts with advantageous nanostructures toward overall water splitting is of great significance for energy conversion. In this work, holey cobalt−iron nitride nanosheet arrays grown on Ni foam substrate (CoFeN x HNAs/NF) are prepared via a facile hydrothermal and subsequent thermal nitridation method. This unique HNA architecture can not only expose abundant active sites but also facilitate the charge/mass transfer. Resulting from these merits, the CoFeN x HNAs/NF exhibits high catalytic performance with overpotentials of 200 and 260 mV at 10 mA cm −2 for the hydrogen evolution reaction (HER) and 50 mA cm −2 for the oxygen evolution reaction (OER), respectively. Furthermore, when using CoFeN x -500 HNAs/NF as both anode and cathode, the alkaline electrolyzer could afford a current density of 10 mA cm −2 at 1.592 V, higher than many other metal nitride-based electrocatalysts. This work signifies a simple approach to prepare holey metal nitride nanosheet arrays, which can be applied in various fields of energy conversion and storage.

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Development of efficient, stable, and low-cost noble metal-free electrocatalysts for overall water splitting is of great significance for sustainable energy conversion, yet it remains highly challenging. Herein, a Co x P–Fe2P heterostructure array electrocatalyst supported on nickel foam (Co x P–Fe2P/NF) is fabricated via phosphating of the CoFe-layered double hydroxide (CoFe-LDH) nanosheets decorated with CoFe Prussian blue analogue (CoFe-PBA) nanocubes. The as-fabricated Co x P–Fe2P/NF heterostructure arrays with an abundant and strongly electronic coupled interface not only guarantee the fast charge transfer and improve the reaction kinetics but also enable the charge redistribution between Co x P and Fe2P, thus possibly optimizing the adsorption capabilities of reactants. Benefiting from the compositional and structural advantages, this as-fabricated Co x P–Fe2P/NF heterostructure can efficiently convert water to H2 and O2 with the potentials of 75 and 265 mV to achieve the current densities of 10 and 50 mA cm–1 in 1 M KOH, respectively. Especially, when Co x P–Fe2P/NF is used as both anode and cathode materials, a cell voltage of 1.61 V is required at the current density of 10 mA cm–2 with excellent stability in long-term operation over 100 h, which is comparable to Pt/C/NF||RuO2/NF. This work highlights the key roles of the interface in accelerating the electrocatalytic reaction kinetics and paves a way for the design of a high-performance electrocatalyst for overall water splitting.