Self‐Templated Synthesis of CoFeP @ C Cage‐In‐Cage Superlattices for Enhanced Electrocatalytic Water Splitting

Abstract Designing highly‐efficient, cost‐effective, and stable electrocatalysts for water splitting is of great significance for implementing renewable energy technologies. Herein, a self‐templated strategy is employed to fabricate 2D porous electrocatalysts of heterometallic phosphides featuring a cage‐in‐cage superlattice architecture. The as‐made heterometallic phosphide electrocatalysts, comprising a layer of close‐packed CoFeP nanocages intimately embedded in an interconnected carbon‐cage framework, are converted from carbon‐coated CoFeO nanocrystal superlattices by one‐step phosphidation. Benefiting from the unique hierarchical porous structure and the ability of modulating the Co/Fe molar ratio, such 2D CoFeP @ C cage‐in‐cage superlattices show remarkable activity and stability for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. Moreover, water electrolyzers constructed using CoFeP @ C superlattices as both cathode and anode require a low cell voltage of 1.55 V to achieve a current density of 10 mA cm −2 , outperforming most nonprecious metal‐based electrocatalysts reported previously. The superior electrocatalytic performance of CoFeP @ C superlattices is revealed by density functional theory calculations. These findings provide new opportunities for developing efficient and stable bifunctional electrocatalysts for water splitting.