Cobalt phosphide nanoarrays with crystalline-amorphous hybrid phase for hydrogen production in universal-pH

To accomplish mass hydrogen production by electrochemical water-splitting, it is a necessary to develop robust, highly active, stable, and cost-effective hydrogen evolution reaction (HER) electrocatalysts that perform comparably to Pt in the universal pH range. In this work, cobalt phosphide hybrid nanosheets supported on carbon felt (CoP HNS/CF) are presented, which exhibit the superior electrocatalytic hydrogen production under a universal-pH. In these nanosheets, a single CoP HNS is composed of polycrystalline CoP and oxygen-enriched amorphous Co-O-P phase. Benefiting from its unique nanoarchitecture, as-fabricated CoP HNS/CF exhibits a tremendous electrocatalytic HER activity and outperforms Pt/C as well as state-of-the-art CoP electrocatalysts in universal-pH. In acidic and neutral media, the CoP HNS/CF shows superior electrocatalytic activity while maintaining its original hybrid crystalline-amorphous phase and morphology. In alkaline medium, the unexpected phase and morphological reorganization of CoP HNS/CF results in outstanding electrocatalytic operation. CoP HNS/CF not only achieves high electrocatalytic activity and kinetics, but also a stable and long operating lifetime even under a high current density of 500 mA·cm^-2. Furthermore, the fabrication of CoP HNS/CF can be scaled up easily, and the large CoP HNS/CF electrode also exhibits similar electrocatalytic activity and stability.