Co₂P@CoPi@NC with engineered heterointerfaces and carbon networks for hydrazine-assisted water splitting

The exploration of efficient electrocatalysts for hydrazine-assisted water splitting is pivotal for energy-saving hydrogen production. Dicobalt phosphide (Co₂P) possesses good conductivity and favorable hydrogen evolution activity, yet its performance in anodic reactions such as hydrazine oxidation (HzOR) remains insufficient for overall water splitting. Constructing a heterointerface with cobalt phosphate (CoPi) is expected to combine the conductive core of Co₂P with catalytically active CoPi species to enhance the reaction kinetics. Herein, a series of metal phosphonate-derived Co₂P@CoPi@N-doped carbon (Co₂P@CoPi@NC) hybrids were developed via a facile hydrothermal synthesis using organophosphonate ligands with different carbon chain lengths, followed by direct pyrolysis under a nitrogen atmosphere. The resulting Co₂P@CoPi@NC derived from the phosphonate with bis(hexamethylene triamine penta(methylene phosphonic acid)) (BHMTPMPA) ligand exhibited remarkable HzOR activity, significantly outperforming its counterparts prepared from other ligands. The superior activity is attributed to the formation of a well-defined Co₂P/CoPi heterointerface, the in situ-generated nitrogen-doped carbon network, and the enhanced electronic coupling among the components. This work provides a high-efficiency electrocatalyst for energy-saving hydrogen production via hydrazine-assisted water electrolysis and highlights the role of ligand design in constructing advanced metal phosphonate-derived heterostructures.