V-doped Co₂P Anchored on the N–P-Doped Three-Dimensional Covalently Cross-Linked Graphene As a Hydrogen Evolution Reaction Catalyst for Alkaline Water/Seawater Splitting

Designing and synthesizing highly efficient and stable electrocatalysts of seawater electrolysis for the hydrogen evolution reaction is important for realizing green hydrogen production. Herein, a heterostructured V-doped Co₂P anchored on N-P-doped three-dimensional covalently cross-linked graphene (V-Co₂P@NPPC/3DG) electrocatalysts was synthesized with the help of V-doped ZIF-67 as an intermediate and a controlled phosphidation process. The as-prepared V-Co₂P@NPPC/3DG-1:5 had low overpotentials of 98.3 and 88.3 mV (at 10 mA cm^-2) in alkaline water and artificial seawater, respectively, and the corresponding Tafel slopes were 56.4 and 51.0 mV dec^-1. The electrolyzer with a flowing alkaline artificial seawater assembled from V-Co₂P@NPPC/3DG-1:5 with a commercial RuO₂ catalyst exhibited a cell voltage of 1.54 V at 10 mA cm^-2, which is close to that of Pt/C||RuO₂ (1.52 V). Notably, the cell voltage of V-Co₂P@NPPC/3DG-1:5||RuO₂ was lower than that of Pt/C||RuO₂ at a high current density (>58 mA cm^-2), which exhibited superior stability. V doping effectively enhanced the intrinsic activity of Co₂P, and the complexation with NPPC/3DG achieved full exposure of the active sites while enhancing the charge transfer rate during HER. This work will attract attention to the role of metal compound-carbon support interactions in enhancing the intrinsic activity, conductivity, and stability of electrocatalysts.