Cobalt Phosphide Nanoparticles Supported by Vertically Grown Graphene Sheets on Carbon Black with N-Doping Treatment as Bifunctional Electrocatalysts for Overall Water Splitting

The rational design of efficacious and low-cost catalysts for water-splitting electrolysis is a key technology to produce hydrogen energy. Herein, CoP nanoparticles supported on nitrogen-doped vertical graphene sheets/carbon black composites (N-VGSs@CB/CoP) are fabricated, in which vertical graphene sheets (VGSs) are grown by facile thermal chemical vapor deposition. As hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bifunctional electrocatalysts, N-VGSs@CB/CoP exhibits remarkable overpotentials of 114 and 256 mV at 10 mA/cm² for the HER and OER in the alkaline medium of 1 M KOH, respectively. Moreover, the assembled overall water-electrolyzing cell of N-VGSs@CB/CoP||N-VGSs@CB/CoP only requires 1.60 V at a current density of 10 mA/cm² for stable running for 40 h, which is compatible with expensive Pt/C||RuO₂. The excellent performance is derived from highly conductive N-VGSs offering fast charge transfer for CoP activation sites. In addition, the multi-branched N-VGSs prevent the agglomeration of CoP nanoparticles and provide a large area to exert the catalytic activity of CoP.