Chrysanthemum-Like CoP Nanostructures on Vertical Graphene Nanohills as Versatile Electrocatalysts for Water Splitting

CoP is a promising catalyst material to replace noble metals in water electrolysis. To further explore the potential of CoP in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), we utilize vertical graphene nanohills (VGNHs) that are known to enhance catalytic performances through superaerophobicity. Unique CoP chrysanthemum-like structures are formed on VGNHs through a facile, one-step electrodeposition reaction. Because of the highly conductive VGNH support and the modified CoP nanostructures, the optimized CoP/VGNHs hybrid catalyst exhibits excellent electrocatalytic activities toward HER in 0.5 M H ₂ SO ₄ , such as a low overpotential at 10 mA cm ^-2 (η ₁₀ ) of 51 mV, a small Tafel slope of 36 mV dec ^-1 , and a long-term stability. Specifically, the overpotential at 100 mA cm ^-2 (η ₁₀₀ ) is merely 125 mV, an outstanding performance for a noble metal-free catalyst. Furthermore, the HER performance in 1.0 M KOH (η ₁₀ of 93 mV) and the OER performance in the same alkaline medium (η ₁₀ of 300 mV) are highly competitive, making CoP/VGNHs also an excellent bifunctional electrocatalyst yielding a current density of 10 mA cm ^-2 at a low voltage of 1.63 V. This novel nanostructure offers an efficient strategy for the development of nonprecious metal catalysts for water electrolysis.