In situ growth of phosphorized ZIF-67-derived amorphous CoP/Cu2O@CF electrocatalyst for efficient hydrogen evolution reaction

Abstract

Transition metal phosphides have been extensively studied for catalytic applications in water splitting. Herein, we report an in situ phosphorization of zeolitic imidazole frameworks (ZIF-67) to generate amorphous cobalt phosphide/ZIF-67 heterojunction on a self-supporting copper foam (CF) substrate with excellent performance for hydrogen evolution reaction (HER). The needle-leaf like copper hydroxide was anchored on CF surface, which acted as implantation to grow ZIF-67. The intermediate product was phosphorized to obtain final electro-catalyst (CoP/Cu₂O@CF) with uniform particle size, exhibiting a rhombic dodecahedron structure with wrinkles on the surface. The electrochemical measurement proved that CoP/Cu₂O@CF catalyst exhibited excellent HER activity and long-term stability in 1.0 mol·L⁻¹ KOH solution. The overpotential was only 62 mV with the Tafel slope of 83 mV·dec⁻¹ at a current density of 10 mA·cm⁻², with a large electrochemical active surface area. It also showed competitive performance at large current which indicated the potential application to industrial water electrolysis to produce hydrogen. First-principle calculations illustrated that benefit from the construction of CoP/ZIF-67 heterojunction, the d-band center of CoP downshifted after bonding with ZIF-67 and the Gibbs free energy (ΔG_H*) changed from −0.18 to −0.11 eV, confirming both decrease in overpotential and excellent HER activity. This work illustrates the efficient HER activity of CoP/Cu₂O@CF catalyst, which will act as a potential candidate for precious metal electrocatalysts.