Cobalt-based phosphide supported on carbon nanotubes for the HER: effect of phosphating degree on HER performance

Abstract

Cobalt-based phosphides have been regarded as advanced electrocatalysts for the hydrogen evolution reaction (HER); however, the effect of the phosphating degree on HER activity is not yet clear. In this work, we developed a novel evaporation crystallization and subsequent phosphorization process to prepare cobalt-based phosphides. By adjusting the dosage of the phosphorus source, the influence of different phosphating degrees on the morphology, composition, and HER performance of the products was investigated. The experimental results indicate that as the amount of phosphorus source increases, the morphology and composition of the products undergo significant changes, and the HER performance first increases and then decreases. That is to say, both insufficient and excessive phosphating do not lead to optimal HER performance. Among them, the S4 (CoP@CNT) catalyst exhibits the best HER performance with a low overpotential of 109 mV at 10 mA cm⁻² and a small Tafel slope of 63 mV dec⁻¹. We attribute the excellent performance to the large C_dl and the optimal energy level position of S4. This work provides a reference and guidance on the preparation of cobalt-based phosphide electrocatalysts for achieving efficient hydrogen evolution.