Correlating Boron Existence Morphologies with Electrocatalytic HER Activity in Ni-B Compounds Synthesized via High Pressure and High Temperature

Nickel boride compounds have attracted considerable attention in the field of electrocatalysis due to their unique electronic structures and excellent chemical stability. However, the difficulty in obtaining single-phase products under traditional experimental conditions hinders the analysis of their intrinsic catalytic performance. Herein, we report the successful synthesis of three single-phase nickel boride compounds (Ni2B, Ni4B3, and NiB) via a high pressure and high temperature (HPHT) method. The configurations of B in their respective structures are distinct. Their electrocatalytic hydrogen evolution reaction (HER) performance was systematically evaluated. The results demonstrate that NiB exhibits the lowest overpotentials of 182 mV (in acidic electrolyte) and 234 mV (in alkaline electrolyte) at a current density of 10 mA cm−2, accompanied by the smallest Tafel slope, the lowest electron transfer resistance (Rct), and the largest double-layer capacitance (Cdl). This superior HER activity is primarily attributed to the presence of strong B-B covalent bonds in NiB, which weaken the Ni-B interaction and reduce the orbital hybridization between Ni 3d and B 2p orbitals. Consequently, the hydrogen adsorption intermediate (H*) achieves the optimal adsorption strength on the NiB surface. This work provides a novel insight for the design of high-performance transition metal boride electrocatalysts.