Tailoring Rhenium to Rhenium Carbide Phases Gradient Composites by High Pressure and High Temperature: Evaluation of Electrocatalytic Hydrogen Evolution in Acidic and Alkaline Environments

The intrinsic electronic and structural properties of the transition metal rhenium (Re) endow it with substantial application potential in electrocatalysis. However, the high cost of Re requires the development of Re-based materials to reduce cost and optimize the performance at the same time. Herein, a one-step high-pressure and high-temperature (HPHT) synthetic strategy is proposed for fabricating Re-C phase gradient composites, presenting a facile and efficient pathway to develop high-performance hydrogen evolution reaction (HER) electrocatalysts. By studying the structural evolution of Re toward ReC and uncovering its intrinsic mechanism, the regulation of the material’s electrocatalytic activity was successfully realized. Experimental results confirm that HPHT conditions of 5 GPa and 1400 °C effectively induce the formation of multiple crystalline phases of Re-C solid solution and ReC in the Re-C composite. These phases have coherent phase boundaries and form the phase gradient composites. Compared with element Re, the synergistic effect of phase gradient composites broadens the electronic state range by increasing electron transfer from Re to C in ReC (increasing the binding energy) and reduces the binding energy in Re-C solid solution. The broad electronic states range in the phase gradient composites exhibits optimal HER overpotentials of 150 mV (acidic electrolyte) and 166 mV (alkaline electrolyte) at 10 mA cm−2. These findings provide a promising strategy to boost catalysts’ electrocatalytic performance via constructing phase gradient composites.