One‐Step Synthesis of Phase‐Controlled Co 2 P Nanoparticles as an Electrocatalyst for Hydrogen Evolution Reaction

Abstract Cobalt phosphides have been investigated as potentially useful electrocatalysts for accelerating hydrogen evolution. Cobalt phosphide electrocatalysts are synthesized in a single step at varied phosphating temperatures (350, 400, 450 °C) via the gas phase approach. Synthesized at a phosphating temperature of 350 °C, Co 2 P (CP‐350) transforms into a mixed phase that contains both Co 2 P and CoP (CP‐400 and CP‐450) as the phosphating temperature goes up which is confirmed by XRD. CP‐350, CP‐400, and CP‐450 exhibited overpotentials of 181, 270, and 293 mV respectively with Tafel slopes of 112, 146, and 175 mV/dec. In contrast to CP‐400 and CP‐450, CP‐350 revealed superior hydrogen evolution reaction (HER) performance and stability for up to 12 h due to its pure phase (Co 2 P), high surface area (151 m 2 /g), and high electrochemical surface area (7.02 cm 2 ) with low charge transfer resistance. According to our work, changing the phase and active surface area of transition metal phosphide catalysts can greatly increase their HER catalytic efficiency.