Benchmarking Three Ruthenium Phosphide Phases for Electrocatalysis of the Hydrogen Evolution Reaction: Experimental and Theoretical Insights

Graphical A fair comparison : A strategy to grow nanoparticles of three Ru phosphides on graphene sheets was developed. The resulting three electrocatalysts for the hydrogen evolution reaction (HER; see figure) show similar morphology, loading density, nanoparticle size, Ru content, and electrochemical surface area, which allows a fair comparison of the effect of the phosphide phase on HER activity. Ru 2 P/graphene shows the best HER performance and highest intrinsic activity in acid solution, and all three electrocatalysts show excellent long-term HER durability. The outstanding electrocatalytic activity of ruthenium (Ru) phosphides toward the hydrogen evolution reaction (HER) has received wide attention. However, the effect of the Ru phosphide phase on the HER performance remains unclear. Herein, a two-step method was developed to synthesize nanoparticles of three types of Ru phosphides, namely, Ru 2 P, RuP, and RuP 2 , with similar morphology, dimensions, loading density, and electrochemical surface area on graphene nanosheets by simply controlling the dosage of phytic acid as P source. Electrochemical tests revealed that Ru 2 P/graphene shows the highest intrinsic HER activity, followed by RuP/graphene and RuP 2 /graphene. Ru 2 P/graphene affords a current density of 10 mA cm −2 at an overpotential of 18 mV in acid media. Theoretical calculations further showed that P-deficient Ru 2 P has a lower free energy of hydrogen adsorption on the surface than other two, P-rich Ru phosphides (RuP, RuP 2 ), which confirms the excellent intrinsic HER activity of Ru 2 P and is consistent with experiment results. The work reveals for the first time a clear trend of HER activity among three Ru phosphide phases.