Anchoring Ru-Ru2P heterojunction on P-doped graphene for enhanced HER performances of water electrolysis

Highly active and stable electrocatalysts are highly desired for the hydrogen evolution reaction (HER) in water electrolysis. In this study, a ruthenium-ruthenium phosphide heterojunction (Ru-Ru₂P) anchored on phosphorus-doped graphene (PCSG) was fabricated via a mild molten salt template method. The graphene was synthesized from discarded coconut shells sourced from Hainan. We found that the heterojunction structure could accelerate electron transfer, while the graphene provided more exposed active sites, significantly enhancing the HER activity of the catalyst. The catalyst prepared at 800 °C with 30 mg of RuCl₃ (Ru-Ru₂P/2D-PCSG-800) exhibited low HER overpotentials of 31 mV in alkaline and 57 mV in acidic electrolytes at a current density of 10 mA cm^-2, respectively, which were comparable to those of commercial 20% Pt/C catalyst (36 mV in alkaline and 40 mV in acidic electrolytes). Moreover, the catalyst demonstrated high stability with no significant change in current density after 125 hours of operation. Density functional theory calculations revealed that the Ru-Ru₂P heterojunction could rearrange charge and modify the Ru d-band center, optimizing the adsorption energy of active ⁎H (|ΔG_⁎H|) and breakage energy of ⁎H-OH bond (ΔG_H2O).