Insights into the High Activity of Ruthenium Phosphide for the Production of Hydrogen in Proton Exchange Membrane Water Electrolyzers

The demand of green hydrogen, that is, the hydrogen produced from water electrolysis, is expected to increase dramatically in the coming years. State‐of‐the‐art proton exchange membrane water electrolysis (PEMWE) uses high loadings of platinum group metals, such as Pt in the electrode where hydrogen is produced. Alternative electrodes based on phosphides, sulfides, nitrides, and other low‐cost alternatives are under investigation. Herein, a simple process for the preparation of RuP electrodes with high activity for the hydrogen evolution reaction (HER) in acidic electrolyte is described. A straightforward one‐pot synthesis that yields RuP nanoparticles with fine‐tuned composition and stoichiometry is presented, as determined by multiple characterization techniques, including lab‐ and synchrotron‐based experiments and theoretical modeling. The RuP nanoparticles exhibit a high activity of 10 mA cm −2 at 36 mV overpotential and a Tafel slope of 30 mV dec −1 , which is comparable to Pt/C. Moreover, a RuP catalyst‐coated membrane (CCM) with a low Ru loading of 0.6 mg Ru cm −2 is produced and tested in a PEMWE cell configuration, yielding 1.7 A cm −2 at 2 V.