Rational Design of Amorphous WOx Overlayer for Catalytic Ruthenium Protection and Spillover Enhancement in Acidic Hydrogen Evolution

초록

Despite its cost-effectiveness for the hydrogen evolution reaction (HER), ruthenium faces commercialization challenges due to oxidative instability. Here, we designed a Ru-WOx/C catalyst with an amorphous WOx overlayer that protects Ru from oxidation and induces hydrogen spillover. TEM and energy-dispersive X-ray spectroscopy (EDS) confirmed that Ru nanoparticles are uniformly coated by an amorphous WOx overlayer. X-ray photoelectron spectroscopy (XPS) revealed the coexistence of W6+/W5+ species and a negative shift in the Ru 3p binding energy, evidencing the formation of WOx and heterojunction. Ru-WOx/C required only 56 mV to reach 10 mA cm-2 and maintained stable operation for 80 h at 100 mA cm-2. The remarkable activity and stability of the developed Ru-WOx/C catalyst originate from hydrogen spillover. This result is supported by potassium thiocyanate (KSCN) poisoning and H/D kinetic isotope effect (KIE) experiments, which confirmed hydrogen migration from WOx to Ru. When applied as a cathode in a proton exchange membrane water electrolyzer (PEMWE), Ru-WOx/C achieved current densities of 0.5, 1.0, and 2.0 A cm-2 at 1.66, 1.85, and 2.10 V, respectively. It also sustained stable operation for 24 h at 1 A cm-2 with nearly 100% Faradaic efficiency. These results show that integrating an amorphous WOx overlayer with Ru nanoparticles is a practical approach to design a durable and efficient cathode for proton exchange membrane water electrolysis.