A MoOx-incorporated RuAu composite electrocatalyst for the hydrogen evolution reaction in proton exchange membrane water electrolysis

Abstract

In the water electrolysis system, Pt is commonly utilized as an electrocatalyst material for the hydrogen evolution reaction (HER). However, the scarcity and high cost of Pt pose challenges for the industrialization of PEMWE. This study proposes a MoO_x-incorporated RuAu composite as an efficient HER electrocatalyst for proton-exchange-membrane water electrolysis (PEMWE). The RuAu alloy electrocatalyst, containing less than 10% molybdenum oxide (RuAu-MoO_x) with an atomically uniform distribution, was successfully synthesized via co-electrodeposition. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the RuAu-MoO_x catalyst was composed of nanometer-sized crystallites and that high-valence states of Mo species interacted with the Ru and Au atoms, influencing their electronic structure. The electrocatalytic properties of RuAu-MoO_x were evaluated under acidic conditions, by varying the amount of MoO_x incorporated in the deposits. By fine-tuning the atomic composition of RuAu-MoO_x, an iR-compensated overpotential of 34.1 mV at −10 mA cm⁻² for the HER was achieved with high stability of the electrocatalyst, outperforming Ru and RuAu. In addition, density functional theory calculations revealed that the synergistic effect of Au substitution and MoO_x incorporation optimized the electronic structure of the surface metal atoms for the HER, including hydrogen adsorption. When RuAu-MoO_x was applied to PEMWE as a catalyst for the cathode, it exhibited high performance (4.55 A cm⁻² at 2 V) and superior mass activity (7.56 A mg⁻¹ at 1.8 V) compared to the other Ru-related catalysts. This study highlights RuAu-MoO_x as an effective HER catalyst and suggests that it is a promising substitute for Pt in PEMWE.