Mo-mediated electronic modulation of RuO2 for improved acidic oxygen evolution activity and Ru retention

Proton-exchange-membrane water electrolysers require active and stable anodic oxygen evolution catalysts. RuO 2 offers high intrinsic activity but dissolves rapidly in acid. Here, high-valence molybdenum is introduced into rutile RuO 2 to regulate the local Ru-O chemical and electronic environment. The sample labels Mo-x-RuO 2 refer to nominal Mo/(Mo + Ru) precursor ratios. XRD, EDS, XPS and DFT analyses support Mo incorporation within the rutile framework and reveal an altered local Ru/O chemical environment, providing insights into the electronic regulation induced by Mo incorporation. Mo-17-RuO 2 requires 207 mV at 10 mA cm −2 , with a Tafel slope of 56.2 mV dec −1 . After 75 h of acidic half-cell operation, it shows 6.64% cumulative Ru dissolution based on the nominal initial Ru loading. The commercial RuO 2 reference exhibited 27.95% cumulative Ru dissolution after approximately 17 h of operation. For the selected computational models, the AEM- and LOM-like pathways exhibit comparable thermodynamic limiting steps, with theoretical overpotentials of 275 and 262 mV, respectively, suggesting that Mo incorporation modulates oxygen reaction energetics without exclusively favoring a single pathway. These findings provide insight into composition-dependent Mo engineering for improving the performance and Ru retention of acidic OER catalysts.