Oxygen-defective ruthenium oxide as an efficient and durable electrocatalyst for acidic oxygen evolution reaction

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for green hydrogen production in combination with renewable energy. However, the high cost and, particularly, the scarcity of iridium (Ir) for use as oxygen evolution reaction (OER) catalysts in the anode severely impede large-scale deployment of PEMWE. Herein, we report the synthesis of oxygen-defective ruthenium oxide (HP-RuOx), which can serve as a cost-effective alternative to Ir-based catalysts, showing outstanding electrocatalytic performance for acidic OER. HP-RuOx was obtained through a sol-gel process using hexamethylenetetramine (HMTA) and polyvinylpyrrolidone (PVP) as co-surfactants. The defect-rich nature of HP-RuOx proves to be effective in enhancing the catalytic activity toward acidic OER. Specifically, HP-RuOx exhibits an overpotential of only 237 mV at a current density of 10 mA cm-2 in 0.05 M H2SO4, outperforming commercial RuO2 and other RuOx control catalysts. Both in situ differential electrochemical mass spectrometry (DEMS) studies and theoretical calculations reveal that the OER occurring on HP-RuOx proceeds predominantly through the adsorbate evolution mechanism (AEM) and the lattice oxygen barely participates in the OER. Consequently, the defect-rich HP-RuOx demonstrates good electrocatalytic stability in 0.05 M H2SO4, with only a 90 mV potential increase after 140 hours of OER at 100 mA cm-2. Furthermore, the performance of HP-RuOx is also evaluated in membrane electrode assemblies (MEAs), which can reach 1 A cm-2 at 1.60 V at 60 degrees C and stably operate at 0.5 A cm-2 for 230 hours with minimal degradation, showing substantial potential for use as an efficient and durable OER catalyst in PEMWE.