Self-supported ruthenium-doped cobalt oxide for high current density anion exchange membrane water electrolysis

Abstract

Despite achievements in catalyst developments for lab-scale anion exchange membrane water electrolysis (AEMWE), industrial demands necessitate robust, high-activity electrocatalysts. Herein, we propose a strategy for synthesising self-supported ruthenium-doped cobalt oxide (Ru-Co₃O₄), prepared via a facile thermal decomposition method, as a high-current-density bi-functional electrocatalyst. Ru-Co₃O₄ exhibits significantly enhanced bifunctional catalytic activity for the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The optimised catalyst requires an ultralow overpotential of 27 mV to reach 10 mA cm⁻² and 190 mV to reach 500 mA cm⁻² for the HER. For the OER, it requires overpotentials of 260 mV to reach 50 mA cm⁻² and 440 mV to reach 500 mA cm⁻². The density functional theory (DFT) calculations revealed that Ru incorporation into Co₃O₄ anchors the water molecule at Ru sites, thereby facilitating its dissociation while optimally tuning the binding of OER intermediates at the Co site leading to significant lowering of the OER overpotential. Furthermore, an anion exchange membrane water electrolyzer assembled using Ru-Co₃O₄ as both the anode and cathode achieved a very low cell potential of 1.78 V to reach 1 A cm⁻², with a high energy conversion efficiency of 70.5%. The cell maintained 80 hours of stability at a high current density of 2 A cm⁻². This performance translates to a competitive hydrogen production cost of 5.49 $ per kg. The combination of low cell potential, high conversion efficiency, and excellent stability at industrial-level current densities provides a novel and promising strategy for designing self-supported bifunctional catalysts for green hydrogen generation at the industrial scale.