Defect-balanced active and stable Co3O4−x for proton exchange membrane water electrolysis at ampere-level current density

Abstract

Active and stable noble metal-free catalysts for the oxygen evolution reaction (OER) are essential for realizing large-scale hydrogen production using proton exchange membrane (PEM) electrolyzers. Herein, we discover that engineering the defect and morphology of spinel cobalt oxide allows us to obtain an optimal vacancy-rich Co₃O₄ hollow nanocube (V_o-Co₃O₄ HNC) catalyst with exceptional activity with a low overpotential of 265 mV at 10 mA cm⁻² and long-term stability for 130 h at 20 mA cm⁻² in acids, far exceeding those of the benchmark catalyst RuO₂ (390 mV and < 6 h) and most reported noble metal-based catalysts. Experimental and theoretical studies reveal that introducing oxygen defects effectively regulates the reaction mechanisms and introduction of an appropriate amount of defects significantly boosts both activity and stability by optimizing the adsorption/desorption energy barrier of intermediate species and suppressing the Co dissolution via the lattice oxygen mechanism pathway, respectively. The hollow cubic structure with highly exposed active sites and a large interfacial contact area further promotes the OER to enable high current density, as evidenced by finite element simulations. The application of V_o-Co₃O₄ HNCs in PEM electrolyzers steadily at 1 A cm⁻² achieves an energy consumption of 48.8 kW h kg⁻¹ H₂ and a projected cost of ∼US $ 0.976 kg⁻¹ H₂ (DOE's target: $2 kg⁻¹ of H₂ by 2026), suggesting the promise of using Earth-abundant materials for PEM water electrolysis.