Rational Design of β-MnO2 via Ir/Ru Co-substitution for Enhanced Oxygen Evolution Reaction in Acidic Media

Abstract

The efficiency of the oxygen evolution reaction (OER) in acidic media is severely limited by the poor stability, low activity, and high cost of available catalysts. Enhancing intrinsic activity while maintaining stability and reducing reliance on precious metals is crucial. The typical adsorbate evolution mechanism (AEM) leads to high overpotentials and low activity, making the transition to alternative mechanisms, such as the lattice oxygen mechanism (LOM) or oxide path mechanism (OPM), highly desirable due to their lower overpotentials. Here, we combine density functional theory (DFT) calculations with experimental validation to enhance the activity and stability of β-MnO₂ via co-substitution with ruthenium (Ru) and iridium (Ir), enabling the transition from AEM to OPM. DFT calculations reveal that AEM is hindered by the weak nucleophilicity of water, while LOM suffers from high kinetic barriers due to structural distortions. In contrast, OPM demonstrates a significantly lower kinetic barrier, facilitated by the synergistic interaction between Ru and Ir. Experimentally, IrRuMnO_x was synthesized through co-precipitation and hydrothermal methods, showing an 80-fold improvement in mass activity and a 96-fold increase in stability compared to commercial IrO₂, with minimal noble metal leaching, as confirmed by inductively coupled plasma optical emission spectroscopy (ICP-OES). IrRuMnO_x exhibited an ultralow overpotential of 475 mV at 1 A·cm^–2 and a Tafel slope of 44.26 mV·dec^–1 in 0.5 M H₂SO₄, maintaining stable performance for over 100 h. Moreover, the IrRuMnO_x-based membrane electrode, with a low Ir loading of 0.075 mg_Ir·cm^–2, achieved remarkable current densities of 1.0 A·cm^–2 at 1.66 V and 2.0 A·cm^–2 at 1.91 V at 80 °C. This performance surpasses that of both unsupported and conventional supported Ir-based catalysts at comparable Ir loading levels. This study offers critical insights into OER mechanisms in acidic media and paves the way for developing efficient and durable OER electrocatalysts for hydrogen production.