Ultrasmall Ir nanoclusters on MnO2 nanorods for pH-universal oxygen evolution reactions and rechargeable zinc–air batteries

Abstract

Decreasing the size of noble metals and integrating with transition-metal oxides have been proven as effective means to promote Ir-based catalysts for the oxygen evolution reaction (OER). Herein, we report a facile approach that can uniformly disperse ultrasmall Ir clusters onto MnO₂ nanorods for the OER in a universal pH range. Among the x%-Ir-MnO₂ (x refers to the mass percentage of Ir) series, 5%-Ir-MnO₂ exhibits superior OER performance than other samples, and also exceeds the IrO₂ benchmark, as evidenced by small overpotentials of 330 mV (0.2 M PBS, pH = 7.0), 240 mV (1 M KOH, pH = 14.0), and 267 mV (0.5 M H₂SO₄, pH = 0) to reach a current density of 10 mA cm⁻², and markedly superior long-term stability in i–t curves. Furthermore, as an air–cathode catalyst for Zn–air batteries, the 5%-Ir-MnO₂ modified battery also demonstrates brilliant performances with large capacities of 655.4 mA h g⁻¹ and 792 mA h g⁻¹, long durability of 120 h and 200 h in alkaline and neutral media, respectively. Such excellent electrocatalytic performances are attributed to the unique structural merits of the ultrasmall Ir clusters, the abundant oxygen vacancies of MnO₂ nanorods, and the catalytic synergistic effects between the Ir clusters and the MnO₂ substrate.