CoII-catalyzed room-temperature growth of MnO2 on the skeleton of carbonized zeolitic imidazolate framework-67 crystals for boosting oxygen reduction reaction

Abstract

MnO₂/C composites are widely used as cathode active materials or electrocatalysts in electrochemical power sources. Compared with a physical mixture of MnO₂ and carbon materials, the growth of MnO₂ on the surface of carbon can greatly improve the electrochemical performance of MnO₂/C, and is usually performed at a temperature higher than 100 °C. From the viewpoint of sustainable development, the room-temperature growth of MnO₂ on carbon would greatly reduce the cost and thermal pollution. Herein, at room temperature, we successfully planted MnO₂ nanosheets over carbon particles, achieving MnO₂/C composites through a redox reaction between MnO₄⁻ ions and carbonized zeolitic imidazolate framework-67 (ZIF-67) crystals (C_ZIF-67). Room-temperature growth of MnO₂ may be attributed to the catalytic effect of Co^II ions of Co₃O₄ nanoparticles formed during ZIF-67 carbonization. The resulting MnO₂/C_ZIF-67 composites exhibit excellent catalytic performance towards the oxygen reduction reaction: the onset potential, the half-wave potential, and the electron transfer number are ∼0.88 V, ∼0.79 V and 3.6, respectively, which are close to the corresponding values of the state-of-the-art Pt/C. Also, the resulting MnO₂/C_ZIF-67 shows better long-term durability and methanol tolerance than Pt/C, indicative of its potential applications in fuel cells and metal–air batteries.