Directly anchoring Ag single atoms on α-MnO2 nanorods as efficient oxygen reduction catalysts for Mg-air fuel cell

Highlights: • Atomic Ag are anchored on α-MnO₂ by a facile solid phase reaction. • Loading of Ag single atoms reaches up to 1.53 wt%. • Ag@α-MnO₂ exhibits excellent electrocatalytic performance for ORR. • Mg-air fuel cell with Ag@α-MnO₂ shows a high power density and discharge voltage. -- Abstract: Neutral electrolyte-based Mg-air fuel cell is a promising alternative of power sources due to low cost, high specific energy and eco-friendly. However, developing high-efficiency and low-cost oxygen reduction catalysts to facilitate the large-scale application of metal air fuel cells remains a significant challenge. In this work, Ag single atoms are directly anchored onto the surface of α-MnO₂ nanorods to enhance the oxygen reduction performance in Mg-air fuel cell. The decoration of atomic Ag significantly improved the catalytic activity of α-MnO₂ due to the increase in content of Mn (III) and oxygen vacancies. The Ag decorated α-MnO₂ (Ag@α-MnO₂) with an extreme low Ag content of 1.53 wt% demonstrates a half-wave potential of 0.85 V (vs. reversible hydrogen electrode), a limited current density of 5.8 mA cm⁻² and a typical four-electron transfer pathway which is close to those of commercial Pt/C. Furthermore, it exhibits better stability and anti-poisoning capability than those of Pt/C. The Mg-air fuel cell containing Ag@α-MnO₂ displayed a high power density of 107.2 mW cm⁻² at current density of 140.1 mA cm⁻² as well as an outstanding discharge performance. This work provides new ideas for preparing efficient and cost-effective ORR catalyst and promote the large-scale commercialization in metal-air fuel cells.