Synergistically enhanced oxygen reduction reaction composites of specific surface area and manganese valence controlled α-MnO2 nanotube decorated by silver nanoparticles in Al-air batteries

Overcoming slow kinetics of cathodic electrochemical reactions is a key factor toward achieving economical and efficient electrocatalysts for practical application of primary Al-air batteries. In this study, a hybrid catalyst with specific surface area and manganese valence controlled α-MnO₂ nanotube decorated by silver nanoparticles (Ag/MnO₂-3) is successful synthesized. A facile hydrothermal method was used, followed by liquid phase reducing treatment. The Ag/MnO₂-3 showed not only superior catalytic activity for the oxygen reduction reaction with more positive onset potential (0.996 V vs. RHE) and comparable half-wave potential (0.870 V vs. RHE) to the commercial Pt/C catalyst but also a higher discharge voltage plateau (∼1.1 V at discharge current density of 50 mA cm⁻²) with superior stability in the primary Al−air battery test. The high electrocatalytic activity of the Ag/MnO₂-3 nanohybrid is attributed to the larger specific surface area of MnO₂ nanotubes and its ultrahigh atomic ratios of Mn³⁺/Mn⁴⁺ on the surface. This results in a strong synergistic effect between manganese dioxide nanotube and Ag nanoparticles to inhibit the accumulation of hydrogen peroxide. This material is promising for applications in Al-air batteries.