Trace Cr(OH)3 modified α-MnO2 electrocatalyst intercalated by Ag+ with superior activity and stability for oxygen reduction reaction

Abstract

To achieve the practical application of MnO2-based oxygen reduction electrocatalysts, two important issues in terms of slow electrochemical kinetics and low stabilities must be resolved. In this work, α-MnO2 nanorods intercalated by Ag+ and decorated by trace amounts of Cr(OH)3 were designed by a simple two-step solution method to improve the electrocatalytic activity. The resulting catalysts exhibited efficient oxygen reduction reaction (ORR) activity with a high half-wave potential (E1/2 = 0.85 V vs RHE) and diffusion-limiting current density (Jlim = -5.99 mA cm−2) comparable to commercial 20 wt% Pt/C catalysts. More importantly, the catalysts displayed a more durable performance after 10 h in terms of the decrease in electrochemical current (3.5 %), much lower than that of Pt/C catalysts (9.1 %). The excellent electrocatalytic activity was attributed to the synergistic effects between MnO2, Ag+ and Cr(OH)3, reduced the charge transfer resistance of α-MnO2, adjusted the ratio of Mn3+/Mn4+, generated abundant oxygen vacancies, and promoted the adsorption and activation of surface O2. Furthermore, density functional theory calculations were also carried out to study the coupling interactions to reveal the mechanism of the excellent electrocatalytic performance. This study provides a co-modification strategy for the design of MnO2-based efficient and stable oxygen reduction electrocatalysts.