Hierarchical Mesoporous NiO/MnO2@PANI Core–Shell Microspheres, Highly Efficient and Stable Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

We report on the new facile synthesis of mesoporous NiO/MnO2 in one step by modifying inverse micelle templated UCT (University of Connecticut) methods. The catalyst shows excellent electrocatalytic activity and stability for both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline media after further coating with polyaniline (PANI). For electrochemical performance, the optimized catalyst exhibits a potential gap, ΔE, of 0.75 V to achieve a current of 10 mA cm–2 for the OER and −3 mA cm–2 for the ORR in 0.1 M KOH solution. Extensive characterization methods were applied to investigate the structure–property of the catalyst for correlations with activity (e.g., XRD, BET, SEM, HRTEM, FIB-TEM, XPS, TGA, and Raman). The high electrocatalytic activity of the catalyst closely relates to the good electrical conductivity of PANI, accessible mesoporous structure, high surface area, as well as the synergistic effect of the specific core–shell structure. This work opens a new avenue for the rational design of core–shell structure catalysts for energy conversion and storage applications.