Rich Surface Oxygen Vacancies of MnO2 for Enhancing Electrocatalytic Oxygen Reduction and Oxygen Evolution Reactions

Development of catalysts for the electrochemical oxygen reactions, namely, oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is critical for the application of various renewable energy technologies. The aim of this work is to prepare low‐cost MnO2 electrocatalyst with high activity for the ORR and OER via introduction of surface oxygen vacancies (OVs). Herein, the procedure of thermal heating treatment under air or H2 has been demonstrated as an efficient way to create OVs on the surface of α‐MnO2 and β‐MnO2 nanorods, which are found to be highly active for both ORR and OER. The existence of surface OVs can modulate the intrinsic activity of α‐MnO2 and β‐MnO2 and improve their ORR and OER kinetics. More importantly, the H2‐treated MnO2 possesses much more surface OVs and thus exhibits much better catalytic performances for ORR and OER in comparison with MnO2 obtained by common annealing treatments under air. Especially, the H2‐treated α‐MnO2 nanorods show the best activity for the ORR and OER. The results confirm that the heating treatment under H2 reducing atmosphere can be a facile and efficient process to develop bifunctional Mn‐based electrocatalysts for electrochemical oxygen reactions.