Enhanced electrocatalytic performance of SrMn1-xCoxO3 perovskite metal oxides for oxygen reactions in Zn-air batteries: Influence of Mn/Co ratio

Metal oxides of perovskite structure and SrMn1-xCoO3 type have been prepared by a sol-gel synthesis method and mixed with carbon black by ball milling for their use as electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in a Zn-air battery. The composites obtained were characterized by different physicochemical and electrochemical techniques. The results of the characterization revealed the existence of two perovskite phases corresponding to Mn and Co as function of the Mn/Co ratio, whose interaction is related to a positive effect for the electrocatalytic activity. The presence of the M-O-C contribution was detected by XPS, which is related to an improvement in the catalytic activity against ORR/OER due to a better interaction and electron transfer between the perovskite and the carbon material. In addition, important differences were observed in the surface chemical species as a function of Mn/Co ratio and the higher the Co content in the composites the higher the amount of oxygen vacancies. The presence of oxygen vacancies is directly related to an improved OER activity; however, the presence of higher Mn content led to better catalytic results for ORR. The best electrocatalyst was studied in a Zn-air battery obtaining an excellent activity with a cyclability higher than 20 h, which is explained by the appropriate amounts of both Mn and Co.