Spinel MnxCo3-xO4 (0 ≤ x ≤ 2.5) as oxygen reduction and evolution electrocatalysts in alkaline medium

Spinel oxides can serve as nonprecious metal-based bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are the two fundamental reactions for energy conversion and storage device. In this report, highly efficient, bifunctional spinel oxide MnxCo3-xO4 (x = 0.5, 0.75, 1, 1.5, 2, 2.5) was developed by solid state reaction under calcination temperature of 300 °C to 900 °C. X-ray diffraction (XRD) was used to investigate the crystal structure and Brunauer-Emmett-Teller (BET) method was used to obtain the active surface area. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements were conducted to investigate the ORR and OER activity. It is observed that at calcination temperature of 900 °C, MnxCo3-xO4 with x ≤ 1 shows much better ORR specific activity compared to those with x > 1, which could be due to the difference of catalytic property between cubic spinel and tetragonal spinel phases. At 400 °C, ORR specific activity of cubic spinel MnxCo3-xO4 increases with increasing manganese substitution, which agrees with previous studies stating that Mn3+ / Mn4+ couple are the active sites for ORR. Whereas the trend of OER specific activity with varying manganese amount does not agree with the findings in previous studies. Best combination of ORR and OER specific activity is achieved in Mn1Co2O4. Comparing different calcination temperatures from 900 °C to 300 °C, it is observed that the ORR and OER specific activity of Mn1Co2O4 increase with increasing temperature. By plotting Koutecky-Levich plot, the electron transfer number of Mn1Co2O4 is obtained, implying 4e- pathway is the major mechanism.Bachelor of Engineering (Materials Engineering