Cu- and Fe-Incorporated Manganese Oxides (MnxOy) as Cathodic Catalysts for Hydrogen Peroxide Reduction (HPR) and Oxygen Reduction (OR) in Micro-direct Methanol Fuel Cells

Improving manganese oxides as cathodic catalysts in direct methanol/hydrogen peroxide fuel cells by incorporation of Cu and Fe to promote oxygen reduction (OR) and hydrogen peroxide reduction (HPR) is reported. The Cu-incorporated and Fe-incorporated MnxOy were prepared by impregnation and solvothermal processes. From XRD, XPS, and XAS analyses, the obtained MnxOy consisted of MnO2 and mixed phases of Mn3O4 and Mn2O3 from impregnation and solvothermal methods, respectively. The Cu-incorporated and Fe-incorporated MnxOy included CuO and Fe2O3, respectively, through both methods. Addition of Cu and Fe decreased the BET surface area and increased the pore sizes as compared to the pristine MnO2. With the Fe : Mn molar ratio of 0.20 : 1, the Fe-incorporated MnxOy from the solvothermal method presented the highest cathodic peaks under the cyclic voltammogram of HPR and OR at around 0.59 V of 11.59 mA cm(-2) and -0.59 V of -12.33 mA cm(-2), respectively. Compared to the Cu-incorporated ones, the highest HPR peak at 0.68 V of 9.20 mA cm(-2) and the highest OR peak at -0.59 V of -6.99 mA cm(-2) were obtained from the Cu-incorporated MnxOy prepared through the solvothermal method at the Cu : Mn molar ratio of 0.15 : 1. Incorporating Cu or Fe into MnO2 brought the improvement of electrocatalytic activity for HPR and OR. The Cu-incorporated and Fe-incorporated MnxOy from both methods showed a higher power density of mu-DMFC than the pristine MnO2.