The Preparation And Study On The Electrochemical Performance Of Oxygen Cathode Catalyst

With ever-increasing wide spread applications of the metal-air and fuel cells inalkaline, the catalyst material for oxygen reduction reaction (ORR) on air cathode isincreasingly urgent. So, the research of ORR catalyst materials is of greatsignificance.This article shows three kinds of carbon materials for the catalyst carrier, carbonmicrospheres (CMs) prepared by reflux-calcinations method, hydrothermal carbon(CS) and graphite oxide (GO), we will make a choice for the best supporter throughcontrast experiment from the three of them. Different compound catalysts are preparedby the same impregnating-calcinations method and the same content of manganeseoxide, but different carrier. CMs and CS were chose by the steady-state polarizationcurve test. It is concluded that the CMs is better than CS by cyclic voltammogramsand ac impedance tests. So, we decided to adopt the CMs as the catalyst loader. Thisarticle also explores the factors on the formation of CMs: different concentration ofsucrose, different sulphuric acid concentration and reaction time.A series of different mass fraction of manganese oxide loaded on carbonmicrospheres were prepared by impregnating-calcinations method. When the massfraction of MnOxis7.32%, the composite catalyst owns the best ORR activity. TheBET surface area of7.32%MnOx/CMs is observed to be1278m2g-1. Via XRD andTEM tests, we can see that manganese oxide appears homogeneously immobilized onCMs surface. From the steady-state polarization curves, Tafel plots, cyclicvoltammograms (CV) and electrochemical impedance spectroscopy (EIS), we canconclude that7.32%MnOx/CMs exhibits a much higher apparent exchange currentdensity0.649mA cm-2(comes from the Tafel plots) for ORR in alkaline media andpositive reduction potential of-0.4V vs. Hg/HgO, owns good electrochemicalcatalytic activity; What’s more, the oxygen reduction on manganese oxides undergoesa two-electron (2e) pathway.The ORR catalyst, cerium oxide and manganese oxide loaded on carbonmicrospheres composite (CeOx-MnOx/CMs), was prepared byimpregnating-calcinations method. The TEM、SEM、EDX and Mapping images showthat manganese oxide and cerium oxide appears homogeneously immobilized on CMssurface. The CeOx-MnOx/CMs shows lower over-potential and higher reductioncurrent for ORR from the steady-state polarization curves, and the apparent exchange current density which comes from the Tafel plots is2.17mA cm-2. What’s more, thereduction peak potential with CeOx-MnOx/CMs cathode is-0.28V vs. Hg/HgO fromthe electrochemical measurement of cyclic voltammetric. Based on theKoutecky–Levich plots, we suggest that the ORR pathway of this composite is a2epathway. We also demonstrate the potential of this hybrid CeOx-MnOx/CMs asefficient catalyst for the ORR in the Al–air cell with a maximum peak power densityof266mW cm-2.