Applied To The Air Electrode Of The Transition Metal Oxide Catalytic Materials

Oxygen electrode is an important issue in the development of fuel cells and metal air battery,and the most critical factor affacting their performances is the catalysis of the oxygen reduction reaction(ORR).In this thesis work,spinel type oxides CoFe₂O₄ and MnCo₂O₄ were synthesed using microwave heating process and conventional heating method.X-ray diffraction(XRD)and scanning electronic micorograph (SEM)were employed to characterize the catalysts prepared,the polarization curve technique and electrochemical impedence spectroscopy(EIS)methodes were used to study the electrocatalytic performaces of the prepared oxides for ORR in alkaline medium;the stability of air electrode was improved remarkably by the heat treatment to the electrode and the optimization to synthesized condition of oxides.The results showed that:(1)In all of the oxides synthesized by conventional heating,MnCo₂O₄ exhibited best in ORR,giving a current density of 60 mA·cm^-2at the potential -0.2 V(vs Hg/HgO)under oxygen atmosphere at room temperature;(2)The CoFe₂O₄ and MnCo₂O₄ particles that synthesed using microwave heating process were obtained. showed nano-crystalline with high purity and a diameter of 10～30 nm. The ORR current density of the air electrode with CoFe₂O₄ as catalyst reached 199 mA·cm^-2in air atmosphere at room temperature,and the air electrode with MnCo₂O₄ reached 240 mA·cm^-2both of them exhibited an excellent catalytic performance for ORR and MnCo₂O₄ had a better performance for ORR;(3)the stability of air electrode was improved remarkably by heat treatment to the electrode and increase of carbon's rate in reactant,and the electrode had a optimal performance of stability and catalysis,when the proportion of carbon'mass to spinel's theoretical output was 2:1 and the air electrode was heat-treated at 200℃for three hours.