Study And Application Of Bifunctional Oxygen Electrode

Bifunctional oxygen electrode is the pivotal part of metal hydride-air(MH-Air) secondary cell and unitized regenerative proton exchange membranefuel cell (URFC). Bifunctional electrocatalyst with high activity and appropriateelectrode structure are the key issues for successfully developing it. In thisdissertation, much in-depth research work was deployed and extended forapplication by focusing on these issues.Pt black, IrO₂ and Pt/C electrocatalysts were prepared by the optimizedmethods. Pt black + IrO₂ and Pt/C + IrO₂ bi-component electrocatalysts wereobtained by combining the respective electrocatalyst components. The influenceof thermal treatment conditions on the synthesis of perovskite La_0.6Ca_0.4CoO₃(LCC)electrocatalyst was investigated in detail and these conditions have beenoptimized. For the first time, LCC was synthesized by the improved organicacid-aided method, which was operated by adding carbon to prohibitagglomeration. The structures and status of electrocatalysts were characterized bythe techniques of XRD, TEM and BET. Among them, the IrO₂ electrocatalystwhich was prepared by modified Admas method shows a status with highdispersed nano-microlite, which contributes IrO2 to getting a large special surfacearea as high as 213.9 m²/g. For the LCC prepared by improved organic acid-aidedmethod, the special surface area was improved 50% and could reach 18.3 m²/g. Aglassy carbon disk film electrode was prepared and modified. With it, theseprepared electrocatalysts were thoroughly investigated to test their activities forbifunctional oxygen electrode by electrochemical characterization techniques,such as cyclic voltammetry (CV), quasi-stationary linear polarization (QSLP) androtating disk electrode (RDE). A series of characteristic dynamic parameters wereattained, and then the mechanisms of bi-direction oxygen reaction on Pt black +IrO2, Pt/C + IrO2 and LCC electrocatalysts were analyzed deeply into. The resultsshow that Pt black + IrO2 electrocatalyst has high activity and is suitable for highcurrent application, while LCC electrocatalyst has low cost advantage and betterperformance in medium and low current application. Bifunctional oxygenelectrode electrocatalyst can't prohibit carbon to be oxidized and eroded when thecarbon tightly touches with bifunctional electrocatalyst. According these results, anovel bifunctional air electrode with function distribution was developed for thefirst time for MH-Air secondary cell. The novel air electrode can effectivelyprevent the carbon of diffusion layer from being corroded, so the cyclic stabilityof air electrode was improved substantially. The novel bifunctional air electrodehas good bifunctional performance. It can be charged and discharged in the way ofair self-breathing. A MH-Air secondary cell was assembled and evaluated. It alsocan be charged and discharged through air self-breathing. Bifunctional compositeelectrode with function distribution was exploited and prepared for the first timefor URFC. The composite electrode exhibited good bifunctional reactionperformance and the cycle life of URFC was improved considerably.