| The world energy consumption and environmental pollution have been rapidly increasing during the last decades, which has at least made two great challenges for us:one is to make use the different forms of solar, wind energy, wave and tidal power, biomass, geothermal, hydropower and so on and the other is to make better and more efficient use of traditional fossil fuels, especially in city transportations. All those challenges requires efficient storage means of electrical energy, for example the batteries. Zinc-air battery system consider one of the most promising candidate for energy storage application. However, it is still need to be improve to fulfill the market requirements.The biggest obstacle that hinder the use of zinc-air battery is the catalyst and their high cost such as platinum, palladium, iridium and ruthenium catalyst which is 24-40% of the battery cost. In addition, the slow ORR kinetics greatly limit the maximum output power of the device. Moreover, the generation of free radicals in ORR (peroxide and superoxide free radicals) catalyst can lead to the failure, serious impact on zinc-air battery life. And it has been clear about the main emphasis at present the research of catalysts is a precious metal catalyst, such as carbon materials, transition metal oxides, perovskite, spinel and pyrochlore, etc.In this article, the existing good catalytic activity non-noble metal catalysts such as manganese oxide, perovskite were mainly doped modification. This article mainly includes three parts. Firstly, the catalytic properties of several common manganese dioxide were researched as the basic data. The effect of the catalytic performance toward ORR and OER were studied about good manganese oxide (Mn3O4) on the catalytic activity of Co doping. Secondly, the effect of Sr (Ca) doped LaMnO3 toward ORR and OER was researched. Finaly, the effect of g-C3N4@MWCNTs loading Mn3O4 and Co3O4 on ORR catalytic performance were studied. This article main content is as follows:1. Manganese oxide and their doped mixed metal oxide(1) The electrocatalytic performance of Co doped Mn3O4 toward ORR and OER was carried out. From polarization curves, the sample Mn2.7Coo.3O4 has the best ORR catalytic performance, the sample Mn2.4Co0.6O4 has the best OER catalytic performance, and the sample Mn2.7Co0.3O4 has the best ORR/OER catalytic performance. It is show that Co doping amount on ORR and OER catalytic performance a greater influence. The ORR and OER catalytic performance of samples is first increases then decreases with increasing amount of Co doping. Constant current discharge tests have shown that the sample Mn2.7Co0.3O4 has the longest discharge time and the highest utilization rate of zinc, at 30 and 50 mA cm-2, the corresponding discharge time and the utilization rate of zinc are 24.6,14.2 h and 70.1% and 70.1% respectively. After 60 Charge-discharge cycle test shown that the sample Mn2.4Co0.6O4 changes the minimum charge-discharge platform and has the best ORR/OER catalytic activity.In conclusion, the ORR and OER catalytic activities of the sample Mn2.7Co0.3O4 than have greatly improved. Although ORR catalytic performance of the sample Mn2.7Co0.3O4 wasn’t up to EMD, it proved that this doped method is effective.2. Doped-type perovskite oxide(1) The electrocatalytic properties of La1-xSrxMnO3(x=0.1～0.4) for ORR and OER were researched. From polarization curves, the doping amount of Sr have an impact on ORR and OER catalytic activities. As a result, the Lao.9Sr0.1MnO3 and the La0.8Sr0.2MnO3 have the best ORR catalytic performance. The La0.8SrO.2MnO3 has the best OER catalytic performance. And, the Lao.8Sro.2Mn03 has the best ORR/OER catalytic performance. Constant current discharge tests have shown that the sample Lao.sSr0.2MnO3 has the longest discharge time and the highest utilization rate of zinc, at 30 and 50 mA cm-2, they are 21.9,15.0 h and 62.5% and 71.1% respectively. After 60 Charge-discharge cycle test shown that the sample La0.8SrO.2MnO3 changes the minimum charge-discharge platform and has the best ORR/OER catalytic activity.(2) The electrocatalytic properties of La1-xCaxMnO3 (x=0.1-0.4) for ORR and OER were researched. The Lao sCao 2MnO3 have the best ORR and OER catalytic property, respectively, and has the best ORR/OER catalytic performance. Constant current discharge tests have shown that the sample La0.8Cao.2Mn03 has the longest discharge time and the highest utilization rate of zinc, at 30 and 50 mA cm-2, they are 23.4,15.0 h and 66.8% and 71.2% respectively. After 60 Charge-discharge cycle test shown that the sample La0.8Cao.2MnO3 changes the minimum charge-discharge platform and has the best ORR/OER catalytic activity.In summary, the Sr and Ca doping can effectively improve the ORR and OER catalytic activity, the effect of Ca doping is slightly better than the Sr doped.3. Load-type composite(1) The catalytic performance of the g-C3N4@MWCNTs/Mn3O4 toward ORR were performed. The loading of Mn3O4 in GMM40, GMM35, GMM30, GMM25 and GMM20 is 39.1%,34.3%,29.7%,24.7% and 19.4%, respectively. ORR catalytic performance test shown that the GMM35 has the best catalytic activity. And, the 35 wt% loading is optimal. Compared with g-C3N4, MWCNTs, g-C3N4@MWCNTs, and 20% Pt/C, the ORR catalytic activity of GMM35 is greatly improved, but not reached the catalytic effect of Pt/C catalyst. The onset of GMM35 is 80 mV negative than Pt/C. The electron transfer number of GMM35 is between 3.6 and 3.8. At-0.4 V (vs. Ag/AgCl), the yield of H2O2 with GMM35 catalyst is 11.4%. The GMM35 has like the Pt/C good electrochemical stability, test for up to 60 h, current strength is still retain about 88%. The peak power density of GMM35 is 192.4 mW cm-2 (at 229.1 mA cm-2), which is lower than Pt/C (260.9 mW cm-2, at 285.4 mA cm-2) around 26%. At 10 and 50 mA cm-2, both GMM35 and Pt/C discharge lasted for 30 and 15 h, respectively, and have good electrochemical durability. However, the battery voltage of GMM35 is lower than Pt/C all the time. The capacity of GMM35 is 505 mAh g-1 and corresponding utilization rate of zinc is 61.6%, but, the capacity of Pt/C is 594 mAh g-1 and corresponding utilization rate of zinc is 72.4%, respectively.(2) The catalytic performance of the g-C3N4@MWCNTs/Co3O4 toward ORR were performed. The loading of Co3O4 in GMM40, GMM35, GMM30, GMM25 and GMM20 is 24.7%,19.5%,14.6% and 9.4%, respectively. ORR catalytic performance test shown that the GMC20 has the best catalytic activity. And, the 20 wt% loading is optimal. Compared with the commercial Pt/C catalyst, ORR catalytic performance did not reach its effect.The onset of GMC20 is 80 mV negative than Pt/C. The electron transfer number of GMM35 is between 3.8 and 3.9. At-0.4 V (vs. Ag/AgCl), the yield of H2O2 with GMC20 catalyst is 6.4%. Under the constant phase step voltage of-0.45 V, the GMC20 has like the Pt/C good electrochemical stability, after 60 h, current strength is still retain about 88%. The peak power density of GMC20 is 208.0 mW cm-2, which is lower than Pt/C (260.9 mW cm-2) around 20%. At 10 and 50 mA cm-2, both GMC20 and Pt/C discharge lasted for 30 and 15 h, respectively, and have good electrochemical durability. However, the battery voltage of GMC20 is lower than Pt/C all the time. The cell using GMM35 corresponding utilization rate of zinc is 64.0%, however, the one using Pt/C is 72.4%.In brief, compare GMM35 and GMC20, the ORR catalytic performance of GMC20 is better than GMM35. However, the ORR catalytic property of both GMM35 and GMC20 are not as good as commercial Pt/C catalyst. |
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