Preparation Of Porous Carbon-based Oxygen Reduction Catalysts And Its Application In Metal-air Batteries

Fuel cells,especially metal-air batteries,are considered to be one of the most promising energy conversion devices due to their high energy density and energy conversion efficiency.The development bottleneck of large-scale applications for fuel cells lies in the slow kinetic rate of the cathodic oxygen reduction reaction,which usually requires a large amount of precious metal,such as Pt catalysts,to meet the large current output.However,the application of Pt catalysts is restricted due to the high price,scarce reserves,and prone to secondary polymerization of nanoparticles during the discharge process,leading to degradation of catalytic performance.Therefore,there is an urgent need to develop new low-Pt or non-Pt high-efficiency oxygen reduction catalysts to promote the development of fuel cells.In this paper,a variety of low-Pt and non-Pt carbon-based oxygen reduction catalysts were synthesized using reduced graphene and MOFs-derived porous carbon as carriers,and the applications in zinc-air batteries and lead-air batteries were studied.The main research work is as follows:(1)silver bismuth oxide was preparated on the reduced graphene oxide carrier.The oxygen reduction performance of the catalyst and its application in the preparation of battery-grade lead oxide from lead-air batteries were studied.It was found that Ag catalysts,uch as Ag alloys and carbon-supported Ag,exhibit excellent oxygen reduction activity and durability in high-concentration alkaline solutions.In order to overcome complex synthesis,uneven doping and easy agglomeration of silver bismuthate,a graphene-coated Ag4Bi2O5 catalyst was prepared.The reduced graphene substrate improves the conductivity of silver bismuthate by anchoring silver bismuthate crystals to suppress its agglomeration.In the alkaline electrolyte,the Ag4Bi2O5/rGO catalyst showed an approximative half-wave potential with the commercial Pt/C,but better methanol tolerance and stability.When used in the cathodes of lead-air batteries,the Ag4Bi2O5/rGO catalyst exhibited higher voltage and energy density than commercial oxygen cathodes.Pure ?-PbO product was obtained from the electrolyte after spontaneous discharge and crystallization process.The ?-PbO product provided superior voltage and discharge capacity to the Shimadzu lead powder in lead-acid batteries.(2)Study on Oxygen Reduction Performance of Co/Zn Bimetallic ZIF Derived Co/NC CatalystsCompared with the previously studied metal oxides,M/NC catalysts may have higher oxygen reduction activity.In view of severe sintering and agglomeration of metal particles during the pyrolysis process,a series of Co/Zn bimetallic ZIFs precursor and template KCl were used to obtain the catalyst Co/NC.The presence of Zn effectively increases the specific surface area and the density of active sites of the Co/NC catalyst;while the high-temperature solidification of the template promotes the graphitization and nitrogen doping of the Co/NC catalyst and suppresses the agglomeration of metallic Co.The catalyst exhibited good oxygen reduction catalytic activity in alkaline electrolyte,and the addition of template greatly shifted half-wave potential and improved cycle stability.(3)Study on Oxygen Reduction Performance of Platinum Supported on Al/Zn-MOF Derived Porous CarbonMOF precursors can not only obtain M/NC catalysts by direct pyrolysis,but also porous carbon supports.To deal with the problem that commercial Pt/C catalysts are easily oxidized and corroded during the cycle,Al/Zn-MOF precursors were used for high-temperature carbonization.After removing the Al2O3 template generated in situ and KOH-KCl activation process,porous carbon AHPC with hierarchical pore structure,oxidation resistance and high graphitization degree was obtained.Pt nano-particles were further anchored on the AHPC support by microwave reduction with ethylene glycol.The Pt/AHPC catalyst showed a half-wave potential close to Pt/C and more excellent stability.When used in a zinc-air battery,it exhibited a higher discharge platform and a longer cycle durability at high current density.