Design And Properties Of Non-noble Metal Carbon-based Electrocatalysts For Oxygen Reduction Reaction

With ever-growing depletion of fossil fuels and subsequent environmental contamination issues,exploring high-efficient energy storage and conversion devices became extremely important.Fuel cells and metal-air batteries have become the greatest potential choices among a variety of new-type devices due to their environmental-friendly nature,relatively high theoretical energy density and energy efficiency.The oxygen reduction reaction（ORR）,which is one of the most significant processes towards fuel cells and metal-air batteries,involves in sluggish charge-transfer kinetic reactions and multiple sophisticated reaction processes.Heretofore platinum（Pt）is generally believed to be the most excellent electrocatalyst for accelerating ORR process.However,large-scale development and application of Pt are impeded by its expensive price,relatively poor stability and narrow natural resource reserves.Therefore,the advancement of non-noble metal based-ORR electrocatalyst is an urgent problem to be solved.Based on this,we synthesized a series of non-noble metal carbon-based ORR catalyst materials with high catalytic activity,and discussed the correlation between the physicochemical properties and the ORR catalytic activities of the catalysts.The main research results are as follows:Firstly,a simple preparation procedure of N-doped hierarchically porous carbon nanospheres loaded with Fe₃O₄/Fe₂O₃/Fe nanoparticles（Fe-CNSs-N）is developed by direct annealing of Fe-doped quinone-amine polymer in NH₃/Ar atmosphere.Fe-CNSs-N presents a half-wave potential of 0.835 V vs.RHE and a limiting current density of5.17 m A cm^-2.It also exhibits outstanding long-cycle durability as well as methanol endurance in alkaline medium,superior to Pt/C catalyst.The Fe-CNSs-N-based battery presents an open-circuit potential of 1.54 V,a maximum power density of 106.8 m W cm^-2 and a specific capacity of 800.1m Ah g^-1.Secondly,N-doped hierarchical porous carbon(Co₃O_4-x@N-C-2)decorated by hollow Co₃O_4-x nanoparticles with oxygen-vacancy defects was prepared via one-step pyrolysis of cobalt-doped quinone-amine polymer in gas mixture of NH₃ and Ar.Compared with Pt/C,Co₃O_4-x@N-C-2 presented a similar ORR onset potential（0.936V vs.RHE）and a more positive half-wave potential（0.845 V vs.RHE）.It also displayed admirable electrochemistry structural stability in alkaline medium.In addition,the Zn-air battery assembled with Co₃O_4-x@N-C-2 possessed an open circuit voltage of 1.524 V,a maximum power density of 105.2 m W cm^-2,and a specific capacity of 799.5 m Ah g^-1.Thirdly,based on electrostatic spinning technology and carbonization process,Lignin-based carbon nanofibers（Co-LCFs-800）decorated by Co O nanoparticles with oxygen-vacancy defects and Co nanoparticles were prepared by using biomass lignin as precursor,PVP as spinning additive and cobalt nitrate as cobalt source.Co-LCFs-800 presents an onset potential of 0.928 V vs.RHE and a half-wave potential of 0.834V vs.RHE.It also exhibits outstanding long-cycle durability as well as methanol endurance in alkaline medium,superior to Pt/C catalyst.The Co-LCFs-800-based battery presents an open-circuit potential of 1.521 V,a maximum power density of 98.7m W cm^-2 and a specific capacity of 780.0 m Ah g^-1.Fourthly,based on electrostatic spinning technology and carbonization process,Boron,nitrogen and fluorine ternary doped lignin-based nanofibers（BNF-LCFs）were prepared by using biomass lignin as precursor,PVP as spinning additive,zinc borate as boron source,ammonium fluoride as fluorine source and partial nitrogen source.BNF-LCFs presents an onset potential of 0.959 V vs.RHE and a half-wave potential of 0.844V vs.RHE.The BNF-LCFs-based battery presents an open-circuit potential of 1.536 V,a maximum power density of 99.4 m W cm^-2 and a specific capacity of 791.5 m Ah g^-1.