Synthesis And Oxygen Reduction Reaction Catalytic Properties Of Flexible Porous Carbon Nanofibers Doped With Copper Zirconium Bimetallic Oxides

Development of stable,efficient and cost-effective electrocatalysts for oxygen reduction reaction（ORR）is of prime importance to renewable energy technologies.Replacing the commercial expensive Pt/C catalysts with the emerging M-N-C catalyst system is considered to be a feasible way because of their high catalytic activity,great corrosion resistance,excellent conductivity and low cost.However,the stability of conventional M-N-C granular catalysts is greatly limited because of the single coordination environment.First,the metal atoms or NPs are usually subject to dissolution in severe electrochemical environments due to the low electronic coupling of M-C and the easy to be attacked M-N by the ORR by-product of H₂O₂,and thus exhibit inferior stability.Secondly,M-N_x centers are particularly easy to agglomerate during high-temperature carbonization and electrochemical reactions,forming big clusters with low catalytic ORR activity.The high-temperature carbonization generally leads to uncontrolled and complex active M-N_x species,it is thus difficult to control the location of metal sites.Therefore,it is difficult to construct high density active sites under the premise of preventing agglomeration.However,it is necessary to construct a high load and a thick catalytic layer in order to achieve high catalytic performance.In order to solve the problems above,an electrospinning mediated anchoring coordination constraint strategy was proposed in this paper,and a fiber based ORR electrocatalyst with high stability and high activity and novel catalytic active sites was synthesized.We propose a new strategy of constructing high density but uniformly distributed ZrO₂into N-doped bubble-like porous carbon nanofibers（N-BPCNFs）as the local coordination environment to support and stabilize Cu active sites,and a stable and efficient Cu-ZrO_3-x structure fiber-based catalyst was prepared.The ORR activity and long-term stability of this new transition metal oxide fiber-based catalyst were verified in detail.The main research contents of this paper are as follows:1.By using PVP as the carbon source,zirconium acetate as the zirconium source,deionized water as the solvent and PTFE as the pore forming agent,we prepared flxible ZrO₂@BPCNFs films by electrospinning with a high weight loading（78.5%）of ZrO₂.The influence of doping with different zirconium content on the physical structure of carbon nanofibers and the influence of different calcination temperatures on the crystal form of zirconia were investigated.The XRD results showed that ZrO₂ had the most complete crystal form when the calcination temperature was 800℃.Subsequently,the performance difference of ORR of ZrO₂@BPCNFs with different content in alkaline electrolyte was investigated.The experimental results showed that the ZrO₂@BPCNFs catalyst prepared by doping 5mmol zirconium acetate showed the best electrochemical catalytic performance,with a half-wave potential of 0.78V and a low Tafel slope of 112m V/dec.2.To improve the electrocatalytic performance of transition metal oxides,on the basis of Chapter 1,the ORR performance of the ZrO₂@BPCNFs catalyst was improved by doping transition metal copper and adding metal Cu as another active center.The results showed that the structure of CuZrO_3-xwas formed by adding Cu,and a series of characterization methods such as XRD and TEM confirmed that a new material CuZrO_3-xwas formed in the catalyst.The electrocatalysis experiment demonstrated that the new substances could improve the ORR performance of the overall catalyst to a certain extent,but excessive doping would lead to the agglomeration of Cu nanoparticles.The electrochemical experiment results confirmed that the catalyst prepared with 1.5 mmol of Cu showed the best electrochemical performance with a half-wave potential of 0.80 V,which was superior to the ZrO₂@BPCNFs catalyst.In order to further improve the performance of the catalyst,we doped melamine as a nitrogen source in the spinning precursor sol,and explored the influence of melamine doping with different quality on the fiber morphology and electrochemical performance.We prepared BPCNF doped with Zr,Cu,N,and designed a ZrO₂ mediated constraint strategy to control the distribution of Cu in BPCNF.Using this synthesis strategy,we prepared the catalyst with a high nanoparticle loading of 40.5wt.%.The corrosion resistance and oxidation resistance of the amorphous carbon matrix in M-N-C were improved by forming stable Cu-ZrO_3-x/ZrO₂heterostructures and anchoring unstable Cu active sites with stable ZrO₂.With this new design,the catalyst showed a great performance with a half-wave potential of 0.856V.The Tafel slope of the new catalyst was as small as 85m V/dec,and the half-wave potential only reduced 0.01m V after 1000 CV cycles,showing excellent stability.