Study Of The Durability/Stability Of Phenylenediamine-based Non-precious Metal Catalyst For Oxygen Reduction Reaction

Fuel cell is an environmental-friendly and high efficiency power supply,which has been widely applied in transportation and other fields in recent years.However,the development of fuel cell industry is seriously hindered by the high price platinum catalyst used in the cathode.Currently,the oxygen reduction catalytic activity of non-precious metal catalysts(NPMCs)is close to commercial Pt/C catalysts.However,the durability/stability gap between NPMCs and Pt/C catalysts is significant,which has become an important factor limiting the large-scale applications of NPMCs.In this paper,optimizing the structure of the catalyst by electrospinning and surface modification of the catalyst with CeO2 are studied to investigate the effect on the durability/stability of phenylenediamine-based NPMC.Firstly,high catalytic activity NPMC is prepared by electrospinning.However,the catalytic durability/stability of oxygen reduction is poor.Secondly,CeO2 is used to modify NPMC prepared by solid phase method so as to eliminate the harmful H2O2 as much as possible.And the durability/stability of NPMC is improved greatly.The main research work is as follows:(1)P-phenylenediamine and polyacrylonitrile are used as the nitrogen source and carbon source,ferric chloride hexahydrate as the iron source,and zinc oxide as the dispersant.Nanofibers are prepared by electrospinning,and then PpPD/PAN-Fe-ZnO catalyst is obtained through polymerization,heat treatment and acid washing.The SEM characterization shows that the prepared catalyst has a disordered and fractured nanofiber microstructure.From the BET characterization,the specific surface area of the catalyst is 512 m2 g-1.And the proportion of micropores is 47.8%,which is more than 1.6 times that of PpPD/PAN-Fe.In acidic and alkaline conditions,the oxygen reduction catalytic activity of PpPD/PAN-Fe-ZnO is high,Under acidic and alkaline conditions,the oxygen reduction half-wave potential(E1/2)of the PpPD/PAN-Fe-ZnO catalyst at 900 rpm is 0.807 V and-0.086 V,respectively.However,after 2,000 cycles of accelerated durability test,the E1/2 degradation of PpPD/PAN-Fe-ZnO is 78 mV in acidic condition.The possible reason for the poor durability/stability is the high H2O2%generated during oxygen reduction process.Therefore,its catalytic durability/stability needs to be further improved..(2)CeO2 is used to modify the surface of the prepared PpPD-Fe-ZnO catalyst samples by hydrothermal method and finally obtain PpPD-Fe-ZnO-CeO2 catalyst with different CeO2 mass ratios.TEM and XRD show that CeO2 is uniformly dispersed on the surface of PpPD-Fe-ZnO catalyst,and the size of the CeO2 clusters is 1-5 nm.Electrochemical characterization shows that,compared with PpPD-Fe-ZnO,the E1/2 of PpPD-Fe-ZnO-6%CeO2 is negatively shifted by only about 20 mV.But its durability/stability has been greatly improved.After 10,000 cycles of accelerated durability test,the E1/2 of PpPD-Fe-ZnO negatively shifts about 110 mV,while the E1/2 of PpPD-Fe-ZnO-6%CeO2 catalyst is only half of that.The H2O2 generated during oxygen reduction reaction is harmful to the durability/stability of the catalyst.The surface modification of PpPD-Fe-ZnO catalyst with CeO2 as free radical scavenger resulted in a significant reduction in H2O2 yield.This significantly reduces the destruction of H2O2 to the active sites of NPMC,thus improving the durability/stability of NPMC.