Design And Construction Of Non-Precious Metal M-N-C Oxygen Reduction Catalyst

The oxygen reduction reaction?ORR?plays an important role in the energy storage and conversion integretions such as metal air batteries and fuel cells.Noble metal catalysts have been intensively developed due to their high oxygen reduction activity.However,precious metal catalysts face the problems of scarce resources,high cost,weak resistance to methanol poisoning in catalytic reactions,and poor stability,which severely limit their application.In view of the above problems,non-noble metal Fe-N-C electrocatalyst and Cu-N-C catalysts and with high oxygen reduction activity and durability were designed to replace precious metal catalysts.For the design of non-noble metal single-atom Fe-N-C catalysts,2-methylimidazole?C₄H₆N₂?and zinc nitrate?Zn?NO₃?₂·6H₂O?was used to synthesis ZIF-8 through a simple liquid phase reaction,during which organic iron salt ferrocene?Fe?C₅H₅?₂,Fc?as iron precursor dissolved in methanol was used iron source.The match of molecular size between ZIF-8 and Fc@ZIF-8 has a pore size of 3.4?,a cavity of 11?,and molecular size of ferrocene is 6.4?)make it possible to the fabrication of Fc@ZIF-8 structure,which can be ultilized as precursor for single-atom Fe-N-C catalyst.On the one hand,the precursor ZIF-8 has a porous structure,which turns to porous carbon skeleton with ultra high specific surface area after high temperature pyrolysis,which may help to improve the mass transfer of oxygen in the catalyst,and the explosion of active sites,enhancing oxygen reduction.On the other hand,the match of molecular size between ZIF-8 and Fc?ZIF-8 has a pore size of 3.4?,a cavity of 11?,and molecular size of ferrocene is 6.4??makes it possible for a single ferrocene molecule to be trapped within the cavity of ZIF-8,making ferrocene molecules uniformly dispersed in the ZIF-8 bore.After pyrolysis at high temperature,the Fe was uniformly monodispersed in the porous carbon skeleton.The Fe-N-C catalyst was analyzed by X-ray absorption fine structure,and Fe was present in the Fe-N coordination form,proving that Fe is single-atom in the catalyst.that the catalyst was FeN_X coordination is an active site.After the introduction of ferrocene,the oxygen reduction performance of the catalyst was significantly increased comparing with N-C catalyst derived from pure ZIF-8 with a half-wave potential of 0.75 V.The half-wave potential of single-atom Fe-N-C catalyst was 0.904 V,suggesting Fe-N coordination structure are highly active in ORR.Furthermore,single-atom Fe-N-C catalysts have significantly improved stability and resistance to methanol poisoning compared to commercial Pt/C catalysts.For the design of the non-precious metal Cu-N-C catalyst,a simple liquid-phase mixing method was used.ZIF-8 was prepared using 2-methylimidazole?C₄H₆N₂?and zinc nitrate?Zn?NO₃?₂·6H₂O?as raw materials.Taking ZIF-8 as the carrier and CuCl₂ as the copper source,the Cu-ZIF-8 catalyst precursor was prepared by Cu²⁺adsorption on the surface of ZIF-8 in a simple manner,and Cu-N-C catalyst was prepared by high-temperature pyrolysis.The structure of the Cu-N-C catalyst was verified by a series of physical characterizations as amorphous carbon materials.After the introduction of Cu,the oxygen reduction performance of the catalyst was significantly increased,as the half-wave potential of 0.76 V for N-C catalyst increased to 0.81 V for the Cu-N-C catalyst.The Cu-N-C catalyst has a significantly increased stability and resistance to methanol poisoning of commercial Pt/C catalysts and is also a valuable non-precious metal catalyst.