| As an extremely promising clean energy conversion device,proton exchange membrane fuel cells（PEMFCs）with great advantages over low operating temperature,high efficiency and zero emission are considered as the important cornerstone for the development of new energy industry in the future.While The oxygen reduction reaction（ORR）of PEMFCs can’t work well if there are no effective platinum（Pt）catalysts at the cathode because of its large over-potential.As the key material of the whole battery,ORR catalyst determines the performance and life of PEMFC.Therefore,it is necessary to overcome the high cost and poor durability of the current commercial Pt/C catalyst,and then develop low-Pt loading catalyst with high activity and high stability.This paper aims to study the ORR performance of low platinum catalyst modified with metal oxide Ce O2which has oxygen storage and acid resistance.By constructing the three-phase interface structure of"platinum-metal oxides-conductive carbon layer"effectively and adjust process later,the catalytic activity and stability of oxygen reduction have been improved,which provides a new design idea for the reduction of platinum and the optimization of the carrier for high efficiency platinum-based catalyst.The main research of this paper is as follows:（1）To construct the three-phase interface as the catalytic active site,we adopted the metal-organic framework ZIF-8 as the precursor for the nitrogen-doped carbon layer,then Pt nanoparticle was modified by Ce O2 on the substrate surface,which had been depositied through hydrothermal method in ethylene glycol system.Combined with XRD,TEM,XPS and other characterization methods,we found that the appropriate introduction of Ce O2could increase the content of oxygen vacancies in the catalyst,and provide more attachment sites for platinum loading when compared with the samples without Ce O2.And the electronic structure characteristics of Pt at the interface structure have been changed at the same time,which is the result of the strong metal-oxide interaction in the prepared three-phase interface composite catalyst.It is this special carrier which can stabilize and highly disperse platinum particles that greatly improved the ORR catalytic activity and durability.（2）The content of CeO2 in the carrier is regulated to maximize the interface interaction between metal and oxide.The TEM characterization and electrochemical tests showed that the concentration of Ce O2 in the carrier had seldom effects on the size of nanoparticles in the catalyst.However,when the content of Ce O2NPs is too high,they will gather on the surface of the catalyst,hindering the active sites and affecting the electron transport process;too low content of Ce O2 NPs will form fewer active sites of the interface structure,resulting in the unconspicuous improvement of ORR performance.The synthesized Pt/0.3Ce O2@NC composite catalyst showed the best catalytic activity（half-wave potential is 34 m V higher than commercial Pt/C and the mass activity is 8.1 than commercial Pt/C）and durability（the half-wave potential decreased by 7 m V after 10000 cycles of stability test;while the commercial Pt/C decreased by 33 m V after only 5000 cycles）.（3）In order to enhance the intrinsic active sites of the composite interfacial catalyst,the optimization of the interfacial environment by doping the transition metal M atoms（M=Fe,Co,Ni,Cu）in the lattice of Ce O2 was investigated.The addition of heteroatom will lead to the formation of lattice defects,and the increase of surface defect sites can improve the interaction between Pt and the support,so as to realize the modification of interfacial catalyst.Furthermore,phase characterization and electrochemical performance tests were carried out on the interfacial catalysts doped with different elements.The results showed that the cobalt doped sample owned the best ORR activity and a more efficient pathway closed to four-electron transfer during the process of oxygen reduction reaction. |
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