Synthesis And Performance Investigation Of Catalysts For Direct Methanol Fuel Cells

Direct methanol fuel cells（DMFCs）,as efficient and environmentally friendly energy conversion devices,have broad application prospects in power sources for transportation,portable electronic equipment and small mobile devices such as mobile phones.However,its practical application still faces many challenges.For instance,the key scientific and technological issues include both anodic methanol oxidation reaction（MOR）and cathodic oxygen reduction reaction（ORR）which are complex multi-electron processes and kinetically sluggish;Furthermore,the anodic Pt catalyst is susceptible to the CO_ad poisoning and the amount of Pt catalysts at the cathode is high.Aiming at the above problems,this thesis focuses on the design of electrocatalysts for efficient photoelectro catalytic methanol oxidation and the synthesis of low-Pt catalysts.Through electrochemistry and microscopy/spectroscopy techniques,the structure-activity relationship of the catalyst has been studied thoroughly.The main contents are as follows:（1）Pt supported on a series of semiconductors（Co₃O₄,Mn₃O₄,Ni（OH）₂,Fe₃O₄,Bi VO₄,Cu O and Zn O）were prepared by the impregnation-hydrogen reduction method.By comparing the energy band structure of the semiconductors with the methanol oxidation performance of the photoelectrocatalysts,we found that the main influences of the band gap of semiconductors on the electrocatalytic performance for methanol oxidation under light irradiation were:（ⅰ）Semiconductors with narrow band gap have high utilization efficiency of visible light,however,they also face the problems of rapid photo-generated carrier recombination and photo-corrosion;（ⅱ）Semiconductors with wide band gap have low utilization efficiency of visible light,but they have good ability of photo-generated charge separation as well as the stability.Therefore,considering the light utilization efficiency and the photoelectrocatalytic performance for methanol oxidation,Fe₃O₄ system and Bi VO₄ system as semiconductor carriers are suitable for photo-electrocatalytic methanol oxidation.（2）To tackle the issue of low efficiencies of light adsorption and photogenerated charge separation/transfer of photoelectrocatalysts in photoelectrocatalysis,a photoinduced strategy was employed to in situ generate Pt/Bi VO₄/Bi₂O₃ heterojunction through light irradiation of Pt/Bi VO₄ in alkaline solution.The obtained Pt/Bi VO₄/Bi₂O₃exhibits excellent photoelectrocatalytic activity for the MOR under irradiation.Compared with Pt/Bi VO₄and Pt/Bi VO₄/Bi₂O₃-M,Pt/Bi VO₄/Bi₂O₃ displays the highest activity of MOR(5.55m A cm^-2)and an enhancement factor（1.8）in the light irradiation,which is attributed to in situ-generated Bi VO₄/Bi₂O₃heterojunction with matched energy band structure and compatible interface that greatly improve the separation and transfer efficiencies of photogenerated charges.The mechanism study of MOR discovers that the OH_ad produced on the Bi VO₄/Bi₂O₃ heterojunction improves the MOR rate by promoting the kinetics of methanol dehydrogenation on Pt.（3）To deal with the problems of high energy consumption and low yield in the preparation of core-shell catalysts by the traditional Cu-UPD method,the Pt/Pd/C core-shell catalyst was synthesized by a modified Cu-UPD/Pt replacement method.The obtained Pt/Pd/C exhibits the better electrocatalytic ORR performance.In an O₂-saturated 0.1 M HCl O₄ solution,the specific activity and mass activity of Pt/Pd/C is 1.8and 1.6 times greater than that of Pd/C,respectively.Compared with Pd/C,the half-wave potential of Pt/Pd/C is positively shifted by 20m V.After accelerated durability test for5000 cycles,Pt/Pd/C displays negligible losses in ECSA and only 10m V of loss in the half-wave potential,which reveals the better stability.The method is simple to operate and suitable for scale-up production,which does not require precise external potential control and special equipment,providing a new idea for preparing low-platinum shell-core-shell electrocatalysts.