Tungsten Oxide/ZIFs-derived Carbon As A Catalyst For Clean Fuel Cells

With the massive use of fossil energy in order to meet the industrial progress,the earth's environment has gradually deteriorated.In this urgent form,the development of new energy has emerged.Direct methanol fuel cell?DMFC?shows a good development prospect since its discovery.It has the advantages of high energy density,easy storage and treatment,low price,simple operation and zero emission,and methanol can be extracted from renewable resources.It is regarded as a worthy alternative to fossil energy.In practical work,the effectiveness of DMFC is mainly determined by the two important reactions of the cathode and anode,oxygen reduction reaction?ORR?and methanol oxidation reaction?MOR?.However,there are unresolved technical problems in the commercial development of DMFC,so the development of environmentally friendly,efficient,and inexpensive catalysts is the key to opening the market.The research and preparation of DMFC dual-function catalyst carrier was set as the goal,and a Pt-based carrier with high stability of MOR and ORR catalytic activity was prepared.In this paper,tungsten oxide(W₂₄O₆₈ and WO₃)in non-precious metal oxides with high price advantage is selected as the object,which is characterized by various detection instruments,such as scanning electron microscope?SEM?,and transmission electron microscopy?TEM?,and other characterization methods were used to investigate the physical and chemical characteristics of the composite materials studied.At the same time using cyclic voltammetry?CV?,chronoamperometry?CA?electrochemical testing means such as discuss the MOR and ORR electrochemical properties and reaction mechanism.In this study,a new synthetic route was adopted,tungsten carbide/tungsten oxide/zeolitic imidazolate framework-8?ZIF-8?-derived carbon(?WC?/W₂₄O₆₈/NC_Z8)composites are prepared as Pt-supports/co-catalysts.Heating temperature is contr olled to adjust structure and crystalline phases of?WC?/W₂₄O₆₈/NC_Z8.For MOR,mass activity(2492.2?m A mg_Pt^-1)of Pt-WC/W₂₄O₆₈/NC_Z8?850?°C,5.0?wt.%?is mu ch superior to commercial Pt/C(499.2?m A mg_Pt^-1,10.0?wt.%).NC_Z8-thin-layer fac ilitates carburization of W atoms(W₂₄O₆₈ to WC)to form WC/W₂₄O₆₈ heterojunct ions.Oxygen vacancies at W₂₄O₆₈ fascinate H⁺to encourage formation of tungsten bronze compounds?H_yWO₃,?0?<?y?<?1??,and reversible reaction between W₂₄O₆₈ a nd H_y?WO?₃?0?<?y?<?1?contributes to a high MOR activity and CO resistance.Pt-WC/W₂₄O₆₈/NC_Z8?850?°C?also exhibits a higher ORR activity?4e^-?than Pt/C in acidic media.WC/W₂₄O₆₈ heterojunctions accelerates mass and charge transfer of the mixed crystal interfaces for ORR.In addition,Co WO₄/WO₃/ZIF-8@ZIF-67-derived nitrogen-doped carbon-carbon nanotube?Co WO₄/WO₃/ZNC-CNT?composites are synthesized for the first time.And Pt-Co WO₄/WO₃/ZNC-CNT composites are prepared by sodium borohydride reduction.Pt-Co WO₄/WO₃/ZNC-CNT shows a very high mass activity(2208 m A mg_Pt^-1)which is 3.34 times that of Pt/C(659.4 m A mg_Pt^-1),because Pt and WO₃ are generated due to hydrogen spillover H_xWO₃ effectively enhances the dehydrogenation step of methanol oxidation,giving it higher MOR activity.Under the protection of the carbon layer?ZNC?,Co WO₄/WO₃ simultaneously enhances the electrical conductivity and the strong metal-support interaction of Pt and the support,which is beneficial to improve the electrochemical activity and CO tolerance.Meanwhile,Pt-Co WO₄/WO₃/ZNC-CNT-850 exhibits excellent ORR catalytic performance,which should benefit from more oxygen vacancies created by tungsten oxide species to increase active sites.This shows that Co WO₄/WO₃/ZNC-CNT can be used as a Pt carrier/cocatalyst in MOR/ORR to continue research and development.In this paper,experimental studies are used to discuss DMFC anode and cathode bifunctional catalyst carrier materials?WC?/W₂₄O₆₈/NC_Z8 and Co WO₄/WO₃/ZNC-CNT,and their performance and principle are explained.It is reasonable to speculate that the material in this paper has the potential to become a commercial MOR/ORR electrocatalyst,and has the potential to continue to be used as a Pt support/cocatalyst.