Research On The Enhancement Of Methanol Oxidation And Oxygen Reduction Performance Of WP_x/carbon Composites

In recent years,with the rapid development and progress of science technology and economy,people's demand for energy has been increasing.Therefore,fossil energy reserves have been declining year by year and gradually disappear.When burning fossil fuels,there is a large amount of harmful gases,such as NO_x,SO_x and CO₂ will be emitted,which will have a serious impact on our living environment.Therefore,the development of new energy sources is imminent.Direct methanol fuel cell?DMFC?was considered to be ideal alternatives to fossil fuels due to its rich methanol resources,ease of storage and transportation,low cost,high energy density,easy operation and zero emissions.The efficiency of DMFC mainly depends on two important reactions:methanol oxidation reduction?MOR?and oxygen reduction?ORR?.Therefore,it is imperative to develop efficient catalysts that promote these two reactions.Due to the irreplaceability of Pt in MOR and ORR,this paper mainly studies and prepares direct methanol fuel cell anode and catalyst carrier to obtain Pt-based carrier with high stability of MOR and ORR promoter activity.In this study,phosphorus tungsten compounds?WP and WP₂?in transition metal phosphides with Pt-like properties were selected with X-ray diffractometry?XRD?,X-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?.The physical and chemical characteristics of the prepared support and catalyst materials were investigated.The MOR and ORR were studied by electrochemical tests such as cyclic voltammetry?CV?,chronoamperometry?CA?and rotating disk electrode?RDE?chemical properties.In this study,tungsten phosphide-embedded carbon-thin-layer/acid-treated expanded graphite?WP-CL/AEG?composites are synthesized as Pt-supports/co-catalysts for MOR/ORR via a one-step synthesis route.For MOR,Pt-WP-CL/AEG-3?molar ratio of P to AEG is 3.6 in precursor?shows the highest electrochemical surface area(123.05 m²g_Pt^-1)and mass activity(2217.6 mA mg_Pt^-1),which is 1.92 and 4.44 times higher than those of commercial Pt/C(64.16 m²g_Pt^-1and499.2 mAmg_Pt^-1).Pt-WP-CL/AEG catalysts exhibit higher CO tolerance and stability than those of Pt/C.Moreover,Pt-WP-CL/AEG-3 also exhibits a higher ORR activity than that of Pt/C in acidic media,which mainly exhibits a 4e^-transfer pathway?OH^-as the main product?for ORR.As expected,AEG greatly enhances the charge transfer capacity of Pt-WP-CL/AEG catalysts;the exposed P active sites induced by W atoms on WP facilitate the methanol/O₂ adsorption and activation during MOR/ORR;the CL originated from citric acid can protect WP from being oxidized in the air,which contributes to the high activity and stability of P active sites;the charges are transferred from AEG?positively charged?to WP via the linked-CL and then from WP to Pt,which contributes to the high MOR/ORR activity of Pt-WP-CL/AEG.In addition,WP₂/C composites were synthesized by solution self-assembly and high-temperature carbonization and Pt-WP₂/C composites were prepared by sodium borohydride reduction.The electrochemical test results show that Pt-WP₂/C-900 has the best MOR performance,including good ECSA of 68.35 m²g_Pt^-1,excellent mass activity of 609.4 m²g_Pt^-1,and excellent electrochemical stability.At the same time,Pt-WP₂/C-900 and Pt-WP₂/C-950 have similar ORR performance to Pt/C,and Pt-WP₂/C-900 and Pt-WP₂/C-950 catalysts are calculated in the oxygen reduction process.The energy conversion efficiency of the battery is effectively improved mainly through the 4e^-transfer process.WP₂ plays a catalytic role in both MOR and ORR.The WP₂ particle successfully increases the rate of MOR and ORR.At the same time,the uniform dispersion of Pt particles on the carbon support can sufficiently expose the active site of Pt,and the catalytic efficiency of Pt is sufficiently improved.