| Proton exchange membrane fuel cells(PEMFCs)is a kind of green and efficient new energy device with the characteristics of high energy conversion efficiency,environmental friendliness and quick start-up,thus it can be widely used in fixed power stations and transportation.As a key material of PEMFCs,proton exchange membrane(PEM)plays the role of transporting protons,blocking fuel and oxidant,and its performance directly affects the performance of PEMFCs.Currently,widely used perfluorosulfonic acid resin membranes(such as Nafion)are highly dependent on liquid water due to proton conduction and are only suitable for low temperature and high humidity environments(eg.temperature ? 80 ?,relative humidity ? 80%).Polybenzimidazole(PBI)polymer has excellent mechanical properties and thermochemical stability,and has good proton conductivity under high temperature conditions after doped with phosphoric acid(PA).It is the only commercial high temperature PEMFCs membrane material that can meet the requirements of the U.S.department of energy.PA-doped PBI membrane(PA-PBI)is slow in proton conduction through PA at low temperature,and PA soluble in liquid water led to the battery performance degradation and electrode corrosion,so it is only suitable for high temperature and low humidity environment(such as 120~200 ?).At present,low temperature or high temperature PEMFCs is only suitable for the narrow temperature range and the harsh requirements of the water environment,which limits the advantages of high energy efficiency and quick start of the battery system.Therefore,it is of great significance to develop a PEM material that is suitable for stable operation in a wide temperature range and uncontrolled humidity environment without the restriction of harsh operation environment of low temperature and high temperature PEMFCs.In this paper,hygroscopic fibrous porous inorganic clay mineral sepiolite(Sep)was modified to prepare composite PEM based on poly(2,5-benzimidazole)(ABPBI)with low PA doping level for application in a wide temperature range.The specific research content is as follows:1)For the problem that sepiolite has high impurity content,narrow pores and low natural specific surface area,the traditional hydrothermal method and microwave assisted method are used to acid activated sepiolite,and the concentration of hydrochloric acid and microwave assist time are controlled.The process parameters were studied by FTIR,XRD,BET,ICP-OES and TEM to study the evolution of the structure and morphology of sepiolite.As a result,the acid-activated sepiolite with large specific surface area and pore volume was obtained.2)In order to enhance the compatibility between organic and inorganic phase,the surface modification of the sulfonic acid-based grafted silane coupling agent to the traditional hydrothermal acid-activated sepiolite is carried out by optimizing the surface modification treatment process.FTIR,XRD,CA,UV and POM were used to characterize the structure,hydrophilicity and dispersion properties of sepiolite before and after surface modification,and the surface modification effect of coupling agent was strongly confirmed.At the same time,the IL-filled modification of the microwave-assisted acid-activated sepiolite was characterized by FTIR,XRD,Raman,XPS,BET,TEM and TG-DSC,and the IL loading and the IL in the sepiolite pore were characterized.The structure and phase distribution have explored the reasonable immobilization of IL,which provides experimental and theoretical basis for further study of the mechanism of proton conduction through IL.3)ABPBI/AAS-PTES-S and ABPBI/MAAS-IL composite proton exchange membranes were successfully synthesized and prepared by in-situ synthesis and solution casting.By optimizing the content of each component and the synthesis process,mangy tests has been conducted such as FESEM-EDS,XRD,DMA,TGA,oxidation stability,water absorption,phosphoric acid doping level,phosphoric acid retention,dimensional stability,proton conductivity and cell performance to characterize the distribution of AAS-PTES-S and MAAS-IL inorganic particles in the composite membrane and the influence on the structure and properties of the composue membranes,at last the relative optimal comprehensive performance of composite membrane was determined.The results showed that the uniform distribution of hygroscopic inorganic particles can promote the regular arrangement of the molecular chain of ABPBI polymer,so that the mechanical strength,thermal stability,oxidation stability and dimensional stability of the composite membrane are significantly improved,while the absorption and fixation capacity of water and PA were enhanced,and thus exhibited excellent proton conductivity and battery performance over the wide temperature range of 40?180 ?,so it has potential application prospects for PEM materials for PEMFCs in a wide temperature range. |
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