Synthesis And Proton Conductivity Of Acid-base Pair Ionomer@Metal Organic Framework Materials

Increasing demands for reliable and powerfol energy sources continue to drive the development of new materials for energy storage and conversion device.Proton exchange membrane fuel cells(PEMFCs)is an important energy storage and conversion systems due to its fast start-up,high energy density and low pollutant emissions.The currently commercial proton exchange membranes(Nafion)have the disadvantage of a narrow operating temperature range.Metal-organic framework materials exhibit unique advantages in proton conduction due to structural adjustment.However,high proton conductivity,low humidity dependence and a wide temperature range are still difficult to trade-off.The high humidity-dependent proton conduction behavior leads to a loss in fuel cell performance because of flooding the cathode or the dehydration of the electrolyte material at high operating temperature.In this paper,the polymer(PEG),ionic polymer(PVPA)and acid-base pair ionomer(Im-PVPA)were introduced into the pores of the highly regular MOFs to increase the overall performance of the proton conductors.The results show that high proton conductivity under high humidity can be obtained,but the dependence of proton conductivity on humidity cannot be reduced by adjusting the doping amount and molecular weight of PEG.Compared with PEG,PVPA exhibits the higher water retention and lower pKa values,which can effectively increase the proton conductivity under low humidity conditions and reduce the humidity dependence of the material.However,due to the self-condensation of phosphonic acid groups at high temperature,the operating temperature range is limited.The introduction of imidazole can well form the acid-base pair ionomer with PVPA,which effectively limits the self-condensation reaction of PVPA and widens the temperature range of proton transport.Im-PVPA@MIL-101(Cr)-48h exhibits the lower humidity dependence and a wider temperature range by controlling the time of the imidazole.Under anhydrous conditions,the proton conductivity of Im-PVPA@MIL-101(Cr)-48h reaches a maximum of 2.28×10-3 S cm-1 at 110?.At 95%RH and 60?,Im@PVPA@MIL-101(Cr)-48h exhibits much higher proton conductivity up to 2.31 ×10-2 S cm-1,which is the best performance among the imidazole-doped MOFs composite materials reported currently.In a word,we have obtained a wide range of temperature(-20?~110?),low humidity dependence(2.24),and high proton conductivity(2.31×10-2 S cm-1)of the material with excellent overall performance by introducing acid-base pair ionomers.To improve the proton conductor comprehensive performance design provides a certain idea.