Microstructural Regulation Of SPPESK Proton Exchange Membrane By Inorganic Doping

Proton exchange membrane(PEM)is the key component of the proton exchange membrane fuel cell(PEMFC).Non-fluorinated PEM has the advantages of low fuel permeability,low price,and friendly environment.However,the high proton conductivity often leads to loss of dimensional stability.In order to solve the trade-off,organic-inorganic composite proton exchange membrane based on non-fluorinated sulfonated poly(phthalazinone ether sulfone ketone)(SPPESK)was prepared by inorganic doping methodThe modified inorganic nano-materials with different types and morphologies induce the regulation of the microstructure while inhibiting the swelling of the composite PEMs,enhancing the overall performance of the membranes.To improve the proton conductivity and dimensional stability of PEM,the SPPESK/SZrO2 composite PEM was prepared by introducing 20 nm sulfated zirconium dioxide(SZrO2)solid superacid nanoparticles into SPPESK matrix.The separation of the hydrophilic and hydrophobic microphases in the membrane was promoted by the aggregation of independently dispersed ion clusters.The hydrophilic channel and the dead end in the membrane were connected to some extent.The acidic sites on the surface of SZrO2 provide more transfer sites for protons.At 80℃,The proton conductivity of SPPESK-1.5 reached 180.3 mS cm-1,which was 66%and 19%higher than that of SPPESK pristine membrane and Nafion 115 membrane,respectively,and higher than the reported values.The dimensional stability of the membrane was improved by the hydrogen bonding between the SZrO2 nanoparticles and the molecular chains of the polymer.The resistance to fuel penetration of the membrane was improved,benefiting from the steric hindrance of SZrO2 nanoparticles.The methanol permeability of SPPESK-1.5 was reduced to 3.1 ×10-7 cm2 s-1,which was 77%and 54%lower than that of Nafion 115 membrane and SPPESK pritine membrane,respectively.The maximum power density of SPPESK-1.5 for DMFC was 133%and 25%higher than that of SPPESK pritine membrane and Nafion 115 membrane,respectively.The maximum power density of H2/O2 fuel cell was 37%higher than that of SPPESK pritine membrane and comparable to that of Nafion 115 membrane.To further improve the performance of PEM,the SPPESK/SSnO2 composite PEM was prepared by introducing sulfated tin dioxide(SSnO2)solid superacid nanoparticles with smaller size(10 nm)and stronger surface acid strength.The ion clusters aggregated and the average size increased by nearly 2 times,which effectively promoted the microphase separation in the membrane.The proton conductivity of the composite membrane with 7.5%SSnO2 reached 194.7 mS cm-1 at 80℃,which was 48%and 30%higher than that of SPPESK pristine membrane and Nafion 115,respectively.The swelling ratio of the composite membrane was significantly reduced,which was 60%lower than that of the SPPESK pritine membrane and comparable to the Nafion 115 membrane.The selectivity was 177%and 342%higher than that of the SPPESK pritine membrane and Nafion 115,respectively.The maximum power density of DMFC was was 125%and 34%higher than that of the SPPESK pritine membrane and Nafion 115,respectively.The maximum power density of H2/O2 fuel cell was 30%higher than that of the SPPESK pritine membrane,and slightly higher than that of Nafion 115 membrane.One-dimensional nanofibers have long-range mass transfer channels and high specific surface area,therefore,the hollow porous SnO2 one-dimensional nanofibers were prepared by electrospinning.The radial asymmetric fiber structure(the inner layer was PAN and the outer layer was PVP)was formed,due to the significant differences in the interaction between PVP and PAN and solvent DMF.The hollow and porous structure was then formed,due to the difference in thermal stability of PAN and PVP,and the difference in diffusion rate between metal ions and metal oxides.The effects of spinning solution properties,process parameters and annealing conditions on fiber morphology were investigated.To further improve the performance of PEM,the SPPESK/SFSnO2 composite PEM was prepared by introducing sulfated SnO2 hollow porous one-dimensional nanofibers(SFSnO2)into the SPPESK matrix with high degree of sulfonation,and compared with the SPPESK/SSnO2 Ccomposite membrane doped with zero-dimensional SSnO2 nanoparticles.The specific surface area of SFSnO2 was 128.0 m2 g-1,which was much larger than that of SSnO2 nanoparticles(24.1 m2 g-1).The ion clusters aggregated along the nanofiber walls and formed a continuous ion cluster aggregation structure,providing a continuous long-range transfer channel for protons.At the same time,the one-dimensional nanofiber structure was beneficial to connect the tortuous channels and dead ends in the membrane,effectively improving the proton transfer efficiency.At 80℃,the proton conductivity of SPPESK/SFSnO2 was 226.0 mS cm-1,which was 72%and 50%higher than that of SPPESK pristine membrane and Nafion 115,respectively,and increased by 16%compared with SPPESK/SSnO2 composite membrane.Both of SPPESK/SFSnO2 and SPPESK/SSnO2 composite membranes showed high dimensional stability and were comparable in swelling ratio to Nafion 115.The maximum power density of DMFC was 146 mW cm-2,which was 150%,11%and 48%higher than that of SPPESK pristine membrane,SPPESK/SSnO2 membrane and Nafion 115 membrane,respectively.The maximum power density of the H2/O2 fuel cell reached 936 mW cm-2,which was 44%higher than that of SPPESK pristine membrane,12%for the SPPESK/SSnO2 membrane and 26%for the Nafion 115 membrane.