| The exhaustions of coal, oil, natural gas and other types of fossil fuel, together with the accelerating deterioration of global ecotope, have sounded the alarm to human for develop clean and renewable energy. Proton exchange membrane fuel cell （PEMFC） is the 5th generation of fuel cell （FC）, which is a novel clean renewable energy highly valued because of its promising application prospect in many pratical fiels such as daily life, scientific products and ational defense. Proton exchange membrane （PEM） is one of the key parts in PEMFC, serving as both the conductor for protons and the separator for the electrons and gases. The current state of the art PEM material, Nafion?, however suffers a number of drawbacks including high cost, low proton conductivity at low relative humidity and high temperature, and potential environmental threat. Therefore, it is an essential direction to develop sulfonated hydrocarbon fluorine-free polymer materials with low cost and low fuel permeability. Sulfonated poly（ether ether ketone） （SPEEK） is environmental-friendly, and has perfect thermal stability, good mechanical properties and relatively high proton conductivity. Besides, its sulfonation source, poly（ether ether ketone） （PEEK）, is a low-cost engineering plastic. As a result, SPEEK has been paid much attention to in recent research.As-cast SPEEK membranes with controlled amount of residual solvent （RS） content were first prepared, and then treated with 1 M H2SO4 and DI water sequentially at room temperature to obtain the treated membranes. Even though the elemental analysis results confirmed that there was no existence of RS in all treated membranes, the morphology and properties of these treated membranes varied very much, indicating the strong effects of RS from the as-cast membranes. For the SPEEK membranes with degree of sulfonation （DS） of 53%, the proton conductivity of the membrane with 38.7 wt% RS was almost twice as high in the liquid water and ten times as high at RH lower than 70%, compared to that of the membranes with the minimum RS （11.7 wt%）.Series of membranes were prepared using dimethylformamide （DMF）, dimethylacetamide （DMAc）, N-methyl-2-pyrrolidone （NMP） and dimethylsulfoxide （DMSO） as the cast solvent according to general solution casting method. The proton conductivities of these membranes show the regulation of DMF<DMAc<NMP, where DMSO displayed a special behavior. At low DS of SPEEK, the membrane prepared by DMSO shows the highest proton conductivity; at high DS of SPEEK, the membrane prepared by DMSO together with other solvent shows a corresponding order with the content of RS, which is DMF<DMSO<DMAc<NMP. We discover that the content of RS is the deeper reason to affect membrane structure and properties regardless solvent type.2-acrylamido-2-methyl-1-propanesulphonic acid （AMPS） is employed as the interpenetrating monomer to form the semi-IPNs with SPEEK. The photoinitiation of polymerization and crosslinking of AMPS in a swollen state of membranes was attempted, where the RS content was carefully controlled during the preparation. The electrochemical properties of SPEEK/CrPAMPS semi-IPN membranes were characterized. The membrane structure and morphology were studied to correlate with the membrane properties.Nanocomposite PEMs with high proton conductivity require good dispersion of inorganic nano-fillers that bear functional groups facilitating proton transport. In this work, a facile approach of dopamine-initiated atom transfer radical polymerization （ATRP） was demonstrated to synthesize sulfonated halloysite nanotubes （SHNTs）. The coating of polydopamine layer on both the internal and external walls of nanotubes ensured the grafting of polystyrene sulfonic acid （PSSA） on both surfaces, as confirmed by the transmission electron microscopy results. The kinetics of PSSA grafting was consistent with the living nature of ATRP process. The existence of sulfonic acid groups on SHNTs significantly improved the interfacial compatibility between the nano-fillers and sulfonated poly（ether ether ketone） （SPEEK） matrix, resulting in uniform and dense morphology of nanocomposite membranes. In addition, the grafted PSSA also provided extra pathways for proton conduction both inside the lumens and along the outer surfaces of nanotubes. Therefore, enhanced proton conductivity and reduced activation energy for proton transport were achieved for the SPEEK/SHNT nanocomposite membranes, with the highest proton conductivity of 0.043 S cm-1 for the membrane with 15 wt% SHNTs, 54% higher than that for SPEEK control membrane. Graphene oxide （GO） was modified by the same method as HNTs to obtain sulfonated GO （SGO）, which has perfect filler-matrix interface miscibility with SPEEK. Compared with SPEEK/SHNT nanocomposite membranes, SPEEK/SGO nanocomposite membranes show higher improvement in proton conductivity. Combined with the restrained methanol permeability, the relative selectivity of SPEEK/SGO nanocomposite membranes is 7times as that of Nafion 212.Polydopamine were obtained by dopamine self-polymerization initiated through ultraviolet light in acidic DMF. After the addition of SPEEK and phosphotungstic acid （PWA）, the solution was cast to prepare SPEEK/Polydopamine/PWA nanocomposite membrane. The proton conductivity of SPEEK/Polydopamine/PWA nanocomposite membrane achieved 2.5 times as that of SPEEK. Compared with those in SPEEK/PWA nanocomposite membrane, the PWA in SPEEK/ Polydopamine/PWA nanocomposite membrane showed an overwhelmingly better stability. After water immersion for 500 h, the proton conductivity of SPEEK/Polydopamine/PWA nanocomposite membrane retained, while the proton conductivity of SPEEK/PWA nanocomposite membrane decreased to the same as SPEEK. With the interactions between amino groups and proton donors （sulfonic groups and PWA）, polydopamine and PWA were both stably existed in nanocomposite membrane. The method for the stabilization of PWA by polydopamine was easy and efficient, which can be generalized in other matrix and research fields. |
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