Construction And Performance Study Of Anion Exchange Membrane With Full Carbon Chain Polymer

Recently,the growing prominence of the greenhouse effect and other environmental concerns has accelerated the demand for renewable energy.As low-carbon,clean,efficient and sustainable secondary energy,hydrogen energy can help solve problems such as a series of energy depletion,climatic anomaly and environmental pollution,and is a major research direction for energy structure adjustment.With the characteristics of excellent energy density,zero pollution and emissions,hydrigen energy is known as the“energy optimization”.Hydrogen fuel cells（FCs）are efficient energy conversion devices.PEMFCs have the advantages of zero emissions,efficient fuel conversion rate,and tunable power.However,the reliance on platinum-based noble metal catalysts hinder the wide applicability of PEMFCs.Compared with PEMFCs,AEMFCs have the advantages of using non-precious metal catalysts,avoidable fuel crossover,controllable catalyst corrosion,inexpensive cell components,and fast cathodic oxygen reduction reaction kinetics.AEMFCs are more promising energy conversion devices.As a key of components of AEMFCs,AEMs act as separators between two electrodes,solid polymer electrolytes and ionic conductors in AEMFCs.Therefore,the development of AEMs with high ionic conductivity,good dimensional stability and alkaline stability is extremely important to promote the development of AEMFCs.The most effective way to improve the alkaline stability of AEMFCs is to prepare full carbon chain polymers without aryl ether linkages.In addition,the construction of crosslinked structures and microscopic phase-separated structures can significantly improve the mechanical properties,anti-swelling and OH^-conductivity of AEMs.Therefore,instead of heightening the composite performance of AEMs,this paper takes the full carbon chain polymer as the backbone and starts from designing the crosslinked structure and constructing microphase separation structure in AEMs.Full carbon chain polymer AEMs were designed and synthesized by using the strategies of UV-initiated free radical crosslingking,free radical initiator-induced free radical crosslinking,“physical crosslinking”,nanocomposite modification and cationic remote grafting.And the relationship between structure and performance in AEMs was also explored.Specific work includes:（1）A series of comb-shaped salt monomers were designed.Comb-shaped crosslinked AEMs（PSAN-MVBCn+2）were prepared by radical polymerization with benzoin ether as photoinitiator and p-vinylbenzene as crosslinking agent by UV-curing method.The formation of crosslinked network structure makes the swelling ratio of PSAN-MVBCn+2 AEMs lower than 25%,which ensures the dimensional stabiity of AEMs.The long alkyl chains in comb-shaped structure broaden the interphase spacing and facilitate the construction of ion transport channels,in which the ionic conductivity of PSAN₇₀-MVBC16₃₀membrane reached 62.4 mS cm^-1at 80℃.The alkaline stability test showed that the PSAN₇₀-MVBC16₃₀membrane could retain 87.34%of its initial value after being soaked in 2 M NaOH at 80℃for 500 h.（2）The SEBS polymer with the unique alternating structure of soft and hard blocks was selected as the backbone of AEMs,and the comb-shaped AEMs（Cn-SEBS）were constructed to explore the effect of different alkyl chain lengths on the performance of AEMs.The research results showed that the C16-SEBS membrane exhibited the best performance.The construction of the comb-shaped structure improved the solubility of SEBS-based polymers,especially C16-SEBS can be dissolved in highly polar solvents such as DMSO,DMF,and NMP.In order to further optimize the membrane material,the free radical crosslinked AEMs（C16-SEBS-DCP）with a spatial network structure were obtained by high-temperature crosslinking using the free radical initiator DCP.This cross-linking method improved the mechanical properties and dimensional stability of AEMs on the premise of ensuring ionic conductivity A simple and effective new strategy was proposed to further improve the comprehensive performance of AEMs.（3）In order to improve the membrane forming properties of the supported spirocyclic cationic polybiphenylpiperidine-based AEMs（PBP-ASU）with excellent alkaline resistance,the flexible C16-SEBS with good solubility was introduced,and a series of physical crosslinked AEMs（PBP-ASU-C16-SEBS）were synthesized.The high ion exchange capacity of PBP-ASU ensures the stable conductivity of PBP-ASU-C16-SEBS,which can reach 97.20 mS cm^-1at 80℃.The formation of the physical crosslinked structure increased the mutual entanglement in the polymer chains and enhanced membrane-forming propertyof PB-ASU.The maximum tensile strength of the PBP-ASU-C16-SEBS membrane can reach 11.4 MPa.After soaking in 2M NaOH solution for 1600 h,the ionic condutivity of PBP-ASU-C16-SEBS still retained 86.53%.（4）To construct excellent microscopic phase separation morphology,broaden the ion transport channels and improve conductivity,piperidinium cation functionalized polyhedral silsesquioxane（Pi-POSS）was synthesized based on the nanocomposite modification strategy.And Pi-POSS_x%/Pi-SEBS composite AEMs were prepared using piperidine grafted SEBS block copolymer（Pi-SEBS）as polyelectrolyte.Benefiting from the abundant cationic groups in Pi-POSS,the aggregation of cationic groups in the membrane was enhanced.The ionic conductivity of the Pi-POSS_x%/Pi-SEBS composite membranes were greatly improved due to the formation of microscopic phase separation morphology.The existence of the hydrophobic Si-O-Si core and rigid cage-shaped structure in Pi-POSS hindered the movement of the backbones and suppressed the excessive swelling of AEMs.The Pi-POSS_15%/Pi-SEBS shown the tensile strength of 30.9 MPa.After 1680 h of alkaline resistance test,the ionic conductivity of Pi-POSS_15%/Pi-SEBS composite membrane still retains82.7%.The peak power density at 80℃ is 219 mW cm^-2.（5）Two kinds of N-heterospirocyclic cations（a-ASU and p-ASU）were synthesized,and SEBS-based AEMs（SEBS-ASU-TMA）with both ASU and TMA cations were prepared by a step-by-step grafting strategy.The synergistic effect of ASU and TMA induced distinctly ordered hydrophilic/hydrophobic microphase-separated structure,and the cationic long-range grafting method constructed connected ion transport channels,which upgraded the OH^-conductivity and chemical stability of SEBS-ASU-TMA AEMs.Theionicconductivityof SEBS-p-ASU-TMA-40 membrane at 80℃was 96.59 mS cm^-1,and after1000 h of alkaline resistance test,its ionic conductivity decreased by only16.15%.The presence of hydrophobic alkyl chains in SEBS-p-ASU-TMA-40 membrane inhibited the swelling of the membrane,and the swelling ratio at 80℃was 35%,showing good dimensional stability.The membrane electrode assembled by SEBS-p-ASU-TMA-40 membrane reached 286 mW cm^-2after single-cell testing.