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Research On Long Lifetime Anion Exchange Membrane For Alkaline Membrane Fuel Cell Applications

Posted on:2020-09-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:N J ChenFull Text:PDF
GTID:1361330602960623Subject:Chemical Engineering and Technology
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Due to excessive exploitation and utilization of fossil energy,the energy shortage and environmental pollution problems have become main challenges to restrict the development of human society.The development and utilization of renewable energy?hydrogen,solar,wind,etc.?have become the competition and cooperation theme in political and scientific research in all countries of the world.Among them,hydrogen energy has been regarded as the most ideal renewable energy source for human society in the future due to its advantages of environmental protection,wide sources,and high energy density.Among them,the development and utilization of hydrogen mainly depend on the fuel cell technology.Fuel cell is a kind of power generation device that directly converts chemical energy of fuels into electrical energy without burning,and the fuel cells have been considered as best energy conversion and storage device for hydrogen energy.In recent years,proton exchange membrane fuel cells?PEMFCs?have been widely concerned and developed due to its high efficiency,environmental protection,and rapid low temperature start-up.However,PEMFCs are highly dependent on Pt-based catalysts,and the perfluorosulfonic acid membrane?Nafion?used in PEMFC is also expensive.Therefore,the high-cost problem in PEMFCs is still difficult to be solved,which greatly restricts the commercialization of the PEMFCs.In this study,we focus on next-generation alkaline membrane fuel cells?AMFCs?to substantially reduce the cost of fuel cells.AMFCs allow to use non-noble metals?such as:Fe,Co,Ni?as catalysts under alkaline conditions,possessing obvious low-cost advantages.In addition,AMFC has a higher oxygen reduction reaction kinetics?ORR?at the cathode.However,the development of AMFC is mainly limited by their key component of anion exchange membrane?AEM?.Nowadays,AEM mainly faces with three key bottlenecks:?1?under alkaline conditions,cationic group and polymer backbone in AEM are susceptible to OH-attack,resulting in complex degradation reactions,thereby reducing the chemical lifetime of AEM.?2?Compared with H+,the molecular volume of OH-is large,thus the ion conductivity of OH-is still insufficient.?3?Most of the AEMs are using inexpensive non-fluoroaromatic polymer as backbone,so the mechanical properties and dimensional stability of the AEMs are still needed to be further improved.Therefore,my dissertation is mainly researched on the technical bottlenecks of AEM,promoting the commercial application of AEMs and AMFCs:?1?Developing high-efficiency and good-durability cationic groups and polymer backbone to improve the lifetime and ion conductivity of AEMs.?Chapter 3 ? Chapter 5?.?2?Proposing novel "organic-inorganic" strategies to develope new-universal approaches for AEM-performance improvement?Chapter 6 to 9?.1.Development of high-efficiency and strong alkali-resistant cationic groups and polymer backbone.?1?We developed a series of cobaltocenium groups as novel cationic groups for AEMs,and systematically evaluated and expoled their alkaline stability and degradation mechanism.?Chapter 3?.Thereinto,1,1'-dimethyl cobaltocenium with electron-donating substituents shows highest alkaline stability?exceeds 500 h in 1 M KOH at 80??,which is significantly higher than conventional benzyltrimethylammonium?BTMA?groups.Based on that,a series of novel cobaltocenium-containg polybenzimidazole AEMs were prepared,and their structure-properties relationship was revealed.?2?To further improve the alkaline stability of the cationic groups,a series of high-stable N-heterocyclic ammonium and polyphenylene ether?PPO?backbone?Chapter 4?were developed.Among them,N,N-dimethylpiperidinium?DMP?and 6-azaspiro[5.5]undecanium?ASU?groups have superior alkaline stability.In this Chapter,a novel piperidine-terminated ASU precursor?P-ASU?was developed,and the lifetime of P-ASU is more than 2500 h at 1 M NaOH 80?.Besides,we successfully prepared a remote-graftingASU-PPO membranes,and realized the application of ASU in AEMs for the first time.These ASU-PPO membranes show outstanding lifetime in 1 M NaOH at 80? for 1500 h and reach a highest ion conductivity of 92 mS/cm,closing to commercial Nafion 212 membrane?100 mS/cm?in PEMFCs.The lifetime of ASU-PPO-based AEMs achieve a high level in current research.?3?To further optimize the microscopic phase structure and dimensional stability of ASU-PPO membrane,in Chapter 5,we developed poly?biphenyl piperidinium??PBP?-based AEMs with more stable polymer backbone.Besides,a series of in-situ crosslinked PBP and ASU-PPO?PBP-ASU-PPO?membranes were prepared to combine the advantage and solve the disadvantage of the ASU-PPO and PBP membranes,which effectively improves the mechanical properties,dimensional stability,and ion conductivity of the ASU-PPO and PBP membranes.The crosslinked PBP-ASU-PPO membrane shows a highest ion conductivity of 129 mS/cm,which exceeds the Nafion 212.Besides,these PBP-ASU-PPO membranes show a maximum power density of 324 mW/cm2.2.Universal organic-inorganic strategies to improve the comprehensive performance of AEMsTo develop a new universal approach for AEM comprehensive performance improvement,we have done the following work:?1?To give full play to the role of inorganic materials in AEM.Chapter 6 developed a universal "inorganic material surface cation modification technology",which endowed ion-exchange capability to inorganic materials,promoting the application of inorganic materials in AEM.First,we grafted ionic liquid?IL?on the surface of SiO2 to prepare functional materials of IL-SiO2,and then IL-SiO2 was added to quaternized polyphenylene ether?QPPO?to prepare organic-inorganic cross-linked IL-SiO2/QAPPO composite membrane.The addition of IL-SiO2 not only effectively enhances the mechanical properties of QAPPO membrane,but also effectively improves the ion conductivity of the QAPPO membrane.?2?To further improve the addition amount and utilization rate of inorganic materials in the composite membrane,Chapter 7 and Chapter 8 modified SiO2?Im-SiO2?and hydrotalcite?QA-LDH?were sprayed onto both sides of the TC-PPO membrane to prepare different types of "sandwich structure organic-inorganic" composite membranes by electrostatic-spraying methods.The construction of the "sandwich structure" not only effectively improves the ion conductivity,mechanical properties,and dimensional stability of the composite membranes,but also improves the durability of the composite membrane because the inorganic layer on both sides can serve as a protective layer.Among them,the "sandwich QA-LDH/TC-PPO composite membranes show higher ion conductivity of 125 mS/cm due to its special QA-LDH inorganic layer structure,which is significantly higher than TC-PPO membrane.The tensile strength of these membranes exceeds 40 MPa,and maximum power density of QA-LDH/TC-PPO membrane reaches 256 mW/cm2.This"sandwich-structure strategy" has good universality,which can be effectively applied in other AEM systems.
Keywords/Search Tags:fuel cell, anion exchange membrane, ion conductivity, alkaline stability, organic-inorganic composite membrane
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