Preparation Of ZIFs-Derived Carbon Filled Sulfonated Poly (Ether Ether Ketone) Proton Exchange Membranes And Investigation Of Their Applications In Direct Methanol Fuel Cells

Direct methanol fuel cell（DMFC）is a promising energy conversion device with potential applications in mobile devices,medical treatment,new energy vehicles and military.The DMFC directly uses renewable methanol（Me OH）as fuel and has the advantages of high energy efficiency,low cost and pollution-free.Proton exchange membrane（PEM）,as a core component of the DMFC,is responsible for transporting protons and blocking Me OH permeation,which has been well recognized as one of main factors influencing the performance of the DMFC.The traditional DMFCs use the perfluorosulfonic ionomers,such as Nafion,as the PEMs due to their high proton conductivity and good chemical stabilities.These perfluorosulfonic ionomers,however,suffer from the shortcomings of high cost,severe Me OH crossover,and high pollution for preparation,which impose big constraints on the commercialization of the DMFCs.The development of alternative cost-effective PEMs with high proton conductivity and low Me OH permeability,which can replace the traditional perfluorosulfonic ionomers based PEMs,is therefore of great importance to promote the commercial favorability of the DMFCs.Due to low cost,high mechanical strength,and excellent chemical and thermal stability,sulfonated poly（ther ether ketone）（SPEEK）,is a most promising alternative to Nafion.However,the disadvantages,such as high swelling ratio and poor stability,have hindered the direct application of the SPEEK in DMFC.Zinc imidazole framework（ZIF）,silica（SiO₂）and carbon nanotubes（CNTs）are ideal filling materials for proton exchange membranes.Therefore,to promote application of the SPEEK membrane in DMFC,the modified is imperatively needed.Aiming at developing high-performance PEMs and promoting the direct application of the SPEEK membranes in DMFC,sereval strategies,such as the filling of the sulfonated ZIF derived porous carbon material（ZIF-C-SO₃H）,the co-filling of the ZIF-C-SO₃H and the sulfonated silica（SSiO₂）,and the co-filling of ZIF-C-SO₃H and the sulfonated carbon nanotubes（SCNT）,have been adopted to improve the proton conductivity and reduce the methanol permeability of the SPEEK membranes in this thesis.Specifically,the follow aspects of research have been carried out:（1）Fabrication of ZIF-C-SO₃H filled SPEEK membrane（ZIF-C-SO₃H@SPEEK）and its application in DMFC.ZIF-8 was used as the starting material for the preparation of the ZIF-C-SO₃H,which was synthesized by the reaction of Zn（II）ions coordinated with 2-methylimidazole.The ZIF-C-SO₃H was obtained by high temperature calcination of the ZIF-8and the subsequent surface grafting and sulfonation.The fabricated ZIF-C-SO₃H showed a high compatibility with the SPEEK membrane matrix.The ZIF-C-SO₃H@SPEEK membrane showed lower swelling ratio and higher proton conductivity than the SPEEK membrane,which arised from the specific interaction between the ZIF-C-SO₃H and the SPEEK matrix.In particular,the methanol permeability of the ZIF-C-SO₃H@SPEEK membrane was much lower than Nafion 115.When used in DMFC,the ZIF-C-SO₃H@SPEEK membrane exhibited a maximum power density of 92.0 mW cm^-2,which was 171%higher than that of the pure SPEEK membrane.Additionally,the ZIF-C-SO₃H@SPEEK membrane showed better stability than the plain SPEEK membrane.（2）Fabrication of ZIF-C-SO₃H and SSiO₂ co-filled SPEEK membrane（SSiO₂/ZIF-C-SO₃H@SPEEK）and its application in DMFC.Compared with single-filling,double-filling can combine the merits of individual fillers,but also provide synergistic effects between them to further improve the performance of SPEEK membranes.The results showed that the co-filling of ZIF-C-SO₃H and SSiO₂ can not only construct the proton transport network in the SPEEK matrix,but also decrease the methanol permeability of the SSiO₂/ZIF-C-SO₃H@SPEEK membrane.The DMFC performance tests showed that the SSiO₂/ZIF-C-SO₃H@SPEEK membrane exhibited a maximum power density of 128.6 mW cm^-2,which was～twice that of the DMFC with Nafion 115.Particularly,the DMFC with the SSiO₂/ZIF-C-SO₃H@SPEEK membrane showed much better the long-time stability than that with Nafion 115.（3）Fabrication of ZIF-C-SO₃H and SCNT co-filled SPEEK membrane（SCNT/ZIF-C-SO₃H@SPEEK）and its application in DMFC.The SCNT was obtained by chemical grafting and sulfonation of the carbon nanotubes.Depending on the specific advantages of the tube-like structured SCNs,such as high surface area and good flexibility,the co-filling of the ZIF-C-SO₃H and the SCNT could improve proton conductivityand reduce methanol permeability and swelling ratio of the SPEEK membrane through the interactions between the ZIF-C-SO₃H,the SCNT,and the SPEEK.The DMFC performance tests showed that the maximum power density of DMFC with the SCNT/ZIF-C-SO₃H@SPEEK membrane was～2.5 times higher than that with Nafion 115.Particularly,the stability of the DMFC with SCNT/ZIF-C-SO₃H@SPEEK membrane was better than that with Nafion 115.The results shown above demonstrated that the filling of the ZIF-C-SO₃H,the co-filling of the ZIF-C-SO₃H and the SSiO₂,and the co-filling of the ZIF-C-SO₃H and the SCNT were reasonable strategies to improve the performance of the SPEEK membrane.These strategies can not only improve the proton conductivity of the SPEEK membranes,but also reduce the methanol permeability of the SPEEK membranes,which are significant to promote the application of SPEEk membranes in DMFC.