New Composite Materials Based On Bismuth Oxide Clusters:Design,Synthesis And Proton Conductivity Properties

The proton exchange membrane fuel cell?PEMFC?,as a new clean energy conversion device,plays an important role because of its high efficiency and pollution-free.As a core component for fuel cell,the proton exchange membrane has an important influence on the power of fuel cell.The research shows that developing a new kind of intrinsic proton conductor material with high conductivity to replace Nafion and making it applicable in device of fuel cell is a key challenge.Therefore,constructing a continuous path for proton conduction and choosing an appropriate proton carrier using traditional polyoxometalates materials as a guide is the foundation for efficient proton conduction.In this work,the bismuth oxide cluster is selected to be the main object of study,whose structure is similar to the molecule of traditional polyoxometalates.A bismuth oxide cation cluster can be composited with different anions to form different types of proton conductors.Therefore,it can be used to clarify therelationship between the structure of bismuth oxide cluster and its proton conductivity.1.A novel inorganic proton conductor made by hierarchical porous ionic nanocrystals was prepared using the interaction between protonated bismuth oxide and polyoxometalate anions.The ionic nanocrystals have provided flexible multiproton channels for fast transmission of proton.Polyoxometalate anion can act as proton carriers and hydrophilic sites to improve the conductivity of the material.Meanwhile,the positive bismuth oxide cluster can inhibit the loss of polyoxometalate anion under high relative humidity by the balance of hydrophilic anion.2.The layered bismuth oxide material was formed by hydrolysis of bismuth nitrate induced by regulation of phytic acid anion.The research was carried out to explore the influences which forms by carrier with high proton concentration and structure of intrinsic proton conductor to performance of proton conduction.3.An efficient material—{H6Bi12O16}/GO for proton conduction was prepared by vacuum assisted selfassembly method via the in situ interaction between hydrophilic protonated bismuth oxide ionic nanocrystals{H₆Bi₁₂O₁₆}and hydrophilic graphene oxide.{H₆Bi₁₂O₁₆}/GO can effectively overcome the trade-off effect between proton conductivity and methonal permeability and meanwhile show catalytic decomposition of hydrogen peroxide,as well as quick humidity response and recovery properties.The composite membrane also showed excellent proton-conducting performance over the temperature range of-40°C to 90°C.4.Nafion-{H₆Bi₁₂O₁₆}hybrid membrane was prepared by the modification of bismuth oxide cluster at the molecular level in ion nanochannels of Nafion.The selective interaction between matching size of the structure of bismuth oxide cluster{H6Bi12O16}in solution and affinity chain of Nafion maintains the microscopic phase separation structure of Nafion membrane.The accurate distribution of fillers,had significant impact on microstructure and performance of membranes:moderate amount of hydrophilic{H₆Bi₁₂O₁₆}were distributed in ionic nanophase and excessive{H₆Bi₁₂O₁₆}were distributed in trunk nanophase.{H₆Bi₁₂O₁₆}in ionic nanophase may increase the sites and improve the hydrophilic zone for proton conduction without loss of mechanical stability.The electrostatic or hydrogen bond interaction between bismuth oxygen cluster{H6Bi12O16}and sulfonic acid group?-SO3H?of Nafion membrane is the main force to construct a continuous proton transport channel.A water molecule can interact with multiple S-OH,or Bi-O-H…OH forms hydrogen bonds,which shortens the O-O distance in the hydrogen bond network and reduces the proton transfer barrier.The continuous transmission path formed by collaborative optimization of physical and chemical microenvironment of channels at the interface of the hybrid membrane had significantly improved the proton transfer efficiency and output power of methanol fuel cell.Therefore,hybrid technology at the molecular level had a significant foreground for improving process efficiency and saving the cost.