Proton Conductive Materials Based On Transition Metal Molybdenum And Niobium Oxide:preparation And Properties

Proton exchange membrane fuel cell?PEMFC?,as a representative of new renewable energy conversion equipment,has attracted more and more attention due to increasingly serious energy and environmental problems.Proton exchange membrane acts as the core component of PEMFC,its performance is closely related to the output power and service life of the fuel cell.Therefore,it is of great significance to design efficient intrinsic proton conductive materials to replace commercial Nafion.The transition metal oxides and clusters occupy the important position in the design and synthesis of proton conductors due to its unique electronic structure and coordination ability.First of all,since the polyoxothiometalate and polyoxometalate has the adjustable structure,the skeleton structure and the proton transmission channel can be microscopically designed to achieve efficient proton transmission.Secondly,niobium oxyhydroxide has rich hydroxyl groups,good thermal stability and water resistance,which can achieve high-efficiency proton conductivity and effectively avoid the problem of Nafion decomposition above 80 ?.In this work,a series of transition metal molybdenum-oxygen clusters and niobium oxide composite materials were designed and synthesized.The structural characteristics and proton conductive properties were explored,and the relationship between the structure and properties was studied.1.A novel polyoxothiometalate [N?CH₃?₄]K₅H₂[?Mo₂O₂S₂?₄?m-dmsa?₄]·40H₂O was prepared using the interaction between sulfur-containing electrophilic cation [Mo₂O₂S₂]²⁺and meso-2,3-dimercaptosuccinic acid?C₄H₆O₄S₂,m-dmsa?,named as compound 1.The cyclic cluster consists of four dinuclear [Mo₂O₂S₂]²⁺moieties and four bridging dmsa^4-ligands,with potassium ions as counter cation.This cluster has a unique pore structure and a large number of active oxygen sites.Subsequently,the proton conduction properties of compound 1 were studied and the proton conduction mechanism was initially discussed.AC impedance analysis showed that the proton conductivity of the compound 1 can reach 7.06×10^-3S cm^-1at 55 ? and 97% relative humidity,and follow the vehicle mechanism.2.A new polyoxometalate [N?CH₂CH₃?₃]₆[H₃Co_0.5Mo₆O₁₅?PO₄?₄]₂·7H₂O based on the {Mo₆O₁₅?PO₄?₄} structural units has been hydrothermally synthesized,named as compound 2.Compound 2 contains the classic 0D dimer cluster {H₃Co_0.5Mo₆O₁₅?PO₄?₄}₂,coordinated water molecules and triethylamines.Protonated phosphate ligand in the outer sphere of the {H₃Co_0.5Mo₆O₁₅?PO₄?₄}₂ can provide numerous sites for proton jumping.At the same time,the hydrophilic properties of polyoxometalate allow the compound to absorb water molecules as proton carriers and form hydrogen bond networks,which can provide shorter paths for proton transport and improve the proton conductivity.Compound 2 can reach a high proton conductivity of 5.20×10^-2S cm^-1at 55 ? and 97% relative humidity.3.A new nanocomposite material NbO₂?OH?-PA has been synthesized using phytic acid and NbCl₅ with a simple sol-gel method,named as Nb-PA.A large number of phosphate and hydroxyl groups in the material form a continuous hydrogen bond network with water molecules,which provides more proton jumping sites for improving the proton conductive behavior and stability.The material showed a high proton conductivity of 1.35×10^-1S cm^-1at 85 ? and 97% RH.In addition,Nb-PA was doped with sulfonated poly?ether ether ketone??SPEEK?in different proportions to prepare a series of proton exchange composite membranes,named as SPEEK-x Nb-PA,and composite membranes can reach a proton conductivity of 0.17 S cm^-1at 80 ? and 100% relative humidity.