| As an important part of fuel cell,proton-conducting materials with pore channels have attracted much attention.Over the past decades,metal-organic frameworks?MOFs?or porous coordination polymers?PCPs?,constructed by metal ions and bridging ligands have emerged as a new class of proton conductors as inorganic and organic hybrid material due to the controllable arrangement,high regularity and high chemical variety of guest molecules.Oxalic acid ion(ox2-)is a simple bidentate ligand.In the structure of metal oxalic acid compounds,oxalic acid ligands can provide more protons for it and forming an infinitely extended hydrogen bond network,which makes the material exhibit excellent proton conduction properties.As the representative of porous crystal materials,phosphorous-based oxides have attracted much attention due to their wide applications in photoluminescence,catalysis,proton conduction,gas adsorption and separation.And M-O-P bond has good stability,which can obtain strong inorganic framework and show good water stability and thermal stability.Recently,attempts have been made to replace phosphoric acid with phosphorous acid with less connection,with the expectation of producing more interesting structures.The introduction of oxalic acid units into metal phosphate compounds is inducing the formation of compounds with high stability and high proton conduction properties.In this paper,main group metals Ga and transition metal V and Ni as metal sources.A series of metal phospho-oxalic acid compounds were synthesized under hydrothermal and solvent-free conditions by continuously changing the reactant ratio,reaction time and temperature.The synthesized compounds were characterized by powder X-ray diffraction,single crystal X-ray diffraction,infrared spectroscopy,thermogravimetry,elemental analysis,etc.In order to further study the proton conduction properties of the materials,ac impedance tests were performed on the synthesized materials.Specific tasks include:1.Using the main group metal Ga as metal source,two new gallium phosphite were synthesized?compounds 1 and 2?.[Ga2?HPO3?2?H2PO3??C2O4?](C4N3H16)]?1?shows a three-dimensional open framework which is constructed by the two-dimensional layers with a4,8-membered window in the bc plane and oxalate groups.The protonated diethylenetriamine molecule is located in the pore channels of the 8-ring.So the compound has good proton conduction properties,and the conductivity reached 2.07×10-3 S cm-1 under high temperature and humidity.Ga?HPO3??H2PO3??C2O4?·(C6N2H14)?2?is a one-dimensional chain structure synthesized under solvent-free conditions.Compound 2 also has good proton conductivity.The proton conductivity reaches 1.84×10-3 S cm-1 under the conditions 60 oC and 98%RH.It is worth mentioning that compound 2 uses solvent-free synthesis method,which is very consistent with modern green chemistry concept.2.Using transition metals?V and Ni?as metal sources,two compounds with two-dimensional layered structures were synthesized using different structural agents:V2O2?HPO3?2?C2O4??C3N2H5?2?3?and V2O2?HPO3?3(C6N2H16)?4?.Compound 3 is a phosphite-vanadium oxalate compound synthesized with imidazole as a structure agent.The protonated imidazole molecules are located between layers.The proton conductivity of compound 3 reached 1.24×10-3 S cm-1 at 75 oC and 98%RH.Compound 4 is a vanadium phosphite compound synthesized with N'N-dimethylpiperazine as a structural agent,N'N-dimethylpiperazine molecule is located between the layers,and the conductivity of compound 4 reached 1.53×10-3 S cm-1 at75 oC and 98%RH.In addition,a one-dimensional chain nickel oxalate compound Ni2?C2O4?4(C5N2H14)2·H2O?5?was synthesized using1-methylpiperazine as the structural agent.Compound 5 has a proton conductivity of 7.54×10-3 S cm-1 at 75 oC and 98%RH.The single crystal structure indicates the presence of free water molecules in the structure,which provide pathways for proton conduction. |
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