| Proton exchange membrane fuel cells(PEMFCs)are renewable energy sources with high energy density and environmental protection.As the core devices of PEMFCs,the performance of pemfcs has a decisive impact on the working efficiency of pemfcs.In recent years,a variety of proton-conducting materials reported in the literature have made breakthrough progress in the study of proton conduction properties under different conditions.However,these materials exhibit excellent conductivity,and the internal structure of the materials is not clear,which makes the conduction mechanism of the materials unclear and the hydrogen bond transmission path vague.Therefore,clarifying the proton transfer path and the reason,and improving the proton conductivity of the complex material based on it,are currently one of the important issues to be solved in this research field.The crystal material of the complex can be subjected to structural analysis by X-ray crystallography,and accurate atomic ordering and intermolecular interaction force can be obtained.In the application of proton conducting materials,it is possible to visualize proton transport paths.On this basis,this paper is committed to the use of N-containing polycarboxylic acid ligands,the use of hydrothermal synthesis with different two-dimensional structure of the complex crystal materials and their in-situ encapsulation of modified materials.The X-ray crystallography structure analysis of the complex was performed,and the proton conductivity was measured.The relationship between the structure and proton conductivity was studied,and the conduction path was simulated,which provided an experimental and theoretical method for the study of proton conductor.Two polycarboxylate ligands containing nitrogen heterocycles were selected to react with Co(II)and Ni(II)respectively,and five crystalline complex materials and nine modified materials were obtained.The composition,structure and proton conductivity of the obtained materials were studied,and the proton transfer path was simulated by theoretical calculation.The specific research contents are as follows:(1)Synthesis,structural analysis and proton conduction properties of the complexes 1-3based on pyrazinedioic acid ligand.4,4’-(2,6-pyrazinediyl)dibenzoic acid(H2L~1)was chosen as the main ligand and the transition metal Co(II)was used to construct the complex crystal material.Under the regulation of auxiliary ligands(4,4’-azopyridine(dpa)and 1,1’-[1,4-phenylene bis(methylene)]bis(1H-1,2,4-triazole)(bit)),three complex crystalline materials(1-3)were obtained.PXRD,IR and structural characterization and analysis of 1-3 indicated that the three complexes had different structures and interlayer acting forces,and all had coordination water molecules as proton donors,which conformed to the basic characteristics of proton conductor materials.Besides,the electrostatic potential and nucleophilic index were analyzed by MS,and the possible proton transport paths were simulated.Compared with the pure Nafion membrane material,the conductivity of Complex 1 is increased by 76.77%at 303 K and 34.78%at 333 K.The activation energy of 0.27 e V is lower than that of pure Nafion membrane(0.32 e V).The conductivity of complex 2 increases by 189.3%at 303 K,which is the optimal proton conductivity in complex 1-3.At 333 K,the conductivity is increased by 82.02%and activation energy is 0.21 e V which lower than that of complex 1.The conductivity of complex 3 increases by 149.3%at 303 K,which is slightly lower than that of complex 2;At 333 K,the conductivity increased by 94.89%and activation energy is 0.18 e V,which is the lowest activation energy in complex 1-3.Through the analysis of MS electrostatic potential and nucleophilic index,it is simulated that the proton of complex 1 may transport along the path of C6→O5,C9→O3,C10→O4,O5→O2,O5→O3.The proton of complex 2 might be transported by the route of C7→O4,C9→O5,C10→O2.The proton of complex 3 might be transported by the route of C19→N4,O5→O3,O6A→O1,O6A→O4.(2)Synthesis,structure analysis and proton conduction properties of the complexes 4-5based on triazine tricarboxylic acid ligand.The 4,4’,4’-(1,3,5-triazine-2,4,6-tris)tribenzoic acid(H3L~2)ligand was selected to obtain complex crystal materials 4 and 5 under the regulation effect of metal ions Co(II)and Ni(II).PXRD,IR and structural characterization and analysis were performed on the crystal materials 4 and 5,which indicated that the two complexes had different structures and interlayer acting forces,and both had non-deprotonated carboxyl groups as proton donors,which met the basic characteristics of proton conductor materials.Besides,the electrostatic potential and nucleophilic index were analyzed by MS,and the possible proton transport paths were simulated.Compared with the pure Nafion membrane material,the conductivity of complex 4 is improved by 527.4%at 303 K,and it is the material with the optimal proton conductivity among the five crystal materials synthesized in this paper.At 333 K,the activation energy is increased by 251.7%and 0.32 e V,which is the same as that of pure Nafion membrane.The conductivity of complex 5 increased by 517.0%at 303 K,which was slightly lower than that of complex 4 but better than that of complex 1-3;At 333 K,the conductivity increased by162.3%and activation energy is 0.14 e V,which is the lowest activation energy of the five crystalline materials synthesized in this paper.Through the analysis of MS electrostatic potential and nucleophilic index,it is simulated that the proton of complex 5 may transport along the route of C04T→O21,C04X→O21,C115→O22.The proton of complex 5 may be transported by the route of C04T→O21,C04X→O21,C115→O22.(3)In-situ encapsulation material,structure analysis and proton conductivity study based on complex 4.It was found that the proton conductivity of complex 4 was the best among all the materials,but the activation energy was not the lowest.Therefore,complex 4 was selected as the base material for modification,and nine in-situ encapsulation materials including 4@2-aminophenol,4@3-aminopyridine,4@L-tartaric acid,4@Kuketo acid,4@imidazole,4@dicyandiamide,4@salicylic acid,4@tetrahydroxydiborane and 4@sodium acetate were obtained.The proton conductivity and activation energy of nine materials were measured.Compared with pure Nafion membrane and complex 4,the effects of different small molecular structures on proton conductivity were analyzed.Within the test range of 303 K～333 K,compared with pure Nafion,the conductivity at303 K is increased by:4@2-aminophenol:24.11%;4@3-aminopyridine:13.03%;4@L-tartaric acid:288.5%;4@Kuketo acid:242.8%;4@imidazole:177.9%;4@dicyandiamide:296.0%;4@salicylic acid:262.9%;4@tetrahydroxydiborane:8.474%;4@sodium acetate:725.8%;At 333 K increased by:4@2-aminophenol:-6.958%;4@3-aminopyridine:-20.70%;4@L-tartaric acid:85.49%;4@Kuketo acid:64.50%;4@imidazole:40.18%;4@dicyandiamide:61.07%;4@salicylic acid:29.90%;4@tetrahydroxydiborane:-11.02%;4@sodium acetate:220.8%.Through comparison,it was found that only 4@sodium acetate,with its proton conductivity increased and activation energy decreased,was a qualified modified material.In summary,9 kinds of modified materials including 5 kinds of nitrogen-containing polycarboxylic acid ligand complexes and complex 4 were obtained by structural adjustment,and their crystal structures and proton conduction properties were studied.The proton transport path of the obtained complex material was simulated by using the ESP charge calculation and nucleophilic index analysis of MS it is hoped that the method in this paper can provide ideas for the design and development of high-performance proton-conducting materials and the exploration of proton conduction mechanism. |
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