| The non-renewable nature of fossil energy makes humans face serious energy problems.As an important category in fuel cells?FCs?,proton exchange membrane fuel cells?PEMFCs?are considered as the high-efficiency form of green energy technology.Proton conductors are one of the core components of the PEMFCs.At present,commercial proton conductors,Nafion membranes,have been used in some applications due to their high proton conductivity,excellent mechanical properties and recyclability.However,Nafion membranes are still limited due to their high costs,complex manufacturing processes and restricted working conditions?60-80? and need high humidity,etc.?,what's more important is that its amorphous structure hinders researchers from further revealing the mechanism of proton conduction,leading to limited research on improving performance.Therefore,solid-state proton conductive materials with high crystallinity have recently received continuous attention.The high crystallinity of these materials helps people to deepen their understanding of the mechanism of proton conduction,thereby,which can provided advantages for the development of new proton conductors with high proton conductivity.Findings from literature research:we know that the introduction of uncoordinated carboxyl groups with high acidity and strong hydrophilic into metal organic frameworks materials?MOFs?is beneficial to the proton conduction property,since-COOH groups can provide a lot of protons and form high-density hydrogen bond network as the proton transmission pathway.Inspired by this,we hope to use ferroceneyl carboxylate frameworks materials?FCFs?constructed by proton carriers to conduct proton conductivity research directly.The reason are:first,the introduction of ferrocene radicals has greatly improved the thermal and water stability of the corresponding carboxylic acids,laying a foundation for conducting proton conduction research,second,the presence of free carboxyl groups in the framework will improve the proton conductivityThe main work in this paper is as follows:1.The following 8 kinds of crystalline hydrogen-bonded ferrocene carboxylic acid frameworks materials?FCFs?were synthesized and cultivated according to the early literature:[FcCO?CH2?2COOH]?FCF 1??Fc=??5-C5H5?Fe??5-C5H4??,{[HOOC?CH2?2OC]Fcc[CO?CH2?2COOH]}?FCF 2??Fee=??5-C5H4?Fe??5-C5H4??,[FcCOOH]?FCF 3?,[?HOOC?Fcc?COOH?]?FCF 4?,[FcCCH3CHCOOH]?FCF 5?,[FcCO?o-C6H4COOH?]?FCF 6?,[m-FcC6H4COOH]?FCF 7?and[p-FcC6H4COOH]?FCF 8?.FCFs 1,3,5-8 are mono-substituted ferrocene carboxylic acid derivatives,FCFs 2 and 4 are di-substituted ferrocene carboxylic acid derivatives.In FCF 2,two substituents?-CO?CH2?2COOH?are located at positions 1 and 3' on the two cyclopentadienyl?Cp?rings,respectively.In FCF 4,two substituents?-COOH?are located at positions 1 and 1' on the two Cp rings,respectively.Structural testing shows:In the frameworks of FCFs 1-8,there are abundant intermolecular forces such as intermolecular hydrogen bonds and ?...? stacking forces on adjacent metallocene rings,especially in the framework of FCF 2,there are intramolecular hydrogen bonding forces.2.We can know that FCFs 1-8 have high structural stability by Thermogravimetric analysis?TG?,X-ray powder diffraction analysis?PXRD?and scanning electron microscope?SEM?.We also investigated the ability of FCFs 1-9 to adsorb water molecules and their specific surface areas through water vapor and Nitrogen adsorption-desorption isotherms.3.The study of proton conduction of FCFs 1-8 were operated at different relative humidity?RHs??53%-98%RH?and temperature?30-100??.We found that the proton conductivities of FCFs 1-8 increases with RH and temperature.At 100? and 98%RH,the proton conductivities of FCFs 1-8 reached the optial value,which are 1.17 × 10-1 S·cm-1,1.14 × 10-2 S·cm-1,1.01 × 10-2 S·cm-1,1.99 × 10-5 S·cm-1,1.58 ×10-3 S·cm-1,7.70 × 10-4 S·cm-1,1.94 × 10-4 S·cm-1,3.46 × 10-3 S·cm-1 and 1.23 × 10-2 S·cm-1,respectively.The above data show that such ferroceneyl carboxylate frameworks materials have good proton conductivity.Further,the proton conduction mechanism and the reasons for the differences in proton conductivity of FCFs 1-8 were explored using the calculation of activation energy,structural analysis and carboxyl substitution,etc.Finally,we confirmed that the structures of FCFs 1-8 did not change significantly after the proton conduction test through X-ray powder diffraction analysis and scanning electron microscopy characterization... |
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