Nowadays,
although research of proton conductive materials has
been extended from traditional sulfonated polymers to novel crystalline
solid materials such as MOFs, COFs, and HOFs, research on crystalline
ferrocene-based carboxylate materials is very limited. Herein, we
selected two hydrogen-bonded and π–π interactions-supported
ferrocenyl carboxylate frameworks (FCFs), [FcCO(CH2)2COOH] (FCF 1) and [FcCOOH] (FCF 2) (Fc = (η5-C5H5)Fe(η5-C5H4)) to fully investigate their water-mediated
proton conduction. Their excellent thermal, water, and chemical stabilities
were confirmed by the means of thermogravimetric analyses, PXRD, and
SEM determinations. The two FCFs indicate temperature- and humidity-dependent
proton conductive features. Intriguingly, their ultrahigh proton conductivities
are 1.17 × 10–1 and 1.01 × 10–2 S/cm, respectively, under 100 °C and 98% RH, which not only
are comparable to the commercial Nafion membranes but also rank among
the highest performing MOFs, HOFs, and COFs ever described. On the
basis of the structural analysis, calculated E
a value, H2O vapor adsorption, PXRD, and SEM measurements,
reasonable conduction mechanisms are highlighted. Our research provides
a novel inspiration for finding new high proton conducting crystalline
solid materials. Importantly, the outstanding conducting performance
of 1 and 2 suggests their, hopefully, potential
in fuel cells and related electrochemical fields.
This work reports the design and fabrication of a proton conductive 2D metal-organic framework (MOF), [Cu(p-IPhHIDC)] (1) (p-IPhH IDC=2-(p-N-imidazol-1-yl)-phenyl-1 H-imidazole-4,5-dicarboxylic acid) as an advanced ammonia impedance sensor at room temperature and 68-98 % relative humidity (RH). MOF 1 shows the optimized proton conductivity value of 1.51×10 S cm at 100 °C and 98 % RH. Its temperature-dependent and humidity-dependent proton conduction properties have been explored. The large amount of uncoordinated carboxylate groups between the layers plays a vital role in the resultant conductivity. Distinctly, the fabricated MOF-based sensor displays the required stability toward NH , enhanced sensitivity, and notable selectivity for NH gas. At room temperature and 68 % RH, it gives a remarkable gas response of 8620 % to 130 ppm NH gas and lower detection limit of 2 ppm towards NH gas. It is also found that the gas response of the ammonia sensor increases linearly with the increase of NH gas concentration under 68-98 % RH and room temperature. Moreover, the sensor indicates excellent reversibility and selectivity toward NH versus N , H , O , CO, CO , benzene, and MeOH. Based on structural analyses, activation energy calculations, water and NH vapor absorptions, and PXRD determinations, proton conduction and NH sensing mechanisms are suggested.
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