Abstract
Polyaniline-metal organic framework (PANI/Fe-BTC) composites were prepared by oxidative polymerization of aniline in the presence of Fe-BTC, using various monomer:Fe-BTC ratios. Introduction of Fe-BTC into polyaniline-based materials led to significant reduction of their thermal stability starting from 2 wt% Fe-BTC content, which further decreased with decreasing monomer concentration in the initial reaction mixture.
Fe-BTC being a low conducting component (2 x 10(-10) S cm(-1)) in comparison to PANI (6 S cm(-1)) was found to negatively affect conductivity of PANI/Fe-BTC composites. Conductivity values gradually lowered with the decrease of aniline fraction in the polymerization mixture: from 4 S cm(-1) for the composite prepared with 80 wt% of the monomer in the reaction mixture to 0.04 S cm(-1) for the 20 wt% of the monomer.
Decreasing aniline fraction during the materials preparation resulted in a smaller amount of PANI particles on the surface of Fe-BTC. When aniline concentration reached 20 wt%, the morphology of the composite was similar to the one of pristine Fe-BTC.
These PANI particles were found to be mainly determining specific surface area of PANI/Fe-BTC composites due to the fact that specific surface area of the products decreased with decreasing monomer fraction from 55 m(2) g(-1) for pristine PANI to 8 m(2) g(-1) for PANI(20%)/Fe-BTC. XRD data showed that the composition of PANI(20%)/Fe-BTC material corresponds to a saturation point, after which aggregation of PANI chains occurs.
Spectroscopic analysis revealed that PANI on the Fe-BTC interface is overoxidized and partially doped by Fe-BTC. These PANI-Fe-BTC interactions were found to affect electrochemical properties of the composites.
Materials prepared using lower monomer fraction in the initial reaction medium were characterized by more favorable reduction transitions which happened at more positive potentials. Increasing aniline:Fe-BTC ratio was also found to enhance gravimetric capacitance of the composites, reaching 346 F g -1 at 20 mV s -1.
Moreover, improved pseudo-Faradaic current response and substantially better reversibility during electrochemical characterization shown for PANI/Fe-BTC compared to pristine PANI can be advantageous for energy applications.