An electronic structure investigation of PEDOT with AlCl4- anions, a promising redox combination for energy storage applications
arxiv(2023)
摘要
The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the
most researched materials. The 1980s bipolaron model remains the dominant
interpretation of the electronic structure of PEDOT. Recent theoretical studies
have provided updated definitions of key concepts such as bipolarons or polaron
pairs, but these have not yet become widely known. In this work, we use density
functional theory to investigate the electronic structure of PEDOT oligomers
with co-located AlCl4- anions, a promising combination for energy storage. By
considering the influence of oligomer length, oxidation or anion concentration
and spin state, we find no evidence for self-localisation of positive charges
in PEDOT as predicted by the bipolaron model at the hybrid functional level.
Our results show distortions that exhibit either a single or a double peak in
bond length alternations and charge density. Either can occur at different
oxidation or anion concentrations. We note that other distortion shapes are
also possible. Rather than representing bipolarons or polaron pairs in the
original model, these are electron distributions driven by a range of factors.
Localisation of distortions occurs with anions, and distortions can span an
arbitrary number of nearby anions. Conductivity in conducting polymers has been
observed to reduce at anion concentrations above 0.5. We show at high anion
concentrations, the energy of the localised, non-bonding anionic orbitals
approaches that of the system HOMO due to Coulombic repulsion between anions.
We hypothesize that with nucleic motion in the macropolymer, these orbitals
will interfere with the hopping of charge carriers between sites of similar
energy, lowering conductivity.
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