The development of sustainable functional materials with
strong
potential to be applied in different areas has been growing and gaining
increasing interest to address the environmental impact of current
materials and technologies. In this scope, this work reports on sustainable
functional materials with electrochromic properties, based on their
increasing interest for a variety of applications, including sensing
technologies. The materials have been developed based on a natural
derived polymer, carrageenan, in which different amounts of the ionic
liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN])
were blended. It is shown that the addition of different amounts of
IL to the carrageenan matrix does not affect the properties of the
samples in terms of morphology or physicochemical and thermal properties,
the most significant difference being the increase of the ionic conductivity
with increasing IL content, ranging from 2.3 × 10–11S·cm–1for pristine carrageenan to 4.6 ×
10–4S·cm–1for the samples
with 5 and 60 wt % IL content, respectively. A electrochromic device
has been developed based on the different IL/carrageenan samples as
electrolyte and poly(3,4-ethylenedioxythiophene) polystyrenesulfonate
(PEDOT:PSS) as electrodes. Spectroelectrochemistry testing demonstrates
functional devices at low voltages between 0.3 and −0.9 V.
Among the different samples, the one with 15 wt % IL content presents
the best conditions for application, presenting an oxidation time
of 6 s, a reduction time of 8 s, and a charge density of 1150 and
1050 μC·cm–2for oxidation and reduction,
respectively. The same sample also presents excellent optical density
as a function of load density, presenting an optical switch (Δ%Tx) of 99%. Thus, it is demonstrated that it is possible
to develop high efficiency and sustainable electrochromic devices
based on natural polymers and ionic liquids.