Microbial Cellulose (MC) is a highly porous macromolecule
with intrinsic
properties that make it a useful substrate for conductive materials within ultracapacitors.
MC has the potential to increase capacitance by serving as a high surface area substrate
for conductive polymers and carbonaceous materials. Electrode surface area is a critical
parameter in ultracapacitors because capacitance depends on the available active sites
that are accessible to counter ions. Commercial ultracapacitors increase electrode surface
area by adding microsize carbonaceous materials. Most commercial devices also require
adhesive compounds to bind the conductive material to the substrate. Adhesive
compounds increase sheet resistance and hinder overall capacitance. MC membranes
possess highlyordered surface hydroxyl groups that readily bind to different types
conductive materials and reduce the need for additive adhesive compounds. This thesis
investigates three unique methods for converting a MC membrane into a working
ultracapacitor electrode. In the first method, polypyrrole and carbon nanotubes (CNTs) are added to a
medium of Acetobacter that incorporates the material into a homogeneous crystalline
matrix of beta1,4 glucan chains. The resulting MC is a fully integrated membrane with a
homogeneous embedded layer of conductive material. SEM imaging shows the
conductive material is incorporated primarily at the core of the membrane. As a result,
this electrode suffered from high sheet resistance and did not generate any significant
capacitance. In the second method, a conductive ink consisting of CNTs, carboxymethyl
cellulose (CMC), polypyrrole, and DI water was used to coat the surface of a dried
cellulose membrane. After 12 hours, the ink dries and leaves a shiny black conductive
layer on the membrane’s surface. CMC’s role in the ink is to increase viscosity and help
bind the conductive material to the membrane surface. CMC is also a dielectric material
that acts as an insulator to the polypyrrole and CNTs, and ultimately impedes electrical
energy storage. In the final method, a MC membrane was soaked in aqueous and non
aqueous pyrrole solutions, and polymerized with FeCl3 and Fe2(SO4)3. Single and double
membrane device configurations were also investigated. Surface polymerization of
pyrrole monomers proved to be the best method for converting microbial cellulose into a
working electrode with good capacitance and cyclability. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2011-12-4789 |
| Date | 17 February 2012 |
| Creators | Young, Nathaniel James |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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