Broad Street Scientific Journal 2020

ode. As it is reduced, protons are consumed, and thus the
local pH becomes basic. The basic pH leads to the capture
of carbon dioxide as a bicarbonate ion because this capture
proves sensitive to subtle pH changes. At the other end of
the cell, quinone is reduced, releasing protons, decreasing
the pH, and regenerating carbon dioxide gas from bicarbonate
ions, that then exits the cell. Carbon dioxide is the
only gas that exits; nitrogen, water, or oxygen are not impacted
by pH changes and do not cross the cell [3].
Unfortunately, although a quinone couple has been
demonstrated to work in a fuel cell to help transfer carbon
dioxide across a membrane, it is not a perfect solution.
Quinones have negative impacts on the environment and
enter largely as air pollutants; since the goal of the fuel cell
is environmental remediation, there has been a push to
move away from using quinones in practical applications
in this technology [4]. Additionally, a species in a common
quinone couple, hydroquinone, is a suspected carcinogen
[5], prompting a search for a more environmentally friendly
option that has similar redox behavior. One compound
that has been singled out for its quinone-like properties is
sesamol [4]. Isolated from sesame seeds, sesamol is unlikely
to have a negative impact on the environment. It is composed
of a fused ring structure, and has a hydroxyl group
attached to the benzene ring. Sesamol’s redox mechanism
is shown in Figure 2 and is slightly more complex than
that of a quinone; the reaction is quasi-reversible. The first
step of the reaction is irreversible, but it creates a quinone
structure (2-hydroxymethoxybenzoquinone or 2-HMBQ)
that then undergoes a second reduction reaction (to form
2-hydroxymethoxyhydroquinone or 2-HMHQ). This second
reaction is reversible, and largely mimics a quinone’s
redox behavior in that it transfers a proton as well [6].
Figure 2. Scheme proposed for the oxidation of sesamol
in aqueous solutions, forming 2-hydroxymethoxybenzoquinone
that undergoes further reduction.
This project aims to identify sesamol as a more environmentally
friendly alternative to quinones in a fuel cell
used for the separation of carbon dioxide from other gases.
First, sesamol’s quasi-reversible reaction was studied
through cyclic voltammetry in sodium bicarbonate and
saturated with both argon and carbon dioxide to examine
if conditions present in a fuel cell would fundamentally alter
the mechanism of the reaction. Two peaks corresponding
to the reversible redox reaction appeared upon repeated
sweeps, demonstrating that a reversible reaction begins
to occur after an irreversible step. Next, it was confirmed
that sesamol undergoes a PCET reaction; this was accomplished
through the use of half-cell liquid-phase testing,
which saw an increased current and gas evolution when
in sodium bicarbonate and saturated with carbon dioxide.
Finally, sesamol was used as a redox mediator in a fuel cell
and carbon dioxide transport across the cell was achieved.
2. Materials and Methods
2.1 – Materials
The polypropylene membrane, Celgard 3501 was a generous
gift from Celgard (Charlotte, NC). The Toray Carbon
Paper 060 electrode was purchased from The Fuel Cell
Store. Gases were industrial grade purchased from Airgas.
All other chemicals were purchased from Sigma-Aldrich,
and used without further purification.
2.2 – Cyclic Voltammetry
Cyclic voltammetry was performed on 10 mM 2,6-dimethylhydroquinone,
10mM 2,6-dimethylbenzoquinone,
and 1mM sesamol with 0.5 M sodium bicarbonate as the
analyte solution using an eDAQ potentiostat (ER466) and
a three electrode arrangement. The concentration of sesamol
was decreased in order to better examine each peak
that appeared. Each trial was performed in a 4 mL conical
vial. The reference electrode was silver/silver chloride, the
counter electrode was platinum/titanium, and the working
electrode was glassy carbon. The working electrode
was polished with a 0.3μM alumina suspension, and then
rinsed with acetone and water. The reference and counter
electrodes were rinsed with acetone and water. The
electrodes were all cleaned between each trial. Solutions
that were saturated with gas underwent 10 minutes of gas
sparging with argon gas, and then 10 more minutes of
sparging with carbon dioxide gas, as necessary. The pH of
each sample was measured with a Vernier pH Probe. Each
trial consisted of three sweeps in total, measuring the continued
electrochemical response of each sample. The scan
rate was 100mV/s for each trial, and data were collected
from -1.0V to 1.5V.
2.3 – Half Cell Liquid Phase Testing
Half-cell testing was performed in a 4 mL conical vial.
The working electrode was a 1cm by 3cm Toray Carbon
Paper 060 electrode (Fuel Cell Store), the reference electrode
was silver/silver chloride, and the counter electrode
was platinum. The carbon paper electrode was rinsed with
acetone and water between each trial, as were the counter
and reference electrodes. The catalyst was added from a
10mg/mL solution of 20% wt. platinum on carbon black
in methanol, which was drop-casted onto the carbon pa-
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