Journal of The Electrochemical Society, 163 (6) B185-B187 (2016) B185
0013-4651/2016/163(6)/B185/3/$33.00 © The Electrochemical Society
Effect of Deposition Conditions on Stability of PB Films at
PEMFC’s Operating Temperatures and pH
H. Akbari Khorami,
a,b, z
N. Jacobs,
c, *
P. Wagner,
c, *
A. Dyck,
c, *
P. Wild,
a,b
A. G. Brolo,
b,d, *
and N. Djilali
a,b, *, z
a
Department of Mechanical Engineering, University of Victoria, Victoria, BC V8W 2Y2, Canada
b
Institute for Integrated Energy Systems (IESVic), University of Victoria, Victoria, BC V8W 2Y2, Canada
c
NEXT ENERGY EWE-Forschungszentrum f¨ ur Energietechnologie e.V., Oldenburg, Lower Saxony 26129, Germany
d
Department of Chemistry, University of Victoria, Victoria, BC V8W 3P6, Canada
Optrodes based on Prussian blue (PB) are promising for hydrogen peroxide detection within PEMFCs to study the Membrane-
Electrode-Assembly degradation. The PB film is however required to sustain the harsh environment of PEMFCs. In this work, PB
films were deposited through different conditions and soaked in Phosphate-Buffer-Solutions with pH 2 at elevated temperatures for
a day. These PB films were characterized using FTIR to analyze their stability following PBS processing at operating temperature
and pH corresponding to an operating PEMFC. The PB film prepared using the single-source-precursor at the temperature of 60
◦
C
is found to be the most stable.
© 2016 The Electrochemical Society. [DOI: 10.1149/2.0301606jes] All rights reserved.
Manuscript submitted October 20, 2015; revised manuscript received February 1, 2016. Published February 25, 2016. This was
Paper 2162 presented at the Chicago, Illinois, Meeting of the Society, May 24–28, 2015.
Hydrogen peroxide (H
2
O
2
) is one of the chemical species asso-
ciated with degradation of the electrolyte membrane in PEMFCs.
1,2
Understanding the underlying degradation mechanisms requires H
2
O
2
sensors that function in the harsh environment of PEMFCs. Various
approaches proposed to date for sensing H
2
O
2
are reviewed in Botero
et al, Sensors and Actuators 2013.
3
Here we focus on sensing based
on Prussian blue (PB), ferric ferrocyanide, which has been success-
fully demonstrated as an indicator of H
2
O
2
.
4
However, PB film was
found to leach into the sensing test solution at the temperatures and
pH levels of an operating PEMFC, leading to an inconsistent sensing
behavior.
5
This paper presents an experimental study of the stabil-
ity of PB films deposited with alternative methods and at various
temperatures.
The presence of H
2
O
2
in PEMFCs has been detected by analysis of
the effluent condensate from the anode and cathode.
6–8
Two pathways
have been proposed for the formation of H
2
O
2
in PEMFCs. First,
oxygen reduction occurs at the cathode according to the reaction 1.
The alternative view is based on the crossover of oxygen from the
cathode to the anode side, which provides the oxygen needed to
react with hydrogen, and produces H
2
O
2
at the anode, reactions 2
and 3.
9
O
2
+ 2H
+
+ 2e → H
2
O
2
[1]
Pt + 1/2H
2
→ PtH [2]
2H
∗
+ O
2
→ H
2
O
2
[3]
Membrane degradation by H
2
O
2
has been investigated by introducing
Nafion membranes to H
2
O
2
solutions at 80
◦
C.
2,9
After H
2
O
2
process-
ing of Nafion, fluoride and sulfate ions (F
−
and SO
4
2−
) were detected
in the solution which are derived from the C-F bonds and the sulfonic
acid groups, respectively. Kinumoto et al. observed that the loss of
sulfonic acid groups of Nafion reduces the proton conductivity, and
the decomposition of the C-F bonds leads to membrane thinning and
the formation of pinholes.
2
Qiao et al. showed that the proton conduc-
tivity, water uptake and the water self-diffusion coefficient gradually
decrease with H
2
O
2
processing.
10
Furthermore, Nafion is used in the
catalyst layer to provide ionic conduction pathways. Therefore, de-
composition of Nafion inside the catalyst layer also causes a reduction
in the effective reaction area and increases the overpotential of the
cell.
2
∗
Electrochemical Society Member.
z
E-mail: hakbarik@uvic.ca; ndjilali@uvic.ca
For in situ detection of H
2
O
2
inside the fuel cell electrochemical
and spectroscopic techniques are preferred among other conventional
techniques such as titrimetric, colorimetric, and gasometric because of
the challenges involved in in situ detection of H
2
O
2
. These challenges
comprise the low concentration of H
2
O
2
, lack of space for insertion of
a sensor into a cell, the corrosive environment, and the electrochemical
noises inside a cell.
To date, the only report of in situ detection of H
2
O
2
is based on
an electrochemical method in which, Pt wires were used as electrodes
to detect H
2
O
2
in a PEMFC.
10
These sensors were able to detect
H
2
O
2
in the fuel cell but were not able to measure concentrations.
The applicability of this or any other amperometric sensors in this
application is limited by interference effects from the electrical fields
created by fuel cell operation. The currents in fuel cells are a potential
source of electromagnetic noise which can induce currents in the Pt
wires, based on Faraday’s law of induction, leading to inaccurate
measurements.
Recently, optrodes have been demonstrated for in situ sensing
of temperature and relative humidity in PEMFCs.
11,12
Optrodes are
well-suited to this application because their small size allows high
spatial resolution and minimally disruptive access to the fuel cell.
Furthermore, optical signals do not interfere with electrochemical
processes in the fuel cell and are immune to electromagnetic inter-
ference. In addition, the fiber material (i.e. silica glass) is compat-
ible with the electrochemically active environment inside the fuel
cell.
In a recent study, the authors developed a H
2
O
2
optrode based
on chemical deposition of PB onto the tip of an optical fiber.
13
The
sensor detects H
2
O
2
in a spectroscopic manner based on the oxida-
tion of Prussian white (PW), PB reduced state, to PB in presence of
H
2
O
2
, reaction 4, and evaluation of corresponding changes of the re-
flected light from the optrode. This sensor responds reliably to H
2
O
2
concentrations in aqueous solutions at room temperature. However,
the sensor responses are not consistent at higher temperatures which
is likely attributed to leaching of the PB film into the sensing test
solution.
K
4
Fe
4
Fe(CN )
6
3( PW)
+ 2 H
2
O
2
→
←
Fe
4
Fe(CN )
6
3( PB)
+ 4 OH
−
+ 4 K
+
[4]
In the present work, we want to address the stability of PB films
at elevated temperatures. PB films were deposited on glass mi-
croscopy slides at different condition. The samples were immersed
in Phosphate-Buffer-Solution (PBS) at elevated temperature and low
pH to investigate the film stability in environment similar to that in an
operating fuel cell. These PB films were characterized using Fourier
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