Anode Catalyst Development for Polymer Electrolyte
Membrane Fuel Cells
Noramalina Mansor1, Rhodri Jervis1, Christopher Gibbs2, Dr. Daniel Brett1
1Chemical
Engineering Department, UCL, London WC1E 7JE
2Amalyst Limited, 97 Tottenham Court Road, London W1T 4TP
Results
Introduction
e-
e-
e-
e-
ee-
e-
Current
Collector
Anode
Catalyst
2.0
H2O
Membrane
E / mV vs RHE
20
30
40
50
60
-1.6
Catalyst
j0ECSA
mV dec-1
mA cm-2geo
mA cm-2ECSA
Pt
28
1.64
0.12
Amalyst
39
1.51
0.43
Pt
Amalyst
-2.4
0.0
Cathode
Catalyst
Tafel
slope
j0
-2.0
0.0
H2O,
H2
GDL
2H2O
H+
-1.2
1.0
O2
inlet
0.1
0.2
0.3
0.4
E/V vs RHE
O2 + 4H+ 4e-
2H2
4H+ + 4e-
H2
inlet
Pt
Amalyst
The results show that Amalyst is at
least as active as commercial Pt at a
lower cost.
The results are reproducible with
several batches of Amalyst.
Figure 3. HOR polarisation curves for Pt and
Amalyst at 1600 rpm in H2 saturated 0.1 M
HClO4. Inset: corresponding Tafel plot.
H2O,
O2
GDL
Table 1. Tafel slope and exchange current
densities of Pt and Amalyst
The kinetic current (ik) at various potentials were extracted using LevichKoutecky analysis (Figure 4A) and normalised to the mass of the catalyst. The
plot on Figure 4(B) shows that the mass activity of Amalyst is better than Pt at
all potentials.
Current
Collector
Figure 1. A schematic diagram of PEM fuel cell operation. The membrane, catalyst layers and gas
diffusion layers (GDL) collectively make up the membrane electrode assembly (MEA).
A
The need to focus on alternative anode catalyst development is due to the
following reasons:
B
0.015 V
1.1
Pt
0.035
1.0
Amalyst
0.9
-1
j / (mA cm )
-2 -1
geo
• Because of hydrogen supply and storage issues, it is more appropriate to
use reformate fuel for practical applications. However, Pt is poisoned by CO
in reformate fuel leading to non-negligible performance degradation;
• The limited natural reserves of Pt and increasing demand means that its
price is high and volatile.
0.020 V
0.8
0.030
E / V vs RHE
e-
3.0
j/mA cm-2
geo
The PEM fuel cell is a promising candidate as an alternative energy conversion
technology for stationary, portable and automotive applications. It allows the
conversion of hydrogen and oxygen to produce electrical current and water as
the only by-product.
1. Hydrogen Oxidation Reaction
The hydrogen oxidation reaction (HOR) was analysed by rotating disk
electrode technique, using commercial Pt (Alfa Aesar) as a comparison.
log jk/A cm-2
The aim of this work is to develop a cost-effective, non-platinum electrocatalyst
for polymer electrolyte membrane (PEM) fuel cell, specifically for the anode.
0.025 V
0.7
0.030 V
0.035 V
0.6
Limiting
current
0.5
0.025
0.020
0.4
0.015
0.3
0.025
0.030
0.035
0.040
0.045
0.050
0.1
0.2
-1/2 / rpm-1/2
0.4
0.5
0.6
0.7
0.8
Mass Activity / A mg-1
Figure 4. (A) Levich-Koutecky plot at various potentials obtained from HOR polarisation curves of
Amalyst at rotation rate (ω) 400 – 1600 rpm. (B) Mass activity plot of Amalyst and Pt.
2. CO Tolerance
The onset potential of the CO
oxidation peak is an indicator of the
activation energy needed to remove
CO from the surface. Amalyst has a
smaller onset potential compared to
Pt, as shown in Figure 5. In addition,
on the hydrogen region, only 82% of
Amalyst catalytic sites are poisoned
compared to 100% in Pt. These
suggest that Amalyst has better CO
tolerance.
1.2
Figure 2.
TEM image of Amalyst nanoparticles
on carbon support
1.2
0.8
Voltage / V
0.6
0.797 V
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
E / V vs RHE
Figure 5. The anodic CO stripping voltammetry
after CO saturation at 0.018 V in 0.1 M HClO4.
V-I polarisation curve
Power density
0.4
0.8
0.3
0.6
0.2
0.4
0.1
0.2
Single-cell MEA test was performed on the Scribner 850 system. The MEA was
fabricated by direct spray of catalyst onto a GDL followed by hot pressing onto
a Nafion membrane. A commercial Pt coated GDL (Johnson Matthey) was
used as a cathode.
Platinum
Amalyst
0.5
1.0
Ex-situ electrochemical measurements were performed in a conventional
three-electrode electrochemical cell (Adams & Chittenden) with Pt counter
electrode and hydrogen reference electrode (Gaskatel, 0 V vs. RHE). A known
amount of catalyst was deposited onto a glassy carbon working electrode.
0.877 V
1.0
j / mA cm-2
geo
A low-cost, non-platinum, alloy catalyst (Amalyst) on carbon support was
synthesised via a standard reduction impregnation method followed by thermal
activation.
0.0
Power Density / W cm-2
Materials & Methods
The physical characteristic of the
catalyst was analysed using
Transmission Electron Microscopy
(TEM) as shown in Figure 2. The
Amalyst
nanoparticles
are
dispersed as spherical and uniform
dark spots on the surface of the
carbon, however agglomerates
were also found sporadically in the
sample (not shown). The estimated
average particle size is 15 nm.
0.3
0.0
0
100
200
300
400
500
600
700
Current Density / mA cm-2
Figure 6. Single-cell (10.9 cm2) H2/O2 performance of
Amalyst anode and commercial Pt cathode at 80oC with
100% relative humidity.
3. Single-cell MEA
The single-cell polarisation
curve
in
Figure
6
demonstrates that Amalyst is
effective in a real fuel cell
environment, producing an
open current voltage (OCV) of
0.96 V and high power
density. Further work is
needed to optimise the
electrode.
Conclusions & Future Work
• Developing an alternative anode catalyst will help mitigate hydrogen storage
and supply issue as well as the high cost and limited supply of Pt;
• Overall, Amalyst is a promising low-cost, alternative anode catalyst for PEM fuel
cell;
• The hydrogen oxidation activity of Amalyst was found to be comparable to
commercial Pt;
• On-going work: corroboration
characterisation within MEA; and
• Preliminary CO stripping experiment indicate that Amalyst has better CO
tolerance;
• Future work: measure binding energies and kinetics of CO adsorption on
Amalyst; and a techno-economic analysis.
noramalina.mansor.09@ucl.ac.uk
+44(0)207 679 7683
www.ucl.ac.uk/centre-for-co2-technology
of
ex-situ
measurements
with
in-situ