Akademik Veri Yönetim Sistemi
4th INTERNATIONAL GRADUATE RESEARCH SYMPOSIUM – IGRS’25, İstanbul, Türkiye, 12 - 14 Mayıs 2025, ss.10-20, (Özet Bildiri)
Aim
Fuel cells have emerged as promising next-generation
electrochemical energy converters due to their high power density and low
emissions, making them attractive for transportation and stationary energy
applications
Fuel cells comprise various components, including the
bipolar plate and membrane electrode assembly. Due to its crucial role in
efficient thermal and electrical management, as well as ensuring proper gas
distribution and mechanical stability, the bipolar plate is one of the most
important components of the system
Graphite, traditionally used as a bipolar plate
material, requires a significant volume to achieve adequate mechanical
strength, which limits its application in compact fuel cell designs such as
automotive systems. To address this challenge, metal bipolar plates offer
superior mechanical properties, allowing more fuel cell units to be integrated
within the same volume. However, metal bipolar plates suffer from poor
corrosion resistance, requiring protective coatings to enhance their
durability. These coatings not only provide benefits in terms of
corrosion resistance but also have an impact on interfacial contact resistance
(ICR)
ICR is an electrical resistance that occurs at the
interface between two contacting surfaces in a fuel cell, such as between the
bipolar plate and the gas diffusion layer (GDL). It arises due to surface
roughness, material properties, and contact pressure
It has been observed that the ICR of coatings is not
typically included in simulations of metal bipolar plate PEM fuel cells. In
this study, The numerical model was first validated using data
from an experimental study, and then ICR values of three widely used coatings
were obtained from the literature and incorporated into the study. The results
were presented comparatively.
Material and Method
This study uses Ansys Fluent
PEM [6] modules to analyse the effect of ICR on PEM fuel cell performance.
Different coating materials are considered, and their influence on interfacial
resistance is examined through numerical simulations. The model incorporates
key electrochemical and transport phenomena within the fuel cell structure. The numerical model, which has also been used in
experimental studies in the literature
Figure 1. Mesh Structure of PEM Fuel Cell
The numerical model presented in Figure 1 was meshed
using Ansys Meshing
Parameters for numerical study were obtained from
the literature study used for validation
Table 1. Parameters
used in the PEM fuel cell simulation (Chen et al., 2021; L. Wang et al., 2003)
|
Parameters |
Value |
Ref |
|
Operating temperature (K) |
343 |
(L. Wang et al., 2003) |
|
Operating pressure (atm) |
2,7 |
(L. Wang et al., 2003) |
|
GDL porosity |
0,4 |
(L. Wang et al., 2003) |
|
CL porosity |
0,4 |
(L. Wang et al., 2003) |
|
Anode exchange coefficient |
0,5 |
(L. Wang et al., 2003) |
|
Cathode exchange coefficient |
2 |
(L. Wang et al., 2003) |
|
H2 reference diffusivity
(m²/s) |
1.10 × 10⁻⁴ |
(Chen et al., 2021) |
|
O2 reference diffusivity
(m²/s) |
3.23 × 10⁻⁵ |
(Chen et al., 2021) |
|
H2O reference diffusivity
(m²/s) |
7.35 × 10⁻⁵ |
(Chen et al., 2021) |
|
H2O reference
concentration(mol/m³) |
56,4 |
(L. Wang et al., 2003) |
|
O2 reference concentration
(mol/m³) |
3,39 |
(L. Wang et al., 2003) |
|
Equivalent weight of membrane (kg/kmol) |
1100 |
(Chen et al., 2021) |
The
numerical analyses were conducted at 343 K and 2.7 atm pressure, in accordance
with the experimental study used for validation. The current density-voltage
curve reflects the general electrochemical behavior of the fuel cell and serves
as a fundamental tool for validation, enabling a direct comparison between the
numerical and experimental performance
Figure 2. Validation using Data from Experimental Studies
When examining Figure 2, the analyses were
validated with a maximum error of 10% within the operating range of fuel cells,
which is between 0.5 V and 0.65 V
Figure 3. Interfacial Contact Resistance between GDL and Bipolar
Plate.
(ICR) assigned to the surfaces shown in Figure
3 vary depending on the coating material. The coating materials used in the
literature are CrN (Chromium Nitride), TiN (Titanium Nitride), and Ti/TiN
(Titanium/Titanium Nitride), and the corresponding contact resistance values
are presented in Table 2.
Table 2. ICR values
of coatings used in metal bipolar plates (Haghighat Ghahfarokhi et al., 2016;
Jannat et al., 2019; Lee et al., 2013)
|
Metal
Material |
Coating |
ICR
(mΩ·cm²) |
References |
|
SS316L |
CrN |
23 |
(Lee
et al., 2013.) |
|
SS316L |
TiN |
7,41 |
(Haghighat
Ghahfarokhi et al., 2016) |
|
SS316L |
Ti\TiN |
11 |
(Jannat
et al., 2019.) |
ICR of different coatings presented in Table 2 were
defined on PEM module. The results of the numerical analyses are presented in
the Findings section.
Findings
As shown in Figure 4, variations in ICR caused by
different coating materials influence fuel cell performance. In this study, numerical
analyses were conducted to examine how current density varies at a constant
voltage level depending on the ICR of the coating material.
Figure
4. Effect of Electrical Contact Resistance on the Voltage-Current
Density Curve
Figure 4 shows that the ICR of the coatings
significantly affects the fuel cell performance. The current density per unit
voltage has considerably decreased compared to the case without contact
resistance. Consequently, this has led to a significant reduction in the power
density per unit area of the single-cell PEM fuel cell.
At an operating voltage of 0.65 V, the current
density is 0.97 A/cm² without contact resistance. However, with the application
of a CrN coating, it decreases to 0.82 A/cm², while Ti/TiN and TiN coatings
result in reductions to 0.89 A/cm² and 0.91 A/cm², respectively.
In the absence of ICR the
power density was determined to be 0.63 W/cm² at an operating voltage of 0.65
V. However, due to ICR of the CrN coating, the power density decreased to 0.49
W/cm², while for the Ti\TiN and TiN coatings, it was observed to decrease to
0.57 W/cm² and 0.59 W/cm², respectively. This
indicates that the CrN coating has an effect of 24.62%, while the Ti\TiN and
TiN coatings have effects of 12.31% and 9.23%, respectively. Additionally, it is noted
that the impact of ICR becomes more evident at lower voltage levels (0.4 V -
0.6 V).
Conclusion
The conclusions of this
study emphasize the significant impact of ICR on coated metal bipolar plates in
fuel cells, affirming that the effect of coatings on ICR should not be
neglected, as observed in previous simulation studies. As the voltage decreases,
the impact of ICR becomes more pronounced, and its influence on the system
becomes increasingly significant. For CrN coating at 0.65 V, there is a 15.46%
decrease in current density and a 24% decrease in power density. For TiN and
Ti/TiN coatings, current density decreases by 6.19% and 8.25%, while power
density decreases by 9.23% and 12.31%, respectively. Furthermore, the results
indicate that the influence of the TiN coating is lower compared to the other
two coating types, suggesting that TiN is currently the most suitable coating
for metal bipolar plate fuel cells.