Lightweight Magnesium Bipolar Plates

Jihyun Kim, Bosun Jang, Taesong Lee and Sejin Kwon*
Lightweight Magnesium Bipolar Plates of Direct
NaBH4/H2O2 Fuel Cell for AIP Application
DOI 10.1515/tjj-2015-0031
Received July 4, 2015; accepted July 13, 2015
Abstract: Fuel cell based power systems have high energy
density. However, using H2 gas as fuel and O2 as oxidizer
in aerospace, UAV or underwater like an AIP (Air
Independent Propulsion) environment has restrictions in
terms of efficient storage. The direct borohydride hydrogen
peroxide fuel cell (DBPFC) which uses aqueous NaBH4
solution as fuel and H2O2 solution as oxidizer has great
advantages over the H2/O2 fuel cell in terms of storage
efficiency, energy density and power density. These excel-
lent characteristics make the DBPFC an appropriate power
source and propulsion system for AIP systems. In this
study, lightweight magnesium bipolar plates for DBPFC
has been fabricated and evaluated for application in
unmanned underwater vehicles. Although magnesium
has many favorable properties such as lightweight, high
electric conductivity and machinability, low corrosion
resistance restricted its use as a bipolar plate. Corrosion
resistive metal, Au electroplated magnesium bipolar plates
exhibited the highest power density and the promising
candidate for future aerospace, UAV and underwater pro-
pulsion systems.
Keywords: Direct NaBH4/H2O2 fuel cell, space power sys-
tem, bipolar plate, unmanned vehicle
PACS®
(2010). 88.30.M-
Introduction
The fuel cell with high energy density is an excellent
power source for mobile systems. Fuel storage, however,
is one of the main issues that needs to be addressed in
order to improve the mobility and applicability of fuel
cells in mobile power systems [1]. The proton exchange
membrane fuel cell (PEMFC) requires a bulky and heavy
storage system due to the low density of hydrogen.
Storage of hydrogen as liquid also raises complication
due to its low storage temperature (–253˚C) and boil off
effect [2–4]. The direct methanol fuel cell (DMFC) utilizes
a high energy density liquid fuel methanol, but suffers
from low efficiency due to methanol crossover [5].
The direct borohydride hydrogen peroxide fuel cell
(DBPFC) has been recognized as a promising power source
that may mitigate the fuel storage problem [6–16]. The
DBPFC uses a sodium borohydride solution as fuel and
hydrogen peroxide solution as oxidizer. The use of high
energy density liquid reactants makes the DBPFC compact,
lightweight and mobile. Moreover, the DBPFC can be used
as an air independent power source, such as space and
underwater, owing to its use of a liquid oxidizer. The
DBPFC is one of the promising candidates for Unmanned
Underwater Vehicle (UUV) application. We fabricated UUV
which size is 25 mm Â 35 mm Â 35 mm (Figure 1). UUV is
a remotely controlled submerging robot which has diverse
expandability from private/research application such as
oceanography, payload delivery to military application
like anti-submarine warfare, mine countermeasures. The
electrochemical reactions at the anode and cathode of the
DBPFC are shown in eqs (1) and (2), respectively [17]:
Anode : BH4
À
þ 8OHÀ
! BO2
À
þ 6H2O þ 8eÀ
ðÀ1:24Vvs:SHEÞ
ð1Þ
Cathode : 4H2O2 þ 8Hþþ
8eÀ
! 8H2O
ð1:77Vvs:SHEÞ
ð2Þ
The anode reaction is the direct oxidation of sodium
borohydride where sodium metaborate is produced. The
cathode reaction is the direct reduction of hydrogen per-
oxide where water is produced. The DBPFC has a high
open circuit voltage of 3.01 V which is higher than 1.23 V
of PEMFC and 1.19 V of DMFC [3, 16].
Many studies have been conducted on DBPFC elec-
trocatalysts [4, 16, 18, 19], electrolytes [20, 21], operating
conditions [22, 23], stacks [9, 24], and regenerative reac-
tion [24]. Research on DBPFC bipolar plates, however,
have not been conducted yet. The bipolar plates occupies
*Corresponding author: Sejin Kwon, Department of Aerospace
Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305–701,
Korea, E-mail: trumpet@kaist.ac.kr
Jihyun Kim, Department of Aerospace Engineering, KAIST, 291
Daehak-ro, Yuseong-gu, Daejeon 305–701, Korea; Agency for
Defense Development Post Box 35–7, Yusong Post Office, Daejeon,
Korea, E-mail: ghyunkim@add.re.kr
Bosun Jang: E-mail: bosun04@kaist.ac.kr, Taesong Lee:
E-mail: song2494@kaist.ac.kr, Department of Aerospace
Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon 305–701,
Korea
Int J Turbo Jet Eng 2015; aop
Authenticated | bosun04@kaist.ac.kr author's copy
Download Date | 8/10/15 10:26 AM

larger part of the weight and volume of the stack.
Existing literature reported the use of graphite bipolar
plates in the DBPFC due to its proven performance in
PEMFC [5, 24]. The disadvantage of graphite, however,
are brittleness, poor mechanical strength and porosity
that becomes severe when integrated in a stack [25].
Miley et al. [24] claimed that liquid fuel and oxidizer
permeates through the porous graphite which required
a complicated chemical vapor deposition process to block
the holes. Therefore, investigation of non-porous, light
weight, and durable bipolar plates for DBPFC are
required. Such lightweight bipolar plates may replace
conventional graphite which occupies up to 80% of the
total weight of the fuel cell stack [26].
In this study, a light weight and non-porous magne-
sium alloy is chosen as the base material for DBPFC
bipolar plates. Magnesium has a density one-fourth that
of steel, one-third that of titanium and two-thirds that of
aluminum. It has excellent electrical conductivity, man-
ufacturability, mechanical strength, and low porosity
[27]. One of the unfortunate aspects of magnesium, how-
ever, is its corrosive nature in acidic environments. In the
DBPFC, the cathode operates at a strongly acidic envir-
onment (pH 0.5–1.5) due to the use of an acidic hydrogen
peroxide. Our approach was to electroplate a corrosion
resistive coating on the magnesium alloy in order to
develop corrosion resistant, non-porous, and lightweight
metallic bipolar plates for the DBPFC. The coating mate-
rial should have high electrical conductivity, high chemi-
cal stability, low interfacial contact resistance and should
adhere well to the base metal. Various metals were
surveyed as candidate materials. Among the materials
listed in Table 1, Au, Ag, and Cr were selected for further
investigation due to their low corrosion rates, low elec-
trical resistivities and high thermal conductivities.
Various tests were done on the bipolar plates with
corrosion resistive coatings to evaluate their perfor-
mances. Interfacial contact resistance was measured to
assess the ohmic resistance between the bipolar plates
and electrodes. The compatibility of the bipolar plates in
acidic environments were tested by immersing them in a
30 wt% H2O2 solution. Short and long term performance
tests were done on a single cell utilizing the bipolar
plates to evaluate the overall performance. Among the
three coating metals, Au had the best performance show-
ing the highest power density and compatibility. The high
performance of the Au coated magnesium bipolar plates
was due to an unexpected catalytic activity from the
coated Au layer, which yielded a performance even
higher than conventional graphite. This phenomenon is
unique to the DBPFC where the liquid reactants serve as
electrolytes. High performance, lightweight and corrosion
resistant metallic bipolar plates for DBPFC are proposed.
Experimental details
Fabrication of corrosion resistant magne-
sium bipolar plates
Prior to carrying out corrosion resistive coating, the fab-
rication and compatibility testing of bare magnesium
bipolar plates in DBPFC operating environments were
carried out. Bare magnesium bipolar plates were made
from a magnesium alloy AZ31B. The plates were pro-
duced by CNC milling where flow channels were intern-
ally machined on the bipolar plates. The plates had
serpentine flow channels with a cross sectional area of
0.5 mm2
and an active area of 33 Â 33 mm2
.
Figure 1: Fabricated UUV configuration.
Table 1: Properties of candidate coating materials.
Material Corrosion
rate* []
(μm year−
)
Electrical
resistivity
(nΩ m)
Thermal
conductivity
(Wm−
K−
)
Au <  . 
Ni >  . .
Ag <  . 
Ti <   .
Cr Not significant  .
*Corrosion test condition: 0.5 M H2SO4 @ room temperature.
2 J. Kim et al.: Lightweight Magnesium Bipolar Plates

Compatibility testing of the bare magnesium bipolar
plates were carried out in a single DBPFC configuration
tested as described in Section 2.3. As soon as the fuel was
supplied, the anode flow channels were blocked due to
accumulation of Mg(OH)2. As soon as the oxidizer was
supplied, the cathode bipolar plates corroded rapidly. It
is likely that the formation of Mg(OH)2 was assisted by
catalyst on the anode gas diffusion electrode (GDE). We
concluded that bare magnesium alloy was not compatible
as material for DBPFC bipolar plates in both anode and
cathode DBPFC environments.
Corrosion resistive metals were coated on the magne-
sium bipolar plates to prevent accumulation of by-pro-
ducts and corrosion. Metals were electroplated on the
surfaces of the fabricated magnesium bipolar plates with
thicknesses of 2.0 µm. During electroplating, the coeffi-
cients of thermal expansion (CTE) were considered to
ensure successful coating. Material expansion rates were
calculated by taking into account the CTEs between the
base metal and coating. The tolerance in difference in
thermal expansion rates was no more than 0.08% [28].
A copper and a nickel layer having CTEs of 16 μm m−1
˚K−1
and 13.4 μm m−1
˚K−1
, respectively, were inserted as inter-
mediate layers to complement the CTE difference between
coating material (14.2 μm m−1
˚K−1
for Au, 18.9 μm m−1
˚K−1
for Ag, and 4.9 μm m−1
˚K−1
for Cr) and Mg (24.8 μm m−1
˚K−1
). Further detailed electroplating recipes are not pro-
vided in this paper due to proprietary reasons.
ICR measurement
Interfacial contact resistance (ICR) was measured to
assess the ohmic resistance between the bipolar plates
and electrodes. A HSVP-050U (Hyundai EE Inc. Korea)
ICR test system was used. Magnesium blocks with the
corrosion resistant coatings were mounted on the test
stand having two sheets of carbon paper put adjacent
onto each side. Two base copper plates were then pressed
toward the carbon sheets thereby applying pressure. The
voltage and current between the copper plates were mea-
sured as the applied pressure continuously increased
[29]. This yielded a relationship between ICR and applied
pressure.
Fuel cell assembly and testing
A single DBPFC was prepared to test the performance of
the fabricated bipolar plates. The single DBPFC consisted
of a membrane electrode assembly (MEA), bipolar plates
and end plates. The MEA consisted of a Nafion 115
(Dupont, USA) membrane and electrodes. To remove con-
taminants, the membrane was first pretreated in a 3 wt%
H2SO4 þ 3 wt% H2O2 þ 94 wt% H2O solution for 1 h at
70˚C. The pretreated membrane was then washed in dis-
tilled water and immersed in a 1 mole NaOH solution for
30 min for activation. The clean and active membrane
was stored in distilled water at room temperature until it
was used for experiment. A carbon cloth gas diffusion
electrode (GDE) with a Pd catalyst loading of 1 mg cm−2
made in-house was used as anode and a commercial 20
wt% Pt/C GDE on carbon paper (Fuel Cell Earth, USA)
was used as cathode. Two end plates made from poly-
ether ether ketone fixed the MEA and bipolar plates
together under a clamping pressure of 20 kgf cm−2
.
Silicon gaskets were used to prevent leakage of liquid
between bipolar plates.
Performance evaluation of the single cell was done
by current-voltage measurements while supplying fuels
and oxidizers to the DBPFC at a constant flow rate of 10
ml min−1
. An electrical load (3315F, Prodigit, Taiwan) was
used to vary the load and a data acquisition unit (midi
Logger GL220, Graphtec Co., Japan) was used to record
data. Tests were carried out at 30˚C by using a thermo-
static chamber (IKA HB10 control, Germany). Liquid by-
products were collected in flasks and gaseous by-product
were vented. The fuel was a 10 wt% NaBH4 þ 5 wt%
NaOH þ 85 wt% H2O solution and the oxidizer was a 10
wt% H2O2 þ 5 wt% H3PO4 þ 85 wt% H2O solution.
NaOH and H3PO4 were used as stabilizers to prevent
hydrolysis and decomposition of fuels and oxidizers,
respectively.
Results and discussion
ICR measurement and compatibility test
ICR values of the fabricated bipolar plates as a function
of clamping pressure are shown in Figure 2. The ICR for
Cr coated magnesium bipolar plate was highest due to
the low electric conductivity of chrome. The ICRs for Au,
Ag and graphite were similar at clamping pressures
higher than 20 kgf cm−2
. At a clamping pressure of 20
kgf cm−2
, the ICR for graphite was 11 m Ω cm2
, 780 m Ω
cm2
for Cr, 10 m Ω cm2
for Au, and 7.5 m Ω cm2
for Ag.
Compatibility tests of the fabricated bipolar plates in
acidic environments were done by immersing them in a
30 wt% hydrogen peroxide solution. Bubble formation on
the surfaces of each block were observed using a camera
J. Kim et al.: Lightweight Magnesium Bipolar Plates 3

(Figure 3). While Cr and Au had almost no bubble forma-
tion, Ag coated magnesium specimen had vigorous bub-
ble formation. Since decomposition of hydrogen peroxide
reduce the electrochemical efficiency at the cathode, Ag
was considered incompatible as coating material.
Single cell test results of the fabricated
magnesium bipolar plates
Single fuel cell test results for the Au, Ag, and Cr coated
magnesium bipolar plates and graphite bipolar plates are
shown in Figure 4. The performance of Au coated mag-
nesium bipolar plates had the highest maximum power
density of 141 mW cm−2
, which was higher than that of
conventional graphite (116 mW cm−2
). The maximum
power density of the Ag coated magnesium bipolar
plate was 135 mW cm−2
, which was slightly lower than
the Au coated bipolar plates. Ag had slightly lower per-
formance than Au despite its lower ICR. Cr coated mag-
nesium bipolar plates had the minimum output power
, which was due to the exception-
ally larger ICR value compared to the other coating
materials.
Figure 2: ICRs of graphite, Au, Ag, and Cr coated magnesium bipolar
plates as a function of compression force.
Time t = 0 minutes t = 1 minutes t = 4 minutes
Au coated
magnesium
alloy
Ag coated
magnesium
alloy
Cr coated
magnesium
alloy
Figure 3: Compatibility test of Au, Ag, and Cr coated magnesium alloy with 30 wt% H2O2.

Durability and catalytic activity of the Au
coated magnesium bipolar plate
The durability of the Au-coated magnesium bipolar plates
which showed the highest output power was further
tested by chronopotentiometric test to see its applicability
as bipolar plate for the DBPFC. The output voltage of
the single DBPFC using the Au coated magnesium
bipolar plates were measured under a constant load of
100 mA cm−2
while circulating 800 gs of fuels and oxidi-
zers each (Figure 5). The output voltage remained stable
for 8 h, steadily decreased at a rate of 14 mV h−1
for the
next 8 h and rapidly decreased at a rate of 32 mV h−1
for
7 h. The decrease in voltage was expected to be due to
crossover of fuel which eventually caused the liberation
of oxygen at the cathode side limiting liquid flow [20].
Inspection of the fuel cell after long term test revealed
that the Au coated magnesium bipolar plates remained
intact. Anode catalyst was slightly deteriorated which
may contributed to the drop in output voltage.
It was peculiar that the Au coated magnesium bipolar
plates had much higher output power than graphite
despite their similar values in ICRs. It was hypothesized
that the Au layer may have had an electrochemical effect.
A single DBPFC using Au coated magnesium bipolar plates
was tested in conjunction with a membrane electrode
assembly having no catalyst layers. The maximum power
density achieved with such a cell configuration was
33 mWcm–2
, which was a comparable output power with
that of other groups (Figure 6(a)) [6, 30]. This implied that
the Au coated layers on the magnesium bipolar plates
served as an electrocatalysts in the DBPFC. Such unique
phenomenon was possible since the liquid reactants of
DBPFC have high ionic conductivities which serve as elec-
trolytes [13]. Fig. 6 (b) shows a conventional MEA config-
uration and Fig. 6 (c) shows the MEA configuration
without a catalyst layer. By conventional wisdom, a fuel
cell configuration like Figure 6(c) is not appropriate since
no electrochemical reactions may occur owing to the
absence of the triple phase boundary or catalyst layer.
However, since reactants of the DBPFC are liquid phase,
ions such as Na þ , OH–, H þ and PO4– may carry
current in the cell producing output power.
The gold coated magnesium bipolar plate may be
adapted in a stack for UUV applications since it enables
high energy density and compact storage. UUV model
called OpenROV can be powered by a 30-Watt DBPFC
stack consisting of 9 stacks. DBPFC powered UUV system
consists of a controller, DBPFC stack, and fuel tank where
its total length lined up in a row is about 60 cm including
its external configuration, which shown schematic in
Figure 7.
Figure 4: P-V-I curves for the Au, Ag and Cr coated magnesium
bipolar plates and graphite bipolar plate (a) V-I and (b) P-I curves.
Figure 5: Durability data for Au coated magnesium bipolar plate at a
constant load of 100 mA cm−2
.

Conclusion
In this study, corrosion resistant magnesium bipolar
plates for the DBPFC were fabricated by electroplating,
and Au was selected as best material for the corrosion
resistant coating. Among the coating materials, Au
coated magnesium bipolar plates exhibited the highest
maximum power density of 141 mW cm−2
, which was
superior over graphite that showed a maximum power
. The superior performance of Au
coated magnesium bipolar plates was accounted for the
additional catalytic activity of Au which assisted the
electrochemical reaction. Since catalyst layers consist of
expensive materials, catalytically active bipolar plates
may save the overall cost of the DBPFC stack.
The gold coated magnesium bipolar plate may be
adapted in a stack for UUV applications since it enables
high energy density and compact storage. The magne-
sium bipolar plate has light weight and smaller volume
than graphite. As long as the fuel cells are used as a stack
Figure 6: (a) P-V-I of a single DBPFC using Au coated bipolar plates without catalyst layers, and schematics of (b) a conventional MEA
configuration, and (c) a MEA configuration with no catalyst layer.

the light weight and structurally sound gold coated mag-
nesium bipolar plate are attractive for AIP system.
Acknowledgements: This paper is based on presentation
in APCATS 2015.
Funding: This work has been supported by the National
Research Foundation of Korea (NRF) grant funded by the
Korean government (MEST) (No. 2012R1A2A1A05026398)
and the High-Speed Vehicle Research Center of KAIST
with the support of Defense Acquisition Program
Administration (DAPA) and Agency for Defense
Development (ADD).
Submission declaration
This paper has not been published previously and it is
not under consideration for publication elsewhere.
References
1. Ross DK. Hydrogen storage: the major technological barrier to
the development of hydrogen fuel cell cars. Vacuum
2006;80:1084–9.
2. Hwang JJ, Wang DY, Shih NC. Development of a lightweight fuel
cell vehicle. J Power Sources 2005;141:108–15.
3. Wee JH. Applications of proton exchange membrane
fuel cell systems. Renew Sust Energy Rev 2007;11:
1720–38.
4. Oh T, Jang B, Kwon S. Electrocatalysts supported on
multiwalled carbon nanotubes for direct borohydride-hydrogen
peroxide fuel cell. Int J Hydrogen Energ 2014;39:
6977–86.
5. Gu LF, Luo N, Miley GH. Cathode electrocatalyst selection and
deposition for a direct borohydride/hydrogen peroxide fuel
cell. J Power Sources 2007;173:77–85.
6. Choudhury NA, Raman RK, Sampath S, Shukla AK. An alkaline
direct borohydride fuel cell with hydrogen peroxide as oxidant.
J Power Sources 2005;143:1–8.
7. Jang B, Oh TH, Kwon S. Effect of heat treatment of electrodes
on direct borohydride-hydrogen peroxide fuel cell perfor-
mance. J Power Sources 2014;268:63–8.
8. Santos DMF, Sequeira CAC. Polymeric membranes for direct
borohydride fuel cells: a comparative study. ECS Transactions
2010;25:111–22.
9. Luo N, Miley GH, Mather J, Burton R, Hawkins G, Byrd E, et al.
Engineering of the bipolar stack of a direct NaBH4 fuel cell.
J Power Sources 2008;185:356–62.
10. Luo N, Miley GH, Kim KJ, Burton R, Huang XY. NaBH4/H2O2 fuel
cells for air independent power systems. J Power Sources
2008;185:685–90.
11. Ma J, Sahai Y, Buchheit RG. Direct borohydride fuel cell
using ni-based composite anodes. J Power Sources
2010;195:4709–13.
12. Raman RK, Prashant SK, Shukla AKA. 28-W portable direct
borohydride-hydrogen peroxide fuel-cell stack. J Power
Sources 2006;162:1073–6.
13. Stroman RO, Jackson GS. Modeling the performance of an
ideal NaBH4-H2O2 direct borohydride fuel cell. J Power
Sources 2014;247:756–69.
14. de Leon CP, Walsh FC, Pletcher D, Browning DJ, Lakeman JB.
Direct borohydride fuel cells. J Power Sources 2006;155:
172–81.
15. Wu HJ, Wang C, Liu ZX, Mao ZQ. Influence of operation condi-
tions on direct NaBH4/H2O2 fuel cell performance.
Int J Hydrogen Energ 2010;35:2648–51.
16. Santos DMF, Saturnino PG, Lobo RFM, Sequeira CAC.
Direct borohydride/peroxide fuel cells using prussian blue
cathodes. J Power Sources 2012;208:131–7.
17. Santos DMF, Sequeira CAC. Zinc negative electrode for direct
borohydride fuel cells. ECS Trans 2009;16:123–37.
18. Cao DX, Gao YY, Wang GL, Miao RR, Liu Y. A direct
NaBH4-H2O2 fuel cell using ni foam supported au
nanoparticles as electrodes. Int J Hydrogen Energ 2010;
35:807–13.
19. Yi LH, Song YF, Wang XY, Yi LL, Hu JF, Su G, et al. Carbon
supported palladium hollow nanospheres as anode catalysts
for direct borohydride-hydrogen peroxide fuel cells. J Power
Sources 2012;205:63–70.
20. Arges CG, Prabhakaran V, Wang LH, Ramani V. Bipolar
polymer electrolyte interfaces for hydrogen-oxygen and
direct borohydride fuel cells. Int J Hydrogen Energ
2014;39:14312–21.
21. Raman RK, Shukla AK. A direct borohydride/hydrogen
peroxide fuel cell with reduced alkali crossover. Fuel Cells
2007;7:225–31.
Figure 7: Schematic of the direct NaBH4/H2O2 fuel cell stack (30 watt
class).

22. Cheng H, Scott K. Influence of operation conditions on direct
borohydride fuel cell performance. J Power Sources
2006;160:407–12.
23. Celik C, San FGB, Sarac HI. Effects of operation conditions on
direct borohydride fuel cell performance. J Power Sources
2008;185:197–201.
24. Miley GH, Luo N, Mather J, Burton R, Hawkins G, Gu LF, et al.
Direct NaBH4/H2O2 fuel cells. J Power Sources 2007;165:
509–16.
25. Tawfik H, Hung Y, Mahajan D. Metal bipolar plates for PEM fuel
cell – A review. J Power Sources 2007;163:755–67.
26. Antunes RA, Oliveira MCL, Ett G, Ett V. Corrosion of metal
bipolar plates for PEM fuel cells: A review. Int J Hydrogen
Energ 2010;35:3632–47.
27. Park T, Oh J, Kim K, Kwon S. Evaluation of silver-coated mag-
nesium bipolar plate for lightweight PEM fuel cell stack.
Int J Green Energy 2014. in press.
28. A.S. Woodman EBA, K.D. Jayne, and M.C. Kimble.
Development of Corrosion-Resistant Coatings for Fuel
Cell Bipolar Plates. American Electroplaters and Surface
Finishers Society, AESF SUR/FIN ‘99 Proceedings.
1999.
29. Wang HL, Sweikart MA, Turner JA. Stainless steel as
bipolar plate material for polymer electrolyte
membrane fuel cells. J Power Sources 2003;115:
243–51.
30. Wei JL, Wang XY, Wang Y, Guo J, He PY, Yang SY, et al.
Carbon-supported au hollow nanospheres as anode catalysts
for direct borohydride-hydrogen peroxide fuel cells. Energy
Fuel 2009;23:4037–41.
Note: Jihyun Kim and Bosun Jang both contributed equally to this
work

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