DEVELOPMENT AND TESTING OF A HIGHLY EFFICIENT PROTON EXCHANGE
MEMBRANE (PEM) ELECTROLYZER STACK
Ömer Faruk SELAMET1,2, Fatih BECERIKLI1, Mahmut D. MAT1, Yüksel KAPLAN1
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2
Nigde University, Mechanical Engineering Department, Nigde, Turkey
Hidronerji Ltd. Şti., Yenimahalle, 06537, Ankara, Turkey
Abstract
Integrated with the renewable energy resources such as wind and solar energy, a Proton Exchange
Membrane (PEM) water electrolyzer is one of the important methods for hydrogen production due
to its high efficiency, compact structure, releasing no harmful emission and possibility to directly
store the product hydrogen directly to high pressure tanks.
In this study, development stages of a highly efficient PEM electrolyzer stack are presented. First, a
single cell is developed and its performance is improved from 74% to 87% through design and
materials enhancement. Then a 10-cell stack is developed and its operating parameters are
optimized for high efficiency. The 10-cell stack produces 5 l/min hydrogen at 1.35 A/cm2. The
single cell is tested for 2000 hours continuously and an acceptable degradation rate of 1.5µV/hour is
measured.
Keywords: Water Electrolysis, Stack Development, Hydrogen Production, Proton Exchange
Membrane
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1. INTRODUCTION
The renewable energies are attractive solution of world energy problems, however, they are usually
not present when they are demanded and they are also not suitable for use in cars, trucks etc. unlike
fossil fuels. Hydrogen can be an excellent solution for storing renewable energy and can be used in
transportation and various other applications. Since today’s most of hydrogen (more than 90%) is
produced from fossil fuels, it gains enormous significance to produce hydrogen with clean and
efficient methods [1]. An idealized “energy cycle” for renewable energy, hydrogen, oxygen and
water discussed by Marshall [2]. The cycle offers hydrogen production by electrolysis as energy
carrier from renewable energy resources and transforming the hydrogen into electricity by
electrochemical conversion in a fuel cell with water as a byproduct, therefore cycle is completed.
The most crucial point in this cycle is that renewable energy is the only input of the cycle and
electrical power is the only output. The electrical energy produced during the daylight and/or windy
days can be converted to hydrogen by an electrolyzer and then can be employed in demand and
transported for automotive industry.
An electrolyzer splits water electrochemically into hydrogen and oxygen molecules with aid of an
electrical energy. There are three kind of electrolysis techniques; alkaline, solid oxide and PEM
(Proton Exchange Membrane) electrolysis. The alkaline electrolysis has currently the most mature
technology, however, has several drawbacks such as, electrolyte contamination, electrode corrosion,
periodic maintenance, relatively low working current, low efficiency and low pressure. Solid oxide
electrolysis is carrying on its development step and expected to commercialize in the near future.
PEM electrolyzers have many advantages over other types of electrolyzers such as high efficiency
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and high working current and pressure, easy operation and compactness etc. PEM electrolyzers
operate at low DC voltages thus direct coupling to PV panels is possible.
Relatively few studies are available in the literature on PEM electrolyzers compared to PEM fuel
cells. Studies on PEM electrolyzers are mainly concentrates on catalyst development for the
electrodes, cell and stack assembly for higher efficiencies [3-12]. Kondoh et al. [3] assembled two
PEM electrolyzer stacks; one uses Pt coated titanium plate while the other one employs uncoated
titanium plate as current collector. They observe that Pt coated stack produces a better performance
than uncoated one. Badwal et al. [4], assembled PEM electrolyzer stacks with different active areas
from 9 cm2 to 150 cm2. They stated that the failure of stack initiated with membrane thinning. They
advised to increase three phase boundary in the catalyst layer for a higher performance instead of
using thin membranes. Millet et al. [5], developed several catalysts for the electrolyzer electrodes
and tested them in laboratory scale (7 cm2 and 23 cm2) cells, then moved to the larger cells and
assembled electrolyzer stacks with 250cm2 active areas. Grigoriev et al. [6] developed PEM
electrolyzer cells and tested them in a wide range of temperature (20oC – 120oC) and high pressures
(0- 25 bar). They found that the maximum performance could be obtained at high temperature and
pressure. Harrison et al. [7], developed a semi-empiric model for the PEM electrolyzer and
compared it with results of a commercial PEM electrolyzer data. Santarelli et al. [8] investigated
operating characteristics of a commercial PEM electrolyzer and determined that the most important
parameters on the performance of a PEM electrolyzer are temperature and pressure. There are also
numerous theoretical and experimental studies in the literature considering electrolyzers a part of
renewable power supply systems which investigate suitability of renewable energy produce full or
partial electricity demand [13-15].
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Although many studies available in the literature on various aspects of PEM electrolyzers, relatively
few studies consider cells and stacks development for a practical use. Therefore, main objective of
this study is to develop PEM electrolyzer cells and stacks for high volume hydrogen production and
investigate operating parameters for a higher efficiency.
2. DEVELOPMENT BACKROUND
In a PEM electrolyzer, water is disassociated in to hydrogen and oxygen gases. Oxygen is generated
at the anode, while hydrogen nuclei move to the cathode in order to compose hydrogen molecules.
The working principle and the schematic view of a PEM electrolyzer is given in Fig. 1. PEM
electrolysis (PEME) is also referred to as solid polymer electrolyte (SPE) or polymer electrolyte
membrane (also, PEM), but all represent a system that incorporates a solid proton-conducting
membrane which is not electrically but ionically conductive. The membrane serves a dual purpose,
as the gas separation device and ion (proton) conductor. Deionized (DI) water is required in PEM
electrolyzers and generally 18.2MΩ-cm resistivity is recommended for longer stack life. PEM
technology was originally developed as part of the Gemini space program [16]. In a PEM
electrolyzer, the electrolyte is contained in a thin, solid ion-conducting membrane rather than the
aqueous solution in a alkaline electrolyzer. This allows a H+ ion (proton) or hydrated water
molecule (H3O+) to transfer from the anode side of the membrane to the cathode side, and separates
the hydrogen and oxygen gases. The protons (H+) are pulled through the membrane under the
influence of an electric field and rejoin with electrons being supplied by the power source at the
cathode to form hydrogen gas-H2.
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Although the working principle is very similar (but vice versa) with the PEM fuel cells, the subelements such as gas diffusion layers, catalyst layers, flow field and bipolar plates, sealing materials
are usually different for well assembled PEM electrolyzers. Since water in liquid form is employed
in a PEM electrolyzer, the materials which are vulnerable to corrosion cannot be used in the anode
section due to high anodic potential. Titanium which is usually employed in a PEM electrolyzer as a
current distributor and flow field is resistant to the corrosion due to formation of passivation film
which can form even in air, however the oxide layer increases the ohmic loss. Since the working
voltage (1.8-2Volts) of a PEM electrolyzer is in the range of corrosion of titanium [17], anodic subelements must be pre-processed such as coating with platinum to prevent corrosion and to obtain a
good contact.
Development of the PEM electrolyzer in Nigde University has been performing since 2007. Study
started with a 25 cm2 single cell with a relatively low efficiency of 74%. Since then, studies on
performance improvements and better designs for the single cells have been carried on. Final CAD
drawing and a photograph of a 50 cm2 single cell can be seen in Fig.2. Initial (2007) and final
(2010) performances of the single cells which are developed in Nigde University is illustrated in
Fig.3. It is seen that the performance of the cells improved from 74% to 87% in a three years period.
2.1. Sub-element selection
All the elements such as endplates, bipolar plate, current collector plates, mesh groups and porous
titanium except Membrane Electrode Assembly (MEA) are designed in house and machined.
Stainless steel and titanium are tested as a bipolar plate material and then titanium is employed due
to higher resistance to corrosion under electrolyzer operating conditions and no metal anions
production which poison the MEA. Serpentine flow field on titanium bipolar plate is tested but a
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flow field with a mesh group on the plain titanium plate is preferred, since machining of a titanium
is difficult, time consuming and expensive. Several MEA’s from different suppliers and various
geometries (rectangular, circular etc.) are tested and a 50cm2 circular shaped MEA from Giner Inc.
is employed in the single cells. The MEA employs Nafion 110 as a membrane and has a catalyst
loading of 3 mg/cm2 IrRuOx at the anode side while 3 mg/cm2 Pt at the cathode side. A rectangular
shaped MEA with mesh flow field is found to be less favorable due to disadvantages on assembling
and applying appropriate pressure to the cell. Carbon paper, fine titanium meshes and sintered
porous titanium are used as current collectors (diffusion media). Aluminum, stainless steel and
Delrin® are employed as end plates in the PEM electrolyzer. The preliminary results showed that
material of the almost all components should be titanium in a PEM electrolyzer, due to its excellent
resistance to corrosion and no poison effect on membrane. Although it is cheaper than titanium,
stainless steel can easily poison the membrane and catalyst, due to high metal anion content.
2.2. Single cell to 10-cell stack
Since the hydrogen generation-rate of a single cell is limited to MEA’s active area, the cells
assembled into series to reach a demanding hydrogen production. While developing a 10-cell stack,
first a 3-cell stack is assembled, problems have determined and fixed, then a 5-cell stack is built,
and finally extended to 10-cells. A photograph of 10-cell stack is shown in Fig.4. 100 cm2 active
area MEAs with same properties with 50 cm2 active area are employed in the stack to increase
hydrogen production per cell.
While designing a PEM electrolyzer stack, homogenous water and current distribution and
appropriate compression in the cell and stack must be obtained. Homogenous water distribution is
important to obtain equal life time of each cell and stack performance. Therefore a design shown in
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Fig.5 for a better water distribution in each cells is developed. The design is similar to that of
suggested by Barbir [18]. Water enters the stack from the anode end plate, circulates all anode
sections of each cell and leaves the stack from the anode end plate. The stack must be compressed
with an appropriate pressure, otherwise ohmic losses due contact resistance decreases the stack
efficiency.
2.3 Thermodynamics and efficiency of PEM electrolysis
The energy needed for the water decomposition is equal to the energy release during the formation
of water from hydrogen and oxygen gases. Therefore the minimum energy for water to decompose
can be calculated by Gibbs free energy. At the standard conditions, Gibbs free (∆G) energy is for
the disassociation of water into hydrogen and oxygen can be calculated as;
(1)
where n is the number of electrons in the reaction, F is the Faraday constant, Erev is the reversible
potential needed for the water decomposition. Using lower heating value of hydrogen, the reversible
potential can be calculated as;
(2)
however, some entropy generated during the water dissolution processes. Therefore, it more
appropriate to employ enthalpy (∆H) instead of ∆G for a potential calculation [19]. Therefore the
minimum voltage required for the water electrolysis can be calculated using enthalpy (∆H), thus;
(3)
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where VTN is the thermo-neutral voltage indicating that at this amount of energy, the system neither
release heat nor requires a heat to proceed [20], ∆S is the entropy change, T is the temperature.
In most of the scientific research, efficiency of water electrolysis is calculated using higher heating
value of the hydrogen. Since the water is supplied to the electrolyzer in liquid phase efficiency can
be calculated as;
(4)
where Vcell is actual voltage of a cell. The efficiency of a PEM electrolyzer can be calculated at any
current density. Since operating the voltage is lower at lower current densities, efficiency of the
electrolyzer becomes higher. The working current density of some of the commercial electrolyzers
is kept below 1A/cm2 for a high efficiency and low cooling requirement. However a larger catalyst
area is required for a prescribed hydrogen production. Most of the scientific studies, the efficiency
of electrolyzers are evaluated at 1A/cm2 current density.
3. EXPERIMENTAL SETUP
A sketch of test bench for performance measurements and determination of the operating conditions
of the PEM electrolyzer is shown in Fig.6. An adjustable Masterflex peristaltic pump (Cole Parmer)
is used for water feed in the set-up. Before entering the stack, water is heated to the required
temperature, and flow rate is adjusted to testing value with a flow meter. Both water and stack
temperatures are controlled with K-type thermocouples (Omega) and a data logger (Pico
Technology). The voltage reading of each cell is recorded by a multichannel multimeter. A 10kW
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(80V-125A) power supply (Sorensen) is used to give the stack required energy for cracking the
water into hydrogen and oxygen. All data are recorded to a computer for further analysis. Hydrogen
and oxygen flow rates are also measured with digital flow meters (Cole Parmer).
Hydrogen and oxygen leaves the stack mixed with water, therefore two phases have to be separated
with a separator. Even after separating the water, the gasses are still in fully humidified condition.
Therefore both gasses are dried in a silica gel beds to measure the amount of the gasses correctly.
When testing the stack performance, the correct measurement of temperature is important. The
temperature of stack is measured at two points; one is in a hole on the end plate, the other is from
anode exit manifold. The feed water temperature is also monitored to ensure that it is the same as
with the stack temperature.
4. RESULTS
The experiments are performed to investigate the effect of temperature and feed water flow rate on
the performance of the PEM electrolyzers. The experiments are performed with a single cell fist for
comparison with stacks developed in the study. The measured efficiency of a single cell as a
function of temperature is shown in Fig.7. It is seen that efficiency increases with temperature
mainly because of enhanced electrochemical reaction at higher temperatures. The efficiency of the
cell at 20oC is measured as 74%, while it increases to 87% at 80oC. This efficiency is comparable
with efficiencies of similar studies in the literature. Badwal et al. [4] obtained a 82% efficiency for a
small 9cm2 laboratory scale electrolyzer at 1A/cm2 and 75oC, while Millet et al. [5] has reached
80% efficiency for a stack at 1A/cm2 and 85oC. Grigoriev et al. [6] performed 88% efficiency at
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1A/cm2 however operating temperature was 90oC in this study. Marshall et al. [11] developed
catalysts for PEM electrolysis and they obtained 94% efficiency at 1A/cm2 and 80oC with relatively
thinner Nafion 115 membrane.
The performance measurement performed first with a 5 cell stack then extended to final the 10 cell
stack. The operation at lower voltages improves the efficiency and reduces anodic potential thus
reduce the corrosion of metallic components.
The performances of both 5-cell and 10-cell stacks are given in the report, since these stacks can be
employed in various systems for different hydrogen demands. For example 5-cell stack can be used
for up to 1l/min and 10-cell stack up to 2.5l/min hydrogen generation. The performance of a 5-cell
stack is shown in Figure 8. It is seen that the operating voltage of 5 cell stack decreases with
temperature which indicates higher efficiencies at higher temperatures. It is also seen that the
operating voltage does not significantly affected from operating temperature at low current
densities. The effect of operating temperature is more apparent at higher current densities. This
result may be attributed to local heating and local increase of temperature. The performance of the
10-cell stack is shown in Fig.9. At higher current densities, the 10-cell stack temperature rises more
rapidly; therefore temperature measurements have been performed up to 1 A/cm2. It is seen that
similar to 5-cell stack, the performance of the 10-cell stack enhances at higher temperatures.
The operating voltage of each cells in a stack should be as close as possible for a stable operation of
the stack. The voltage distribution of the cells in the stack should be homogenous for a long stack
life. To check the integrity of each cells in the 10-cell stack, the voltages of each cells are measured
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separately and shown in Fig. 10. The slight differences at cell voltages are attributed to the contact
resistance variation between the individual cells.
To investigate the effects of water flow rate on the performance the 10 cell stack is operated in a
range of flow rate from 750 ml/min – 1500 ml/min. As seen is in Figure 11, the water flow rate does
not play a significant role on the performance of the PEM electrolyzer. However, if the flow rate of
water is too low, the stack temperature rises uncontrollably, and then generally water flow rate is
chosen for cooling purpose at a operating current density.
To evaluate the long term stability, the single cell which has 50 cm2 active area is tested for 2000
hours. The long term test result is shown in Fig.12. The feed water is renewed with fresh deionized
water every two days during the testing period. It is seen that the performance of the cell decreases
in first 300 hours then improves again and stabilizes. The cell is operated at ambient temperature.
The degradation rate is found to be 1.5µV/hour. The lifetime of a PEM electrolyzer stack is
expected to be similar to the single cell, since the degrading components are the same in both a
single cell and a stack (i.e., MEA and are metallic parts) [4, 5, 13]
5. CONCLUSION
The major achievements of the study can be summarized as:

A single cell with 50 cm2active area is developed and efficiency of cell is improved from
74% to 87%.

A five cell stack is developed and its performance is measured depending on operating
temperature and flow rate. It is found that the 5 cell stack operates with %80 efficiency, at
1A/cm2 and 50oC. The performance of the stack enhanced at high operating temperatures.
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
The stack is then extended to 10-cells. It is shown that with the stack design developed, the
efficiency does not change significantly as the number of the cell increased. The 10-cell
stack is shown to produce 5 l/min hydrogen at 1.35 A/cm2 and 19 volt consuming around
1280 Watt power.

A single cell is tested for 2000 hours and degradation rate is calculated as 1.5µV/hour. The
degradation rate is found to be reasonable for commerciable PEM electrolyzers.
Cost reduction by employing cheaper materials or coating will be subject to future studies.
6. ACKNOWLEDGEMENTS
The authors would like to thank the Scientific and Technical Research Council of Turkey
(TUBITAK) for the financial support under the contract number of 106G086.
7. REFERENCES
[1] World Energy Outlook, 2006, obtained from http://www.iea.org/weo/2006.asp.
[2] Marshall A. Electrocatalysts for the Oxygen Evolution Electrode in Water Electrolyzers using
Proton Exchange Membranes: Synthesis and Characterisation. 2005;PhD Thesis, Norwegian
University, Trondheim, Norway.
[3] Kondoh M, Yokoyama N, Inazumi C. et al. Development of solid polymer-electrolyte water
electrolyser. Journal of New Materials for Electrochemical Systems 2000;3:61-66.
[4] Badwal S P S, Giddey S, Ciacchi F T. Hydrogen and oxygen generation with polymer
electrolyte membrane (PEM)-based electrolytic technology. Ionics 2006;12:7–14.
[5] Millet P, Ngameni R, Grigoriev S A, Mbemba N, Brisset F, Ranjbari A, and Etie´vant C. PEM
water electrolyzers: From electrocatalysis to stack development. International J. Hydrogen Energy
2009;1-10.
[6] Grigor’ev S A, Khaliullin M M, Kuleshov N V. and Fateev V N. Electrolysis of Water in a
System with a Solid Polymer Electrolyte at Elevated Pressure. Russian Journal of Electrochemistry
2001;37:819–822.
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[7] Harrison K W, Pacheco E H, Mann M, Salefhar H. Semiempirical model for determining PEM
electrolyzer stack characteristics. Journal of Fuel Cell Science and Technology 2006;3:220-223.
[8] Santarelli M, Medina P, Cali M. Fitting regression model and experimental validation for a
high-pressure PEM electrolyzer. Int. J. Hydrogen Energy 2009;34:2519-2530.
[9] Marangio F, Santarelli M, Cali M. Theoretical model and experimental analysis of a high
pressure PEM water electrolyzer for hydrogen production. Int. J. Hydrogen Energy 2009;34:11431158.
[11] Marshall A T, Sunde S, Typskin M, Tunold R. Performance of a PEM water electrolysis cell
using IrxRuyTazO2 electrocatalysts for the oxygen evolution electrode. Int. J. Hydrogen Energy
2007;32: 2320-2324.
[12] Slavcheva E, Radev I, Bliznakov S, Topalov G, Andreev P, Budevski E. Sputtered iridium
oxide films as electrocatalysts for water splitting via PEM electrolysis. Electrochimica Acta
2007;52:3889–3894.
[13] Barbir F. PEM electrolysis for production of hydrogen from renewable energy sources. Solar
Energy 2005; 78:661-669.
[14] Shapiro D, Duffy J, Kimble M. Pien M, Solar-powered regenerative PEM electrolyzer/fuel cell
system. Solar Energy 2005;79:544–550.
[15] Gibson T L. and Kelly N A. Optimization of solar powered hydrogen production using
photovoltaic electrolysis devices. International Journal of Hydrogen Energy 2008;33:5931-5940.
[16] Konopka A, and Gregory D. Hydrogen Production by Electrolysis: Present and Future. in 10th
Intersociety Energy Conversion Engineering Conference. 1975;IEEE Cat. No. 75CHO 983-7 TAB.
[17] Pourbaix M., Atlas of electrochemical equilibria in aqueous solution” National Association of
Corrosion Engineers. Huston; 1974.
[18] Barbir F. PEM Fuel Cell: Theory and Practice. Newyork: Elsevier Academic Press; 2005.
[19] Schroeder D V., Introduction to thermal physics, Addison-Wesley, 2000.
[20] Laoun B., Thermodynamics aspect of high pressure hydrogen production by water electrolysis,
Revue des energies renouvelables, 10, 435-444, 2007.
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8. FIGURE CAPTIONS
Figure 1. Schematic view of components, working principle of PEM Electrolyzer
Figure 2. Final CAD drawing and photograph of the PEM electrolyzer
Figure 3. Comparison of initial (2007) and final (2010) efficiencies of the PEM electrolyzers
Figure 4. Photograph of the 10-cell stack
Figure 5. Water distribution in the 5-cell stack
Figure 6. Schematic view of the experimental setup for stack testing
Figure 7. Effect of temperature on the efficiency of the PEM electrolyzer cell
Figure 8. Effect of temperature on the performance of the "5-cell stack"
Figure 9. Effect of temperature on the performance of the "10-cell stack"
Figure 10. Performance of each cells in the 10-cell stack at 60oC
Figure 11. Effect of water flow rate on the performance of the “10-cell stack”
Figure 12. Long term testing of the single cell.
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9. FIGURES
Figure 1.
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Figure 2.
Figure 3.
17
Figure 4.
18
Figure 5.
19
Figure 6.
20
Figure 7.
21
Figure 8.
22
Figure 9.
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Figure 10.
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25
Figure 11.
Figure 12.
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