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Parallel serpentine-baffle flow field design for water management in a proton exchange membrane fuel cell
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Parallel serpentine-baffle flow field design for water management in a proton exchange membrane fuel cell Pablo Martins Belchor a,b,c, Maria Madalena Camargo Forte b,*, Deyse Elisabeth Ortiz Suman Carpenter a a
The Foundation Regional University of Blumenau (FURB), GEAM, Rua Sa˜o Paulo 3250, Blumenau 89030-000, Brazil Federal University of Rio Grande do Sul (UFRGS), School of Engineering, Department of Materials, LAPOL, Av. Bento Gonc¸alves 9500, P.O. Box 15.010, Porto Alegre 91501-970, Brazil c University for the Development of the Upper Valley of the Itajaı´ (UNIDAVI), PEP, Rua Guilherme Gemballa 13, Rio do Sul 89160-000, Brazil b
article info
abstract
Article history:
In a proton exchange membrane fuel cell (PEMFC) water management is one of the critical
Received 16 February 2012
issues to be addressed. Although the membrane requires humidification for high proton
Received in revised form
conductivity, water in excess decreases the cell performance by flooding. In this paper an
11 May 2012
improved strategy for water management in a fuel cell operating with low water content is
Accepted 17 May 2012
proposed using a parallel serpentine-baffle flow field plate (PSBFFP) design compared to the
Available online 19 June 2012
parallel serpentine flow field plate (PSFFP). The water management in a fuel cell is closely connected to the temperature control in the fuel cell and gases humidifier. The PSBFFP and
Keywords:
the PSFFP were evaluated comparatively under three different humidity conditions and
Fuel cell
their influence on the PEMFC prototype performance was monitored by determining the
Proton exchange membrane fuel cell
current densityevoltage and current densityepower curves. Under low humidification
PEMFC
conditions the PEMFC prototype presented better performance when fitted with the PSBFFP
Flow field design
since it retains water in the flow field channels.
Water management
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
Hydrogen
1.
Introduction
In a proton exchange membrane fuel cell (PEMFC), hydrogen and oxygen react electrochemically to form water, producing electricity and heat. The electrons and protons generated in the catalyzed hydrogen oxidation reaction flow from the anode to the cathode through, respectively, an electrical circuit and an electrolyte membrane. In the cathode, oxygen is catalytically reduced by the electrons and combines with the protons producing water. In a PEMFC, both thermal and water management are critical to prevent the fuel cell from
reserved.
overheating and deteriorating [1]. The water management is one of the considerable technical challenges that have received considerable attention in the fuel cell technology field [2e15]. In a PEMFC operating at 80 Ce100 C, the proton conductivity of the membrane is strongly dependent on its water uptake and low humidification reduces the fuel cell performance and even causes physical damage to it [6]. Proton conductivity is better under wet conditions because the protons move through the hydrated regions of the membrane, in which the ionomer sulfonic acid groups are dissociated, by jumping from one sulfonic group to another [7,8]. Under low
* Corresponding author. Tel.: þ55 51 3308 9417; fax: þ55 51 3308 9414. E-mail addresses: [email protected] (P. Martins Belchor), [email protected] (M.M. Camargo Forte), [email protected] (D.E. Ortiz Suman Carpenter). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.05.091
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humidification conditions there is almost no dissociation of the sulfonic acid groups and thus the proton migration to the cathode is hindered depressing the membrane conductivity. A fully hydrated membrane exhibits up to 300 times higher conductivity than a dried one [16]. Besides the water produced at the catalyst layeremembrane interface in the cathode, water is also supplied to the fuel cell by the humidification of the reactant gases or by direct water addition when the reactant is liquid, i.e. methanol or ethanol [10,11,15,17]. The hydrogen humidification is of greater concern since water is only produced by chemical reaction in the cathode. At low current densities, back diffusion will prevail over electro-osmosis, while at high current densities, electro-osmosis will prevail over back diffusion and the anode will tend to dry out, even if the cathode is highly hydrated [7,8]. Moreover, while the membrane hydration is extremely relevant, the diffusion and catalytic layers and the flow field channels should not have an excess of water, because this causes flooding in the system hindering the gas diffusion or reactant access to the catalyst layers [5,6,14,15,18,19], generating overpotential or reactant gas pressure loss [20]. Water management and flooding mitigation are of paramount importance to PEM fuel cell technology and must be addressed with due consideration to the overall system design. In this regard, a flow field bipolar plate (BPP) with an appropriate design is one of the best strategies used for dealing the fuel cell flooding [21e33]. The BPPs supply the reactant gases through the flow channels to the electrodes and also have the purpose of electronically connecting the cell units in the electrochemical cell stack. The BPPs also provide mechanical support to the weak membrane assemblies (MEAs) and must facilitate water management within the cell. The bipolar plate is one of the most important components in PEMFC stacks and must guarantee a good stack performance and long lifetime. A variety of different geometrical configurations are known and the designs that have been typically used include the pin-type flow field, serieseparallel flow field, serpentine flow field, integrated flow fields and interdigitated flow field [21]. A serpentine flow field plate yields better fuel cell performance than a parallel flow field plate, since in the former the gas concentration is well distributed in the flow field channels [22]. An interdigitated flow field plate, compared to the parallel and serpentine types, yields fuel cells with improved performance since the reactant transport in the diffusion and catalyst layers is mainly driven by forced convection [23e27]. However, interdigitated flow field plates present very large pressure losses [27]. In this study, an improved strategy for water management in a fuel cell operating with low water content is proposed using a parallel serpentine-baffle flow field plate (PSBFFP). The PSBFFP configuration proposed is a variation of the novel serpentinebaffle flow field (SBFF) design proposed by Wang et al. [28]. The PSBFFP design has the characteristics of the parallel serpentine flow field plates (PSFFP), the most used design [29e31], and the interdigitated flow field plates (IFFP), the best design for the removal of liquid water from the flow channels [26,27,31]. The PSBFFP and a PSFFP were evaluated in a PEMFC prototype under different humidification conditions. The performance of the PEMFC prototype equipped with the
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PSBFFP was evaluated by determining the current densityevoltage and current densityepower curves.
2.
Material and methods
2.1.
Materials
Membraneeelectrode assemblies (MEA) were prepared as previously reported [34] using the commercial membrane Nafion 117 (Du Pont). The electrodes were prepared with an electrocatalyst ink on Toray graphite paper (EC-TP1-060T, 0.49 g/cm2) used as a gas diffusion layer (GDL) by spraying the electrocatalyst ink on one side of the GDL (GDE). The electrocatalyst ink consisted of an emulsion of 20 wt.% Pt supported on a carbon black catalyst from E-TEK Inc. (Vulcan XC-72R) in a water-based 5 wt.% Nafion solution (DuPont DE-520). The platinum contents in the dry anode and the cathode electrodes were 1.07 and 1.1 mg Pt/cm2, respectively. Before preparing the MEA, a pre-cut Nafion membrane piece was activated to ensure full conversion to its acid form. The MEA was obtained by pressing the GDE þ Membrane þ GDE sandwich-type system for 2 min under a pressure of 5 ton at 120 C. All MEAs used had the same gas diffusion layer, catalyst layer and proton exchange membrane thicknesses. The gas diffusion layer was 0.17 mm thick, the catalyst layer was approximately 0.120 mm thick, and the proton exchange membrane was 0.175 mm thick.
Fig. 1 e Image of the graphite plates. (a) PSFFP and (b) PSBFFP.
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2.2.
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Flow field plate and PEMFC prototype
The flow field plates were made up of graphite by machining commercial solid graphite used in specially-manufactured refractory pieces. The solid graphite was produced by Graphitas Com. Rep. Ltda (BR), from raw material provided by Poco Graphite Co. (USA), with a very thin lattice structure and consistent grain quality through an isostatic process. Two flow field plates with parallel serpentine-baffle flow field (PSBFFP) were produced and two with the parallel serpentine flow field plates (PSFFP). Images of these plates are shown in Fig. 1. Miniature plate pairs were produced with dimensions of 46.8 mm 46.8 mm 10 mm in a chiral way with two holes for connecting a thermocouple and a dynamic load device. Both plate types were made with 3 flow channels with the same cross sectional area, 2 mm wide and 1 mm height, and 2 ribs 1.37 mm wide. The flow field channel area was 29 mm 29 mm. The PEMFC prototype single cell consisted of the MEA sandwiched between two graphite flow field plates in an external stainless structure which allowed the compression of the fuel cell components. Teflon plates were used as thermal insulators to prevent heat exchange between the plates and the environment. Fig. 2 shows the frontal and lateral views of the fuel cell test station built and used in the experiments. The reactant inlet and outlet in the cell were fitted perfectly onto the flow field plates which support the MEA. Insulating gaskets of silicon elastomeric were used to seal the plates and the PEMFC prototype was tightened by screws at a torque of 3 Nm. Crossover and leak flows tested before use of the unit cell were negligible.
2.3.
Test setup and instrumentation
Fig. 3 shows a schematic configuration of the PEMFC unitary cell flow diagram in which both hydrogen and oxygen were
Fig. 2 e PEMFC unit used in the experiments. Frontal (a) and lateral (b) views.
supplied to the anode and cathode, respectively, at fixed stoichiometry controlled by a flowmeter. The hydrogen flow was 161 mL/min and the oxygen flow was 218 mL/min. Both reactants were humidified by passing the reactant gas in a closed container filled with deionized water, thermally insulated with a temperature controller, before reaching the cell. The gas humidification degree was controlled by the water temperature of the container and the higher the water temperature the higher the gas humidification. The overall temperature of the cell was determined using two thermocouples oppositely located on the two flow field plates. The fuel cell temperature was controlled by heaters in contact with the flow field plates and a thermostat connected to one of the plates (both plates were in thermal equilibrium). The heaters and thermostat were also connected to a temperature control system (model CTT-10) manufactured by Electrocell. The fuel cell was connected in parallel with a dynamic load (Electrocell model cdr50a-2) and to a computer. The PEMFC prototype performance was evaluated by recording densityevoltage and current densityepower curves under different conditions. Through the ohmic resistance variation of the dynamic load the electric current (I ) values could be checked along with the corresponding electric potential (V). The software SCDinamica (Electrocell) was used to register the current densityevoltage and current densityepower curves.
3.
Results and discussion
The bipolar plate is a vital component in a PEMFC as it supplies fuel and oxidant to reactive sites, collects produced current and removes reaction products, besides providing mechanical support for the cells in the stack. Many studies have been carried out to investigate the use of the PEMFCs at higher temperatures than those usually employed (80e100 C) to
Fig. 4 e PSFFP (a) and PSBFFP (b) dimensionless drawings illustrated by applying Solidworks software.
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Fig. 3 e Schematic PEMFC unit flow diagram.
overcome many technological problems related to the use of polymer electrolyte membranes which need to be hydrated to provide good conductivity. In this study a bipolar plate with a more suitable flow field channel is proposed aiming to prevent water loss in a fuel cell with a low degree of humidification as a way to manage the water content in the system by controlling the operational conditions. In order to evaluate the PSBFFP with the proposed configuration, a conventional PSFFP having the same channel dimensions was used under the same operational conditions for comparison. Fig. 4 compares, qualitatively, the flow field channels of the PSBFFP and PSFFP via dimensionless drawings produced in the Solidworks software program. In the PSBFFP the central flow field channel is connected only to the reagent outlet, while in the PSFFP all three channels are connected to the reagent inlet and outlet. The effect of the flow field design on the performance of the PEMFC was evaluated by carrying out tests using the PSFFP pair or the PSBFFP pair or the same plate type in both the anode and the cathode. Three different operational conditions were used in this study by changing the temperature in the fuel cell and in the reactant humidifier as summarized in Table 1. The temperatures were chosen mainly to generate a different degree of humidification in the system that could directly affect the
membrane hydration and thus its conductivity and the fuel cell performance. In a PEM fuel cell water is produced at the cathode and carried by the gas streams. It is eventually absorbed by the membrane or released by evaporation. Water transport through the membrane occurs through electroosmotic drag by protons and back-diffusion. Excess water must be removed from the cell to minimize the diffusion overpotential due to flooding. Electro-osmotic drag involves the transport of water molecules from the anode to the cathode by the protons moving across the membrane and is dependent on the current density. When the membrane is sufficiently conductive the number of water molecules dragged per proton is independent of the degree of membrane hydration [40]. Water gradients inside the membrane may occur due to the production of water on the cathode, water uptake by the membrane and water evaporation. These gradients cause water diffusion in the opposite direction to the electro-osmotic drag, referred to as back-diffusion. The net transport of water across the entire area of the membrane may not be homogeneous and at high current densities it approaches the electro-osmotic drag. At low current densities the net transport of water is more complex and harder to predict. Fig. 5 shows a schematic diagram of the water transport mode in a fuel cell (a) and schematic diagrams of the
Table 1 e Fuel cell and gas humidifier temperatures used in the evaluation of the flow field plates. Temperature ( C)
Condition
(1) (2) (3)
Fuel cell prototype
H2 humidifier
80 75 75
70 80 90
O2 humidifier None None 80
Membrane water content (qualitative) Low Medium High
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PSBFFP (b) and PSFFP (c) type channel configurations. The PSBFFP flow field design proposed has two loops instead of three as proposed by Wang et al. [28], (Fig. 1b) and has the three channels connected to the same gas inlet instead of being connected to different inlet. The current densityevoltage and current densityepower curves obtained for the PEMFC prototype fitted with PSBFFP or PSFFP were comparatively analyzed. The experiments under a given condition were repeated to obtain at least three reproducible curves and the average curve was taken as representative for the evaluated condition. Fig. 6 shows the current densityevoltage (a) and current densityepower (b) curves obtained with the PEMFC prototype fitted with the PSFFP or PSBFFP obtained under condition (1), which aimed to obtain the lowest water content in the system. The temperature in the fuel cell prototype was 80 C and in the H2 humidifier it was 70 C aiming at a low content of water in the anode. The O2 added into the cathode was not humidified. Under this condition the water in the system was that produced chemically in the cathode and introduced with the H2 gas into the anode the membrane hydration was quite low compared to the other conditions and any possible flooding was avoided. Under condition (1) the fuel cell presented quite different curve profiles and the best performance was obtained with the interdigitated parallel plate. With the PSBFFP plate power density values of approximately 1.8 W/ cm2 were obtained at current densities of 0.4e0.6 A/cm2, the maximum of 0.9 W/cm2 being obtained at lower current densities (0.3e0.4 A/cm2) when the fuel cell was fitted with the PSFFP. The better performance of the fuel cell with the PSBFFP
anode
MEA
water diffusion
a
cathode
water production
electro-osmotic drag by protons
can be attributed to the fact that some of the channels are connected to the gas inlet and not connected to the gas outlet, which avoids the elimination of water from the system. The PSBFFP configuration proposed for the flow field channels in this study causes a differential pressure across the channels and generates the partial pressure of H2 necessary to drive H2 through the GDL. In this case the humidity inside the channels is retained and the membrane reached good water content for proton transportation improving the cell performance. Um et al. [35] have previously discussed, in a study with an interdigitated flow field plate, that forced convection of the gases through the GDL helps to improve the fuel cell performance at high current densities. On the other hand, the lower performance of the fuel cell equipped with the PSFFP can be attributed to lower water content in the flow field channels since the water produced in the cathode could be more easily removed from the cell by the continuous gas flow reducing the water content in the membrane. Fig. 7 shows the current densityevoltage (a) and current densityepower (b) curves obtained for the PEMFC prototype equipped with both PSFFP and PSBFFP operating under condition (2). In this case the temperature in the fuel cell prototype was 75 C and in the H2 humidifier it was 80 C. The O2 added to the cathode was not humidified. Using condition (2), up to a current density of 0.6 A/cm2, the fuel cell prototype presented the same curve profile or performance for both types of plates.
water back-diffusion
b anode-
-cathode
c anode-
-cathode
Fig. 5 e Modes of water transport in a fuel cell (a) and schematic diagram of the parallel serpentine-baffle (PSBFFP) (b) and parallel serpentine (PSFFP) (c) flow fields configurations used in this work.
Fig. 6 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 1: FC [ 80 C; H2 humidifier [ 70 C; O2 not humidified.
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Fig. 7 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 2: FC [ 75 C; H2 humidifier [ 80 C; O2 not humidified.
At current density values higher than 0.6 A/cm2 the fuel cell fitted with the parallel PSFFP presented better performance. At current densities lower than 0.6 A/cm2 the water content did not depress the fuel cell performance regardless of the plate type used, since the current density level was not high enough to create diffusion overpotential. It can be seen from the curve slopes that the fuel cell performance was affected by the flooding and the curves became much steeper at higher current densities when the water quantity produced was higher. As previously discussed [18,36], when the humidification in the fuel cell increases at the anode side the water condenses causing flooding, which reduces the active catalytic area and hydrogen mass transport depressing the cell performance. Thus, the temperature decrease from 80 C to 75 C in the fuel cell and increase from 70 C to 80 C in the hydrogen humidifier increased the anode humidification causing flooding. An increasing in the water content in the anode depresses the water removal rates in the cathode by back diffusion leading to a reduction of the downstream segments [36]. Since the fuel cell temperature under condition (2) was lower than that used in condition (1) (80 C) more water could be retained in the system and thus the membrane could also have a higher degree of humidification. In this case only when the fuel cell operated at current densities higher than 0.6 A/cm2 did the parallel PSFFP appear have a more suitable design for
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the management of the water concentrated in the flow field channels and diffusion layers resulting in better performance. In spite of the fact that the flooding generally occurs during fuel cell operation at high current densities, several studies have indicated that liquid water storage can be an issue in all operating regimes, particularly at low gas flow rates, or low temperatures [18], or if liquid water is not properly removed from the channels [37,38]. According to Chang et al. [39], a marked loss in the cell performance can be attributable to a large reduction in the oxygen transport rate incurred by the flooding at high current densities, when the water production rate exceeds the removal rate. Thus, the water content in the membrane is crucial for good performance of the fuel cell, and when it is low the membrane becomes dehydrated and its resistance to proton conduction increases sharply, as previously reported in Ref. [40]. On the other hand, if flooding occurs the liquid water hinders the reactant transport through the channels and gas diffusion layer, and consequently to the electrocatalyst reactive sites, affecting the fuel cell performance particularly at high current densities [41,42]. In this study, at current densities over 0.6 A/cm2 the diffusion overpotential decreased the cell performance and a better result was obtained when parallel plates (PSFFP) were used because the water content was more successfully reduced or only a very slight degree of flooding occurred. Fig. 8 shows the current densityevoltage (a) and current densityepower (b) curves obtained for the PEMFC prototype equipped with the PSFFP or PSBFFP operating under condition (3), in which both reactants were humidified. The temperature in the fuel cell was 75 C and in the H2 and O2 humidifiers it was 90 C and 80 C, respectively. Water was introduced at both the anode and cathode sides. The higher temperature in the hydrogen and oxygen humidifiers, compared to that in the fuel cell, increased the humidity in the system, mainly on the cathode side in which water is usually chemically produced. The operating temperature of the fuel cell, which affects or changes the water saturation pressure, has a strong influence on the water evaporation and water absorption by the membrane. Under condition (3), the fuel cell with both types of flow field plates presented the same performance, except when the current densities were much lower (0.1 A/cm2) than that observed under condition (2), which could also be a consequence of overpotential. At current density values higher than 0.1 A/cm2, the fuel cell equipped with PSFFP showed much better performance than when fitted with the PSBFFP plates since the latter was built with the capacity of retain water at both the anode and cathode sides because three channels are connected to the inlet reactant gas and only one is connected to the outlet reactant gas. Although flooding can occur in both electrodes [42,43], it is especially crucial when it occurs in the cathode in which water is also chemically produced [44]; however, in the literature [45,46] the focus is almost exclusively on flooding at the cathode side, with a few exceptions. If the gas added at the cathode side is humidified, the exit water stream in the cathode is usually saturated and part of the water leaves the cell in the liquid state. Hence, it can be concluded that when air is humidified at the cathode side the prevention of flooding is much greater than the prevention of drying. A major characteristic of the PSBFFP in retaining water in the flow field
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prevents water loss from the channels. This plate can also dispense with the need for the use of a peripheral humidifier device for water management. On the other hand, when the PEMFC prototype equipped with the PSBFFP was operated with a high degree of humidification an excess of water was observed in the channels decreasing the fuel cell performance. If a fuel cell operates under conditions of high current density, pressure and humidity with a low fuel cell temperature and reactant flow there will be a water surplus in the plate channels. On the other hand, if the operating conditions are low current density and pressure, high fuel cell temperature and high reactant flow there will be a water deficit in the channels. Thus, if a fuel cell must be operated under the latter conditions and is equipped with the designed PSBFFP plates it will have a good performance, since the proposed design assures a higher humidity by retaining water in the channels. In this case, the PSBFFP with the configuration here proposed will depress the water output from the channels, which is beneficial in terms of the membrane hydration and fuel cell performance.
Acknowledgments
Fig. 8 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 3: FC [ 75 C; H2 humidifier [ 90 C; O2 humidifier [ 80 C.
The financial support of the Brazilian Government Agencies Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior (CAPES/PROCAD Project n 200/2007) and Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) is gratefully acknowledged. The authors are grateful to Dr Marcelo Linardi of the The Centro de Ce´lulas a Combustı´vel e Hidrogeˆnio (CCCH) for his kind contribution and support.
Nomenclature channels, having a greater tendency to generate flooding at both the anode and the cathode side, is anticipating the diffusion overpotential. Exposed to the same situation of high water content, the fuel cell equipped with the PSFFP showed a much higher capacity to remove the excess of water, preventing flooding and providing better fuel cell performance. Thus, under conditions of low water content in the system a fuel cell equipped with the PSBFFP with the proposed configuration will retain water in the channels, which is beneficial in terms of the membrane hydration and fuel cell performance.
4.
Conclusions
The water management in a fuel cell is closely connected to the temperature control in the cell and gases humidifier. The humidification of H2 and O2 gases was a decisive factor for the PEMFC prototype performance, and a low content or excess of water in the flow field channels permitted the designed flow field channel to be evaluated by monitoring changes in the fuel cell performance caused by flooding and overpotential. The results showed that the designed parallel serpentine-baffle flow field plate (PSBFFP) is potentially a more suitable plate or a good solution for use in a fuel cell operating at temperatures higher than 100 C, since it
IFFP PSBFFP MEA PEMFC PSFFP
interdigitated parallel flow field plate parallel serpentine-baffle flow field plate membrane electrode assembly proton exchange membrane fuel cell parallel serpentine flow field plate
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[26] Hu G, Fan J, Chen S, Liu Y, Cen K. Three-dimensional numerical analysis of proton exchange membrane fuel cells (PEMFCs) with conventional and interdigitated flow fields. J Power Sources 2004;136:1e9. [27] Spernjak D, Prasad AK, Advani SG. In situ comparison of water content and dynamics in parallel, single serpentine, and interdigitated flow fields of polymer electrolyte membrane fuel cells. J Power Sources 2010;195:3553e68. [28] Wang X-D, Duan Y-Y, Yan W-M. Novel serpentine-baffle field design for proton exchange membrane fuel cells. J Power Sources 2007;173:210e21. [29] Maharudrayya S, Jayanti S, Deshpande AP. Flow distribution and pressure drop in parallel-channel configurations of planar fuel cells. J Power Sources 2005;144:94e106. [30] Suresh PV, Jayanti S, Deshpande AP, Haridoss P. An improved serpentine flow field with enhanced cross-flow for fuel cell applications. Int J Hydrogen Energy 2011;36:6067e72. [31] Yan W-M, Li H-Y, Chiu P-C, Wang X-D. Effects of serpentine flow field with outlet channel contraction on cell performance of proton exchange membrane fuel cells. J Power Sources 2008;178:174e80. [32] Taccani R, Zuliani N. Effect of flow field design on performances of high temperature PEM fuel cells: experimental analysis. Int J Hydrogen Energy 2010;36:10282e7. [33] Wang X-D, Huang Y-X, Cheng C-H, Jang J-Y, Lee D-J, Yan WM, et al. An inverse geometry design problem for optimization of single serpentine flow field of PEM fuel cell. Int J Hydrogen Energy 2010;35:4247e57. [34] Th Frey, Linardi M. Effects of membrane electrode assembly preparation on the polymer electrolyte membrane fuel cell performance. Electrochim Acta 2004;50:99e105. [35] Um S, Wang CY, Chen KS. Three-dimensional analysis of transport and electrochemical reactions in polymer electrolyte fuel cells. J Power Sources 2004;125:40e51. [36] Buchi FN, Geiger AB, Neto RP. Dependence of current distribution on water management in PEFC technical size. J Power Sources 2005;145:62e7. [37] Liu X, Guo H, Ye F, Ma C. Water flooding and pressure drop characteristics in flow channels of proton exchange membrane fuel cells. Electrochim Acta 2007;52:3607e14. [38] Liu X, Guo H, Ma C. Water flooding and two-phase flow in cathode channels of proton exchange membrane fuel cells. J Power Sources 2006;156:267e80. [39] Chang PAC, St-Pierre J, Strumper J, Wetton B. Flow distribution in proton exchange membrane fuel cell. J Power Sources 2006;162:340e55. [40] Zawodzinski TA, Derouin C, Radzinski S, Sherman RJ, Smith VT, Springer TE, et al. Water uptake by and transport through Nafion 117 membranes. J Electrochem Soc 1993; 140:1041e7. [41] Baschuk JJ, Li X. Modelling of polymer electrolyte membrane fuel cells with variable degrees of water flooding. J Power Sources 2000;86:181e96. [42] Barbir F, Gorgun H, Wang X. Relationship between pressure drop and cell resistance as a diagnostic tool for PEM fuel cells. J Power Sources 2005;141:96e101. [43] Natarajan D, Nguyen TV. Current distribution in PEM fuel cells. Part 1: oxygen and fuel flow rate effects. AIChE 2005;51: 2587e98. [44] Meng H, Wang C-Y. Model of two-phase flow and flooding dynamics in polymer electrolyte fuel cells. J Electrochem Soc 2005;152:A1733e41. [45] Ge S, Wang CY. Liquid water formation and transport in the PEFC anode. J Electrochem Soc 2007;154:B998e1005. [46] Holmstrom N, Ihonen J, Lundblad A, Lindbergh G. The influence of the gas diffusion layer on water management in polymer electrolyte fuel cells. Fuel Cells 2007;7:306e12.
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Parallel serpentine-baffle flow field design for water management in a proton exchange membrane fuel cell Pablo Martins Belchor a,b,c, Maria Madalena Camargo Forte b,*, Deyse Elisabeth Ortiz Suman Carpenter a a
The Foundation Regional University of Blumenau (FURB), GEAM, Rua Sa˜o Paulo 3250, Blumenau 89030-000, Brazil Federal University of Rio Grande do Sul (UFRGS), School of Engineering, Department of Materials, LAPOL, Av. Bento Gonc¸alves 9500, P.O. Box 15.010, Porto Alegre 91501-970, Brazil c University for the Development of the Upper Valley of the Itajaı´ (UNIDAVI), PEP, Rua Guilherme Gemballa 13, Rio do Sul 89160-000, Brazil b
article info
abstract
Article history:
In a proton exchange membrane fuel cell (PEMFC) water management is one of the critical
Received 16 February 2012
issues to be addressed. Although the membrane requires humidification for high proton
Received in revised form
conductivity, water in excess decreases the cell performance by flooding. In this paper an
11 May 2012
improved strategy for water management in a fuel cell operating with low water content is
Accepted 17 May 2012
proposed using a parallel serpentine-baffle flow field plate (PSBFFP) design compared to the
Available online 19 June 2012
parallel serpentine flow field plate (PSFFP). The water management in a fuel cell is closely connected to the temperature control in the fuel cell and gases humidifier. The PSBFFP and
Keywords:
the PSFFP were evaluated comparatively under three different humidity conditions and
Fuel cell
their influence on the PEMFC prototype performance was monitored by determining the
Proton exchange membrane fuel cell
current densityevoltage and current densityepower curves. Under low humidification
PEMFC
conditions the PEMFC prototype presented better performance when fitted with the PSBFFP
Flow field design
since it retains water in the flow field channels.
Water management
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
Hydrogen
1.
Introduction
In a proton exchange membrane fuel cell (PEMFC), hydrogen and oxygen react electrochemically to form water, producing electricity and heat. The electrons and protons generated in the catalyzed hydrogen oxidation reaction flow from the anode to the cathode through, respectively, an electrical circuit and an electrolyte membrane. In the cathode, oxygen is catalytically reduced by the electrons and combines with the protons producing water. In a PEMFC, both thermal and water management are critical to prevent the fuel cell from
reserved.
overheating and deteriorating [1]. The water management is one of the considerable technical challenges that have received considerable attention in the fuel cell technology field [2e15]. In a PEMFC operating at 80 Ce100 C, the proton conductivity of the membrane is strongly dependent on its water uptake and low humidification reduces the fuel cell performance and even causes physical damage to it [6]. Proton conductivity is better under wet conditions because the protons move through the hydrated regions of the membrane, in which the ionomer sulfonic acid groups are dissociated, by jumping from one sulfonic group to another [7,8]. Under low
* Corresponding author. Tel.: þ55 51 3308 9417; fax: þ55 51 3308 9414. E-mail addresses: [email protected] (P. Martins Belchor), [email protected] (M.M. Camargo Forte), [email protected] (D.E. Ortiz Suman Carpenter). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.05.091
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humidification conditions there is almost no dissociation of the sulfonic acid groups and thus the proton migration to the cathode is hindered depressing the membrane conductivity. A fully hydrated membrane exhibits up to 300 times higher conductivity than a dried one [16]. Besides the water produced at the catalyst layeremembrane interface in the cathode, water is also supplied to the fuel cell by the humidification of the reactant gases or by direct water addition when the reactant is liquid, i.e. methanol or ethanol [10,11,15,17]. The hydrogen humidification is of greater concern since water is only produced by chemical reaction in the cathode. At low current densities, back diffusion will prevail over electro-osmosis, while at high current densities, electro-osmosis will prevail over back diffusion and the anode will tend to dry out, even if the cathode is highly hydrated [7,8]. Moreover, while the membrane hydration is extremely relevant, the diffusion and catalytic layers and the flow field channels should not have an excess of water, because this causes flooding in the system hindering the gas diffusion or reactant access to the catalyst layers [5,6,14,15,18,19], generating overpotential or reactant gas pressure loss [20]. Water management and flooding mitigation are of paramount importance to PEM fuel cell technology and must be addressed with due consideration to the overall system design. In this regard, a flow field bipolar plate (BPP) with an appropriate design is one of the best strategies used for dealing the fuel cell flooding [21e33]. The BPPs supply the reactant gases through the flow channels to the electrodes and also have the purpose of electronically connecting the cell units in the electrochemical cell stack. The BPPs also provide mechanical support to the weak membrane assemblies (MEAs) and must facilitate water management within the cell. The bipolar plate is one of the most important components in PEMFC stacks and must guarantee a good stack performance and long lifetime. A variety of different geometrical configurations are known and the designs that have been typically used include the pin-type flow field, serieseparallel flow field, serpentine flow field, integrated flow fields and interdigitated flow field [21]. A serpentine flow field plate yields better fuel cell performance than a parallel flow field plate, since in the former the gas concentration is well distributed in the flow field channels [22]. An interdigitated flow field plate, compared to the parallel and serpentine types, yields fuel cells with improved performance since the reactant transport in the diffusion and catalyst layers is mainly driven by forced convection [23e27]. However, interdigitated flow field plates present very large pressure losses [27]. In this study, an improved strategy for water management in a fuel cell operating with low water content is proposed using a parallel serpentine-baffle flow field plate (PSBFFP). The PSBFFP configuration proposed is a variation of the novel serpentinebaffle flow field (SBFF) design proposed by Wang et al. [28]. The PSBFFP design has the characteristics of the parallel serpentine flow field plates (PSFFP), the most used design [29e31], and the interdigitated flow field plates (IFFP), the best design for the removal of liquid water from the flow channels [26,27,31]. The PSBFFP and a PSFFP were evaluated in a PEMFC prototype under different humidification conditions. The performance of the PEMFC prototype equipped with the
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PSBFFP was evaluated by determining the current densityevoltage and current densityepower curves.
2.
Material and methods
2.1.
Materials
Membraneeelectrode assemblies (MEA) were prepared as previously reported [34] using the commercial membrane Nafion 117 (Du Pont). The electrodes were prepared with an electrocatalyst ink on Toray graphite paper (EC-TP1-060T, 0.49 g/cm2) used as a gas diffusion layer (GDL) by spraying the electrocatalyst ink on one side of the GDL (GDE). The electrocatalyst ink consisted of an emulsion of 20 wt.% Pt supported on a carbon black catalyst from E-TEK Inc. (Vulcan XC-72R) in a water-based 5 wt.% Nafion solution (DuPont DE-520). The platinum contents in the dry anode and the cathode electrodes were 1.07 and 1.1 mg Pt/cm2, respectively. Before preparing the MEA, a pre-cut Nafion membrane piece was activated to ensure full conversion to its acid form. The MEA was obtained by pressing the GDE þ Membrane þ GDE sandwich-type system for 2 min under a pressure of 5 ton at 120 C. All MEAs used had the same gas diffusion layer, catalyst layer and proton exchange membrane thicknesses. The gas diffusion layer was 0.17 mm thick, the catalyst layer was approximately 0.120 mm thick, and the proton exchange membrane was 0.175 mm thick.
Fig. 1 e Image of the graphite plates. (a) PSFFP and (b) PSBFFP.
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2.2.
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Flow field plate and PEMFC prototype
The flow field plates were made up of graphite by machining commercial solid graphite used in specially-manufactured refractory pieces. The solid graphite was produced by Graphitas Com. Rep. Ltda (BR), from raw material provided by Poco Graphite Co. (USA), with a very thin lattice structure and consistent grain quality through an isostatic process. Two flow field plates with parallel serpentine-baffle flow field (PSBFFP) were produced and two with the parallel serpentine flow field plates (PSFFP). Images of these plates are shown in Fig. 1. Miniature plate pairs were produced with dimensions of 46.8 mm 46.8 mm 10 mm in a chiral way with two holes for connecting a thermocouple and a dynamic load device. Both plate types were made with 3 flow channels with the same cross sectional area, 2 mm wide and 1 mm height, and 2 ribs 1.37 mm wide. The flow field channel area was 29 mm 29 mm. The PEMFC prototype single cell consisted of the MEA sandwiched between two graphite flow field plates in an external stainless structure which allowed the compression of the fuel cell components. Teflon plates were used as thermal insulators to prevent heat exchange between the plates and the environment. Fig. 2 shows the frontal and lateral views of the fuel cell test station built and used in the experiments. The reactant inlet and outlet in the cell were fitted perfectly onto the flow field plates which support the MEA. Insulating gaskets of silicon elastomeric were used to seal the plates and the PEMFC prototype was tightened by screws at a torque of 3 Nm. Crossover and leak flows tested before use of the unit cell were negligible.
2.3.
Test setup and instrumentation
Fig. 3 shows a schematic configuration of the PEMFC unitary cell flow diagram in which both hydrogen and oxygen were
Fig. 2 e PEMFC unit used in the experiments. Frontal (a) and lateral (b) views.
supplied to the anode and cathode, respectively, at fixed stoichiometry controlled by a flowmeter. The hydrogen flow was 161 mL/min and the oxygen flow was 218 mL/min. Both reactants were humidified by passing the reactant gas in a closed container filled with deionized water, thermally insulated with a temperature controller, before reaching the cell. The gas humidification degree was controlled by the water temperature of the container and the higher the water temperature the higher the gas humidification. The overall temperature of the cell was determined using two thermocouples oppositely located on the two flow field plates. The fuel cell temperature was controlled by heaters in contact with the flow field plates and a thermostat connected to one of the plates (both plates were in thermal equilibrium). The heaters and thermostat were also connected to a temperature control system (model CTT-10) manufactured by Electrocell. The fuel cell was connected in parallel with a dynamic load (Electrocell model cdr50a-2) and to a computer. The PEMFC prototype performance was evaluated by recording densityevoltage and current densityepower curves under different conditions. Through the ohmic resistance variation of the dynamic load the electric current (I ) values could be checked along with the corresponding electric potential (V). The software SCDinamica (Electrocell) was used to register the current densityevoltage and current densityepower curves.
3.
Results and discussion
The bipolar plate is a vital component in a PEMFC as it supplies fuel and oxidant to reactive sites, collects produced current and removes reaction products, besides providing mechanical support for the cells in the stack. Many studies have been carried out to investigate the use of the PEMFCs at higher temperatures than those usually employed (80e100 C) to
Fig. 4 e PSFFP (a) and PSBFFP (b) dimensionless drawings illustrated by applying Solidworks software.
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Fig. 3 e Schematic PEMFC unit flow diagram.
overcome many technological problems related to the use of polymer electrolyte membranes which need to be hydrated to provide good conductivity. In this study a bipolar plate with a more suitable flow field channel is proposed aiming to prevent water loss in a fuel cell with a low degree of humidification as a way to manage the water content in the system by controlling the operational conditions. In order to evaluate the PSBFFP with the proposed configuration, a conventional PSFFP having the same channel dimensions was used under the same operational conditions for comparison. Fig. 4 compares, qualitatively, the flow field channels of the PSBFFP and PSFFP via dimensionless drawings produced in the Solidworks software program. In the PSBFFP the central flow field channel is connected only to the reagent outlet, while in the PSFFP all three channels are connected to the reagent inlet and outlet. The effect of the flow field design on the performance of the PEMFC was evaluated by carrying out tests using the PSFFP pair or the PSBFFP pair or the same plate type in both the anode and the cathode. Three different operational conditions were used in this study by changing the temperature in the fuel cell and in the reactant humidifier as summarized in Table 1. The temperatures were chosen mainly to generate a different degree of humidification in the system that could directly affect the
membrane hydration and thus its conductivity and the fuel cell performance. In a PEM fuel cell water is produced at the cathode and carried by the gas streams. It is eventually absorbed by the membrane or released by evaporation. Water transport through the membrane occurs through electroosmotic drag by protons and back-diffusion. Excess water must be removed from the cell to minimize the diffusion overpotential due to flooding. Electro-osmotic drag involves the transport of water molecules from the anode to the cathode by the protons moving across the membrane and is dependent on the current density. When the membrane is sufficiently conductive the number of water molecules dragged per proton is independent of the degree of membrane hydration [40]. Water gradients inside the membrane may occur due to the production of water on the cathode, water uptake by the membrane and water evaporation. These gradients cause water diffusion in the opposite direction to the electro-osmotic drag, referred to as back-diffusion. The net transport of water across the entire area of the membrane may not be homogeneous and at high current densities it approaches the electro-osmotic drag. At low current densities the net transport of water is more complex and harder to predict. Fig. 5 shows a schematic diagram of the water transport mode in a fuel cell (a) and schematic diagrams of the
Table 1 e Fuel cell and gas humidifier temperatures used in the evaluation of the flow field plates. Temperature ( C)
Condition
(1) (2) (3)
Fuel cell prototype
H2 humidifier
80 75 75
70 80 90
O2 humidifier None None 80
Membrane water content (qualitative) Low Medium High
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PSBFFP (b) and PSFFP (c) type channel configurations. The PSBFFP flow field design proposed has two loops instead of three as proposed by Wang et al. [28], (Fig. 1b) and has the three channels connected to the same gas inlet instead of being connected to different inlet. The current densityevoltage and current densityepower curves obtained for the PEMFC prototype fitted with PSBFFP or PSFFP were comparatively analyzed. The experiments under a given condition were repeated to obtain at least three reproducible curves and the average curve was taken as representative for the evaluated condition. Fig. 6 shows the current densityevoltage (a) and current densityepower (b) curves obtained with the PEMFC prototype fitted with the PSFFP or PSBFFP obtained under condition (1), which aimed to obtain the lowest water content in the system. The temperature in the fuel cell prototype was 80 C and in the H2 humidifier it was 70 C aiming at a low content of water in the anode. The O2 added into the cathode was not humidified. Under this condition the water in the system was that produced chemically in the cathode and introduced with the H2 gas into the anode the membrane hydration was quite low compared to the other conditions and any possible flooding was avoided. Under condition (1) the fuel cell presented quite different curve profiles and the best performance was obtained with the interdigitated parallel plate. With the PSBFFP plate power density values of approximately 1.8 W/ cm2 were obtained at current densities of 0.4e0.6 A/cm2, the maximum of 0.9 W/cm2 being obtained at lower current densities (0.3e0.4 A/cm2) when the fuel cell was fitted with the PSFFP. The better performance of the fuel cell with the PSBFFP
anode
MEA
water diffusion
a
cathode
water production
electro-osmotic drag by protons
can be attributed to the fact that some of the channels are connected to the gas inlet and not connected to the gas outlet, which avoids the elimination of water from the system. The PSBFFP configuration proposed for the flow field channels in this study causes a differential pressure across the channels and generates the partial pressure of H2 necessary to drive H2 through the GDL. In this case the humidity inside the channels is retained and the membrane reached good water content for proton transportation improving the cell performance. Um et al. [35] have previously discussed, in a study with an interdigitated flow field plate, that forced convection of the gases through the GDL helps to improve the fuel cell performance at high current densities. On the other hand, the lower performance of the fuel cell equipped with the PSFFP can be attributed to lower water content in the flow field channels since the water produced in the cathode could be more easily removed from the cell by the continuous gas flow reducing the water content in the membrane. Fig. 7 shows the current densityevoltage (a) and current densityepower (b) curves obtained for the PEMFC prototype equipped with both PSFFP and PSBFFP operating under condition (2). In this case the temperature in the fuel cell prototype was 75 C and in the H2 humidifier it was 80 C. The O2 added to the cathode was not humidified. Using condition (2), up to a current density of 0.6 A/cm2, the fuel cell prototype presented the same curve profile or performance for both types of plates.
water back-diffusion
b anode-
-cathode
c anode-
-cathode
Fig. 5 e Modes of water transport in a fuel cell (a) and schematic diagram of the parallel serpentine-baffle (PSBFFP) (b) and parallel serpentine (PSFFP) (c) flow fields configurations used in this work.
Fig. 6 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 1: FC [ 80 C; H2 humidifier [ 70 C; O2 not humidified.
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Fig. 7 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 2: FC [ 75 C; H2 humidifier [ 80 C; O2 not humidified.
At current density values higher than 0.6 A/cm2 the fuel cell fitted with the parallel PSFFP presented better performance. At current densities lower than 0.6 A/cm2 the water content did not depress the fuel cell performance regardless of the plate type used, since the current density level was not high enough to create diffusion overpotential. It can be seen from the curve slopes that the fuel cell performance was affected by the flooding and the curves became much steeper at higher current densities when the water quantity produced was higher. As previously discussed [18,36], when the humidification in the fuel cell increases at the anode side the water condenses causing flooding, which reduces the active catalytic area and hydrogen mass transport depressing the cell performance. Thus, the temperature decrease from 80 C to 75 C in the fuel cell and increase from 70 C to 80 C in the hydrogen humidifier increased the anode humidification causing flooding. An increasing in the water content in the anode depresses the water removal rates in the cathode by back diffusion leading to a reduction of the downstream segments [36]. Since the fuel cell temperature under condition (2) was lower than that used in condition (1) (80 C) more water could be retained in the system and thus the membrane could also have a higher degree of humidification. In this case only when the fuel cell operated at current densities higher than 0.6 A/cm2 did the parallel PSFFP appear have a more suitable design for
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the management of the water concentrated in the flow field channels and diffusion layers resulting in better performance. In spite of the fact that the flooding generally occurs during fuel cell operation at high current densities, several studies have indicated that liquid water storage can be an issue in all operating regimes, particularly at low gas flow rates, or low temperatures [18], or if liquid water is not properly removed from the channels [37,38]. According to Chang et al. [39], a marked loss in the cell performance can be attributable to a large reduction in the oxygen transport rate incurred by the flooding at high current densities, when the water production rate exceeds the removal rate. Thus, the water content in the membrane is crucial for good performance of the fuel cell, and when it is low the membrane becomes dehydrated and its resistance to proton conduction increases sharply, as previously reported in Ref. [40]. On the other hand, if flooding occurs the liquid water hinders the reactant transport through the channels and gas diffusion layer, and consequently to the electrocatalyst reactive sites, affecting the fuel cell performance particularly at high current densities [41,42]. In this study, at current densities over 0.6 A/cm2 the diffusion overpotential decreased the cell performance and a better result was obtained when parallel plates (PSFFP) were used because the water content was more successfully reduced or only a very slight degree of flooding occurred. Fig. 8 shows the current densityevoltage (a) and current densityepower (b) curves obtained for the PEMFC prototype equipped with the PSFFP or PSBFFP operating under condition (3), in which both reactants were humidified. The temperature in the fuel cell was 75 C and in the H2 and O2 humidifiers it was 90 C and 80 C, respectively. Water was introduced at both the anode and cathode sides. The higher temperature in the hydrogen and oxygen humidifiers, compared to that in the fuel cell, increased the humidity in the system, mainly on the cathode side in which water is usually chemically produced. The operating temperature of the fuel cell, which affects or changes the water saturation pressure, has a strong influence on the water evaporation and water absorption by the membrane. Under condition (3), the fuel cell with both types of flow field plates presented the same performance, except when the current densities were much lower (0.1 A/cm2) than that observed under condition (2), which could also be a consequence of overpotential. At current density values higher than 0.1 A/cm2, the fuel cell equipped with PSFFP showed much better performance than when fitted with the PSBFFP plates since the latter was built with the capacity of retain water at both the anode and cathode sides because three channels are connected to the inlet reactant gas and only one is connected to the outlet reactant gas. Although flooding can occur in both electrodes [42,43], it is especially crucial when it occurs in the cathode in which water is also chemically produced [44]; however, in the literature [45,46] the focus is almost exclusively on flooding at the cathode side, with a few exceptions. If the gas added at the cathode side is humidified, the exit water stream in the cathode is usually saturated and part of the water leaves the cell in the liquid state. Hence, it can be concluded that when air is humidified at the cathode side the prevention of flooding is much greater than the prevention of drying. A major characteristic of the PSBFFP in retaining water in the flow field
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prevents water loss from the channels. This plate can also dispense with the need for the use of a peripheral humidifier device for water management. On the other hand, when the PEMFC prototype equipped with the PSBFFP was operated with a high degree of humidification an excess of water was observed in the channels decreasing the fuel cell performance. If a fuel cell operates under conditions of high current density, pressure and humidity with a low fuel cell temperature and reactant flow there will be a water surplus in the plate channels. On the other hand, if the operating conditions are low current density and pressure, high fuel cell temperature and high reactant flow there will be a water deficit in the channels. Thus, if a fuel cell must be operated under the latter conditions and is equipped with the designed PSBFFP plates it will have a good performance, since the proposed design assures a higher humidity by retaining water in the channels. In this case, the PSBFFP with the configuration here proposed will depress the water output from the channels, which is beneficial in terms of the membrane hydration and fuel cell performance.
Acknowledgments
Fig. 8 e Current densityevoltage curve (a) and current densityepower curve (b) of the PEMFC unit equipped with PSFFP (d-d) and PSBFFP (dCd). Temperature conditions 3: FC [ 75 C; H2 humidifier [ 90 C; O2 humidifier [ 80 C.
The financial support of the Brazilian Government Agencies Coordenac¸a˜o de Aperfeic¸oamento de Pessoal de Nı´vel Superior (CAPES/PROCAD Project n 200/2007) and Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo´gico (CNPq) is gratefully acknowledged. The authors are grateful to Dr Marcelo Linardi of the The Centro de Ce´lulas a Combustı´vel e Hidrogeˆnio (CCCH) for his kind contribution and support.
Nomenclature channels, having a greater tendency to generate flooding at both the anode and the cathode side, is anticipating the diffusion overpotential. Exposed to the same situation of high water content, the fuel cell equipped with the PSFFP showed a much higher capacity to remove the excess of water, preventing flooding and providing better fuel cell performance. Thus, under conditions of low water content in the system a fuel cell equipped with the PSBFFP with the proposed configuration will retain water in the channels, which is beneficial in terms of the membrane hydration and fuel cell performance.
4.
Conclusions
The water management in a fuel cell is closely connected to the temperature control in the cell and gases humidifier. The humidification of H2 and O2 gases was a decisive factor for the PEMFC prototype performance, and a low content or excess of water in the flow field channels permitted the designed flow field channel to be evaluated by monitoring changes in the fuel cell performance caused by flooding and overpotential. The results showed that the designed parallel serpentine-baffle flow field plate (PSBFFP) is potentially a more suitable plate or a good solution for use in a fuel cell operating at temperatures higher than 100 C, since it
IFFP PSBFFP MEA PEMFC PSFFP
interdigitated parallel flow field plate parallel serpentine-baffle flow field plate membrane electrode assembly proton exchange membrane fuel cell parallel serpentine flow field plate
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