Development and applications of portable systems based on conventional PEM fuel cells

Development and applications of portable systems based on conventional PEM fuel cells

6

A. Rodrı´guez-Castellanos, J.L. Dı´az-Bernab
e, S. Citala´n-Cigarroa, O. Solorza-Feria Chemistry Department, Center for Research and Advances Studies, CINVESTAV-IPN, National Polytechnic Institute, Mexico City, Mexico

Chapter Outline 6.1 Introduction 91 6.2 Schematic layouts of PEMFCs and their configuration

94

6.2.1 Monopolar and bipolar current collectors 94 6.2.2 Membrane electrode assembly (MEA) 95

6.3 Power electronic interfaces for portable PEMFC systems 97 6.4 Water and heat 99 6.5 Modeling 100 6.6 Performance and durability 100 6.7 Portable power prototype devices 101 Acknowledgments 104 References 104

6.1

Introduction

The polymer electrolyte membrane fuel cell (PEMFC) has long been recognized as a promising zero-emission, versatile power source for a wide range of applications like portable electronic telecommunications. Growing power demands by modern, energyintensive electronics are unlikely to be satisfied through current battery technology due to its low energy capability and long charging time. Hydrogen, a clean energy source with the highest specific energy density, represents the best alternative to batteries and fossil fuels used in conventional energy production (Wang et al., 2011; Debe, 2012; Wu and Yang, 2013). PEMFCs are devices that efficiently convert diverse chemical fuels into electricity and are a key component toward a sustainable clean energy economy. However, their mass commercialization is hindered by the slow kinetics of the cathodic reaction and by the high cost of platinum-based catalyst electrodes (Shao et al., 2016). In low-temperature fuel cells, hydrogen is fed to the anode and carries out an oxidation process on the catalytic surface of the electrode, releasing electrons that form Portable Hydrogen Energy Systems. https://doi.org/10.1016/B978-0-12-813128-2.00006-1 © 2018 Elsevier Inc. All rights reserved.

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Portable Hydrogen Energy Systems

Gas diffusion layers

Anodic collector

Cathodic collector

MEA O2 in H2 in

O2 excess and water out

H2 excess

Insulating gaskets Graphite bipolar plates

Fig. 6.1 PEMFC components: bipolar plates, gaskets, gas diffusion layers, and membraneelectrode assembly (MEA).

an electric current that is channeled by an external circuit for use in a specific application (Fig. 6.1). At the anode, protons are generated in the form of H+
nH2O (Bagotsky, 2009; Bagotsky et al., 2015) and are diffused to the cathode through the polymer electrolyte membrane via a proton-exchange mechanism where they combine with pure oxygen (oxidizing reagent) either fed to the system or taken from the air. This enables a reduction process on the catalytic surface that produces water and heat as waste products. The half-electrochemical reactions occurring on the cathode and anode are presented: Anode : 2H2 + nH2 O ! 4H +
nH2 O + 4e

(6.1)

Cathode : O2 + 4H +
nH2 O + 4e ! ð4n + 2ÞH2 O

(6.2)

Overall : 2H2 + O2 ! 2H2 O

(6.3)

The simple structure of hydrogen-air fuel cells has allowed for a rapid development of portable power prototypes; they provide uninterrupted electric power from the hydrogen oxidation with a high level of efficiency and power density. PEMFCs also possess other notable advantages: low working temperatures, minimal maintenance, long service lifetime, and compactness. Additionally, the lack of moving parts in a PEMFC allows for noiseless operation. Individual single fuel cells are each capable of

Development and applications of portable systems based on conventional PEM fuel cells

93

producing an electric potential of <1 V. By connecting individual cells in series, it is possible to form a stack of bipolar plates in an arrangement that increases the overall electric potential generated (Bagotsky et al., 2015; O’Hayre et al., 2016). A complete fuel cell system integrates a hydrogen fuel cell, a DC converter, and electric loads corresponding to various applications; see Fig. 6.2. The current-voltage relation is a cell characteristic, and sometimes, this relation can be simplified as a linear equation (Eq. 6.4). Since electrode polarization varies in each system, the difference between the open-circuit potential (OCP) U0 and the discharge or operating voltage Ui depends on the nature of the electrode reaction. Discharge current and discharge power are two parameters used in the performance evaluation and are calculated through Eqs. (6.5), (6.6); the voltage across an external load with resistance, Rext; and an apparent internal cell resistance, Rapp, assumed to be constant (Bagotsky, 2009): Ui ¼ U0  IRapp I¼

(6.4)

U0 Rapp + Rext

W¼

Ui2 Rapp Rapp + Rext

(6.5)


2

(6.6)

Under current flow through the external circuit, the operating voltage Ui is lower than OCP. This corresponds to a maximum in the power-current relation, commonly observed in PEMFC performance curves. Of significant importance is the overall Load Communication and entertainment PEMFC power source I + Ui

+ DC-DC converter

−

V − Transportation

Fig. 6.2 PEMFC systems with diverse applications.

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Portable Hydrogen Energy Systems

chemical-to-electric energy transformation efficiency, a function dependent on thermodynamic, voltage, coulomb, and design efficiencies (Prater, 1994). Fuel Cell Today classifies a fuel cell as “portable” (Fuel Cells Today, 2017) when it is, built into or powering, a nonstationary device. Mobile devices where fuel cells have been installed include portable military machines (e.g., personal power supply for soldiers and skid-mounted fuel cell generators), auxiliary power units or APUs (e.g., used in travel and trucking industries), and various educational kits and toys. Fuel cell systems are marketed according to their power output, with existing systems capable of operating at <5 W and up to several kilowatts. Standard output classifications are <2, 10–50, and 100–250 W systems (Revankar and Majundar, 2014; Meyers and Maynard, 2002). Higher-output systems require greater cell stacking; consequently, new miniaturized PEMFC prototypes use Nafion membranes coated with electrocatalytic inks to form a layered MEA arrangement that reduces the overall size of a stack. Portable hydrogen fuel cell technology has drawn significant attention due to its simplicity, mass implementation feasibility, fast start-stop cycles, and a wide spectrum of power applications (Wang et al., 2016; Wilberforce et al., 2016; Kim and Kim, 2014).

6.2

Schematic layouts of PEMFCs and their configuration

An electrochemical H2-O2 (air) fuel cell consists in an arrangement of at least two electrodes, a negatively charged anode that produces electrons by the oxidation of hydrogen on its surface and a positively charged cathode, which transfers electrons from its surface to reduce oxygen, generating electricity and heat as by-products of the electrochemical reaction. Fig. 6.3 shows the components of a multilayered membrane-electrode assembly used in the construction of a stacked fuel cell. The MEA consists of catalyst-coated anode and cathode electrodes prepared by hotpressing, gas diffusion layer built into the two sides of a proton-conducing membrane, high-density graphite bipolar plates, aluminum end plates with stainless steel tie blocks and gas inlet ports, and insulating Teflon gaskets.

6.2.1 Monopolar and bipolar current collectors Monopolar plates (MP) are located between the end plates, and they have gas distribution channels on just one side, whereas bipolar plates (BP) are situated among the individual cells and have channels of distribution of flow and exit of water on both sides. The MP and BP uniformly distribute reactants, gas fuels, and air, over the active areas; remove heat; conduct current in the series circuit; and prevent leakage of reactants in high-power PEMFCs (Rodrı´guez-Castellanos et al., 2007). There are a variety of flow field channel configurations in conducting collector plates that may be used in PEMFC prototypes: mixed multichannel serpentine with wide channels, single-channel serpentine, double-channel serpentine, and mixed multichannel serpentine with narrow channels. A mixed multichannel design is the preferred choice for optimum operation of the BP (Urbani et al., 2007; Hermann et al.,

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Fig. 6.3 Components for a fuel cell stack: MEA, gaskets, and bipolar and terminal plates are shown in the upper part of the figure. Tie rods and brass terminal contacts are shown in the lower part of this figure.

2005). BP play a key role in the long-term performance of a fuel cell; diverse materials are used for their construction, including graphite, metals with or without coatings, and composite materials. Traditionally, these plates are produced from graphite due to its excellent resistance to corrosion, chemical stability, low bulk resistivity, low specific density, and low electric contact resistance with electrode-backing materials—essential factor for operation with an acid environment. Disadvantages of graphite plates are high material costs and difficult for machining. The size and number of plates in a stack is dependent on the power requirements of the system. Fig. 6.4 shows a schematic and two commonly serpentine channel designs used for H2 and O2/air transport in a bipolar plate. The final component on the outside of the fuel cell is the end plate, which has the responsibility of closing and sealing the stack, and requires enough mechanical strength and chemical stability. Nevertheless, high electric conductivity is not important if end plates are not used as direct-current collectors (Pozio et al., 2003).

6.2.2 Membrane electrode assembly (MEA) In a PEMFC, the membrane acts both as a separator and as an electrolyte. To reduce material processing costs and complexity of preparation techniques, new membranes other than the Nafion perfluorosulfonic acid membrane are being developed.

Portable Hydrogen Energy Systems

12.7 mm

50 mm 1 mm

1.585 mm

96

3.172 mm 30 mm

1.5

85

mm

3.172 mm

1.585 mm

3.172 mm

30 mm

50 mm

1 mm

Plato monopolar Cátodo

(A)

(B)

(C) Fig. 6.4 (A) Blueprint of serpentine flow path. (B) Machined plate with serpentine flow field for H2. (C) Direct air flow serpentine path for cathode electrode in the other adjacent side.

These new membranes possess improved conductivity, water permeability, and thermal stability. Electrocatalysts also play a key role in the energy conversion of PEMFCs and generally in electrochemical transformation technologies, because they increase the rate, efficiency, and selectivity of the chemical transformations involved (She et al., 2017). Due to their low operating temperatures and survivability in acidic environments, platinum electrocatalysts are the most effective for the hydrogen oxidation and oxygen reduction reactions. However, the activity of platinum electrocatalysts may be severely reduced in the presence of small concentrations (> 10 ppm) of carbon monoxide in the reactant gas. This is of particular concern for systems using hydrogen produced from reformate natural gas. For this reason, alloys more resistant to carbon monoxide poisoning, like PtRu, are often used as an anode electrocatalysts (Hinds, 2004). The US DOE technical targets for PEMFC cathodes are Pt-based mass activity of >0.44 A m1 Pt at 0.9 V, catalyst loading of 0.125 mgPGM cm2 (PGM, Pt group metal), cost per power of $15 kW1, and stability target of <40% loss in catalytic activity after 5000 h of operation. See complementary information summarized in Table 6.1 (US DOE, 2012). Recent years have marked considerable progress in the production of novel electrocatalysts for energy conversion and storage, as evidenced by greater numbers of publications on this subject (Debe, 2012).

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Table 6.1 DOE electrocatalyst performance targets for PEMFCs Description

Units

2015 status

2020 targets

Platinum group metal (PGM) content in both electrodes Mass activity

g kW1

0.16

0.125

A mg1 PGM @ 900 mVIR-free % Mass activity loss % Mass activity loss A cm2 @ 900 mVIR-free

>0.5

0.44

66 41 0.024

<40 <40 >0.044

Loss in initial catalytic activity Electrocatalyst support stability PGM-free catalyst activity

Another important issue that affects PEMFC performance is the manufacturing of the membrane-electrode assembly (MEA). The catalyst ink preparation for MEA fabrication techniques and evaluation requires specific skills, sophisticated equipment, and abundant nanoparticulate materials synthesized from various chemical compositions (Shao et al., 2016). The development of the most common technique for MEA preparation has been reported (Schmidt and Gasteiger, 2003) and has since been improved by different research groups. The ink used to prepare MEAs follows various recipes, especially those that control the weight ratio of ionomer to catalyst at the cathode. Thickness of the ionomer membrane, fuel cell temperature, gas supply ratio (H2/ O2 or H2/air), gas humidity, and pressure are also variables that should be considered for the assembly preparation. The ink may be deposited directly onto the membrane or most commonly onto the gas diffusion layer (GDL), which is then hot-pressed to coat the membrane. Another important requirement is the effective cell sealing, which is needed to avoid gas leakage between components, a crucial factor in performance loss. In low-power prototypes, silicone gaskets are the choice option to prevent gas leakage.

6.3

Power electronic interfaces for portable PEMFC systems

In a PEMFC system, the DC-DC converter is the interface between a fuel cell stack and the load; its purpose is to escalate the unprocessed electric power from the PEMFC source to an appropriate magnitude for the load. PEMFC stack modules have no standard voltage output; cell output is tailored to the specific power need, with common system outputs being 6, 12, 24, 48 V, or more. Therefore, the design of the DC-DC converter in a PEMFC system requires special consideration. DC-DC functions in a portable system are (Yu et al., 2007) (i) to provide control and operating point tracking of the PEMFC module, (ii) to meet the nominal voltage required for load demands, and (iii) to regulate the output voltage V during input

98

Portable Hydrogen Energy Systems

voltage Ui and equivalent load resistance Req transients. DC-DC design should meet other requirements: (i) perform power conversion with high efficiency and (ii) generate a V with a total harmonic distortion (THD) <5%. Several DC-DC topologies for fuel cell applications have been summarized in recent literature (Zhang et al., 2012, 2016; Ali et al., 2014). Commonly, these devices perform voltage conversion by means of one or several switches that are opened and closed at very high frequencies with pulse-width modulation (PWM). This method continuously modifies the positive width of a square fixed-frequency signal until voltage regulation is reached. Due to its number of components, the most common DC-DC converter used in portable PEMFC systems is the hard-switching nonisolated type. Its structure comprises a direct path for the electric current between the PEMFC module and the load. On the other hand, an isolated structure includes a high-frequency transformer to provide a high-voltage conversion factor in a single stage, as well as galvanic isolation. Galvanic isolation protects PEMFC modules from the high-voltage or high-current surges of the load transients. If the PEMFC is used to power equipment that uses AC current, the direct-current output must undergo conversion to alternating current. Isolated converters are frequently used as a former stage for DC-AC inverters in stand-alone and grid-connected PEMFC applications, where galvanic isolation may be a fundamental constriction. Hard-switching topologies are widely used in portable PEMFC applications with estimated power transformation efficiencies of 90%. However, resonant converter topologies can reach power conversion efficiencies above 95% but with added costs and greater design complexity. An exhaustive analysis of circuits, waveforms for the most important signals, and basic design guidelines have been reported in (Agrawal, 2001; Hart, 2011; Erickson and Maksimovic, 2001). Fig. 6.5 shows schematic diagrams of basic nonisolated DC-DC topologies, where ideal models are assumed for every electronic component. The buck is shown in Fig. 6.5A; this circuit is suitable when the load voltage, V, is less than the PEMFC voltage, Ui, at the worst operating point. The L and C parameters, forming a low-pass filter, produce a low-ripple output voltage, V. Frequently, a voltage-divider circuit formed by two resistors, R1 and R2, estimates the output voltage. In a digital control solution, a general-purpose microcontroller (uC) or digital signal processor (DSP), IC1, numerically implements a control algorithm to perform the voltage regulation. This solution provides a flexible way to modify the suggested V according to load requirement. However, with an analog solution, a related single-chip buck controller circuit works with other discrete components to implement the control algorithm (Inman et al., 2011). The controller uC modifies the control variable d to maintain the V voltage regulated during PEMFC voltage transients. Fig. 6.5B shows a boost topology. This electronic arrangement is suitable when load voltage is always greater than maximum PEMFC voltage. In an optimum design, the L parameter helps to reduce ripple current at the PEMFC module terminals. A voltage-divider circuit formed by R1 and R2 approximates the voltage to control. An interpolated dual-stage boost converter prototype (Diaz-Bernabe, 2010) was attached to a 150 W PEMFC module to provide a 24 V regulated output. In this configuration, a 16-bit, 40 MHz digital signal processor (DSP) was used to implement a

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Fig. 6.5 Schematic diagrams of basic DC-DC converter topologies: (A) buck converter, (B) boost converter, and (C) buck-boost converter. Reproduced with permission from Erickson, R.W., Maksimovic, D., 2001. Fundamentals of Power Electronics, second ed. Springer, New York.

nonlinear slide-mode control algorithm for a PEMFC portable system to make output voltage regulation. Sometimes, the load voltage is close to the nominal PEMFC voltage; a large deviation of the PEMFC nominal operating point may produce erratic behavior in a system that exclusively uses buck or boost circuitry. In this sense, the well-known buck-boost circuit is a convenient choice to regulate the output voltage, as illustrated in Fig. 6.5C. The buck-boost increases or decreases output voltage according to a control variable d. In an effective design, the output voltage will decrease when d < 0.5. Otherwise, the voltage will increase if d > 0.5.

6.4

Water and heat

Water management is a key factor influencing the operation and performance of PEMFC prototypes (Ruksawong et al., 2017); performance losses occur when there is flooding of the catalyst layer limiting the mass transport process inside. Water is formed as a by-product of the cell reactions; see Eq. (6.2) for a description of cathodic water production; note that water generation occurs at the cathode. Therefore, to simultaneously ensure high membrane-proton conductivity and sufficient reactant delivery to reaction sites, it is vital to implement water management techniques. Such management requires a good understanding of the water transport through different components of PEMFCs (Jiao and Li, 2011). The conductivity of the membrane is highly dependent on its hydration state. The pressure gradient between both sides of the polymer membrane allows for continuous water transport due to electroosmosis, where water molecules move from the anode to the cathode. This results in membrane

100

Portable Hydrogen Energy Systems

dehydration on the anodic side and excess moisture at the cathode. Excess water at the cathode can cause flooding of the cathodic flow field channels, affecting the catalytic activity toward the oxygen reduction, thus decreasing overall performance. Dehydration of the anodic side increases ohmic resistance, reduces proton transport capacity, and leads to membrane damage due to the formation of fissures that allow hydrogen and oxygen gases to seep through and combine. A proposed model (Nguyen and White, 1993) considers the effects of water transport across the membrane: electroosmosis and diffusion, heat transfer from the solid to the gaseous phase, latent heat associated with water evaporation, and condensation in the flow channels. As an anionic water management solution, prehumidified gases are supplied to maintain adequate water balance. In portable power prototypes, proper water and heat management is of greater importance for achieving high power density at high energy efficiency. The amount of thermal energy released during the operation of a fuel cell is directly related to the discharge voltage. Substantial amounts of heat are generated in the operation of high-power-density PEMFCs. Efficient heat management is only possible by using water or other heat-exchange media. To achieve efficient heat transfer, the cooling water temperature must be at least 10°C below the fuel cell temperature. Proper heat removal and humidification are needed to keep the membrane well hydrated and conductive, which translates into lower ohmic losses and higher cell output and performance.

6.5

Modeling

Design modeling has been used to study the distribution of water within the membrane, during operation. A model with two-dimensional heat and mass transfer was presented by Nguyen and White (1993) and developed under a steady-state condition. The model consists of two flow channels on both sides of the membrane, one for the anode and one for the cathode. Analyses considered are water and gaseous reactant transport along the channels and membrane and heat transport from the solid-gaseous phases through the flow channels. A mathematical transport (Fuller and Newman, 1993) rendering for a solid-polymer-electrolyte fuel cell has also been proposed in the past; this model considers a two-dimensional membrane-electrode assembly and examines water management, thermal management, and fuel consumption by assuming that the fast hydrogen oxidation does not represent a significant overpotential for the fuel cell. Fast absorption/evaporation of water was also assumed, revealing that the rate of heat removal is a critical parameter that should be controlled in the operation of PEM fuel cells.

6.6

Performance and durability

Performance (current-voltage-power behavior) and durability remain critical limiting factors for mass commercialization of PEMFC prototypes. Significant work is necessary to address the limitations of poor oxygen reduction kinetics and carbon monoxide

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poisoning of the anode (Suwannawong et al., 2015). The three serious issues currently confronting fuel cell manufacturers are component cost, establishment of fuel delivery infrastructure, and durability of integrated PEMFC systems. From a performance standpoint, durability is the most pressing issue in fuel cell prototypes, as it is critical for effective implementation, mass commercialization, and distribution opportunities (Hinds, 2004). Most PEMFC stack degradation occurs due to membrane degradation by uneven distribution of reactants and temperature, sintering of the electrocatalysts, instability of supported catalysts, poisoning, flooding of catalyst reaction sites, fuel crossover, and corrosion of current-collector plates. Nevertheless, progress has been attained in this area. Recently, a miniaturized single-cell PEMFC prototype with thin stainless steel bipolar plates was reported as a potential power source for portable electronics (O’Hayre et al., 2016). The prototype’s dimensions included a thickness of 2.6 mm, stainless steel bipolar plate area of 16 cm2, overall reaction area of 4 cm2, and 300 μm width by 250 μm depth as dimensions of the bipolar plate’s flow channel. Cell performance and stability tests were conducted with different standard cubic centimeters per minute (SCCM) of pure oxygen and hydrogen gas flow, achieving stability with 173 mW cm2 at 49 °C and power generation between 0.4 and 0.55 W (75 and 110 mW cm2) at temperature between 49 and 52°C.

6.7

Portable power prototype devices

Prototype PEMFCs are energy conversion devices that operate under constant gas flow rates and with constant stoichiometry. A constant flow rate ensures that a fixed supply of hydrogen, regardless of how much is needed, is available to reach a specific current density. Generally, hydrogen intake is regulated to prevent maximum current. Often, hydrogen and oxygen allocation is adjusted according to the cell’s power demands, and more hydrogen than is required is always supplied for any load. The H2-air PEMFC currently exhibits the highest power density of all the fuel cells (500–2500 mW cm2). It also provides the best fast-start and on-off cycling characteristics. For these reasons, it is well suited for use as a portable power source and in mobile applications like vehicular transport. Our research group at CINVESTAV has developed H2/O2 and H2/air PEMFC prototypes to power electronic devices for academic and workshop demonstrations. Fig. 6.6A shows a miniaturized 5 W PEMFC prototype that operates with high-purity H2 and O2 gas feeds (Pt:Pt/C, Nafion 117, MEAs) and that is capable of powering a CD player. Expanding on that concept, another PEMFC prototype, where high-purity H2 and air were supplied through convection with an electric fan, was built to power a 35 W low-power TV (Fig. 6.6B). Fig. 6.6C shows a commercially available PEMFC apt for use with an MP3 player, produced and distributed by Fuel Cell Store (Fuel Cell Store, 2017). Table 6.2 summarizes the performance characteristics of PEMFCs presented in Fig. 6.6. One of the most important manufacturers of multifunctional, low- and mediumtemperature PEMFC stacks with optimized assembly technology and with power

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Portable Hydrogen Energy Systems

10

25

8

20 15

6 C 4

10

2

A

B

0

(C)

(D)

0

2

4 6 Current (A)

8

Power (W)

(B)

Voltage (V)

(A)

5 0 10

Fig. 6.6 PEMFC stacks with three different applications: (A) portable CD player, (B) portable TV, and (C) portable MP3 player. (D) Performance of (A), (B), and (C) PEMFC prototypes (A–C). Reproduced with permission from Fuel Cell Store Education, 2017. http://www.fuelcellstore. com/fuel-cell-stacks/5w-100w-fuel-cell-stacks (accessed 15 June 2017). Table 6.2 Performance of PEMFCs corresponding to Fig. 6.6 Specifications

Portable (A)

Portable (B)

Portable (C)

Type of fuel cell Number of cells Rated power (W) Reactants Reactant pressure (bar) Max. stack temperature (°C) MEA area (cm2)

PEM 4 4 H2/O2 2.3, 3 50 2

PEM 10 24 H2/air 0.5 60 9

PEM 10 20 H2/air 0.5 60 19

outputs ranging from 50 to 500 W is Fraunhofer ISE (2017). Many of their fuel cells incorporate single-cell cooling with in-plane elements on both sides of the collector plates, as is shown in Fig. 6.7. This institute also produces PEMFC stacks with parallel hydrogen flow fields and open air-cooled cathodes, where the performance of the stack presents similar polarization curves of each of the membrane-electrode assembly.

Development and applications of portable systems based on conventional PEM fuel cells

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Fig. 6.7 Commercially available low temperature fuel cell stacks: (A) 150 W with cooling elements; (B) 250 W with tension bar; and (C) Polarization curves of the five single cell of the B stack. Reproduced with permission from Fraunhofer ISE, 2010. https://www.h2fc-fair.com/hm10/ images/pdf/fraunhofer04.pdf.

Recent advances have allowed for PEMFCs to be installed in cutting-edge technologies. A new generation of drones with integrated H2/air PEMFCs is now commercially available and in development. Ballard Power Systems announced that Protonex and FlyH2 Aerospace will develop unmanned aerial vehicles (UAVs) powered with PEMFC. A prototype fuel cell flagship, UA Alpha, will be used as an agricultural reconnaissance aircraft (UA Alpha, 2017) and will map surfaces, vegetation growth, vegetation density, and ground elevation. Another company, MicroMultiCopter Aero Technology (MMC T1, 2017), launched HyDrone 1550, the world’s first hydrogen PEMFC-powered drone designed and manufactured to overcome limitations of traditional lithium-polymer (Li-poly)/Li-ion power systems. The HyDrone 1550 has a PEMFC system that weighs 5.2 kg, possesses H2 endurance up to 150 min, and holds a nominal power rating of 1800 W. Fig. 6.8 shows PEMFC power systems installed in commercially available drones. Technical challenges remain in the successful development and deployment of commercially viable portable hydrogen/oxygen and hydrogen/air PEMFCs systems: most prominently, (a) production and use of novel low-cost, high-performance Pt-reduced or Pt-free electrocatalysts; (b) manufacturing of low-cost and lightweight advanced bipolar plates and hydrophobic/porous electrodes; and (c) new engineering design, improved physical properties, and greater levels of performance and durability. Nonetheless, considerable progress has been accomplished recently, and a new generation of PEMFC-powered devices is beginning to emerge as a rival to traditional battery-based equipment.

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Portable Hydrogen Energy Systems

Fig. 6.8 Drones powdered by H2-PEMFCs. (A) FCM-1800 series of AC10 lightweight 3 stack of 650 W from Intelligent Energy Inc. (reproduced with permission) an (B) HyDrone 1550 of 1.5 kW from MMC Aero Technology (reproduced with permission).

Acknowledgments This study was financially supported by the Mexican Council of Science and Technology, CONACYT (grant no. 245920).

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Further reading Jungmann, T., Kurz, T., Groos, U., 2010. HT- and LT-PEM Fuel Cell Stacks for Portable Applications. Fraunhofer Institute for Solar Energy Systems ISE, Freiburg. San, B., G€ul, F., Tekin, G., 2013. A review of thermoplastic composites for bipolar plate applications. Int. J. Energy Res. 37 (4), 283–309.