Proton Exchange Membrane Fuel Cells - Essay Example

Proton Exchange Membrane Fuel Cells Contents Introduction ......................................................................................................... 1 1.1 Electrodes…………………………….................................................................... 1 1.2 Anode Reactions and Catalysts……………………………………………………... 2 1.3 Cathode Reactions and Catalysts…………………………………………………… 2 1.4 Issues: Advantages and Disadvantages............................................................... 3 1.5 Gas Diffusion Layer............................................................................................... 4 2 Fuel cell operating: Reactants Flow…………………................................................. 5 2.1 Mass and Energy balance...................................................................................... 6 3 Fuel cell stack design.............................................................................................. 8 3.1 Sizing ...................................................................................................................... 8 3.2 Bipolar Plates.......................................................................................................... 9 3.3 Heat Removal........................................................................................................ 10 4 Fuel cell system design............................................................................................... 12 4.1 H2, O2 or other fuel supply......................................................................................... 14 4.2 Water management.................................................................................................... 15 5 Life-cycle analysis of fuel cells...................................................................................... 16 5.1 Environmental Impact.................................................................................................. 18 5.2 Opportunities, Challenges and Obstacles.................................................................... 19 6 References...................................................................................................................... 20 Chapter 1 1. Introduction Proton exchange membrane material (PEM) fuel cell technology promises an alternative source of clean, secure and green energy with varied applications including automobile, portable and stationary. A fuel cell is basically an electrochemical device which has the capability of continuously converting chemical energy of a fuel and an oxidant to electrical energy. A major factor which has impacted ob the invention of fuel cells is environmental concern. Important to note is the growing concern for better and safer environment for human health. In this circumstance, the development of fuel cells helps in reducing dependence on fossil fuels hence reducing the levels of toxic and poisonous emissions to the atmosphere. However, this form of energy exemplified by proton exchange membrane fuel cells has to compete with reliability, cost and energy efficiency with established energy sources. The commercialization of the proton exchange membrane fuel cells are closely related to vital materials considerations including performance, durability and cost. The major setback is to find a combination of materials that will give a valid outcome on the basis of the above three mentioned factors. The proton exchange membrane fuel cell is also referred to as the polymer electrolyte membrane fuel cell. This is so because the name variant depends on the type of electrolyte employed in the model. When the membrane is conveniently hydrated, the fuel cell is referred to as the polymer electrolyte membrane fuel cell. In this case, there is high conductivity of protons across the polymeric membrane. Various state of the art proton exchange membrane fuel cells have been developed. Exemplified by thinner membranes of less than 40 micrometers and smaller Pt/C electrodes, some fuel cells have been devised for cost reduction. However, these models have demonstrated significantly less operating time of close to 15, 000 hours. This called for the invention of an ion-conductive polymeric membrane as a gas electron barrier. This idea was first coined by William T. Grubb of the General Electric Company in 1955. Currently, the most widely employed membrane electrolyte is DuPont’s Nafion. This is because it possesses good chemical and mechanical stability in the challenging proton exchange membrane fuel cell environment. Basically, the physical structure of the proton exchange membrane fuel cell comprises of seven components. These are feeding channels, diffusion layers, catalytic layer in the anode, membrane; catalytic layer, diffusion layer and feeding channels in the cathode layer. The proton exchange membrane fuel cell combines in a compact unit the electrodes and the electrolyte. This configuration referred to as the membrane electrode assembly (MEA) has a thickness of less than 100 microns. It is the main hub of the fuel cell and is constantly supplied with hydrogen and oxygen. The supply of these critical starting materials is critical for the generation of electrical power with a power density of 1W per centimeter square. The polymeric solid electrolyte forms a thin electronic insulator and a barricade for gases between both electrodes allowing rapid proton transport and high current bulk. Solid electrolytes are preferred compared to liquid ones because they allow the fuel cell to operate in any spatial orientation. 1.1 Electrodes The cathode and anode electrode layers are classically manufactured of platinum or platinum alloys dispersed on a carbon support for efficient catalyst utilization. Ionomers and polytetrafluoroethylene (PTFE) resins can be assembled to the electrode layers. Ionomers extends the path of transport of protons beyond the electrode membrane interfaces. On the other hand, polytetrafluoroethylene facilitates liquid water removal from the electrode layers. Additionally, both components in electrodes also aid in binding together the various components of the electrode. The electrodes are composed of catalytic layers which offer a large surface area on a substratum of coal and which is permeable to gases. Furthermore, electrocatalyst materials are required to obtain a good operation thus increasing the rate of chemical reaction. 1.2 Anode electrode: reactions and catalysts At the anode electrode of the proton exchange membrane fuel cell, the hydrogen oxidation reaction (HOR) takes place. The reaction that occurs is shown below: H2 2H+ + 2e- E⁰= 0 V The above shown reaction is a thermodynamically reversible process and serves as a standard reference electrode. It is therefore referred to as reversible hydrogen electrode (RHE) for all other electrochemical processes. The anode electrode must complete some basic functional requirements including transport of hydrogen to catalyst site and catalyzing the HOR process. Additionally, it must carry proton away from the reaction sites to the membrane electrolyte, must also remove electrons from the anode and also transfer heat in and out o the reaction zone. The hydrogen oxidation reaction proceeds through the following steps: H2 + 2 M 2 MH ads Tafel reaction H2+ H2O + M → MHads + H3O+ + e- Heyrovsky reaction MHads + H2O → H3O+ + e- + M Volmer reaction Where M is the catalyst. In all these reactions, the rate limiting stage is dependent on the specific catalysts and the reaction conditions. For a proton exchange membrane fuel cell fitted with a platinum anode, the hydrogen oxidation reaction involves the Tafel and Volmer reactions. In such a reaction series, the Tafel reaction becomes the rate limiting step and the rate of reaction can be represented by the equation referred to as the Butler-Volmer reaction depicted as: j = j0 [ e (1-β1) F ηs /RT – e β1 F ηs /RT ] j0 which is the exchange current density is dependent on the morphology of the catalyst, the interface between the electrolyte and catalyst as well as the properties of the reaction media. Research on anode materials has focused mainly on platinum loading reduction, systems operating with CO-contaminated fuels as well as low cost substitutes. 1.3 Cathode electrode: reactions and catalysts At the cathode electrode, the most dominant reaction is the thermodynamically irreversible four electron oxygen reduction electrochemical process. This reaction is depicted as: O2 + 4 H+ + 4 e- n 2 H2O E0 = 1.229 V When joined to an external circuit, the net outcome of the two half cell reactions is the generation of water and electrical energy for hydrogen and oxygen. Additionally, heat is generated in the reaction. However, at meaningful rates under a normal functional proton exchange membrane fuel cell, and in the absence of proper catalyst, the reactions do not occur. In these reactions, the catalyst of choice is platinum just like the one preferred in the anode electrode reaction. The cathode electrode serves as the location for oxygen reduction reaction (ORR) and must fulfill the following basic conditions. It must transport oxygen to the catalyst positions; it must catalyze the oxygen reduction reaction, carry proton from the membrane electrolyte to catalyst sites. Additionally, it must remove water which is the product, remove electrons from reaction sites and also transfer heat to and from the reaction area. The oxygen reduction reaction mechanism remains a debatable topic but two methodologies have been coined. These include the dissociative and associative mechanisms depicted respectively below: However, the final two reactions of the various mechanism are similar and can be shown as: 1.4 Issues: advantages and disadvantages Current studies have indicated that at the platinum surface of the cathode electrode, there is formation of a peroxy intermediate. Therefore, suggesting associative mechanism as the dominant one. From the DFT calculations by Norskov et al, the associative mechanism which is somehow complex results in the oxygen reduction reaction over potentials. However, at pragmatic oxygen reduction reaction over potentials which is less than 0.8V, the two mechanisms run in tandem and in parallel. Whichever which mechanism is dominant, the oxygen reduction reaction still remains the rate limiting step in the fuel cell. The oxygen reduction reaction kinetics is rather slow and when depicted graphically, there is a steep slope in the activation polarization segment. The open circuit which plays a critical role in hydrogen crossover current is responsible for voltage loss. This problem is persistent also in state of the art membrane electrolytes. Ongoing research has been geared towards finding a cathode catalyst that can improve the slow ORR kinetics. Additionally, these advances are also geared towards pointing out a cheaper replacement for the conventional platinum catalyst. The lifetime durability of cathode poses major challenge to proton exchange membrane fuel cells. The main problems associated to catalysts include sintering, redistribution, platinum agglomeration and dissolution. The environment in the cathode electrode is highly oxidative and corrosive. This is because of presence of oxygen and water, low potential difference and high temperatures. Despite having a low solubility property at normal fuel cell operating voltages, platinum’s solubility surges upward drastically. It reaches its highest dissolution rate at approximately 1.1 voltages, hence making the fuel cell susceptible at higher voltages. 1.5 Gas diffusion layer The gas diffusion layer allows for homogeneous movement of reactant gases to the electrodes, help in the conduit of electrons and provide mechanical backbone for the MEA. The layer also assists in the transfer of heat hence regulating the fuel cell temperature. Finally, the layer removes water which is the end product from the electrodes. In order to perform all these duties, the gas diffusion layer should be a good thermal and electron conductor. The gas diffusion layer must also have a small gas transfer resistance. A critical parameter for reactant transport in the fuel cell is the porosity of the gas diffusion layer. A significant challenge in the proton exchange membrane fuel cell is water management. In evaluating the performance and design of a fuel cell, ability to remove water plays a critical role. Performance of the fuel cell can be improvised by placing a fine coating between the gas diffusion layer and the catalyst. This is important because it creates a saturation shift across the interface. Most gas diffusion layers are manufactured using porous materials such as carbon paper and fibers. This is because carbon materials have low tortuosity as a result of the pore structure and rough texture. Chapter 2 2. Fuel cell operating: Reactants Flow A fuel cell is basically defined as an electrochemical gadget whereby chemical energy of a fuel is converted directly to electrical energy. In this case, the fuel is typically an alcohol or hydrocarbon or alternatively its derivatives. There must be constant supply of the fuel into the system for efficiency and optimal performance. Some of the fuel types that are not used in such a fuel cell system include atomic fuel of uranium and metals. In the definition, the term directly implies that the device possesses an anode a point where the fuel is electrocatalytically oxidized. This reaction results in the production of electrons. Additionally, the fuel system has a cathode where oxygen undergoes reduction. In a proton exchange membrane fuel cell, fuels are constantly injected into the anode while an oxidant is fed into the cathode. Within the anode catalyst surfaces, these fuels are converted into protons and electrons. The protons migrate through the proton exchange membrane which also has a prohibitive effect to electrons. As such, the electrons are directed towards the cathode surface. Electrons are forced to pass through an external route in which they deliver part of their energy to a load onto the cathode. At the cathode, the energy deficient electrons and the protons react with oxygen to produce water. In theoretical terms, any substance capable of chemical oxidation that can be supplied constantly can be used as a fuel at the anode. In the same case, the oxidant can be any fluid which is capable of reducing oxygen at a significant rate. Pragmatically, the selection criterion of such important materials is based on reactivity, cost and availability. In most proton exchange membrane fuel cells, hydrogen and methanol are used as fuels. This is mostly because these substances have a relatively high activity rates at low temperatures. Oxygen of gaseous air is the preferred choice of oxidants in most PEM fuel cells. This is because these forms of oxidants are readily and economically available. The conversion of chemical to electrical energy takes place on the surface of electrodes which are attached to carbon papers or cloths. Carbon is preferred because it is conductive and porous thus allowing the flow of electrons and gases through it easily. The membrane used in most PEM fuel cells is typically a solid electrolyte called Nafion ®, a perfluorosulfonic acid polymer manufactured by DuPont. This specialized membrane allows protons to pass through but also inhibits the passage of electrons through it. By virtue of the electric field created across the membrane, proton transfer is easily achieved. Hydrogen fuel cells employ hydrogen gas as the fuel. These types of cells provide extremely high fuel cell performance and efficiency for the pure hydrogen. On the other hand, methanol fuel cells employ the use of methanol as the fuel. In contrast to hydrogen fuel cells, these cells provide relatively low performance and efficiency. The oxygen reduction reaction (ORR) is the more rate determining step in a properly functional fuel cell. As a result, decreasing the activation overpotential for the oxygen reduction reaction is a critical factor in performance enhancement. Slow ORR kinetics an be tackled by increasing temperature, reactant concentration, pressure and electrode roughness. 2.1 Mass and Energy Balance Rates; The half cell reactions of both methanol and hydrogen fuel cells can be shown as: Hydrogen fuel cell Anode: H2 n 2H+ + 2e- ΔG0 = 0.00 [1] Cathode: 0.5 O2 + 2H+ + 2e- n H2O ΔG0 = -237 kJ/mol [2] Overall: H2 + 0.5 O2 = H2O ΔG0 = -237 kJ/mol [3] Methanol fuel cell Anode: CH3OH + H2O n CO2 + 6H+ + 6e- ΔG0 = 9.3 kJ/mol [4] Cathode: 1.5O2 + 6H+ + 6e- n 3H2O ΔG0 = -237 kJ/mol [5] Overall: CH3OH +1.5 O2 n 2 H2O + CO2 ΔG0 = -227.7 kJ/mol [6] Chapter 3 3. Fuel cell stack design: A classic proton exchange membrane fuel cell comprises of a cell stack, water an thermal management modules, power conditioning and system control mechanisms. Additionally, the typical PEM fuel cell has hydrogen and oxygen management mechanisms. The cell stack is an assembly of catalysts coatings, membranes, bipolar plates, gas diffusion layers and seals. A typical cell stack is depicted in the diagram below: 3.1 Sizing The improvement of the fuel cell stack performance requires the pairing of a number of designs and operating factors. Operating factors include flow channels of bipolar plates, stack operating conditions as well as stack manifold designs. By exploring innovative materials, component design and manufacturing procedures, significant improvements can be achieved in enhancing fuel cell performance. Additionally, the compression pressure that arises from stack assembly force plays a crucial role in determining fuel cell efficiency and performance. Therefore, it is imperative for manufacturing companies to clearly understand the relationship between fuel cell performance, assembly and design. During the assembly of the fuel cell stack, bipolar plates, gas diffusion layers and the membranes are joined mechanically. In order to allow room for gas sealing, proper clamping force must be exerted. This also reduces contact resistances created between the interfaces of the various components. High pressure exerted by mechanical devices during clamping of the components results in crushing of porous structures and cracking of the bipolar plates. Furthermore, high pressure can significantly alter the electrical contact resistance which forms a critical component in ohmic resistance of the fuel cell. Assembly pressure makes the part of the gas diffusion layer beneath the land area to be constricted and part under the conduit to be protruded. This inconsistent compression leads to unevenness of the material properties of the gas diffusion layer. The resulting deformation within the stack cell and specifically in the gas diffusion layer greatly impacts on cell performance and durability. Moreover, when there is an upsurge in relative humidity and temperature, during operation, the membrane absorbs water leading to swelling. Because the relative position between the bottom and top end plate is fixed, the electrolyte membrane is spatially confined. As a result, the gas diffusion layer is further constricted beneath the land and intrusion into the passage is greatly increased. 3.2 Bipolar plates The practical operating voltages from an individual cell which can also be referred to ath e membrane electrode assembly is approximately 0.7 V. Desirable voltages can be achieved by joining cells in series, and this is accomplished by inserting highly conductive material between the MEA. These highly conductive materials exemplified by bipolar plates are the most critical components of a fuel cell stack. Critical factors to consider in bipolar plates include volume, weight and cost. It is imperative to note that bipolar plates account for approximately 40% of the total stack cell cost and about 80% of the weight. Due to these factors, there has been concerted effort to reduce their cost, size and improve their lifetime and performance. Bipolar plates play a number of critical roles simultaneously in a fuel cell stack to ensure acceptable margins of power output and long cell stack lifespan. They serve as current conductors between adjacent membrane electrode assemblies. Bipolar plates provide conduits for reactant gases enhance water and heat management within the cell stack. Lastly, they provide structural base for the whole fuel cell stack. In order to undertake these functions, the bipolar plates must fulfill excellent chemical stability. They must also exhibit electrical and thermal conductivity, corrosion resistance and low gas permeability. However, the specific requirements of unique bipolar plates are dictated by the type of application and operating environment under which the fuel cell stack is utilized. Therefore, the bipolar plates requirement utilized in mobile and transportation applications are quite dissimilar from ones used in stationary applications. Bipolar plate materials can be largely divided into two broad groups namely metallic and carbon based. In the past research and development focused on carbon-based plates as exemplified by high density graphite. This was because graphite possesses excellent electrical and chemical properties in the adverse PEM fuel cell conditions. A disadvantage of the use of graphite was its limitation to laboratory setup and stationary applications. Furthermore, the exorbitant cost of machining gas passages and the inherent brittleness of the material limited its use in terrestrial applications. These setbacks have revolutionalized the shift of carbon-based plates to metallic bipolar plates. Although metals including noble metals show desirable characteristics of bipolar plates, they also show drawbacks. Metallic plates have chemical instability in the corrosive conditions of the PEM fuel cells. The end result is corrosion and formation of thin coats of oxide layers on the electrode surface. They can also lead to poisoning of the solid membrane electrolytes and catalyst coatings. Additionally, the corrosion byproducts can increase interfacial contact resistance (ICR) between the plates and gas diffusion layers. Consequently, the fuel cell performance is compromised. A number of developments have been put forward to improve interfacial contact resistance and corrosion of metallic bipolar plates. These processes include application of a slim, conductive protective coating on the metallic surface plates. Other techniques include surface modification techniques. 3.3 Heat removal The heat and temperature subsystem comprises the fuel cell stack cooling system and the reactant heating system. Thermal management of the fuel cell is critical because the performance of the fuel cell is strongly dependent on the temperature. Stack cell temperature regulation can be achieved by using a fan or a water refrigeration subsystem. Chapter 4 4. Fuel cell system design: The physical structure of a proton exchange membrane fuel cell comprises of seven components. These are feeding channels, gas diffusion layer and a catalytic coating in the anode. After this layer in the anode, the PEM fuel cell design progresses to a membrane usually electrolyte in nature,. The same series of components is extended on the cathode side which also has diffusion layer, feeding channels and catalytic layer. In a very compact design the proton exchange membrane fuel cell include the electrodes and electrolyte membrane. This structure referred to as the membrane electrode assembly is thinner and measures not more than 100 microns. It sis essentially the driving force of the uel cell and is constantly fed with hydrogen and oxygen. The polymeric solid electrolyte constitutes a thin electronic insulator and a barricade or gases between the two electrodes. In such an orientation, there is faster proton transfer and equally high current density. In comparison to the liquid electrolyte, the solid electrolyte allows the fuel cell to operate in spatial position. Membranes such as DuPont’s Nafion comprise of a polytetrafluoroethylene (PTFE) backbone with perfluorinated-vinyl-polyether side chains possessing sulfonic acid end groups. When the membranes are hydrated with water, protons become freely mobile. The requirement for high power density in the proton exchange membrane fuel cell ha led to the development of thinner membranes. The use of thinner membranes in PEM fuel cell also increases the resulting reactant crossover thereby reducing fuel utilization. This scenario poses a major problem in fuel cell that utilize methanol as the fuel source. This is because methanol has simla properties like water. More thick membranes results in a decrease in reactant crossover but at increased resistance hence low power density. To counter his limitation in methanol driven cells, the use of composite membranes has been employed. In such a setting, the composite membranes have dual properties of high proton conductance and low crossover of methanol. Catalyst coatings on the electrodes include composite structures comprising proton conductivity polymer and carbon supported metal catalyst. The thickness of the catalyst layer varies from 10 to 20 microns depending on the loading levels of the catalyst itself. The most preferred catalyst for both the anode and the cathode is platinum. However, the selection of the anode catalyst and its loading level is also dependent on the source of the fuel. For instance, when the fuel source is pure hydrogen, relatively less platinum is required. This is because the hydrogen oxidation reaction (HOR) is simple and the resultant overpotential is minimal. On the other hand, if the fuel source is reformate exemplified by mixtures of hydrogen, carbon dioxide, nitrogen and traces of carbon monoxide, then catalysts of platinum alloys are used. This is because alloys of platinum catalysts such as PtRu or PtRh help in reducing the adverse impacts of CO poisoning. The basic architecture of electrodes in most proton exchange membrane fuel cells is similar. The catalyst particles o approximately 5-20 nanometers are distributed on a carbon support such as Vulcan XC72. Minute sizes of the catalyst particles result in a large active area of reaction and better performance of catalyst loading per milligram. The gas diffusion layers disperse the reactants from the gas passages evenly along the active surface o the catalyst coating. In addition, the gas diffusion layer ensures proper movement of electrons, product water and heat of reaction in the fuel cell. It also creates a protective barrier over the slim layer of the catalyst. They are mostly manufactured using carbon paper or hydrophobicity. Integrated gaskets and seals provide for a solid design while performing primary role of eliminating leaks and over constriction. 4.1 H2, O2 or other fuel supply The reactant flow subsystem allows for continuous movement of hydrogen and oxygen into the fuel cell. The purpose is to ensure availability and adequate reactant flow or rapid transient response and minimal supplementary power usage. The hydrogen supply conduit is made of a pressurized tank with pure hydrogen gas connected to the anode electrode. This channel has a pressure regulation valve and a pressure reduction valve. On the other hand, the air supply mainly atmospheric oxygen passes through a circuit via an air compressor. This air is pressurized and is conducted directly to the cathode electrode. The anode output is generally driven in a dead-ended mode. The purge valve in the anode is intermittently opened to get rid of water and accumulated nitrogen gas. In the situation when the anode output is not closed, it is possible to reinject the out flowing hydrogen in the anode input. On the other hand, the cathode output is normally open through a fixed restriction. 4.2 Water management Water is the major vector by which protons are transferred through the electrolyte membrane. Therefore, the uptake of water of the proton exchange membrane fuel cell is closely related to the performance of the fuel cell. However, as a result of the elevated humid environment and temperature at which this fuel cell operated, excessive water uptake is not allowed. This excessive water uptake leads to high dimensional swelling ratio. Therefore, appropriate uptake of water and proper dimensional stability are essential demands for proton exchange membrane. The main purpose of water management subsystem is to sustain an effective hydration of the polymer membrane and an adequate water balance. This is because the fuel cell performance is strongly dependent on membrane hydration. The hydrogen and oxygen are usually humidified before entering the fuel cell with humidifiers in both circuits. The water that exits through the cathode can be recovered in a water separator and reinjected in the humidifiers through the pump. Chapter 5 5. Life-cycle analysis of fuel cells The fuel cell technology is already sufficiently developed for commercialization but only hindered by he cost of technology. The most critical factor is to consider cost reduction and improve the fuel cell performance. Of all the areas, performance enhancement and cost reduction, proton exchange membranes are considered to be one of the key elements. At the moment, there is only one commercial membrane type called perfluorosulfonic acid PEMs. Ongoing research and development strategies are geared towards cost reduction, improved conductivity and ease of manufacture. Additionally, such studies tackle optimization of specific applications, high temperature operation, low methanol crossover and zero external humidification. A key hindrance is the development of compact and efficient fuel reformers for distributed hydrogen production. 5.1 Environmental impact The recent interest and paradigm shift towards fuel cells has arisen due to technical challenges of viable power generation systems. Increasing apprehension on the environmental consequences fossil fuel use in electricity generation has stimulated research on fuel cell research. Proton exchange membrane fuel cells can be used in a wide range of power production scaleable to meet the power needs. PEM fuel cells have no mobile parts and require less maintenance compared to conventional engines and generators. PEM fuel cells also provide power directly at the site of application and evade costly losses attributed to energy distributions from centralized locations. Additionally, their use in homes and offices is ideally suited to the highly energy efficient co-production of heat and electricity. Recent developments in cost reduction and performance improvement of the fuel cells promise reliable, environmentally friendly and clean power systems. 5.2 Opportunities, Challenges and Obstacles To attain acceptable specific performance of the cost effective proton exchange membrane fuel cell stack, low cost weight materials must be used as bipolar plates and gas separators. Extensive methodical research and development undertakings have resulted in the invention of an in-house rapid and simple method in performance improvement. This research has particularly played a critical role in the development of low platinum loading gas diffusion electrodes and membrane electrodes assemblies. By employing gas diffusion electrode (GDE) template, new polymer electrolytes and electro catalysts have been introduced at the MEA in low platinum loading. Due to its high efficiency, relatively fats start up, high power density and low temperature operation, the PEM fuel cells offers great potentiality for near zero emission power source in stationary, mobile and transportation applications. In order or such a fuel source to gain market and competitive advantage over the existing energy sources, various factors are critical. These include cost, public acceptance, durability and reliability. Of these factors, cost and durability are the most impeding factors in development of this novel power source. Consequently, determining the avenues for cost reduction and cost avoidance in manufacture and selection of the various PEM fuel cell components is critical. Additionally, increasing fuel cell lifetime can aid in marketing this new source of power within the energy sector. Bipolar plates play a critical role in cost and performance improvement of proton exchange membrane fuel cells. As such, decreasing the plate cost while increasing performance are desirable properties for efficiency in PEM fuel cells. Therefore, bipolar plates must be conductive, rigid, durable and stable in harsh environmental conditions. Furthermore, he plates must resist dimensional deformations under compressive loads and relatively high temperatures. Great deal of work is currently in progress with an aim of producing novel materials and fabrication processes to satisfy the market needs. Conventional graphite based plates are continuously being replaced by metallic plates that offer higher strength and electrical conductivity. These metal plates also offer low gas permeability, formability, better shock resistance and manufacturability than graphite plates. However, a major setback in using metal plates in PEM fuel cells is their vulnerability to corrosion. This adversely impacts on he durability and performance of the plates and eventually hamper the normal functioning of the fuel cell. This impediment has necessitated the application of a layer of corrosion resistant coatings on the metal plates. More recently, noble metals, titanium and aluminum have been employed in the manufacture of metal plates. This has been a paradigm shift from the iron and its alloys that were used for availability and cost factors. Finally, metallic bipolar plates are easily manipulated through stamping, embossing and compression molding as opposed to graphitic plates. References F. 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