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62-411: PEMFCs are built out of membrane electrode assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. The pivotal part of the cell is the triple phase boundary (TPB) where

124-413: A PEM fuel cell directly without being reformed, thus making a direct methanol fuel cell ( DMFC ). These devices operate with limited success. 3. Limitation of Operating Temperature The most commonly used membrane is Nafion by Chemours , which relies on liquid water humidification of the membrane to transport protons. This implies that it is not feasible to use temperatures above 80 to 90 °C, since

186-399: A PEMs is in the range of 50–60% . Main factors that create losses are: The external electrodes, often referred to as bipolar plates or backplates, serve to distribute fuel and oxygen uniformly to the catalysts, to remove water, to collect and transmit electric current. Thus, they need to be in close contact with the catalyst. Because the plates are in contact with both PEM and catalyst layers,

248-464: A result, the power generation from this flow field is uniform across the cross-section and self-humidification is enabled. 2. Vulnerability of the Catalyst The platinum catalyst on the membrane is easily poisoned by carbon monoxide, which is often present in product gases formed by methane reforming (no more than one part per million is usually acceptable). This generally necessitates the use of

310-506: A thin, polymeric membrane as the electrolyte. This membrane is located in between the anode and cathode catalysts and allows the passage of protons to pass to the cathode while restricting the passage of electrons. Compared to liquid electrolytes, a polymeric membrane has a much lower chance of leakage [2]. The proton-exchange membrane is commonly made of materials such as perfluorosulfonic acid (PFSA, sold commercially as Nafion and Aquivion), which minimize gas crossover and short circuiting of

372-455: A wide range of humidity conditions. Below 100 °C and under hydration, the presence of hydrogen bonding and solvent water molecules aid in proton transport, whereas anhydrous conditions are suitable for temperatures above 100 °C. MOFs also have the distinct advantage of exhibiting proton conductivity by the framework itself in addition to the inclusion of charge carries (i.e., water, acids, etc.) into their pores. A low temperature example

434-427: Is Miller indexes with large integers, such as Pt (730)) provide a greater density of reactive sites for oxygen reduction than typical platinum nanoparticles. Since the most common and effective catalyst, platinum, is extremely expensive, alternative processing is necessary to maximize surface area and minimize loading. Deposition of nanosized Pt particles onto carbon powder (Pt/C) provides a large Pt surface area while

496-490: Is a product of the electro- chemical reaction as CO poisons the PEM and impacts the efficiency of the fuel cell. Due to the high cost of these and other similar materials, research is being undertaken to develop catalysts that use lower cost materials as the high costs are still a hindering factor in the widespread economical acceptance of fuel cell technology. Current service life is 7,300 hours under cycling conditions, while at

558-464: Is added between the GDL and catalyst layer to ease the transitions between the large pores in the GDL and small porosity in the catalyst layer. Since a primary function of the GDL is to help remove water, a product, flooding can occur when water effectively blocks the GDL. This limits the reactants ability to access the catalyst and significantly decreases performance. Teflon can be coated onto the GDL to limit

620-458: Is an optimal thinness to this catalyst layer, which limits the lower cost limit. Below 4 nm, Pt will form islands on the paper, limiting its activity. Above this thickness, the Pt will coat the carbon and be an effective catalyst. To further complicate things, Nafion cannot be infiltrated beyond 10 um, so using more Pt than this is an unnecessary expense. Thus the amount and shape of the catalyst

682-411: Is being done on potential applications in transportation as well as wearable technology. Fuel Cells based on PEM still have many issues: 1. Water management Water management is crucial to performance: if water is evaporated too slowly, it will flood the membrane and the accumulation of water inside of field flow plate will impede the flow of oxygen into the fuel cell, but if water evaporates too fast,

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744-766: Is cheaper. However, acid leaching is a considerable issue and processing, mixing with catalyst to form ink, has proved tricky. Aromatic polymers, such as PEEK, are far cheaper than Teflon ( PTFE and backbone of Nafion) and their polar character leads to hydration that is less temperature dependent than Nafion. However, PEEK is far less ionically conductive than Nafion and thus is a less favorable electrolyte choice. Recently, protic ionic liquids and protic organic ionic plastic crystals have been shown as promising alternative electrolyte materials for high temperature (100–200 °C) PEMFCs. An electrode typically consists of carbon support, Pt particles, Nafion ionomer, and/or Teflon binder. The carbon support functions as an electrical conductor;

806-427: Is however a very complicated process, that also requires purification from the carbon monoxide the reaction produces. A platinum- ruthenium catalyst is necessary as some carbon monoxide will unavoidably reach the membrane. The level should not exceed 10 parts per million . Furthermore, the start-up times of such a reformer reactor are of about half an hour. Alternatively, methanol, and some other biofuels can be fed to

868-403: Is limited by the constraints of other materials. A second method of increasing the catalytic activity of platinum is to alloy it with other metals. For example, it was recently shown that the Pt 3 Ni(111) surface has a higher oxygen reduction activity than pure Pt(111) by a factor of ten. The authors attribute this dramatic performance increase to modifications to the electronic structure of

930-443: Is longer than the inter-channel distance. Furthermore, the contact pressure between the GDL and the rib also compresses the GDL, making its thickness non-uniform across the rib and channel. The large width and non-uniform thickness of the rib will increase potential for water vapor to accumulate and the oxygen will be compromised. As a result, oxygen will be impeded to diffuse into catalyst layer, leading to nonuniform power generation in

992-431: Is sandwiched between two electrodes which have the catalyst embedded in them. The electrodes are electrically insulated from each other by the PEM. These two electrodes make up the anode and cathode respectively. The PEM is typically a fluoropolymer (PFSA) proton permeable electrical insulator barrier. Hydrocarbon variants are currently being developed and are expected to succeed fluoropolymers. This barrier allows

1054-405: Is to optimize the size and shape of the platinum particles. Decreasing the particles' size alone increases the total surface area of catalyst available to participate in reactions per volume of platinum used, but recent studies have demonstrated additional ways to make further improvements to catalytic performance. For example, one study reports that high-index facets of platinum nanoparticles (that

1116-420: Is used in current PEM fuel cell designs in order to represent a realistic alternative to internal combustion engines . Consequently, one main goal of catalyst design for PEM fuel cells is to increase the catalytic activity of platinum by a factor of four so that only one-fourth as much of the precious metal is necessary to achieve similar performance. One method of increasing the performance of platinum catalysts

1178-420: Is work by Kitagawa, et al. who used a two-dimensional oxalate-bridged anionic layer framework as the host and introduced ammonium cations and adipic acid molecules into the pores to increase proton concentration. The result was one of the first instances of a MOF showing "superprotonic" conductivity (8 × 10 S/cm) at 25 °C and 98% relative humidity (RH). They later found that increasing the hydrophilic nature of

1240-465: The electrochemical reaction of hydrogen and oxygen to electrical energy , as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy . A stream of hydrogen is delivered to the anode side of the MEA. At the anode side it is catalytically split into protons and electrons . This oxidation half-cell reaction or hydrogen oxidation reaction (HOR) is represented by: At

1302-692: The parasitic load of water management in fuel cells from 20% to 0.5% of the fuel cell power. High pressures or high flow rates are obtained by positioning several regular electroosmotic pumps in series or parallel respectively. Pumps based on porous media can be created using sintered glass or microporous polymer membranes with appropriate surface chemistry . Planar shallow electroosmotic pumps are made of parallel shallow microchannels . Electroosmotic effects can also be induced without external fields in order to power micron-scale motion. Bimetallic gold/silver patches have been shown to generate local fluid pumping by this mechanism when hydrogen peroxide

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1364-401: The proton exchange membrane in the membrane electrode assembly (MEA) of the proton exchange membrane fuel cells . Additionally, electroosmotic pumps have gained significant attention due to their potential applications in microfluidic channels, lab-on-a-chip devices, and biomedical engineering. Electroosmotic pumps are fabricated from silica nanospheres or hydrophilic porous glass ,

1426-423: The pumping mechanism is generated by an external electric field applied on an electric double layer (EDL), generates high pressures (e.g., more than 340 atm (34 MPa ) at 12 kV applied potentials) and high flow rates (e.g., 40 ml /min at 100 V in a pumping structure less than 1 cm in volume). EO pumps are compact, have no moving parts, and scale favorably with fuel cell design. The EO pump might drop

1488-582: The water gas shift reaction to eliminate CO from product gases and form more hydrogen. Additionally, the membrane is sensitive to the presences of metal ions, which may impair proton conduction mechanisms and can be introduced by corrosion of metallic bipolar plates, metallic components in the fuel cell system or from contaminants in the fuel/oxidant. PEM systems that use reformed methanol were proposed, as in Daimler Chrysler Necar 5; reforming methanol, i.e. making it react to obtain hydrogen,

1550-408: The 3D micro-lattices in the complex field, which act as baffles and induce frequent micro-scale interfacial flux between the GDL and flow-fields. Due to this repeating micro-scale convective flow, oxygen transport to catalyst layer (CL) and liquid water removal from GDL is significantly enhanced. The generated water is quickly drawn out through the flow field, preventing accumulation within the pores. As

1612-465: The FC. This new design enabled the first FC stack functions without a humidifying system meanwhile overcoming water recirculation issues and achieving high power output stability. The 3D micro lattice allows more pathways for gas flow; therefore, it promotes airflow toward membrane electrode and gas diffusion layer assembly (MEGA) and promotes O2 diffusion to the catalyst layer. Unlike conventional flow fields,

1674-487: The PEM as well as moves water vapor away from the PEM. Imbedding ELAT with noble metal catalyst allows this carbon cloth to also act as the electrode. Many other different methods and procedures also exist for the production of MEAs which are quite similar between fuel cells and electrolyzers . Platinum is one of the most commonly used catalysts, however other platinum group metals are also used. Ruthenium and platinum are often used together, if carbon monoxide (CO)

1736-556: The Pt particles are reaction sites; the ionomer provides paths for proton conduction, and the Teflon binder increases the hydrophobicity of the electrode to minimize potential flooding. In order to enable the electrochemical reactions at the electrodes, protons, electrons and the reactant gases (hydrogen or oxygen) must gain access to the surface of the catalyst in the electrodes, while the product water, which can be in either liquid or gaseous phase, or both phases, must be able to permeate from

1798-546: The TiN coating can easily lead to corrosion of the underlying material, most commonly steel. To perform their main function of distributing gas and fuel, these plates often have straight, parallel channels across its surface. However, this simple approach has led to issues such as uneven pressure distribution, water droplets blocking gas flow, and output power oscillations. Innovative approaches, such as nature-inspired fractal models and computer simulations are being explored to optimize

1860-403: The anode: The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the fuel cell. Meanwhile, a stream of oxygen is delivered to the cathode side of the MEA. At the cathode side oxygen molecules react with the protons permeating through

1922-421: The backplate needs to be structurally tough and leakage-resistant in case of structural failure due to fuel cell vibration and temperature cycling. As fuel cells operate in wide ranges of temperatures and in highly reductive/oxidative environments, plates must have high surface tolerances over the wide ranges of temperatures and should be chemically stable. Since the backplate accounts for more than three-quarters of

Proton-exchange membrane fuel cell - Misplaced Pages Continue

1984-423: The carbon allows for electrical connection between the catalyst and the rest of the cell. Platinum is so effective because it has high activity and bonds to the hydrogen just strongly enough to facilitate electron transfer but not inhibit the hydrogen from continuing to move around the cell. However, platinum is less active in the cathode oxygen reduction reaction. This necessitates the use of more platinum, increasing

2046-403: The catalyst to the gas outlet. These properties are typically realized by porous composites of polymer electrolyte binder (ionomer) and catalyst nanoparticles supported on carbon particles. Typically platinum is used as the catalyst for the electrochemical reactions at the anode and cathode, while nanoparticles realize high surface to weight ratios (as further described below) reducing the amount of

2108-436: The catalyst, but conductivity and porosity can act as opposing forces. Optimally, the GDL should be composed of about one third Nafion or 15% PTFE. The carbon particles used in the GDL can be larger than those employed in the catalyst because surface area is not the most important variable in this layer. GDL should be around 15–35 μm thick to balance needed porosity with mechanical strength. Often, an intermediate porous layer

2170-468: The cations introduced into the pores could enhance proton conductivity even more. In this low temperature regime that is dependent on degree of hydration, it has also been shown that proton conductivity is heavily dependent on humidity levels. A high temperature anhydrous example is PCMOF2, which consists of sodium ions coordinated to a trisulfonated benzene derivative. To improve performance and allow for higher operating temperatures, water can be replaced as

2232-405: The cell's expense and thus feasibility. Many potential catalyst choices are ruled out because of the extreme acidity of the cell. The most effective ways of achieving the nanoscale Pt on carbon powder, which is currently the best option, are through vacuum deposition, sputtering, and electrodeposition. The platinum particles are deposited onto carbon paper that is permeated with PTFE. However, there

2294-479: The costly platinum. The polymer electrolyte binder provides the ionic conductivity, while the carbon support of the catalyst improves the electric conductivity and enables low platinum metal loading. The electric conductivity in the composite electrodes is typically more than 40 times higher as the proton conductivity. The GDL electrically connects the catalyst and current collector. It must be porous, electrically conductive, and thin. The reactants must be able to reach

2356-875: The durability of these proposed MOF-based catalysts is currently less than desirable and the ORR mechanism in this context is still not completely understood. Much of the current research on catalysts for PEM fuel cells can be classified as having one of the following main objectives: Examples of these approaches are given in the following sections. As mentioned above, platinum is by far the most effective element used for PEM fuel cell catalysts, and nearly all current PEM fuel cells use platinum particles on porous carbon supports to catalyze both hydrogen oxidation and oxygen reduction. However, due to their high cost, current Pt/C catalysts are not feasible for commercialization. The U.S. Department of Energy estimates that platinum-based catalysts will need to use roughly four times less platinum than

2418-429: The electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. Importantly, the membrane must not be electrically conductive so the half reactions do not mix. Operating temperatures above 100 °C are desired so the water byproduct becomes steam and water management becomes less critical in cell design. A proton exchange membrane fuel cell transforms the chemical energy liberated during

2480-475: The field of fuel cell research, MOFs are being studied as potential electrolyte materials and electrode catalysts that could someday replace traditional polymer membranes and Pt catalysts, respectively. As electrolyte materials, the inclusion of MOFs seems at first counter-intuitive. Fuel cell membranes generally have low porosity to prevent fuel crossover and loss of voltage between the anode and cathode. Additionally, membranes tend to have low crystallinity because

2542-427: The formation of one water molecule. The potentials in each case are given with respect to the standard hydrogen electrode . To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect " short circuit " the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover . Finally, the membrane must be resistant to

Proton-exchange membrane fuel cell - Misplaced Pages Continue

2604-475: The fuel cell mass, the material must also be lightweight to maximize the energy density. Materials that fulfill all of these requirements are often very expensive. Gold has been shown to fulfill these criteria well, but is only used for small production volumes due to its high cost. Titanium nitride (TiN) is a cheaper material that is used in fuel cell backplates due to its high chemical stability, electrical conductivity, and corrosion resistance. However, defects in

2666-519: The fuel cell. A disadvantage of fluor containing polymers is the fact that during production (and disposal) PFAS products are formed. PFAS, the so-called forever chemicals, are highly toxic. Newer polymers such as the recently patented SPX3 (POLYMERS COMPRISING SULFONATED 2,6-DIPHENYL-1,4-PHENYLENE OXIDE REPEATING UNITS -US 11434329 B2) are fluor free and therefore do not carry the PFAS risk. 2. Low Operating Temperature Under extreme sub-freezing conditions,

2728-777: The function of these bipolar plates. Metal-organic frameworks (MOFs) are a relatively new class of porous, highly crystalline materials that consist of metal nodes connected by organic linkers. Due to the simplicity of manipulating or substituting the metal centers and ligands, there are a virtually limitless number of possible combinations, which is attractive from a design standpoint. MOFs exhibit many unique properties due to their tunable pore sizes, thermal stability, high volume capacities, large surface areas, and desirable electrochemical characteristics. Among their many diverse uses, MOFs are promising candidates for clean energy applications such as hydrogen storage, gas separations, supercapacitors, Li-ion batteries, solar cells, and fuel cells. Within

2790-438: The membrane will dry and the resistance across it increases. Both cases will cause damage to stability and power output. Water management is a very difficult subject in PEM systems, primarily because water in the membrane is attracted toward the cathode of the cell through polarization. A wide variety of solutions for managing the water exist including integration of an electroosmotic pump . Another innovative method to resolve

2852-518: The membrane would dry. Other, more recent membrane types, based on polybenzimidazole (PBI) or phosphoric acid , can reach up to 220 °C without using any water management (see also High Temperature Proton Exchange Membrane fuel cell , HT-PEMFC): higher temperature allow for better efficiencies, power densities, ease of cooling (because of larger allowable temperature differences), reduced sensitivity to carbon monoxide poisoning and better controllability (because of absence of water management issues in

2914-406: The membrane); however, these recent types are not as common. PBI can be doped with phosphoric or sulfuric acid and the conductivity scales with amount of doping and temperature. At high temperatures, it is difficult to keep Nafion hydrated, but this acid doped material does not use water as a medium for proton conduction. It also exhibits better mechanical properties, higher strength, than Nafion and

2976-404: The polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules. This reduction half-cell reaction or oxygen reduction reaction (ORR) is represented by: At the cathode: Overall reaction: The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and

3038-512: The possibility of flooding. Several microscopic variables are analyzed in the GDLS such as: porosity, tortuosity and permeability. These variables have incidence over the behavior of the fuel cells. The maximal theoretical efficiency applying the Gibbs free energy equation ΔG = −237.13 kJ/mol and using the heating value of Hydrogen (ΔH = −285.84 kJ/mol) is 83% at 298 K. The practical efficiency of

3100-767: The potential to play an important role in PEMFCs in the near future. MOFs have also been targeted as potential replacements of platinum group metal (PGM) materials for electrode catalysts, although this research is still in the early stages of development. In PEMFCs, the oxygen reduction reaction (ORR) at the Pt cathode is significantly slower than the fuel oxidation reaction at the anode, and thus non-PGM and metal-free catalysts are being investigated as alternatives. The high volumetric density, large pore surface areas, and openness of metal-ion sites in MOFs make them ideal candidates for catalyst precursors. Despite promising catalytic abilities,

3162-522: The preferred choice of proton-conducting membrane, they require humidification for adequate performance and can sometimes physically degrade due to hydrations effects, thereby causing losses of efficiency. As mentioned, Nafion is also limited by a dehydration temperature of < 100 °C, which can lead to slower reaction kinetics, poor cost efficiency, and CO poisoning of Pt electrode catalysts. Conversely, MOFs have shown encouraging proton conductivities in both low and high temperature regimes as well as over

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3224-418: The proton carrier by less volatile imidazole or triazole molecules within the pores. The maximum temperature achieved was 150 °C with an optimum conductivity of 5 × 10 S/cm, which is lower than other current electrolyte membranes. However, this model holds promise for its temperature regime, anhydrous conditions, and ability to control the quantity of guest molecules within the pores, all of which allowed for

3286-444: The reducing environment at the cathode as well as the harsh oxidative environment at the anode. Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been discovered, and platinum is the best option. 1. Easy sealing PEMFCs have

3348-486: The same time reducing platinum group metal loading to 0.2 mg/cm2. At this time most companies manufacturing MEAs specialize solely in high volume production, such as W. L. Gore & Associates , Johnson Matthey , and 3M . However, there are other companies which produce MEAs, allowing different shapes, catalysts or membranes to be evaluated as well, which include Fuel Cell Store, FuelCellsEtc, and many others. The global market for Membrane Electrode Assemblies (MEA)

3410-464: The surface, reducing its tendency to bond to oxygen-containing ionic species present in PEM fuel cells and hence increasing the number of available sites for oxygen adsorption and reduction. Membrane electrode assembly A membrane electrode assembly ( MEA ) is an assembled stack of proton-exchange membranes (PEM) or alkali anion exchange membrane (AAEM), catalyst and flat plate electrode used in fuel cells and electrolyzers . The PEM

3472-739: The transport of ions is more favorable in disordered materials. On the other hand, pores can be filled with additional ion carriers that ultimately enhance the ionic conductivity of the system and high crystallinity makes the design process less complex. The general requirements of a good electrolyte for PEMFCs are: high proton conductivity (>10 S/cm for practical applications) to enable proton transport between electrodes, good chemical and thermal stability under fuel cell operating conditions (environmental humidity, variable temperatures, resistance to poisonous species, etc.), low cost, ability to be processed into thin-films, and overall compatibility with other cell components. While polymeric materials are currently

3534-443: The transport of the protons from the anode to the cathode through the membrane but forces the electrons to travel around a conductive path to the cathode. The most commonly used Nafion PEMs are Nafion XL, 112, 115, 117, and 1110. The electrodes are heat pressed onto the PEM. Commonly used materials for these electrodes are carbon cloth or carbon fiber papers. NuVant produces a carbon cloth called ELAT which maximizes gas transport to

3596-470: The tunability of proton conductivity. Additionally, the triazole-loaded PCMOF2 was incorporated into a H 2 /air membrane-electrode assembly and achieved an open circuit voltage of 1.18 V at 100 °C that was stable for 72 hours and managed to remain gas tight throughout testing. This was the first instance that proved MOFs could actually be implemented into functioning fuel cells, and the moderate potential difference showed that fuel crossover due to porosity

3658-760: The water produced by fuel cells can freeze in porous layers and flow channels. This freezing water can block gas and fuel transport as well as cover catalyst reaction sites, resulting in a loss of output power and a start-up failure of the fuel cell. However, the low operating temperature of a PEM fuel cell allows it to reach a suitable temperature with less heating compared to other types of fuel cells. With this approach, PEM fuel cells have been shown to be capable of cold start processes from −20°C. 3. Light mass and high power density (transport applications) PEM fuel cells have been shown to be capable of high power densities up to 39.7 kW/kg, compared to 2.5 kW/kg for solid oxide fuel cells. Due to this high power density, much research

3720-490: The water recirculation problem is the 3D fine mesh flow field design used in the Toyota Mirai, 2014. Conventional design of FC stack recirculates water from the air outlet to the air inlet through a humidifier with a straight channel and porous metal flow fields.The flow field is a structure made up of a rib and channels. However, the rib partially covers the gas diffusion layer (GDL) and the resultant gas-transport distance

3782-414: Was estimated to be worth US$ 672 million in 2023 and is forecast to reach US$ 3853 million by 2030, with a CAGR of 28.2% during the forecast period 2024-2030. Electroosmotic pump An electroosmotic pump is used for generating flow or pressure by use of an electric field. One application of this is removing liquid flooding water from channels and gas diffusion layers and direct hydration of

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3844-528: Was not an issue. To date, the highest proton conductivity achieved for a MOF electrolyte is 4.2 × 10 S/cm at 25 °C under humid conditions (98% RH), which is competitive with Nafion. Some recent experiments have even successfully produced thin-film MOF membranes instead of the traditional bulk samples or single crystals, which is crucial for their industrial applicability. Once MOFs are able to consistently achieve sufficient conductivity levels, mechanical strength, water stability, and simple processing, they have

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