PHOSPHORIC ACID FUEL CELLS
vijay tharad
Director Operations at Corporate Professional Academy for Technical Training & Career Development
Summary
Phosphoric acid fuel cells (PAFC) currently represent one of the fuel cell technologies that have been demonstrated in many countries around the world and for many applications. PAFCs can be purchased, complete with a warranty, maintenance and spare parts service. The first PAFC power plants were installed in the 1970s, and now more than 500 units have been installed all around the world.
The phosphoric acid fuel cell (PAFC) is the most widely used and best documented type of fuel cell. Since the 1970s, more than 500 PAFC power plants have been installed and tested around the world. With every new product release, the number of units sold became larger as well as the power rating per unit. The largest fuel cell ever built to date is an 11?MW PAFC power plant for the Tokyo Electric Power Co. (TEPCO) in Japan, which was operated for more than 230?000?h between 1991 and 1997 . The most important PAFC developers are UTC Fuel Cells , Toshiba and Fuji Electric. All the installations have been used for stationary applications, with the exception of the Georgetown University Fuel Cell Transit Program, in which a 100?kW UTC fuel cell was deployed . PAFCs have shown a remarkable reliability. UTC PAFC systems are characterized by a Mean Time Before Failure (MTBF) that ranges between 2500?h for the PC25 to 6750?h for the 400?kW advanced PAFC . Due to the high reliability, that is well above those of traditional systems, PAFC represents, for some applications, the answer to electricity quality and availability needs.
The PAFC is the first type of FC that has been commercialized. It is commercially available in hotels, houses, hospitals, and some power stations in a range from 50?kW to 11?MW.
Efficiency of PAFC is ~?35%–45%, which is higher than PEMFC, but lower than MCFC and SOFC. When it works with CHP, heat and power are applied simultaneously, so the efficiency grows dramatically and reaches to about 80%.
PAFCs have been found useful in stationary power distribution, defense, and military applications. Heat and power cogeneration is another major advantage. In spite of these advantages, PAFC technology is constrained by various factors. Use of precious metal electrocatalyst makes it costly. The system weight is high owing to the use of heavier materials for bipolar plates. The power density of the PAFC Systems is therefore low.
Introduction
Of the hydrogen-oxygen fuel cell systems the most mature is the phosphoric acid fuel cell (PAFC). It operates at 150-190°C and pressure ranging from ambient to 5 atm. PAFC systems use primarily Pt as catalyst both for hydrogen and oxygen electrodes. The operating temperature range of PAFC allows it to take up hydrogen directly from hydrogen sources like reformer gases. Less than one percent of CO present in the reformer gases are not adsorbed on Pt sites owing to high operating temperature. The other components used in PAFC are mainly made of graphite and carbon. All these factors make PAFC a versatile member of the hydrogen-oxygen fuel cell family.
Concentrated phosphoric acid (90-100% based on ortho phosphoric acid) is used as electrolyte in this fuel cell, that operates at 150 to 190°C. Some of the pressurized systems are reported to work upto 220°C. At lower temperatures, phosphoric acid is a poor ionic conductor), and CO poisoning of the Pt electrocatalyst in the anode becomes severe. The relative stability of concentrated phosphoric acid is high compared to other common acids; consequently the PAFC is capable of operating at the high end of the acid temperature range (100 to 220°C). In addition, the use of concentrated acid minimizes the water vapor pressure and hence water management in the cell is not as difficult as it is for polymer electrolyte fuel cell (PEMFC). The matrix, that is universally used to retain the acid, is silicon carbide. The electrocatalyst typically used in both the anode and cathode is Pt loaded on carbon.
Phosphoric Acid Fuel Cell (PAFC): System Definition and Principle of Operation.
A phosphoric acid fuel cell (PAFC) is composed of two porous gas diffusion electrodes, namely, the anode and cathode (Fig. 1) juxtaposed against a porous electrolyte matrix. The gas diffusion electrodes are porous substrates that face the gaseous feed. The substrate is a porous carbon paper or cloth. On the other side of this substrate, which faces the electrolyte (phosphoric acid), platinized fine carbon powder electrocatalyst is roll coated with polytetrafluroethylene (PTFE) as a binder. PTFE also acts as a hydrophobic agent to prevent flooding of pores so that reactant gas can diffuse to the reaction site easily.
At anode, hydrogen ionizes to H+ and migrates towards cathode to combine with oxygen, forming water. The product water then diffuses out to the oxygen stream and comes out of the system as steam. An emf is generated between the two electrodes through conversion of reaction free energy to electricity and on connecting an external load, electrical power can be extracted. The reactions at anode and cathode are as follows.
Fuel cells, which use phosphoric acid solution as the electrolyte, are called phosphoric acid fuel cells (PAFCs). As Eq. 1 indicates, the phosphoric acid in aqueous solution dissociates into phosphate ions and hydrogen ions; the hydrogen ions (H+ ) act as the charge carrier.
H3PO4 → H+ + H2PO4 (1)
Phosphoric acid is chemically stable, and is easy to handle. It also has an extremely low vapor pressure even at an operating temperature of 200 °C (473 K). This implies that phosphoric acid in the electrolyte layer cannot be easily discharged from the fuel cell together with the cell exhaust gas, although even such minute discharge, results in the degradation of cell performance in the long term.
A conceptual working principle is described in Figure 1.
At the fuel electrode, pure hydrogen or reformate fuel gases the principal component being hydrogen is supplied, and air is supplied at the air electrode; the resulting electrochemical reaction yields an electric power output. At the fuel electrode, hydrogen reacts at the electrode surface to become hydrogen ions and electrons, and the hydrogen ions migrate toward the air electrode within the electrolyte.
Fuel electrode: H2 → 2H+ + 2e- (2)
At the air electrode, the hydrogen ions, which have migrated from the fuel electrode; electrons, which have passed through the external circuit, and oxygen supplied from outside, combine to produce water in the following reaction:
Air electrode: (1/2)O2 + 2H+ + 2e – → H2O (3)
Hence the net fuel cell reaction produces water as follows:
H2 + (1/2) O2 → H2O (4)
Figure 1. Principle of Operation of Phosphoric Acid Fuel Cells (PAFCs)
2. Cell Structure
The PAFC itself consists of a pair of porous electrodes (the fuel electrode and air
electrode) formed from mainly carbon material, between which is placed an electrolyte layer consisting of a matrix impregnated with highly concentrated phosphoric acid solution. The catalytic layer of the electrodes where reactions take place consists of the carbon material, minute metal catalyst particles, and water repellant material, in a construction such that the reaction gas is supplied and the electrolyte retained effectively.
The voltage obtained from a single fuel cell is from 0.6 to 0.8 V or so; in actual power plants several hundred cells are stacked and connected in series, forming a sub unit called a “cell stack.” Heat is generated due to energy losses in the course of the electrochemical reaction of hydrogen with oxygen, and so cooling plates are inserted at regular intervals between fuel cells, and cooling water is passed through them to maintain a cell operating temperature of about 200 °C (473 K).
3. Features of Phosphoric Acid Fuel Cells
The PAFC do not suffer the carbon dioxide-induced electrolyte degeneration seen in alkaline fuel cells, and so can use reformed gas derived from fossil fuels, though expensive platinum catalyst is necessary in order to promote the electrode reactions.
Thus it can make use of city gas (natural gas-based) and other existing fuel
infrastructure. However, when CO exists at high concentrations, as in coal-gasified gas, the platinum catalyst used in electrodes is poisoned, leading to performance degradation, so that use of such fuels is impractical without effective means of eliminating CO. This gives an additional constraint.
The operating temperature is about 200 °C (473 K). Consequently if the cell is designed such that it does not make direct contact with the phosphoric acid, copper, iron and other metals can be used. Also, in order to endow the electrode catalyst layer with water-repelling properties, a fluoride resin (PTFE) or other highly heat-resistant organic material may also be used. In order to remove the heat generated by the electrode reactions, the fuel cell is itself water-cooled as mentioned above.
Waste heat at a temperature range below 200 °C is available; which cannot just be used for space heating and water heating, but can also be extracted in part as steam and used as the heat source of refrigeration equipment for cooling. The electric power generation efficiency of PAFCs under atmospheric pressure operation is approximately 40% (LHV basis), which is superior, or at least competitive with existing gas turbine and gas engines. Properties of low Nox and low noise make them suitable for cogeneration systems for urban environmentally friendly power sources.
Unlike the high temperature fuel cell systems such as MCFCs and SOFCs, a combined cycle system with gas turbine or steam turbine generators to maximize the system efficiency is generally difficult for PAFCs, since the quality of plant exhaust heat is inadequate for such purposes.
In pressurized PAFC systems, thought reformer exhaust gas at elevated pressure and temperature can be passed through an expander to drive an air compressor or an electric power generator, the total power generation efficiency stays in a range of 44–46% (LHV basis).
PAFC technology is the most mature fuel cell technology. About 100 MW of PAFC systems have been installed and operated worldwide over the past 20 years with installations in the size range from 50 kW to 11 MW. Some of the field test systems supplied by UTC and Fuji Electric have demonstrated the “magical” 40 000 h operational lifetime mark. Up to the mid-1990s there were a number of developers in the USA, Europe and Japan, but currently only UTC Power, Fuji Electric and more recently HydroGen LLC (acquired Westinghouse's air cooled technology) are still producing PAFC. The major hurdle to large-scale commercialisation is still the cost of the units of 4000–5000 USD/kW that needs to be reduced by a factor of three. Interest in PAFCs has been revived as PEMFC have not been able to match the lifetimes demonstrated by PAFC, and UTC, HydroGen and Fuji Electric believe that a target market price of USD 1500 is achievable through further development and through economies of scale.
Typical applications lie in hospitals, where the waste heat can be used in laundry and other areas and where consistent and reliable power is required; in computer equipment power provision, where the absence of power surges and spikes from the fuel cell enables systems to be kept running; and in army facilities and leisure centers that have a suitable heat and power requirement.
Advantages of Phosphoric Acid Fuel Cell
Disadvantages of Phosphoric Acid Fuel Cell
Applications
PAFC have been used for stationary power generators with output in the 100?kW to 400?kW range and are also finding application in large vehicles such as buses.
Major manufacturers of PAFC technology include Doosan Fuel Cell America Inc.(formerly ClearEdge power & UTC Power and Fuji Electric.
India's DRDO has developed PAFC based air-independent propulsion air-independent propulsion for integration into their Kalvari-class submarines.
Typical applications lie in hospitals, where the waste heat can be used in laundry and other areas and where consistent and reliable power is required; in computer equipment power provision, where the absence of power surges and spikes from the fuel cell enables systems to be kept running; and in army facilities and leisure centers that have a suitable heat and power requirement.
PAFC FUEL CELL APPLICATIONS
1. Electrical Power Generation
a. Quiet electrical power generation for recreation vehicles, mobile homes, etc.
b. Lighthouse applications (propane powered).
c. Short-term underwater power plants.
d. Emergency and standby electric power (hospital, industry).
e. Offshore oil/gas drilling rig.
f. Offshore oil production platform.
g. Remote power for entertainment industry.
2. Non-Conventional Applications (Remote/Third World)
a. Rural water pumps.
b. Third world power generation (indigenous fuels).
c. Arctic village power generation.
d. Power generation for food processing - Third World.
e. Power for remote mineral processing plants.
3. Agriculture
a. Tractors.
b. Farm machines (self-powered).
c. Logging machines.
d. Grain drying.
e. Lumber mills.
f. Water desalination plant power.
4. Mining
Underground Rock Mines
a. Load haul dumps (LHDs).
b. Digging equipment.
c. Locomotives.
Surface Mining
d. Small hauling equipment.
e. Large hauling equipment.
f. Small digging equipment.
g. Large digging equipment.
Underground Coal Mining
h. Auxiliary vehicles inside mines.
i. Continuous mining equipment.
j. Large-wall equipment.
k. LHDs.
5. Transportation
a. Passenger cars.
b. Highway trucks and buses.
c. Distribution van.
d. Mail car.
e. Long haul locomotives.
f. 'Switching locomotives.
g. Taxi.
h. Total energy system for pleasure boats.
i. Delivery trucks.
j. City buses.
k. Rail maintenance equipment.
1. Above ground rail rapid transit.
6. Construction
a. Construction vehicles.
b. Portable welders.
c. On-site power.
d. Portable air compressors.
e. Concrete pumps.
7. Industrial Applications
a. Indoor forklift trucks.
b. Mobile refrigeration equipment.
c. Natural gas pipeline compressors.
d. Pipeline auxiliary power.
e. Submersibles or crawlers for offshore oil and gas industry.
f. Undersea mining equipment.
g. Oil and gas field power.
h. Oil pipeline remote pump stations,
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i. Coal slurry pipeline pumping.
8. Marine Applications (Commercial)
a. LNG/LPG tanker.
b. VLCCs.
c. Petroleum product tankers.
d. Methanol tankers.
e. Other merchant vessels.
f. Cruise ships.
g. Coastal and inland waterways diesel vessels,
h. Submersible tankers.
CONCLUSION
Developed in the mid-1960s and field-tested since the 1970s, the PAFCs are one of the most mature types of fuel cells and the first type to be commercially used. Phosphoric acid fuel cells (PAFCs) use phosphoric acid as an electrolyte and an anode and cathode made of a finely dispersed platinum catalyst on a carbon and silicon carbide structure. They have been typically used for stationary power generation in buildings, hotels, hospitals, and utilities in USA, Europe and Asia. The units have been technically successful and very reliable, with 40% plus efficiency levels and tens of thousands of operating hours. Water management in these fuel cells is easier than in PEMs, and they are more tolerant of impurities in hydrogen. However, the emission of phosphoric acid vapor is problematic and good ventilation is mandatory. PAFCs are less powerful than other fuel cells for the same weight and volume and require much more platinum than other fuel cells, which raises their cost.
A fuel cell is a device which reacts a fuel with an oxidant electrochemically, directly generating DC power. Several classes of fuel cells are being developed for application using oxygen from the air as the oxidant and a hydrogen-rich gas as the fuel. Among these is the phosphoric acid fuel cell. It takes its name, as do most other fuel cell systems, from its electrolyte: phosphoric acid.
The phosphoric acid fuel cell has several advantages over most conventionally used fuel-based systems for generating electricity or shaft power. Perhaps most important, it offers high fuel efficiency.
Even allowing for the inefficiency involved in processing a light hydrocarbon or alcohol fuel into a hydrogen-rich gas, it can offer efficiencies of power generation between 40 and 48%.
The phosphoric acid fuel cell is a very clean power source. It can be operated with essentially negligible emissions of carbon monoxide, oxides of nitrogen, unburned hydrocarbons, and sulfur dioxide, with no discharge of polluted water. In addition to being much cleaner than any currently commercial internal combustion engine it is also much quieter. Furthermore, being based on a continuously conducted electrochemical process, with moving parts limited to a few pumps and valves, it might be expected that technologically mature fuel cell systems would display higher reliability than internal combustion engines with all their moving parts.
Given these attractions, it is not surprising that the phosphoric acid fuel cell is being actively evaluated for several classes of applications. Most notable are large, grid connected electric utility applications, residential/commercial total energy system applications, and small military power sources. The U. S. Department of Energy and the National Aeronautics and Space Administration concluded that it would be advantageous to commission a multi-disciplinary study to identify and begin evaluation of additional classes of applications, with the hope of finding highly promising but heretofore overlooked uses for the phosphoric acid fuel cell. The study was meant to consider:
? Major market segments. An example would be the railroad locomotive application .
? Market entry application. Examples of these potentially high, value applications would include the mine locomotive and Arctic village systems.
? Specialty applications. An example of such an attractive but small market application would be the robotic submersible.
? Space applications
? Industrial cogeneration in the developed world;
? Opportunistic use of industrial waste hydrogen;
? Applications smaller than 10 kilowatts.
Merits & Shortcomings of Phosphoric Acid Cells
Five conclusions are developed on the comparative advantages and disadvantages of PAFC vis-a-vis conventional alternatives:
? In situations where it is feasible to provide the necessary power via a steam cycle, based on a solid fuel fired boiler, this is likely to be the preferred system. Under these circumstances, the modest energy efficiency advantage of the
fuel cell can seldom overcome the capability of the steam system to use a much less expensive fuel.
? In most other applications of concern in this study, the principal obstacle to fuel cell use is capital cost. PAFC capital costs are higher than those of Conventional systems, and must be reduced substantially for the fuel cell to be
competitive in most applications. Careful investigation can, however, identify applications which might be economically served by fuel cell systems whose capital costs do substantially exceed those of the conventionally used systems.
? Current phosphoric acid fuel cell systems probably cannot compete with internal combustion engines in applications where weight and volume are of substantial importance. This includes most light duty vehicles, whose overall fuel
efficiency will be reduced significantly by the fuel cell's added weight.
The fuel cell's key advantage over internal combustion engines is fuel efficiency. This can yield substantial savings in applications where high load factors are achieved for large numbers of operating hours per year.
? Industrial practice is to substitute batteries for internal combustion engines in applications where the fuel cell's cleanliness was expected to offer a large advantage over these engines. Essentially all of these applications are vehicular. The fuel cell can offer substantial advantages over the battery in weight, utility of use, and possibly even in capital costs in situations where the vehicle in question
must be capable of performance of lengthy missions without battery pack charge or recharge.
Specific Applications
The principal conclusion concerning use of PAFC in remote applications is that economics will probably be attractive in Arctic applications before they compete in other environments. Outside the Arctic PAFC must compete with photovoltaic power as well as diesel generators. This competitor, which eliminates the need for costly remote-delivered fuel altogether, probably has an overwhelming long-term advantage in this market, particularly as its capital costs decline.
Concerning vehicular applications, fuel cells appear to be well suited for use in traction vehicles in which fuel cell weight can be tolerated. Examples of such traction vehicles which have attractively high load factors and large numbers of annual operating hours include railroad locomotives and some underground mine locomotives (such as those used in tunnelling and some hardrock mines). Farm and construction traction vehicles are not good applications since they exhibit limited annual operating hours.
For use in vehicles which operate in environments where ventilation is limited, the fuel cell is likely to be in competition with lead acid batteries. Here, the fuel cell can enjoy substantial advantages in applications which daily consume energy equivalent to that required for full power operation for 8 to 12 hours. While most
indoor industrial utility vehicles and underground mining vehicles receive far less use than this, some few high duty vehicles can be identified in which PAFC looks quite attractive. The best example is probably the underground mine locomotive and some forklift truck applications.
For the robotic submersible PAFC offers substantial opportunities for improving utilization. This may prove of great importance to the full development of the robotic submersible, which will swim untethered for many hours, performing simple tasks. For the foreseeable future, however, the phosphoric acid fuel cell must be considered to offer an opportunity to the submersible designer,
rather than the submersible be considered an opportunity for PAFC.
The size of the PAFC market which would be created by full development of the submersible is insignificant in terms of producing capital cost reduction via learning curve effects.
Phosphoric Acid Fuel Cells have the following characteristics:
These four characteristics make PAFC fuel cells one of the most exciting types of fuel cells out there for stationary co-generation power applications. The last characteristic specifically, the low temperature, is a very intriguing one. Because PAFCs operate at a low temperature, around 400 F, they essentially operate at lower cost because the stack does not need replacement as often as compared to higher temperature fuel cells like molten carbonate and solid oxide fuel cells. Carbon oxides will “poison” most types of fuel cells by dirtying the electrodes and diminishing the fuel cell’s functional efficiency over time. An advantage of PAFCs is that they can tolerate a concentration of carbon oxide “poisoning” of about 1.5%.
The stack is the heart of any fuel cell regardless of type. If you follow RMP, you know our mantra: always follow the money. If PAFCs can operate at a lower costs, that means they will make customers happier by providing more value. Listen to Jeff Chung, the President & CEO of Doosan Fuel Cell explain why his company is focused on PAFCs has extensive knowledge in all types of fuel cells. They are focusing on the PAFC because they think they can make this type of fuel cell deliver increased value creation for their customers because of lower operating costs. Always follow the money, it is what drives decisions in the real world and is the shortest route to the truth.
In 2013, CBS installed a Doosan PureCell Model 400 phosphoric acid fuel cell at their Los Angeles studio at 4024 Radford Avenue.?? This time-lapse video shows CBS removing their old power generators and installing a sustainable, reliable, clean, and low emissions PAFC for generating electricity and heat at upwards of 80% efficiency because of co-generation. Many companies operating large facilities in urban areas are switching to PAFCs because no other form of power generation can compete with a fuel cell’s power density; not solar, not wind, nor any other form of power generation. This is good news for America’s & the world’s most storm vulnerable cities.?? Hurricane Sandy in October of 2012 was a category 3 storm that hit New York City & New Jersey and?cut power to many people in and around major population centers.?? Fuel cells and a distributed grid can help stop large outages caused by future storms similar to Sandy because fuel cell systems like the ones discussed here have no transmission lines; electrical power and heat are?generated on site. The cost advantages and resiliency in life & death situations make fuel cells like PAFCs a very smart choice for America’s hospitals when the power has just gotta stay on 24/7. ?Even if fuel cells polluted our air & water like our current centralized power plants pollute, they would still make more sense economically than centralized power plants. Fuel cells, however, do not pollute and are therefore a win-win solution for energy production. Fuel cells provide clean energy on top of all their other fundamental economic advantages.
Frequently asked Questions:
What are the properties of phosphoric acid fuel cell?
PAFC power plants supply usable thermal energy at an efficiency of 37–41% HHV. A portion of the thermal energy can be supplied at temperatures of ～120 °C to ～150 °C; however, the majority of the thermal energy is supplied at ～65 °C. The PAFC has a power density of 1.7–1.9 KW m?2 of active cell area.
What are the major input parameters of any fuel cell?
The fuel cell operating temperature is considered a crucial parameter in a fuel cell operating system. The operating temperature influences the membrane conductivity, current density, synthesis of input gas streams, and water vapor pressure.
What are the important points on fuel cell?
Fuel cells work like batteries, but they do not run down or need recharging. They produce electricity and heat as long as fuel is supplied. A fuel cell consists of two electrodes—a negative electrode (or anode) and a positive electrode (or cathode)—sandwiched around an electrolyte.
What is the efficiency of phosphoric acid fuel cell?
Phosphoric Acid Fuel Cell Efficiency of PAFC is ~ 35%–45%, which is higher than PEMFC, but lower than MCFC and SOFC.
What is a phosphoric acid fuel cell?
Phosphoric acid fuel cells (PAFC) operate at temperatures around 150 to 200 C (about 300 to 400 degrees F). As the name suggests, PAFCs use phosphoric acid as the electrolyte. Positively charged hydrogen ions migrate through the electrolyte from the anode to the cathode.
What are the three types of phosphoric acid?
phosphoric acid May be one of three types: orthophosphoric acid (H 3PO 4), metaphosphoric acid (HPO 3), or pyrophosphoric acid (H 4P 2O 7).
What are 3 interesting facts about phosphoric acid?
It serves as an acidic, fruitlike flavouring in food products. Pure phosphoric acid is a crystalline solid (melting point 42.35° C, or 108.2° F); in less concentrated form it is a colourless syrupy liquid. The crude acid is prepared from phosphate rock, while acid of higher purity is made from white phosphorus.
What are the uses and importance of phosphoric acid?
Uses. Phosphoric acid is a component of fertilizers (80% of total use), detergents, and many household cleaning products. Dilute solutions have a pleasing acid taste; thus, it's also used as a food additive, lending acidic properties to soft drinks and other prepared foods, and in water treatment products.
What is the advantage of phosphoric acid?
Phosphoric acid also occurs naturally in many fruits and their juices. Apart from use of phosphoric acid itself, the greatest consumption of phosphoric acid is in the manufacture of phosphate salts. Taking advantage of its ability to lower blood pH, phosphoric acid has been used therapeutically to treat lead poisoning.
Which material is suitable for phosphoric acid?
The recommended alloy for use with phosphoric acid are Incoloy 825, Inconel 625 and Hastelloy C276. There are limited applications of Nickel 200 in phosphoric acid. In pure and unaerated acid, the corrosion rates of Nickel 200 are nominal at all concentrations at normal temperatures.
Is phosphoric acid positive or negative catalyst?
negative catalyst
Phosphoric acid acts as a negative catalyst to decrease the rate of decomposition of hydrogen peroxide.
What are the different types of phosphoric acid?
Cyclic phosphoric acids
There are four design parameters to be optimized: electrolyte, anode, cathode thickness, and anode porosity.
What are the parameters that raise the efficiency of a fuel?
Combustion efficiency is affected by fuel type, bed temperature, gas velocity, and excess air levels. Combustion efficiency increases with fuel volatile matter content and bed temperature. Combustion efficiency decreases with increasing superficial gas velocity.
What is the pressure in a fuel cell?
Generally, if the operating pressure of PEM fuel cells is increased above 4 bar, the effect of the voltage increase is getting smaller due to mass transport issues. Therefore, the optimal PEM-fuel cell operating pressure lies typically between 3 and 4 bar
What are the factors affecting fuel cell performance?
The load current, temperature, relative humidity, membrane thickness, membrane-active area, electrode active area, corrosion, purity, pressure, and concentration of hydrogen fuel, maintenance of water inside the cell, pressure in the electrode particularly on both side of the membrane etc. are the factors.
What are the limitations of fuel cells?
Expensive to manufacture due the high cost of catalysts (platinum) Lack of infrastructure to support the distribution of hydrogen. A lot of the currently available fuel cell technology is in the prototype stage and not yet validated.
What is polarization in fuel cell?
Polarization is caused by chemical and physical factors associated with various elements in the fuel cell, such as temperature, pressure, gas composition, and fuel properties and reactant utilization. These factors limit the reaction processes when the current flows through.
What is the efficiency of a fuel cell?
A conventional combustion-based power plant typically generates electricity at efficiencies of 33 to 35%, while fuel cell systems can generate electricity at ef- ficiencies up to 60% (and even higher with cogeneration).
What are the two most common elements used in fuel cells?
Fuel cells have two main supplies. In order to make electricity, fuel cells will use an external source of fuel and oxygen. The source of fuel could be an element such as hydrogen. Fuel is electrochemically oxidised.
What is the current density of a fuel cell?
The limiting current density of the fuel cell is increased proportional to increase in hydrogen flow rate. The limiting current density for 0.07 lpm is 960 mA/cm2 which is comparably higher than the limiting current density of 915 mA/cm2 corresponding to 0.04 lpm.
How does a phosphoric acid fuel cell work?
Phosphoric acid fuel cell (PAFC) anodes accelerate the hydrogen oxidation reaction rate in phosphoric acid. The anode materials must be stable at high operating temperature in phosphoric acid. During operation, hydrogen starvation may cause reverse polarization and electrochemical corrosion of the anode material.
What is the basic principle of fuel cell?
Fuel cells require a continuous input of fuel and an oxidizing agent (generally oxygen) in order to sustain the reactions that generate the electricity. Therefore, these cells can constantly generate electricity until the supply of fuel and oxygen is cut off.
What are 3 advantages of fuel cells?
Hydrogen fuel cell technology offers the advantages of a clean and reliable alternative energy source to customers in a growing number of applications – electric vehicles, including forklifts, delivery vans, drones, and cars – primary and backup power for a variety of commercial, industrial, and residential buildings;
What are the main components of fuel cell and their function?
A fuel cell is composed of: Negative electrode or anode. Positive electrode or cathode. Intercalated electrolyte between each electrode of a material that facilitates the passage of ions (positively or negatively charged atoms), but not electrons (which are conducted to generate electricity).
What is a fuel cell used for?