Week 2 Challenge
1. Compare four different types of fuel cells and state their applications.
Fuel cells are classified primarily by the kind of electrolyte they employ. This classification determines the kind of electro-chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications. Learn more about the following types of fuel cells.
1. Polymer Electrolyte Membrane (PEM) Fuel cells
Polymer electrolyte membrane (PEM) fuel cells also called proton exchange membrane fuel cells deliver high power density and offer the advnatage of low weight and volume compared with other fuel cell. PEM fuel cell use a solid polymer as an electrolyte and porous carbon electrodes containing s platinum or platinum alloy catalyst. They need only hydrogen oxygen from the air and water to operate They are typically fueled with pure hydrogen supplied from storage tanks or reforms
PEM fuel cells operate at relatively low temp around 80 c low temperature operation allows them to start quickly and results in less wear on system components resulting in better durability However it require that a noble metal catalyst be used to seperate the hydrogen electrons and protons adding to system cost. The platinum catalyst is also extremely sensitive to carbon monoxide poisoning making it necessary to employ an additional reactor to reduce carbon monoxide in the fuel gas if the hydrogen is derived from a hydrocarbon fuel This reactor also adds cost
Application:
PEM fuel cell are used primarlily for transportation applications and some stationary application PEM fuel cell are particularly suitable for use in vehicle applications Such as cars buses, and heavy-duty trucks.
Solid Oxide fuel cell (SOFCs)
Solid oxide fuel cell SOFC used non-porous ceramic compound as the electrolyte SOFCs are around 60% efficient converting fuel to electricity. In application designed to capture and utilize the system's waste heat (co-generation) Overall fuel use efficiences could top 85%
SOFCs Operate at very high temperature operation removes the need for precious metal catalyst thereby reducing cost . It also allows SOFCs to reform fuels internally which enables the use of variety of fuels and reduces the cost associated with adding a reformer to the system
SOFCs are also the most sulfur-resistant fuel cell type they can tolerrate several orders of magnitude more sulfur than other cell types can in addition they are not posioned by carbon monoxide which can even be used as fuel. This property allows SOFCs to use natural gas biogas, and gases made from coal. High temperature operation has disadvantage. It result in a slow startup and requires significant thermal shieleding to retain heat and protect personal which may be acceptable for utility application but not for transporatation the high opearting temperature also place stringent durability requirements on materials. The development of low cost materials with high durability at cell operating temperature is the key technical challenege facing thie technology
Alkaline Fuel cell:
Alkaline fuel cell were one of the first fuel cell technologies developed and they were the first type widely. used in the U.S space program to produce electrical energy and water ob board spacecraft. These fuel cell use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non precious metals as a catalyst at the anode and cathode. In recent years novel AFCs that use a polymer membrane as the electrolyte have been developed These fuel cell except that they use an alkaline membrane instead of an acid membrane The high performance of AFCs is due to the rate att which electro-chemical reaction take place in the cell They have also demonstrated efficiencies above 60% in space applications
A Key challenge for this fuel cell type is that it is suspectible to poisoning by carbon dioxide in fact event the small amount of CO2 in the air can dramatically affect cell performance and durability due to carbonate formation. Alkaline cells with liquid electrolyte can be run in recirculating mode. which allows for electrolyte regenartion to help reduce the effects of carbonate formation in the electrolyte. but the recirculating mode introduces issued with shunt currents. The liquid electrolyteb system also suffer from additional concerns including wettability. increased corrosion and difficulties handling differntial pressures. Alkaline membrane fuel cell address these concerns and have lower suspectibility to C02 poisioning then liquid eletrolyte., HOwever CO2 still affects performance and performance and durability of the AMFs still lag that of PEMFCs AMFCs are being considered for applications in the W to KW Scale challenge for AMFCs include tolerance to carbon dioxide membrane conductivity and durability higher temperature operation water management power density, and anode electrocatalysis.
APPLICATIONS:
On the word wide automobile market technical development are increasingly determined by the dramatic restriction on emmissions as well as the regimentation of fuel connsumption by legislation Therefore there is an increasing chance of c completly new technology breakthrough if it offers new opportunites. Meeting the requirements of resource preservation and emission restriction Fuel cell technology offers the possibilty to excel in today motive power techniques in terms of ewnvirnonment compatbility consumers profit costs of maintenance and efficieny The key question is economy This will be decided by the cost fo fuel cell system if they are to bu used as power generators for future electric vehicle the alkaline hydrogen air fuel cell system which circulating KOH eletrolyte and low cost catalysed carbon electrodes could be promising alternative.
Direct Methanol Fuel cells:-
Most fuel cells are powered by hydrogen which can be fed to the fuel cells system directly or can be generated within the fuel cell system by reforming hydrogen-rich-fuels such as methanol, ethanol, and hydrocarbon fuel Direct methanol fuel cell (DMFCs) however are powered by pure methanol which is usually mixed with water and feed directly to the fuel cell anode.
Direct methanol fuel cell do not have many of the fuel storage problems typical of some of fuel cell system because methanol has a higher energy density than hydrogen through less than gasoline or diesel fuel. Methanol is also easier to transport and supply to the public using our current infrastructure beacuse it is liquid like. gasoline.
Application:
DMFCs are often used to provide power for portable fuel cell applications such as cell phones and laptop computers.
2. Using a plot with energy density and power density on the X and Y axis, arrange various battery types like lithium ion, lead acid, Nickel Cadmium, Ultracapacitor, fuel cell.
Sln.
Thus from the graph we found that the lithium ion leas acid Nickel Cadmium batteries have low Power density and moderate energy density.
Ultracapacitor or super capacitor have moderate power density and moderate enegry density
the fuel cell have low power density and high energy density
CONCLUSION:
Thus all the objectives are achieved.