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If you look at the molten carbonate fuel cell again you know as the name suggests it is the carbonate ion that is involved here. So, CO3 2 minus is the ion. So, on the anode side actually, two possible reactions are there you can supply hydrogen or you can also supply carbon monoxide. Both of them can react with this ion CO3 2 minus and will either generate water or they will generate CO2. So, interestingly in a molten carbonate fuel cell, you can use carbon monoxide also as a fuel ok. So, if you have polluting carbon monoxide from somewhere and you stream it off into a molten carbonate fuel cell you can clean it up it will just convert it to a CO2 ok. So, first of all, you don’t want to collect CO anywhere. So, it is not the same gas to be working with, but what I am saying is you know if there is a stream which already has some exhaust stream from some other plant which has some CO you can send it of into this and it will convert it to into a CO2 and also generate some electricity in the process. So, that’s how you are getting this CO2 and H2O here you also get some more CO2 here and then in both these reactions electrons are released ok. So, in both these cases oxidation has occurred electrons have been released they are being released into the external circuit. And in the external circuit again they travel all the way around to the cathode side where you have oxygen, you have some carbon dioxide being supplied there on the cathode side and the electrons that have arrived through the external circuit and they generate the CO 3 to minus ion, ok. So, CO2 is continuously being generated on the anode side. So, you have to keep re-circulating it and bring in bringing it back to the cathode side only then you can keep this reaction running because CO3 2 minus is moving across. So, you need to keep that in supply right. So, this is the way it works on molten carbonate fuel cell. Finally, we have the solid oxide fuel cell were also the same you know the same point is true on the anode side you can use both the hydrogen as a fuel as well as CO as a fuel. You can use a variety of different fuels, but these are two that I am highlighting here. Both of them will react with oxygen in this case and generate either water or CO2 and in both these reactions as a result you also have electrons spring released. These electrons again as usual travel through the external circuit complete some reaction on some activity the external circuit and arrive at the cathode side that these electrons react with oxygen gas and generate the O2 minus ion. That’s the O2 minus they travel through the electrolyte ok. So, in all these cases that we have just seen you have some reaction occurring at the anode, some reaction occurring at the cathode and depending on which reaction generates the ion that ion correspondingly goes through the electrolyte and then completes the reaction on the other side, in all cases, electrons go in the external circuit from the anode to cathode. So, that is some things are common about all of these reactions and some things are slightly different because of the nature of the ion being used and which direction it travels. And as a result of the choice of the electron which also depends on which impacts which iron is travelling and in which direction it is travelling the temperature of operation of these fuel cells also changes. (Refer Slide Time: 41:18) I mentioned a little while earlier that you know once you select this fuel cell based on this you know the temperature of operation it also impacts many other things that are present in the fuel cell. One of the most important things that are that is impacted by this choice of the electrolyte and therefore, the temperature of operation is the material that can be used at the anode as a catalyst and the material that can be used at the cathode as a catalyst. So, the lower the temperature of operation you tend to need much more expensive materials which are typically precious metals to be present at the anode as well as the cathode, to catalyze the reaction ok. So, they provide much better sites active sites for the reaction to occur and so they become necessary at lower temperatures to enable the reaction to occur. So, for example, in a PEM fuel cell as far as the in a phosphoric acids fuel cell which is all operating you know just under 100 degrees C or just over 100 degrees C at the lower temperatures the catalyst material that is used at the anode, as well as the cathode in the lower temperature fuel cells, happens to be platinum, both at the anode as well as the cathode. And that is large because the temperature of operation is you know around 100 degrees C or less may be marginally more if you go to higher temperatures. So, alkaline fuel cell or molten carbonate fuel cell you suddenly find that you can get away with vastly cheaper materials. So, things like nickel, okay silver is still an expensive material, but it is vastly cheaper than platinum, you know you can easily go and buy you know a significant amount of silver for the same amount of money that you would pay for a few grams of platinum. So, it’s vastly cheaper than platinum, it is still it is an expensive metal, but you can use nickel as well. So, nickel and silver can be used various kinds of metal oxides can be used which are you know which are all going to be much much cheaper. Again as you go up in temperature you have nickel here, nickel oxide here, again very cheap relatively cheap materials. And then when you go too much higher temperatures these are not necessarily cheap materials, but they give you some other advantages so that is why they are still being considered Strontium doped lanthanum manganate and different kinds of you know metals with ceramics like cobalt with zirconia and nickel with the cornea these are called cermets. So, both ceramic materials as well as metals are being used. The electrolyte as I said this series of materials that I am showing you here one is this is referred to as a perfluorinated sulphonic acid we will see this in some detail later in the class is involved in the other classes. This is phosphoric acid in silicon carbide is the electrolyte that is used for PAFC phosphoric acid fuel cell. For alkaline fuel cells, you have KOH which is held in an in asbestos I mean these were the primary designs that have there that had been explored and investigated for a long period. If you look at the literature you may find you know much more you know some variations on these materials or some newer materials that are being used for electrolytes. But fundamentally these are the kinds of materials that people studied for long periods. And so, a lot of understanding is there of these systems using these materials and that is why I wish to highlight them. You can have for a molten carbonate fuel cell, alkali carbonate in Lil O3 as the typical kind of electrolyte combination that is used. And Yttria stabilized zirconia is another electrolyte that is used commonly for solid oxide fuel cells. Solid oxide fuel cells also use things like cerium oxide, samarium oxide, germanium oxide, doped materials of that nature wide range of oxides are used. So, this is just a sample of what kind of material can be used for an electrolyte in these systems and this is not the only material that can be used. So, that is something that you have to keep in mind. (Refer Slide Time: 45:18) Just a couple of slides as we close this class; The, I would like to emphasize again that the electrolyte is a very critical part of the fuel cell even though it is not the one that generates the power. And primarily it is because it affects the temperature of operation of the fuel cell and that impacts many many things about the fuel cell. So, for example, many of the advantages and disadvantages of each type of fuel cell are directly related to the temperature of operation of the fuel cell. So, if you look at PEM fuel cells proton exchange membrane fuel cells, so these are basically since they are operating at the low temperature they are very easy to start. So, typical automobile application requires you to have the ability to do what is called or what is referred to as a cold start. So, you come out of your house your car sitting in the garage or sitting out in you know maybe in rain, maybe in snow depending on which country you are in or which region of the country you are in and then you go to start it. So, the engine is sitting at you know close to 0-degree centigrade could be or at room temperature, maybe 10 20 degrees centigrade from there the engine has to start. So, if the fuel cell is operating at a relatively low temperature it can handle the start from you know temperature which is room temperature. So, therefore, it's quick to start. But as I said the water is available here in liquid form and therefore, this water actually can you know collect inside the fuel cell and block the reaction from occurring. So, water management is a is what is it is referred to how you handle that water, how do you make sure that the water leaves the fuel cell and leaves the path clear so that fresh reactants can occur come there. So, water management is a very critical aspect of these PEM fuel cells. Also since they are at low temperatures they are susceptible to various types of impurities, various types of impurities will go and just sit there, they will not leave they will block the path of the catalyst on the surface of the catalyst. Typically, for example, carbon monoxide is one of those things that can sit on top of a catalyst particle and block that site from the reaction, and once it blocks the site from the reaction will not occur there. Then slowly you lose the ability to generate current from the fuel cell. So, at lower temperatures, they sit much more effectively and therefore, this poem fuel cell is more susceptible to impurities which means you have to have a fairly pure stream of reactants going into the fuel cell. So, that adds to the expense associated with the fuel cell. We can have alkaline fuel cells, they are very reliable, but they handle carbon dioxide rather poorly and that’s a little bit of a problem because you will have some carbon dioxide in even in ambient air there is going to be some tiny bits of carbon dioxide always present in ambient air. And that carbon dioxide can be it becomes a problem with alkaline fuel cells because it reacts with KOH and forms potassium carbonate. And then the KOH which is present in the electrolyte is no longer there it has reacted with CO2 and formed potassium carbonate and then you don’t have KOH and then no longer you know there is the ionic conductivity, deteriorates very fast and then it stops working even though you have the right temperature of operation. So, therefore, it is a problem. If you go to molten carbonate fuel cell you are going up in temperature. So, it can operate with a wide range of fuels. So, carbon dioxide is not a problem, CO is not a problem, the things that are problems at both alkaline fuel cells and PEM fuel cell are not problems here, water is not a problem. So, all those things which we are problems are no longer problems, but because you have gone to a higher temperature you can end up having you know corrosion which means unwanted reactions can also occur fast, reactions that you want will occur fast reactions that you doN’t want will also occur fast. So, various materials that are present in the fuel cell can degrade faster. So, this is an issue with higher temperature fuel cells such as molten carbonate fuel cell. The last fuel cell that’s up here on your slide is the solid oxide fuel cell. It can again operate with a wide range of fuels it is not the aspect of you know this idea that CO will poison it or CO will be poisoning it in some ways does not exist you can send almost any kind of fuel into it it will just work just fine. It is just that because it operates at 1000 degrees C the main disadvantage is that every component associated with it is not easily available, you have to make special components each component has to be able to handle 1000 degrees centigrade or something very close to that and therefore, these auxiliary parts that are these are all the parts that go with the fuel cell to make it work are all also getting complicated. So, even something as simple as you know you want to seal the fuel cell you put some kind of you know sealant on the fuel cell that sealant will break down and then once it breaks down you have gas leaking all over the place. So, that’s again dangerous and it is also a waste of energy plus it is also not a safe way of operating the fuel cells. So, that becomes a problem. So, you can see here that each type of fuel cell has some advantage and some disadvantage and therefore, you have to when you select a type of fuel cell you have to understand that there is a package of issues associated with that some bright and some not so bright. (Refer Slide Time: 50:14) So, if you look at international efforts on fuels cells largely they are on two types of fuel cells, the proton exchange membrane fuel cell and the solid oxide fuel cell. These are the two types of fuel cells that are significantly researched internationally and interestingly they represent two extremes of the issues faced with fuel cell applications, the fuel cell work and fuel cell applications. And they are typically suited for completely different end uses. So, if you look at the world today in terms of energy usage and where they would like to apply fuel cells, largely they look at the automotive sector or they look at a stationary sector which could be household, buildings, hospitals of different kinds ok, so buildings of different kinds. So, now, if you look at stationary applications the power is typically consumed on a steady basis. So, the issue of start-up and shutdown is not so high ok. So, you have many houses powered using a fuel cell that fuel cell can sit operating comfortably for a long period. So, they're having a solid oxide fuel cell works very well you can set it up I mean or that potential is there it still has issues, but the potential is there because it can all be set at a high temperature and can remain there. You don’t have repeated you know to start up and shutdown cycles that are occurring on the fuel cell. On the other hand for an automotive application, it is the PEM fuel cell that works best because it is at a lower temperature of operation and you can you know do a start-up and shutdown vastly more easily than in a SOFC and it does not have any of the major issues that SOFC faces with this startup and shut down kind of cycling. So, therefore, they are two different types of fuel cells, they are again people researching these fuel cells, trying to use them for all sorts of applications and they are pushing the boundaries by trying to do that and that is a nice thing about doing science or research in these areas. But these are the limits of these capabilities and limits of these types of fuel cells and therefore, you have to be aware of them as you try to use them. So, as I conclude this class I would like to again highlight that in this class we have looked at the range of fuel cells, different types of fuel cells that are present. We have looked at you know what are positive aspects of mode each of these fuel cells what is some negative aspects of these fuel cells or rather what are their capabilities and what are their limitations. In this class, we will look at fuel processing and it will be from the perspective of PEM fuel cells. In that context it is also often referred to as reforming, reforming of the fuel. (Refer Slide Time: 00:27) So, the learning objectives for this class are as follows. We will look at why is fuel processing necessary ok. So, we will look at, so when you complete this class you will have an understanding of that as to why is fuel processing necessary. What are the different approaches to fuel processing? So, that is something that we will look at or at least the different stages involved in fuel processing. And when you get done with it, what are you know important issues associated with the fuel processing activity? So, why is fuel processing necessary? What are the different approaches or different steps involved in the fuel processing process? And what are important issues associated with this fuel processing? So, these are important things that we will look at as we proceed with this class. (Refer Slide Time: 01:14) So, what we have here is the schematic of a fuel cell and schematic of a fuel cell in the sense that if you ever visit a fuel cell lab or if you have a fuel cell lab or you get access to a fuel cell lab. In the lab the testing of the fuel cell where they are developing fuel cells, they are trying to come up with new you know materials for fuel cells trying to improve a fuel cell etcetera, in that lab you will see a set up for testing a fuel cell that once you convert it to some kind of you know the outline of a schematic of that set up you will see roughly what you are seeing on your screen. So, central to it will be the fuel cell which is what you are testing in the test setup, but important ingredients going into it are the two reactants. So, you will have hydrogen, that is being supplied to the fuel cell and oxygen which is being supplied to the fuel cell. So, these are two important ingredients that will be getting supplied to the fuel cell. And in a lab setting, this is typically in the with the help of a bottle or you know a cylinder as you may want to call it. A cylinder of hydrogen or a cylinder of oxygen which you can get commercially from suppliers of gases for research activities etcetera you can get a cylinder of hydrogen or cylinder of oxygen and this is then installed in the lab it sometimes it's installed just outside the lab. So, that you have some manifold through which you can pipe this gas into the lab in an in a controlled manner that also helps you with some safety issues associated with the gas etcetera. But fundamentally you will have a piping process, through some pipes. You will have these two gases arriving at the fuel cell and that’s how the lab setup is. And in the lab then you know to operate the fuel cell you use these two gases as inputs to the fuel cell you generate electricity from the fuel cell, and that electricity is out is the output from the fuel cell. So, that’s in the form of DC power. So, this is what you are getting out of the fuel cell and usually. So, then there is you know since you are trying to do this in a controlled setting there is a load bank there is somewhere there’s an instrument that is referred to as the load bank. So, this is an electronic you know instrument that is put in place to which your fuel cell is connected or the output the current output coming from your fuel cell is then connected to this load bank. And using the load bank you can draw current from the fuel cell in a controlled manner. So, you can know test it under low current conditions, under high current conditions the more useful parameter there is current density, so you can test it under low current density conditions and high current density conditions and a wide range of different things you can make it cycle through different you know operating conditions. All, of those things, are done by controlling the input these two parameters that you see here, the two inputs that are going into the fuel cell and the DC power that you are drawing from it. So, you can have you know excess gas going in you can be drawing low power you can have just the right amount of gas for the right amount of power that you are trying to draw or you send in a little less of one gas and try to draw more power. You would be limited by the gas that is coming in, so you cannot draw more power then what the gas can support, but you can make it you know deficient in one gas versus deficient in the other gas and lot of such tests you can do to understand what is the fuel cell doing, how is the anode of the fuel cell behaving, how is the cathode of the fuel cell behaving, how is the electrolyte of the fuel cell behaving. So, these gases, in fact, depending on the type of fuel cell you are testing. So, for example, if you are testing a proton exchange membrane fuel cell or a PEM fuel cell then these two gases that I am referring to here that the hydrogen and oxygen would also go through a humidifier which will then humidify the gas and so in a humidified manner they will enter the fuel cell and you can also use that level of humidity as a parameter that you can control. So, you can run the cell in you know the fully humidified condition in which means that the hydrogen is running at 100 per cent relative humidity and the oxygen is also running at 100 per cent relative humidity or rather it’s entering the cell at 100 per cent RH for that operating point. So, the cell may be tested at 60 degrees C or 70 degrees C and so on. And so at that temperature whatever is the relative humidity it will reach 100 per cent relative humidity and with that, you send it into the cell and, so you can test it a 100 per cent RH, you can test it at 80 per cent RH, you can test it at 50 per cent RH. Meaning you are testing the cell in either a fully wet condition or an I mean relatively drier condition. So, the extent of dryness in the cell use is something that you can control. So, these are all the things you can control. You can control the gas flow rates individually, you can control the humidity individually. So, one gas could be running dry, one gas could be running wet you can control you know the temperature at which the cell is sitting and you can control the power that is being drawn from the cell. So, a lot of parameters you can control and use this you test the cell. So, this is how you test in a laboratory condition. (Refer Slide Time: 06:22) However, if you so that is something that is in a lab condition that kind of you know test setup where you have many things under control and your testing it and it is really necessary only then you truly understand what is possible with the fuel cell, you understand what are the limits of the fuel cell that you can operate within and how you can consider pushing you to know boundary concerning the fuel cell. So, these are all things that you can do if you do it in a lab setting. Now, from there if you move to a real-life system so, then it says let’s say it is sitting in an automobile or you are deploying it in you know the residential sector. So, now, that is not a test setup it’s not a test setup in a lab. It is the actual utilization of this fuel cell in a real-life condition. So, there you have a complete system that is sitting there and that gets referred to as a fuel cell system and what you see on your screen is a schematic of a typical fuel cell system. So, if you compare against what we previously had there are some variations between what you would do in the lab versus what you will do in an in the real-life situation. Of course, in the lab also you can create the same situation you can now, is because the lab is complete in under your control you can simulate this real-life situation in your lab and fact, normally when they develop fuel cells that’s exactly what they do. First, they will test it under this kind of controlled conditions where you have hydrogen, and oxygen and the fuel cell and the power bank or the load bank which is drawing your DC power. And then once you understand what it is doing under these control conditions you will mimic real-life conditions and then you will create some slightly different setup which is what this schematic shows you in which you can test the real-life conditions. Once you are satisfied that your fuel cell system is working well under real-life conditions you would deploy it on the field. So, this is sort of you know the gradual progression of how you study a fuel cell, understand it and then send it out to the field. This is exactly what is going on in you know even in the battery industry, for example, some similar analogy analogous conditions you can think of, but this is what goes on in any fuel cell company for example. You will have an R&D part I mean there will be some scientists who work on the individual cell, trying to understand how well to improve it. And then there will be people who will also be looking at what is required to move this into the field and so they will look they will do the testing under the simulated you know field conditions and then finally, you take it out to the field. So, that is what you do. So, now, when you look at this schematic of what you did in the lab which is a typical fuel cell operation versus what you do in the field which is the typical fuel cell system that is out there, there are specific differences that are of interest. So, let’s just see what those differences are. So, the first thing is the reactant, reactant stream. So, what we had previously in the lab were pure hydrogen and pure oxygen and as I said these are coming off of two bottles. So, you have two cylinders, one cylinder is hydrogen one cylinder is oxygen then you have a flow meter later the in the pathway which controls the flow and then you send the gases. Now, in real-life conditions you don’t only use hydrogen you have the choice of using hydrogen or you can use some other fuel and in this case, you have the option of sending that other fuel may be, for example, methanol directly into the fuel cell. So, you can take hydrogen to send it directly into the fuel cell or you can take some other fuel such as methanol and send that also directly into the fuel cell. So, that depends really on the capability of the fuel cell whether it can handle methanol. So, some fuel cells may handle it some may not, but basically, that is the idea you can either send hydrogen in or you may consider sending methanol in or you will take some other fuel and send it through another unit called a reformer and in fact, in today’s class that is exactly what we are going to talk about what is this reformer and what does it do and what are some issues associated with it. So, you can take some other fuel which could be methanol, it could be methane, it could be some other gas and you can send it into this reformer. The output from the reformer will be a stream which will consist of a bunch of a mixture of gases that gas that mixture may be further processed in to clean up certain you know some ingredients of that mixture and then that output is then sent into the fuel cell. So, that kind of output. So, some processing is done to some other gas the output of that processing is then sent to the fuel cell ok. So, that is the activity that is happening on the fuel side of the fuel cell. On the oxygen side, the oxidant side of the fuel cell as I said you could you have that you still have the choice of sending in pure oxygen, but more generally to you know look at you know the convenience of operation and many other operational details which we will see. From the point of view of convenience of operation, it makes sense to just send air ambient air into the fuel cell. So, even in your automobiles, for example, existing automobiles which are not running of fuel cells you need to send air into the engine for the engine to work and that air is being taken from the ambient air. So, normally in your typical automobile car or any other, you know the automobile you can get a chance to look at they will have something called an air filter. So, in other words, they pull air in from the ambient conditions, and that air goes through the air filters primarily removing dust and other such you know things that they would like to prevent going into the engine and then the cleaned up air is then sent into the engine and then the engine runs. So, the same idea can be used even in a fuel cell, if you can just take ambient air that of course, contains oxygen. So, we have you know 21 per cent oxygen there you just take that air you send it through some filter and then you send it into the fuel cell. So, that is the other possibility that you have here and that is how you would do this. So, you then turn air and this reformed fuel or some other fuel and that goes into the fuel cell stack. So, that, so these are the ingredients that have now, go into your fuel cell stack. Now, once they are in the fuel cell stack again you have you know power generation that is going on and now, the characteristics may be slightly different from what you tested in the lab in the original condition where you had pure hydrogen versus pure oxygen, but in any case, you would have tested it also under simulated conditions. So, hopefully, you have a good understanding of how your fuel cell is going to behave. And then the output from that fuel cell is the same DC power. So, that you get DC power which is you know. So, some current and some voltage which you will get from the fuel cell and it turns out that most of our households are all set up for AC power, right. So, somehow the infrastructure that we have all gotten used to over the years has been AC power primarily because you can you know go to high voltages and then transmit it over long distances and that way you can control losses and that’s why we use AC power in many of the situations. And then when it comes home you just come closer to the hole you just drop the voltage to something acceptable internationally its typically somewhere between 110 volts and 220 volts and then that is sent into your household appliances. So, often DC power is not directly being used in the household. So, or in many other places, so the output from the fuel cell is often not directly usable. You can make it directly usable if you accordingly design your appliances that run off of a fuel cell.