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The first is the type of fuel cell. So, some types of fuel cells will operate with certain fuels only they will not operate with certain other fuel cells other will operate with certain types of fuel only and will not operate with certain other types of fuel. So, you have to also look at what is available. So, you may have a particular version of fuel available to you and that may not be the type of fuel that the fuel cell will accept. So, this does not mean that you cannot use the fuel cell under those conditions. So, you have to find a way to make that fuel acceptable to the fuel cell. So, you do this conversion of that fuel you take the fuel you process it in some way, you convert it to a form that is acceptable to the fuel cell and then you send that into the fuel cell ok. And you have all these other fuels available you have hydrogen available, but hydrogen typically we have we are trying to make it from some source could be you know electrolysis of water, you could be catalytically splitting, photocatalytic catalytically splitting water etcetera and there are other fuels which you can get off of you know the existing carbon-based fuels that hydrocarbon-based fuels that we are already having available. So, you have to keep in mind the availability of the fuel both of these are there some may be more readily available. So, the other types of fuels are typically more readily available and therefore, it from a commercial perspective from an ease of use perspective using readily available fuel is of interest. Of course, then you may ask then what is the purpose of using the fuel cell it is just that it takes this other fuel and uses it with much more efficiency, so you can use less fuel and get more work done and therefore, a fuel cell is still meaningful to have even though you are using some other fuel. And there is always this question of infrastructure. So, you have existing infrastructure all over the world. That existing infrastructure already deals with the supply of specific types of fuel. So, you have gasoline or petrol, you have diesel, you have compressed natural gas all of these are available in you know in a wide extend extended version of infrastructure that is there in many countries. So, this is readily available. So, now, suppose you want to deploy new technology in the automotive sector it helps if you are using the infrastructure that is already there. If you are going to ask for you know complete overhaul of the infrastructure naturally there is going to be a lot of resistance it’s going to take a lot of time to enable that to happen. So, it makes sense to try and use the infrastructure that is already there and that infrastructure usually helps works very well with a lot of fuels that are already being used. So, that is, therefore, it makes sense to look at fuel that is already available and then do some fuel processing with it. So, that the fuel cell can use it and therefore, you get the benefits of the fuel cell without doing a large scale overhaul of the infrastructure which is being set up for some other fuel. So, therefore, we do fuel processing. So, that’s the whole idea of fuel processing. (Refer Slide Time: 18:55) So, what is fuel processing? So, if you take the basic idea concerning at least the fuel cell you want the inlet of the fuel cell to receive a stream of fuel that is rich in hydrogen ok. So, as opposed to the lab setting where you are testing just pure hydrogen you now want a situation where the inlet is some processed fuel and that output of that processing step is a fuel stream that has a lot of hydrogen in it and therefore, the fuel cell can work with that hydrogen ok. So, the hydrogen may not have been inherently present as a separate entity in the original fuel you process it to separate the hydrogen out and then with that hydrogen you send it into the fuel cell. So, that’s the basic idea. So, certain ways of procedures are used for fuel reforming from the perspective of fuel cells. So, the first one is referred to as steam reforming ok. So, you take some fuel here. So, for example, you have in general it would be some you know carbon, hydrogen and oxygen containing entity which would be your fuel. So, generically I have simply put Cn Hm and Op as the generic formula that the fuel would represent, you may have a mix of fuel level it may not even necessarily be one single molecule so to speak, and you mix some steam with it. The output you will get when you do this is a system of gases which will contain different types of carbon-based oxides. So, you could have carbon dioxide, you could have carbon monoxide etcetera and then you will have hydrogen. So, you are not going to get pure hydrogen. So, that’s something that you would keep in mind. The reforming processes that we are talking about generally are not going to give you pure hydrogen stream ok, so at least not immediately. What comes off the reformer will not be pre hydrogen. It will typically have hydrogen and some other byproducts of the reforming process typically those byproducts are carbon-based oxides which are what you will have. And this whole this reaction is endothermic. So, delta H is greater than 0 which means you have to provide heat. So, the whatever is that processor you have to keep supplying heat. So, it is strongly endothermic. You have to provide a fair bit of heat for this process to occur and naturally when you have a reformer which is strongly a very when you have a reaction that is strongly endothermic and you have some kind of a reactor in which this endothermic reaction is happening the heat which you are supplying externally has to find a way to reach all the locations where the reaction is happening. So, the reactor design is limited by the heat transfer process ok. So, the reactor design is limited by the heat transfer process primarily because the heat has to reach the various locations where the reaction is likely to occur. And therefore, if you simply look at steam reforming the reactors tend to be large and heavy you have to have lot of you know heat exchange processes involved to for the heat to go in and come out and all these reactions to be distributed throughout this region and so on, and that is how this steam reforming based reactor is set up. And, but that does take an existing fuel and converts it to a stream that is hydrogen-rich and therefore, creates a stream that is acceptable to a fuel cell ok. So, at least in a general sense may be some further processing is required, but you are getting closer to a fuel that is acceptable to the fuel cell ok. And usually, this will require some catalyst to enable you to know these you simply cannot just mix the fuel and a and the steam and expect things to happen the way you are hoping for. Usually, a catalyst is required to ensure that the reaction occurs at some appreciable rate and in the manner that you wanted to proceed and typically that catalyst is nickel. So, I mean nickel is not expensive it’s quiet you know cheap inexpensive metal to work with relatively speaking and therefore, this is you know a very acceptable process it is not you know prohibitive in some fundamental sense. The only issue here is that you are supplying heat. So, naturally, you are now, wasting some energy, you are using creating energy somewhere you are using that energy to do this splitting process and then you know taking this hydrogen-rich stream to use it for some other process. Generally in all, you know energy circumstances say energy-related technologies we are always interested in knowing how effectively we have done the process and how efficiently we have done the process. So, you have to look at the process as a whole. You cannot simply look at the efficiency of the fuel cell alone. If you are going to spend a lot of energy creating the fuel stream that goes into the fuel cell that energy should also be included in your calculation as wasted energy because that energy is not driving whatever is your end goal. Now, if it is supposed to power the house that energy is not powering the house that energy is being used by the fuel cell to create electricity and that electricity is used to power your house. So, this energy should also go in as energy that has been consumed in the process of running your house ok. So, these are things that we have to look at. (Refer Slide Time: 23:58) There is another way in which you can do this reforming and that is referred to as partial oxidation ok, partial oxidation of the fuel ok. So, you are sort of doing a little bit of burning of the fuel, but partial oxidation is what it is referred to. So, in some controlled circumstances, you mix the fuel and air. So, again fuel is this generic formula that we have here and in that, in some controlled circumstances in a reactor, you mix it with a little bit of air. So, when you do this again you get the same kind of output you have carbon-based oxides you have hydrogen as output and of course, you have nitrogen because you started with air and air is you know 79 per cent nitrogen. So, you are going to have nitrogen in your stream right. So, this is the general output that you are going to have. But the difference between say steam reforming and this is the fact that now, you are actually doing some amount of combustion and therefore, you have a strongly exothermic reaction. So, delta H is negative it is just releasing energy into the process and therefore, the temperature can climb up very high. So, you can have a temperature climbing past 1000 degrees C very rapidly ok. So, that is the issue here with partial oxidation and in fact, it happens so easily that you may not even require a catalyst to enable it to happen. So, you carry you can even do it without a catalyst and you can have this situation happening. So, one point you have to remember in both let’s say the steam reforming as well as you know partial oxidation is the fact that you no longer have a pure hydrogen exit stream. So, here you had carbon oxides with hydrogen and in partial oxidation, you have carbon oxides you have hydrogen and you have nitrogen ok. So, if you want to look at it from a technical perspective what this means is that the partial pressure of hydrogen is not 1 ok. So, even if this whole thing is 1 atmosphere you know gas that you have generated gas at 1 atmosphere the part of the pressure of hydrogen is not 1 ok. So, it’s going to be much a gas with much lower partial pressure of hydrogen. If you were testing this in a lab and you were trying to run it under ambient conditions and you sent in pure hydrogen the partial pressure of hydrogen would be 1 atmosphere then whereas, in these two cases if you send this same stream to let’s say you simulate this stream in the lab and you send this into the cell with an ambient exit pressure. So, then the partial pressure of hydrogen will not be 1, if it is only 20 per cent hydrogen the partial pressure of hydrogen is only 0.2 atmospheres, right. So, this changes the thermodynamics of the cell and therefore, changes the voltage associated with the cell the open-circuit voltage associated with the cell or at least the wave manner in which the voltage of the cell will change as you draw current from it. So, all these parameters associated with the cell will start changing because your partial pressure of the gas is not 1 and all these parameters are dependent on that. But at the same time as I said in real life, this is what you have, so this is what you have to work with ok. So, now, that you have seen partial oxidation and steam reforming and you realize that in one case it is strongly endothermic and in the other case it is strongly exothermic there is an interesting way you can do this where you mix both of these processes. So, that you are setting up a situation where the heat released by 1 process assists the other process. (Refer Slide Time: 27:05) So, suddenly you don’t need as much of heat exchangers etcetera relatively speaking because you now, take the fuel you mix both breaths of air as well as stream steam to the fuel both of them are being added to the fuel, and you take this complete mix and allow it to undergo this process of reforming. Again now, the output will contain carbon oxides it will have hydrogen, it will also have nitrogen because after all, you are sending in air. So, this is what you do. But the advantage is that you don’t have to separately do any heating process and you you know take the heat from one reaction and supply it to the other reaction and both reactions are doing reforming. So, in both cases, you are always assisting the reforming process. So, you are not generally burning some other fuel to create the reforming process, it is happening simultaneously both reactions are doing the reforming process of the fuel processing activity and therefore, the end goal is being served by both reactions. And the nice thing is since one is consuming the heat the temperature doesn’t climb up in an uncontrolled manner. So, you can set it up. So, it is slightly exothermic. So, that you have some control over the temperature and you can manipulate that temperature. So, this is how you can set it up so that you know you can manage the temperature and hold the temperature and then continue the reaction. And then based on the amount of steam reforming you are doing you can limit the maximum temperature to which you know the reactor begins to climb. So, this is called auto thermal refining, rifts or reforming auto thermal reforming. And as the name suggests it means, you don’t have to supply heat externally, you don’t have to remove heat using some other process it is all happening internally. So, that, therefore, that and hence the autothermal reforming your name. So, this is an interesting way in which you deal with the reforming processes. So, this is these are 3 different ways that I have told you 3 different approaches to do the reforming steam reforming and partial oxidation and this auto thermal reforming. So, 3 different ways in which you can do the reforming. (Refer Slide Time: 29:07) So, what is the output of this reforming process? So, as I said you have typically carbon-based oxide. So, let’s just say CO and CO2 and you have hydrogen and you have nitrogen. Largely this is what you are looking at as the output from the reformer. Now, the question is it good enough ok? So, that is a question that is for which the answer depends on what fuel cell is this output going to ok. So, so that is very dependent on that, based on that this itself may be good enough ok. But in many cases let’s say a typical PEM fuel cell if you send this into a PEM fuel cell which is the one that as I said you know you have solid oxide fuel cells or PEM fuel cells being actively looked at for you know deployment of this fuel cell technology. In a PEM fuel cell which is what would be typically looked at for the automotive sector. This is not this kind of a mix of gases needs to be looked at carefully to understand whether it is acceptable or not. Most specifically since it operates less than 100 degree C the CO is an issue, carbon monoxide is an issue. The issue to what degree? Even even if you have you know say 1 per cent carbon monoxide it will completely kill the operation of the cell, kill meaning it will completely stop the operation of the cell within minutes of the cell starting. Basically what it does is the carbon monoxide goes and sits on the catalyst sites platinum is the catalyst, that is being used in the PEM fuel cell let’s say typically platinum or some other catalyst also may be there. Typically when platinum is used the carbon monoxide goes and sits on top of the platinum and does not leave the site of the platinum. So, every location of platinum that it sits on it blocks the hydrogen from reaching the platinum site and then as even if you have 1 per cent CO in the fuel stream in a matter of minutes it will completely block all the platinum sites that are available in the within the fuel cell and then the hydrogen will be sort of you know uselessly travelling through the fuel cell it will not undergo any reaction. It will also come to the surface of the fuel cell, it will find all sides are blocked and simply go out the exit. So, it will come in and go out without getting utilized. If it doesn’t get utilized you do not get any current. So, that is the problem. So, CO is an issue. So, as opposed to something like a per cent or so that will come out as on the exit side of the reformer the fuel cell itself can tolerate the only ppm of several let’s say less than say 50 ppm be parts per million. So, you should have a fuel stream that has less than 50 parts per million of CO for the fuel cell to tolerate it whereas, what is coming off the reformer is typically 1, like 1 or 2 per cent of CO. So, you may have something like that maybe half a per cent, 1 per cent something like some reasonably large quantity which is distinctly larger than this 50 ppm that I am mentioning ok. So, therefore, you need to do something to this exit stream. You have to further process this exit stream before it can go into the fuel cell, you cannot just directly put this into the fuel cell. These other gases CO2 and nitrogen end up diluting the gas I spoke about partial pressure and that is exactly what happens here. So, if you end up with a stream that says 40 per cent hydrogen per cent20 per cent CO2 and another 40 per cent nitrogen something like that, then 60 per cent of the gas that is present there which is nitrogen and carbon dioxide are useless concerning the fuel cell. So, 60 per cent of the gas that goes into the fuel cell does nothing it just goes in and it comes out ok, and it dilutes the 40 per cent hydrogen that is going in and. So, in terms of you know statistically the hydrogen reaching the catalyst site these other gases are getting in the way. So, that’s the issue here. So, they just get in the way and you know eventually you still have to use the hydrogen you find a way to use the hydrogen, but basically, these are acting as diluting the gas stream and then that naturally affects you know voltage-current characteristics of the fuel cell. But generally speaking nitrogen and carbon dioxide are not you know poisonous from the perspective of a proton exchange membrane fuel cell. I told you that CO2 is not good for an alkaline fuel cell, but in this case, it is for a proton exchange membrane fuel cell it is not an issue, CO2 is not an issue, nitrogen is not an issue it generally goes through without any impact on the fuel cell. So, these to act as diluting agents, but they don’t make any other impact CO is the one that you have to deal with much more carefully because it would poison the fuel cell and stop the fuel cell from the operation. So, more generally it is not good enough. The output of the reforming process is not good enough to be directly used in the fuel cell. So, you have to do something more to the output to make it usable in the fuel cell. (Refer Slide Time: 33:45)



















So, what we do is we enable you to know two, other two more processes are often made available in a fuel cell reforming you know set up which then helps you to do the cleaning of the gas stream cleaning from the perspective of reducing the CO content. So, one is called a water gas shift reaction which is what we have put here a water gas shift reaction which takes CO and allows it to react with water moisture in this case and then that converts that to CO2 plus hydrogen. And interestingly this means that when you do the water gas shift reaction you are getting a little bit more hydrogen into your stream. So, this is a very welcomed reaction to have in your system. So, if you encourage this to happen and this is also slightly exothermic you get some you know exothermic reaction that’s going on here. So, it is something that you know without having to put in some energy you can get this process running. And it does require some catalyst. So, typically you know Fe3O4, copper oxide, zinc oxide etcetera is a catalyst that is used for this process and you take steam you take the water you get them to react you get hydrogen and carbon dioxide. So, now, what has happened is you have slightly increased the amount of hydrogen that is present and you have taken CO and converted that to CO2. So, CO, as I said, is poisonous for the fuel cell, but CO2 is a dilutant that is it doesn’t affect the fuel cell in any way. So, this poisoning process has now been stopped. So, using this reaction you can drop from you know percentage down to you know several ppm kinds of range. So, this is one way in which you can enable this drop in the amount of carbon monoxide that is present in the fuel cell. (Refer Slide Time: 35:29) The other way in which you could do it is called selective oxidation or preferential oxidation and they are also you take CO and then you mix it with oxygen and then you get CO2. So, you are sort of oxidizing the CO to get CO2 and that again convert CO to CO2 and therefore, what was previously poisonous to the fuel cell is no longer poisonous to the fuel cell. But you have to be careful. So, when you introduce oxygen into the stream it is not going to work selectively only on the carbon monoxide, it may react with the hydrogen too, right. It is a statistical process you are providing some carbon monoxide you are providing some hydrogen and in fact, you are providing a lot of hydrogen you 40 per cent of the stream is already hydrogen and you have you know let’s say 1 per cent CO sitting somewhere. So, now, when you introduce oxygen it has you know 40 times more a chance that it will find hydrogen then it will find the CO. So, you are going to waste some fuel also in this process. It’s not going to be that you know you will only remove the CO you will go it wastes some fuel some hydrogen is going to get wasted in this process and so you have to look at this a little bit carefully, but it is done it is necessary for some ways because you have to get this CO off the system and so we do have this selective oxidation or partial oxidation, preferential oxidation so to speak being done to take care of this activity. And you do need some catalysts to enable this and so usually ruthenium or rhodium are used and they are supported on alumina this supporting process is something which ensures that the catalyst is nicely dispersed and it does not you know collect at one location but gives you a much wider area. You can also use copper and zinc oxide, also on alumina and so you have some options there on what can be done and so when you do all this you get this process. So, you know, get a stream from the reformer, that has then been analyzed and then we understood that there is you know it is a step in the right direction, but not a completely solved issue you still have some cleaning that you have to do and so we are now, done some cleaning. And hopefully, at this point, we have a stream that is distinctly cleaner and also acceptable to the proton exchange membrane fuel cell. (Refer Slide Time: 37:31) So, having come this far it is interesting to take a moment to look at some issues associated with the reforming process. The first is system complexity. See ultimately if you want any technology to you know become prevalent in large scale, across you know a wide range of uses across various locations in the world system complexity is a very important parameter to look at. The more complex the system is there is more there is a greater likelihood that some part of the system will fail and when some part of the system fails you need a service engineer to visit the site and set it right. So, generally speaking, it the expenses associated with the system, the inconvenience is associated with the system, all of those go up when you have highly complicated systems which are represented. I mean it turns out that you know with the advances of science and engineering we can get by with a lot of complicated systems we use you know sophisticated aeroplanes, we use highly sophisticated automobiles they are quite complicated systems. So, there is nothing that says that you cannot have a complicated system, but if you step back and look at the options available if you have a simpler system versus a complicated system that does a particular activity any industrial process will tend to prefer the simpler system. So, that is one thing that we have to keep in mind. And so when you put in a reformer when you say that you know directly I cannot send this fuel into the fuel cell I need to put in a reformer. Once you take that kind of a decision the just that decision has distinctly increased the complexity of your fuel cell system. So, reforming does improve the sorry does increase the complexity associated with the fuel cell system. As I told you there is carbon monoxide. So, you you have to do cleaning you and which is what we discussed we have a process by which we have to clean the fuel cells stream and create a much cleaner stream which can then go into the fuel cell, and so we have to do something, and we are doing something to deal with the carbon monoxide that is coming off the stream with the through the reformer. And even then we are not completely done with the carbon monoxide we just drop it to several ppm because beyond that it becomes difficult the more you try to push it down towards 0, more energy, and time and complexity you will start putting into the system just to keep moving it lower and lower and lower and you know the content. So, you stop somewhere and you make some you know accommodation for it and you handle it and go. People do look at catalysts that are more tolerant to CO which don’t you know which don’t hold on to the CO that strongly and so there is a lot of research that goes on, on that as well. So, to look at catalysts that do not care as much about CO and therefore, you can send in the stream directly. There is another very critical performance parameter that you have to look at when you are looking at this as a system that is being deployed in say automobile or in a house. So, when you come to your house let’s say in your house you come in, I mean let’s say the house has been sitting idle you have gone out to work you come home maybe let us say at 6 pm you have come into your home. You come home and you start switching on lights, you switch on a lot of lights, you switch on let’s say the air conditioner, you switch on the television, and then let’s say you want to get something to eat, you may be put on a microwave oven or something. Let’s assume that all the activities you are doing in start switching on various electrical devices. So, suddenly the power demand that you are placing on the source of power is going up ok. So, whereas, previously it was just using say a few 100 watts to some base power you know powering your refrigerator quietly or something it was running suddenly you come and turn on a whole bunch of things you maybe you turn on even your washing machine etcetera, and suddenly you climbed up from few 100 watts to let’s say 2 kilowatts of power you say just to give you an example ok. So, you have gone up you know an order of magnitude in power usage suddenly. And this change has happened in the matter of let’s say a couple of minutes you walk in and you just start flipping up this is flipping on the switches at different places you switch on the TV, you just quickly walk into the kitchen you turn something on, you turn on your washing machine in a couple of minutes suddenly you have changed to the complete power demand on the power source in your house. Now, if a fuel cell system is the only thing that is powering your house the fuel cell system should suddenly ramp up in power, for it to ramp up in power everything going into the fuel cell should get ramped up. So, if suddenly you have increased the power demand on the fuel cell by a factor of I mean one order of magnitude by a factor of 10, 10 times more fuel has to go into the fuel cell, 10 times more air or oxygen has to go into the fuel cell. For the air or oxygen to go into the fuel cell by for that to go up by a factor of 10 is quite easy because you usually just have a blower, the blower is you know a different form of a fan you can think of it as a different form of fan and that just blows more air into you you know you just change the power setting on it suddenly it just blows 10 times more air into fuel cell system. So, that is very quick. But the reformer on the other hand may take several minutes ok. So, it may take several minutes for it to suddenly go from whatever was the previous setting to a value that is you know 10 times as high ok, as an output ok. You can send sender suddenly you can increase the input, but it still takes some time to do all the processing and then send you an output that is you know now, 10 times higher. So, the response time of your power supply power source is much less it's much I am sorry much longer and therefore, its much slower the response time then what you can do by just coming in and turning on switches. So, if this were the only thing that is powering your house you will have a problem, you cannot just turn things on, if you turn things on your circuit breaker will go it will just say no not possible and then only some 10 minutes later it will allow you to do that, right. So, that is why in many fuel cell systems they have some other way in which they can augment the power supply for those critical few minutes during which there is a transition in power ok. So, the response time of the fuel cell system is an important parameter that you have to look at, either you have to use grid power or something more that you have stored in a battery which you throw-in into the system for several minutes till everything stabilizes and then you run. So, it