Hello, in today’s class we are going to look at fuel cells from concept to product. So, I think that’s an interesting journey for us to see as part of this course because we talk of so many technologies some work happens in the lab may be depending on where you are, you are working with one aspect of some technology, but there is a long journey from that you know work that happens in your lab to a product that you see that is being deployed. So, there are many more steps then maybe are covered in this class, but it does give you I expect that it will give you an idea of what is involved when you know see when you read something in a textbook when you try out an initial experiment in your lab. And then from there what are the kinds of steps and thought processes that are involved as you try and make a product out of it. So, this is our journey today which is fuel cells concept to product. (Refer Slide Time: 01:10) So, this is a schematic of a fuel cell. So, you can see here we have electrode with the access to hydrogen and so, that’s something that is one of the; I mean basic requirements for a fuel cell and there is an electrode with access to oxygen. So, all you are doing is you are taking hydrogen and you are reacting it with oxygen. So, that’s all the fuel cell does at least in one one of the versions of it the most common version that people tend to discuss. So, there’s hydrogen or some fuel and then it reacts with oxygen and generates energy and it also gets the fuel also gets oxidized. So, that’s the general process that is involved. So, the only, so in principle, you can just burn hydrogen in air and use that heat to run some engine. So, so in fact, people do work with you know engines which are you know internal combustion engines where hydrogen is the fuel. So, instead of filling your petrol tank or gasoline tank with the gasoline or petrol or diesel, you would have a tank that is filled with hydrogen and this hydrogen is piped to the engine and in the engine, it mixes with air and you know combusts generates water as the product and in the process of combustion, it runs the engine. In quite the same way similar to what you see your existing internal combustion engine in your automobile. It would still be a clean way of doing things because your product is water it’s not carbon dioxide or carbon monoxide for that matter and therefore, is a clean way of you know generating energy in a manner that is portable and it is also good for the environment. However, we still look at the technologies such as fuel cells because that combustion that I just discussed with you which happens inside an internal combustion engine is direct combustion or oxidation in the form of a combustion process. Whereas when you use a fuel cell you are doing the oxidation through an electrochemical process as opposed to a chemical process. So, in the engine, you are doing what is referred to as chemical oxidation which means physically hydrogen mixes with oxygen combust and generates water and energy. In a fuel cell, we are doing the same combustion process same reaction between hydrogen and oxygen except that we do not do it in a manner that is described as chemical instead we do it in a manner that is described as electrochemical. So, that may seem like not much of a difference, but it is a distinct difference both in terms of how the setup of the fuel setup of this process changes and also most importantly it changes the efficiency of the process. So, here for example, as I said there is an electrode with access to hydrogen and an electrode with access to oxygen. So, importantly hydrogen and oxygen do not directly mix in a fuel cell as opposed to becoming a direct mixture of these two inside an engine in an internal combustion engine. Instead, we are now, splitting this reaction into two parts there is a part that where hydrogen reacts independently with an electrode and then you have protons moving through this electrolyte H plus that moves through this electrolyte. And arrives at the other electrode which is the oxygen electrode and in that process, it reacts, now reacts with oxygen with some electrons appearing in the external circuit and that is how you operate the system. So, this transfer of charge between an electrode phase and an electrolyte phase that is between this electrode phase and this electrolyte phase this chance for transfer of charge similarly transfer of charge between this electrolyte location here, and the electrode location here. This transfer of charge is what is ending up in resulting in this reaction being referred to as an electrochemical reaction. And the big difference between this and the other combustion process that we previously discussed is that the normal combustion process of an IC engine is limited by the efficiency of a Carnot cycle which means that you know you are roughly levelling off at about twenty per cent efficiency of energy that you can get out of the reaction which you can usefully use somewhere else. Whereas here when you do it electrochemically just the electrical efficiency itself would put you at 40 per cent plus or maybe even more than that, and then when you take the heat and other things included into the process you are looking at efficiencies which may even hit close to 80 per cent. So, you have much higher efficiencies possible with the same amount of fuel. So, you could go twice the distance for even 3 times the distance etcetera with the same amount of you simply because it’s a more efficient process. So, this is the schematic of a fuel cell, this is the kind of diagram that you would see in a textbook and a significant amount of explanation on what is happening in the fuel cell. So, we will start from here and we will take this as a starting point and see how we can move till we get a product at the end of it. (Refer Slide Time: 06:00) So, as I mentioned at the anode there, there is a reaction you have two hydrogen molecules they give you 4 protons H plus is a proton because once you remove the electron you only have a proton and electron in an in a hydrogen atom. So, once you remove the electron you are left with only a proton. So, the 4 H plus are just basically 4 protons and 4 electrons. These 4 electrons are travelling through the external circuit, whereas this H plus is travelling through the electrolyte. So, once this journey completes the H plus that arrives through the electrolyte and the 4e minus which arrives through the external circuit react with oxygen and you generate water. So, this is the reaction that happens in a fuel cell and in that process energy is released for us for useful activity. (Refer Slide Time: 07:01) So, let’s look briefly at the timeline of this kind of technology and how it has evolved. So, if you look at the timeline it traces itself back to the 1800s where initial experiments were made which result in resulted in what we are now, referring to as the battery the original batteries that appeared. So, the credit for this goes to Alexandro Volta. So, he is the one who created this battery that you know at his the first version of the battery that we currently use. It’s a very interesting history in the sense that then there was a lot of discussion going on between Galvani the other famous personality in this topic and Volta. And it was centred around this experiment that Galvani had a chanced upon where he found that the limbs, limbs of dead animals such as frogs could get to twitch when they were touched by the different metals there was no clear understanding as to why it was twitching due to you know the presence of these other metals. But the conclusion that Galvani drew was that there was some life force inside this the leg which was in the form of electricity and that was what was getting the legs to twitch. Volta had another view he said that the electricity was not coming from inside, but it was coming from outside and it had to do with the kinds of metals that were used to contact that dead frog's leg. So, he created this Volta pi where he had two dissimilar metals one on top and one in the bottom, and he had material in the middle which was something like a cloth which was soaked in brine solution salt kind of solution. And in this process he had several of them stacked up and the stack has. Now, become famously referred to as the Volta pile this is the first you know demonstration of a battery in action. And he was very successful in doing it and therefore, he is credited with this invention. The interesting you know aside of this whole story and activity is that this discussion between Volta and Galvani about what was this life force and you know this idea that a dead animals leg could get to twitch because of electrical signals, resulted in this famous storybook which I am sure at least you have heard of even if you have not read it called Frankenstein written by Mary Shelly. It was written around that time and her inspiration for that book was this discussion between Volta and Galvin. So, in any case, that is in the 1800s and that’s the story behind the battery and an interesting story associated with that story. After that and around the year 1839s, William Grove, Sir William Grove who was an English lawyer turned scientist maybe perhaps these days there are maybe scientists who turn into lawyers, but in those days there were people with a wide range of different backgrounds who also had a keen interest in science and therefore, dabbled along with different experiments. So, he was a lawyer who dabbled along with certain experiments and he created a version of this battery which he referred to as the gas battery and that had to do with the fact that the reactants were gases and he could still generate electricity out of it. And this gets gas battery that he created is the original version of the fuel cell that we are talking about and today what we have is essential traces itself back to this first demonstration of this gas battery. (Refer Slide Time: 10:26) If you look it took about 100 years you know of a lot of things going on in the background well about a 100 years went by before this fuel cell technology began to get used in any sense in any grand scale so to speak. So, in the 1930s and 1940s, these fuel cells or one version of the fuel cell referred to as the alkali fuel cell began to get used for the royal navy for their submarines. So, I mean one of the nice things about the fuel cell is that it’s a very quiet power source, it does not create any noise and therefore, is particularly useful in the military you know utilities where they want complete silence where they don’t want to be you know detected. So, it was used extensively for the royal navy submarines and was the first you know one version of it which is credited to bacon was then used for these submarines. And in the 1960s very famously it was the same fuel cell which was used by the royal navy the same kind of fuel cell which is credited to bacon, the Pratt and Whitney licensed this, but took the license for this bacon cell and used it for the space program. So, the people who walked on the surface of the moon the only people who walked on the surface of the moon used spacecraft where one aspect of the power of that spacecraft which was the Apollo 11 spacecraft the satellites associated with those spacecraft which was which were the modules in which these astronauts travelled one aspect of the power for those satellites was provided by fuel cells. Those fuel cells where these alkali fuel cells the product of the fuel cell was water and so that was clean water. So, it could even be used for drinking purposes. So, this was the combination that was used. This you can see here is an image of the Saturn rocket launch system and that’s the image of people on the moon, of course, credit for both these images goes to NASA. So, this is something which if you go and look up a history of space flight you will find fuel cells a manned space flight you will find fuel cells have played a very critical role in this. Also as an aside if you watch the movie Apollo 13 one of the critical issues that happens in that movie or that if you read up about Apollo 13 you will find that the issue that occurred during that flight was also associated with one of the supply sources for a fuel cell so that’s just an interesting aside if you are interested please look it up and you will get some interesting information on how it was handled and how the fuel cell played a role there. So, in any case, this was the progression of the development of your cell still till about 1960s. (Refer Slide Time: 13:12) If you take it forward one of the critical aspects of the development of the fuel cell or the limitation in the development of the fuel cell lay with the fact that the electrodes being used for the fuel cells had catalysts in them. Generally speaking, the catalyst being used were you know noble metals or precious metals typically platinum was the catalyst that was being used, and platinum is inherently very expensive. So, it was always felt that you know you could use this only for specialized purposes you may never be able to use it for mass-market purposes because so much platinum was necessary. And so so people were you know just researching because they felt maybe there was a possibility that something could be done, but this was one you know one roadblock so to speak that they had to overcome. So, in the 1990s it turned out that scientists working at the Los Alamos National Lab figured out a way in which you could get the same kind of a performance from a fuel cell with a lot less platinum. You know more than an order of magnitude less platinum, in fact, 40 times less amount of platinum they could use and still get the same kind of current densities that fuel cells previously had been demonstrating. That breakthrough made a difference because that suddenly made it possible to look at fuel cells from a mass-market perspective that at least you know there was at least a hope that it could be used for mass-market perspectives. Even now, the I mean the cost issues associated with the fuel cell have not been completely overcome there are still issues that have to be worked on and dealt with, but still this has this was one promising step in the right direction. So, since the late 1990s still today till date there have been several companies which have tried to make commercially available fuel cells. In other words fuel cells that have in some ways, the possibility of standing on their own in a commercial sense wherein you know the cost of the product is recovered during the usage of the product and some profit is made in the process as well. So, many companies have been around I have just listed a couple of them which were notable in the sense that they were the early companies that started working on it. One is based in New York it’s called plug power, it has tended to focus on the residential type of applications or stationary applications in a more general sense. So, a fuel cell that could be used for a house or you know office or you know or you know let’s say a hospital or something like that and that’s the kind of application that they have looked at and at least in the earlier days of their operation and the other company is based on Canada called Ballard they are still significant players in this arena. And they have tended to focus on the automotive sector of the fuel cell I mean nothing prevents either of them from looking at other sectors. But this is generally how they have tended to be in the artists in the early stages of their development. (Refer Slide Time: 16:01) So, there are various types of fuel cells and in another class, I discussed them in great detail. But just to give you an idea this is just a table that shows you a wide range of fuel cells. Conceptually they are all the same there is an electrolyte and there are two electrodes and both of them have access to gas and then you generate electricity. The real difference between these fuel cells that you see here is the choice of electrolyte. So, the electrolyte is different in each case and that’s the real difference between these fuel cells. That may not seem like much because the electrolyte does not generate any electricity it simply completes the circuit for one of the components of that fuel cell which is the ion that is moving along. But the choice of the electrolyte decides the temperature of operation that you see here, this entire scheme of the temperature of operation that you see here this temperature of operation is primarily decided by the choice of the electrolyte because it is you need to get to these temperatures for that electrolyte to conduct that ion at a reasonable rate ok. So, whatever ion it is conducting as an electrolyte has to be conducted at a reasonable rate only then the circuit will complete and you can generate current at a reasonable rate.
Otherwise, you simply have a buildup of charge and then it’s just not you know transferring the current in you know a reasonable rate. So, you will never be able to use it. So, the rate at which the ion is transferred is dependent on the temperature and typically the higher the temperature the faster the transfer of the ion or faster the conductivity of the ion in that electrolyte. And based on the electrolyte material the temperature you have to reach for it to be reasonably good conductivity to maintain you know sustain good current in the external circuit happens to be what you see on your left-hand side of your of the slide that you are seeing right now. So, I will discuss this in greater detail in another in another class, but you can see that there is a wide range of temperatures here starting from less than 100 degrees C to over 1000 degree C. Each of these fuel cells differs from the other in terms of what are some strong points of them what are some weak points, what are some challenges associated with developing those fuel cells and maybe the kind of application where they are better suited to you know be applied. So, these kinds of challenges are there and in fact so if you decide to work on the in the field of fuel cell based on which fuel cell you select to work on chances are you will have a certain range of challenges that you have to work on. Mostly the first and the last that you see here are the ones that are being worked on extensively in many fuel cell companies and research groups and fact, maybe perhaps much more the first one because you can envision even room temperature usage with it. The solid oxide fuel cell gets looked at more from the perspective of a very large scale power generation which is at a stationary location, but they all have some issues which they have to be which have to be overcome for this technology to succeed in a large scale ok. (Refer Slide Time: 19:07) So, now, let’s look at this movement from the concept to a product that I kept referring to with this background that I have just given you on how the fuel cell you know historically evolved and where it is now, and also the fact that you have all these types of fuel cells. I told you at the beginning that William Grove created this gas battery. So, what you see here is a schematic of you know roughly what was being tried then. So, you have an electrode here which is the platinum electrode on both sides you have a platinum electrode. The electrolyte is sulfuric acid which is known, this container containing sulfuric acid. So, you have two platinum electrodes dipped into this sulfuric acid as you can see here. So, you have this electrode here and this electrode here and around 1 electrode you have some kind of a container of this nature here that you see here into which you can flow this hydrogen gas and it fills up that container. And similarly, you can flow oxygen gas into this container it fills up this container. And when you do that you find that you can sustain some electricity in the external circuit. So, this is what is happening in the fuel cell in an early attempt to create a fuel cell. So and when you do this when you arrive at this stage you know you have hit upon something because you have now, got a situation where you have two gases which are getting into some region in some controlled manner and you can generate some electricity out of it is showing up in your external circuit you can sense the electricity in the external circuit. So, then your next challenge is to see how you can increase the amount of electricity, maybe you are getting some minuscule amount of electricity. So, as a concept, you have shown something, but that’s not good enough you want to raise that to a value that is acceptable and you have to define what is acceptable to you what is the amount of current that should come given that you have made this massive setup out there are you satisfied with just getting you to know pico amps or nanoamps, microamps would you rather prefer milliamps or amps or even more. So, that’s something that you have to look at. So, the early researchers tried to see taking this set up in as the background as the basis of what should be improved, what should be modified. So, that the current can go, so as it played around with various things say the size of the platinum electrode, the amount of electrolyte that was present maybe you add more electrolyte you add less electrolyte you change the shape of this container which hold the gas etcetera a lot of things they tried. And then they realized that the current was being controlled by this region that you see here that I have marked as A, that region A here and the region A here. So, the size of this region was what was decided the current was having the most impact on the current. In other words, if they increase this region A, they got more current if they decrease the region A they got less current. So, then they tried to understand what is it that we have got in that region ok. If you look carefully at this region, for example, if I just clear this up if you see at this region you have the gas that is available here. So, that gas is available here you have electrolyte available here and you have electrode available here. So, you have electrode, electrolyte and the reactant gas all being present here similarly here as well, you have the electrode the gas and the electrolyte all 3 are present. So, the presence of all 3 at one location led to this location being referred to as the 3 phase interface. So, 3 phases are present the gas, the electrode and the electrolyte, so the 3 phase interface. So, 3 phase interface is present there and all the 3 phases are in a position to participate in the reaction. So, they understood that if you increase the region of 3 phase interface in your cell then you can produce more electricity. So, they took this idea and they tried to modify it. So, that you would have a cell where you still have gas coming in you have two gases coming in and you have an electrolyte, but the region where the gas the electrolyte and the electrode are present that region the total area associated with that region was increased significantly. So, the next version of the fuel cell as they tried to make a product out of it began to look something like this. (Refer Slide Time: 23:22) So, whereas, previously you had a beaker containing sulfuric acid, instead they now, came up with a porous material which was soaked in sulfuric acid. So, you suddenly came up with the porous material soaked with sulfuric acid. And on either side instead of having you know a rod of platinum dipped in sulfuric acid there was a perforated thin perforated platinum electrode the thin perforated platinum electrode something like a mesh and that mesh was now, you know you know it was a porous mesh. So, gas could penetrate it and when the mesh was pressed against the electrolyte material the porous electrolyte material then it increased the amount of area over which the electrode-electrolyte and the gas were present simultaneously was greatly increased. So, in this manner by simply going from you know the previous design that we had to this design suddenly the amount of 3 phase interface was increased dramatically. So, here in the on the left side which I am calling the exploded view, I am showing you the 2 electrodes separately and the electrolyte separately and then on the right side I am simply assembling them as they would stay assembled in a fuel cell. So, this is how it actually would be you would have hydrogen flowing one side you have oxygen flowing the other side, this is the electrolyte that is present and this is the porous platinum on one side and porous platinum on the other side. So, this is how these parts come together and they become the assembled fuel cell. So, they have realized that you have already you know improved the fuel cell quite a bit. So, then they studied in this somehow they said ok, look this is the right direction in which we are going let’s see if you can improve it even further. So now, instead of simply having a perforated platinum electrode which was already increasing the area significantly they tried to see if we can increase it even further. (Refer Slide Time: 25:09) So, to do that what they had what they have done is instead of simply having perforated platinum they had finely powdered platinum. So, this means now, it’s the same amount of platinum but has significantly massively more amount of area associated with it finely powdered platinum which was mixed with the electrolyte and then applied as a paste onto the electrolyte. And even the electrolyte whereas, previously it was a porous material soaked in sulfuric acid they did have issues with that because the sulfuric acid would evaporate or you know it would eventually leave it would leak out of that separator etcetera. So, instead of that they now, came up with a polymer electrolyte which was capable of proton transfer, so capable of transporting protons. So, and there are electrolytes like that you can create you can synthesize the polymers which have groups in them which will permit the proton to keep moving from location to location. So, it takes such a material that would then be your electrolyte. And on either side of it, you put a structure like this which has a mix of that electrolyte as well as this finely divided platinum. And then you also make it such that this structure that you see here is a very porous structure it is not a very you know solid structure it’s a very porous structure. So, when you have such a porous structure with finely divided platinum in it and also a fair amount of you know the polymer electrolyte in it. You have dramatically increased the amount of 3 phase interface because gas can go into the pores when it goes into the pores it sees a mix of the finely divided platinum as well as the mixed polymer electrolyte which is present inside the electrode itself and therefore, you have a very dramatically increased the 3 phase interface. So, again a very similar you know assembled side view that you see here except that now, you have here an electrolyte which is a polymer it is not something soaked in sulfuric acid and you have 2 electrodes here which are both a mix of finely divided platinum and some polymer the same polymer that has been used in the electrode-electrolyte as far as it’s a porous structure. So, this is how it is now, in a steadily progressed from two solid electrodes I dipped in sulfuric acid to now, material to construction where you have a polymer electrolyte with you know extremely porous electrodes on either side. (Refer Slide Time: 27:26) So, this is the version of the current versions of the fuel cell that are there in the market that
people are you know the sort of investigating or working on scientifically in the lab has this construction.
So, today's fuel cell has this construction may maybe if you are interested in research in this area you can think if there are ways to further improve it. But the current you know the structure that is used for a fuel cell is this structure that I just described you consisting of a polymer electrolyte an anode and a cathode which are both again a mix of polymer electrolyte plus finely divided catalyst and made in a porous structure. When this operates you have electrons being released into the external circuit from the anode and these electrons then travel through the external circuit then they carry out some work for you may be powering your fan, or power a ceiling light or whatever it is and then find their way back to the cathode. At the cathode, they complete the reaction and therefore, your electrical chemical reaction is complete. So, this is you know scheme in which the fuel cell operates these days. (Refer Slide Time: 28:29) Now, this is again you know the same structure that I just showed you, you have a polymer electrolyte and your I am just showing you one electrode this side there’s another electrode on the other side which is not visible in this image and that is visible in this side view that you assemble side view that you see here. Now, although I can show you or described to you a setup like this where I say you know this is the polymer electrolyte with catalyst on either side and you simply have to flow gases on either side that is not how you can run this as a technology. So, I cannot simply hold this polymer electrolyte in my hand, I cannot just hold it in my hand and then have a hose have one person hold a hose which sends oxygen on one side another person who holds the hose and send you to know hydrogen from the other side and then loosely holds onto wires and then generate electricity. So, that is not how it happens you need to have some set up where you can you know do this for this entire process in a very controlled manner and then generate your electricity. So, your gas flow has to be
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