WEBVTT - What is a Redox Flow Battery? 0:00:04.400 --> 0:00:07.800 Welcome to Text Time, a production from my Heart Radio. 0:00:12.200 --> 0:00:15.280 Hey there, and welcome to tech Stuff. I'm your host, 0:00:15.440 --> 0:00:18.880 Jonathan Strickland. I'm an executive producer with I Heart Radio, 0:00:18.920 --> 0:00:22.599 and I love all things tech, and today we're going 0:00:22.720 --> 0:00:27.760 to go to a listener request. Andrew firmly reached out 0:00:27.920 --> 0:00:30.800 on Twitter and asked if I might do an episode 0:00:30.880 --> 0:00:34.800 about redox flow batteries. That's a topic that I've not 0:00:35.040 --> 0:00:38.760 ever touched upon in more than twelve hundred episodes. So 0:00:39.080 --> 0:00:41.320 when you come up with a chance to do something 0:00:41.720 --> 0:00:44.879 you know new, you jump on it. So thanks Andrew. 0:00:45.479 --> 0:00:48.320 To explain this method of energy storage, I will need 0:00:48.400 --> 0:00:51.000 to refer to a couple of things I have covered 0:00:51.040 --> 0:00:55.000 in previous episodes, so maybe not totally new, but this 0:00:55.080 --> 0:00:59.200 is okay. Let's talk about batteries in general. First. Now, 0:00:59.200 --> 0:01:02.320 I'm not gonna go into the history of voltaic piles 0:01:03.000 --> 0:01:08.759 and their evolution in the to the electrochemical battery of today, 0:01:08.800 --> 0:01:12.440 because I've actually done episodes on those topics already, But 0:01:12.520 --> 0:01:14.959 I do need to talk about what is actually going 0:01:15.040 --> 0:01:20.280 on with a battery, how it generates electricity. The fundamental 0:01:20.440 --> 0:01:23.679 thing that is happening with a battery is that it 0:01:23.800 --> 0:01:28.319 is storing chemical energy and then converts that chemical energy 0:01:28.600 --> 0:01:32.800 into electrical energy. Now we all know energy cannot be 0:01:32.920 --> 0:01:37.400 created or destroyed, but you can convert it from one 0:01:37.480 --> 0:01:41.880 type into another. The classic example of potential energy, you know, 0:01:41.880 --> 0:01:44.000 you've got a rock at the top of a hill. 0:01:44.440 --> 0:01:47.520 Transfer that into kinetic energy. You give the rock a 0:01:47.520 --> 0:01:50.960 little push and it begins to move and gravity pulls 0:01:51.000 --> 0:01:53.440 it downward, and you've got kinetic energy as the rock 0:01:53.560 --> 0:01:57.000 is moving. So that goes from potential to kinetic. Well, 0:01:57.240 --> 0:02:02.000 this case we're talking about chemical to electrical, but still 0:02:02.080 --> 0:02:04.600 same sort of concept, the conversion of energy from one 0:02:04.640 --> 0:02:08.800 format to another. Inside a battery are chemicals that undergo 0:02:08.840 --> 0:02:12.440 a reaction that causes a build up of electrons. Those 0:02:12.440 --> 0:02:16.440 electrons gather at the anode. There are two electrodes on 0:02:16.600 --> 0:02:19.760 a battery, the anode and the cathode. The anode is 0:02:19.800 --> 0:02:22.760 the negatively charged end of the battery. It is the 0:02:22.880 --> 0:02:26.880 end that gives up electrons. So the chemical reaction is 0:02:26.919 --> 0:02:31.840 between essentially the electrode at the anode end and the electrolyte. 0:02:31.840 --> 0:02:36.320 But we also know that like charges repel one another, right, 0:02:36.520 --> 0:02:39.480 two negative charges are going to repel each other. It's 0:02:39.480 --> 0:02:42.480 like putting the north end of two different magnets close 0:02:42.560 --> 0:02:45.239 together and they're gonna push against each other. Same sort 0:02:45.240 --> 0:02:49.120 of thing. So each electron is trying to get away 0:02:49.120 --> 0:02:51.640 from all the other electrons. It's trying to maintain the 0:02:51.720 --> 0:02:54.480 ideal amount of space between it and all of its 0:02:54.800 --> 0:02:57.720 fellow negative nancies. Now on the opposite end of the 0:02:57.720 --> 0:03:01.760 battery is the cathode. This is the positive electrode, the 0:03:01.800 --> 0:03:04.920 positive charge due to its own chemical reactions with the 0:03:04.919 --> 0:03:09.239 electro light. Technically, it's drawing in positively charged ions. The 0:03:09.400 --> 0:03:14.000 ions are atoms that have a net charge, whether positive 0:03:14.080 --> 0:03:17.000 or negative. In this case, they are positively charged ions 0:03:17.080 --> 0:03:21.880 or cat ions. Opposite charges attract each other correct so 0:03:22.280 --> 0:03:25.520 negative attracts positive and vice versa. So that means the 0:03:25.560 --> 0:03:29.760 electrons are attracted to that positive side of the of 0:03:29.800 --> 0:03:32.720 the battery, to the cathode end of the battery. But 0:03:32.880 --> 0:03:37.640 unfortunately for these poor little electrons, between them and the 0:03:37.680 --> 0:03:43.000 cathode where they want to go, there's more door. No wait, sorry, 0:03:43.000 --> 0:03:46.920 I read that wrong. Between them is the electro light, 0:03:47.040 --> 0:03:49.160 which in this case acts kind of like a really 0:03:49.200 --> 0:03:53.600 big bouncer who will explain quite convincingly that the electrons 0:03:53.640 --> 0:03:56.280 are not allowed to cross the line. In an electro 0:03:56.440 --> 0:04:01.520 chemical battery, we typically talk about semi permeable barriers or membranes, 0:04:01.920 --> 0:04:05.200 and these allow some types of particles to go through 0:04:05.560 --> 0:04:09.000 but not others. You can think of it kind of 0:04:09.040 --> 0:04:12.840 like a filter, except this particular filter isn't based on 0:04:12.960 --> 0:04:16.719 particle size. Instead, it's based on particle charge. You got 0:04:16.720 --> 0:04:19.400 a positive charge, Hey, you can come on through, but 0:04:19.600 --> 0:04:22.800 only in one direction? Are you a negative nancy aka 0:04:22.960 --> 0:04:27.440 an electron? Sorry, can't get in boss's orders. So in 0:04:27.480 --> 0:04:31.359 this analogy, the cathode is like a popular nightclub and 0:04:31.400 --> 0:04:34.160 the electrons are folks who really want to get in 0:04:34.200 --> 0:04:37.240 there where the party is, but the bouncer just won't 0:04:37.320 --> 0:04:40.560 let them in. But what if there were a side 0:04:40.760 --> 0:04:44.440 door that was unguarded, Well, then the electrons could take 0:04:44.440 --> 0:04:47.960 a different path to get inside the nightclub. And that's 0:04:47.960 --> 0:04:51.240 what happens. When a battery is placed into a circuit. 0:04:51.760 --> 0:04:56.000 The circuit is a path for electrons, and ultimately the 0:04:56.040 --> 0:04:59.000 circuit will connect the anode end of a battery to 0:04:59.080 --> 0:05:01.880 the cathode end of a battery, though it might not 0:05:02.120 --> 0:05:05.320 be the same battery depending on how the circuit arranges batteries. 0:05:05.360 --> 0:05:08.760 We'll talk about putting batteries in series or in parallel 0:05:08.800 --> 0:05:11.600 in a little bit. So when a path is available, 0:05:11.880 --> 0:05:15.360 the electrons politely tipped their imaginary hats to the electrolyte 0:05:15.360 --> 0:05:17.880 bouncer and then they make their way through the circuit 0:05:17.960 --> 0:05:21.320 to get to that positively charged cathode nightclub, where the 0:05:21.320 --> 0:05:25.640 electrons will rejoin chemicals and another reaction will occur. The 0:05:25.680 --> 0:05:28.520 technical term for this type of chemical reaction in which 0:05:28.600 --> 0:05:33.279 there is an exchange of electrons is a reduction oxidation reaction, 0:05:33.880 --> 0:05:37.680 and we can actually look at those chemical reactions at 0:05:37.680 --> 0:05:40.279 the two electrodes that we talked about earlier as the 0:05:40.360 --> 0:05:46.279 two halves of this reduction oxidation reaction. Reduction refers to 0:05:46.480 --> 0:05:51.440 gaining electrons. That sounds counterintuit if I understand, because typically 0:05:51.440 --> 0:05:55.520 you don't refer to something gaining anything as a reduction, 0:05:55.640 --> 0:05:57.719 but in this case is because we're talking about the 0:05:57.760 --> 0:06:01.800 electric charges here, not sub atomic particles. We're talking about 0:06:01.839 --> 0:06:06.160 the reduction of electric charge going more negative, which would 0:06:06.160 --> 0:06:09.720 happen when you take on an electron. So the component 0:06:10.120 --> 0:06:13.919 is accepting electrons and it undergoes a reduction and electric charge. 0:06:13.960 --> 0:06:18.760 Technically it goes from more positive to typically neutral oxidation 0:06:19.080 --> 0:06:23.719 refers to giving up electrons. When an element oxidizes, it 0:06:23.800 --> 0:06:28.640 is losing electrons. So when iron oxidizes, it rusts, and 0:06:28.680 --> 0:06:32.720 if you break off tiny pieces of iron, they oxidize 0:06:32.920 --> 0:06:37.159 so quickly in the atmosphere, and that chemical reaction gives 0:06:37.160 --> 0:06:40.520 off so much heat it does an exothermic reaction, you 0:06:40.640 --> 0:06:44.440 end up with sparks. There is a faster way to 0:06:44.600 --> 0:06:49.719 say reduction oxidation reactions, and that would be redos. So 0:06:49.960 --> 0:06:51.240 that gives you a hint that we're going to be 0:06:51.320 --> 0:06:53.599 coming back to this when we move on to redox 0:06:53.680 --> 0:06:56.640 flow batteries. But we've got a little bit more finishing 0:06:56.680 --> 0:07:00.240 up to do with classical batteries first. Now, typically the 0:07:00.320 --> 0:07:04.559 circuit the electrons must travel through isn't just an open path. 0:07:05.040 --> 0:07:08.680 We expect those electrons to do some work along the way, 0:07:08.720 --> 0:07:11.600 and the electrons don't really care about that. They just 0:07:11.760 --> 0:07:14.440 want to get to that sweet cathode nightclubs. So we 0:07:14.440 --> 0:07:17.800 tell each electron, hey, buddy, i'm gonna let you in, 0:07:18.000 --> 0:07:20.040 but first i'm gonna need your help to light this 0:07:20.160 --> 0:07:23.200 light bulb or pow are this radio or I don't know, 0:07:23.760 --> 0:07:27.200 give my captain Kirk realistic figuring with real gorn punching 0:07:27.240 --> 0:07:31.320 action the ability to hit that jab, and the electrons 0:07:31.360 --> 0:07:34.440 do this always with the goal of getting through it 0:07:34.480 --> 0:07:39.160 to the cathode nightclub. Doing work is hard, but getting 0:07:39.200 --> 0:07:43.040 past the electro light bouncer is physically impossible. I mean 0:07:43.160 --> 0:07:45.880 in the real sense of the word physics, though I 0:07:45.880 --> 0:07:49.640 guess I really should use chemistry. At least, the electrons 0:07:49.720 --> 0:07:53.800 will do the work if they have the energy necessary 0:07:53.920 --> 0:07:57.840 to do that work. So let's say that in our analogy, 0:07:58.200 --> 0:08:00.280 the work that the electrons have to do is to 0:08:00.360 --> 0:08:03.680 lift a very heavy weight, and the electrons all have 0:08:03.840 --> 0:08:08.040 the same amount of energy or weightlifting ability, but collectively 0:08:08.160 --> 0:08:10.440 their ability is not enough to move that heavy weight. 0:08:10.480 --> 0:08:14.120 They can't budget well. In that case, the battery will 0:08:14.200 --> 0:08:17.080 fail to power the circuit. The electrons will not make 0:08:17.120 --> 0:08:19.520 that journey after all, It's almost as if they ran 0:08:19.560 --> 0:08:23.400 into a second bouncer. So the energy that the electrons 0:08:23.520 --> 0:08:27.360 have is dependent upon the standard potential between the cathode 0:08:27.360 --> 0:08:31.000 and the anode. That is, how great is the difference 0:08:31.080 --> 0:08:34.520 between the negative charge on one side and the positive 0:08:34.600 --> 0:08:37.680 charge on the other side. The greater the difference, the 0:08:37.760 --> 0:08:40.880 greater the potential between the two. This gives us the 0:08:40.920 --> 0:08:45.520 batteries overall electrochemical potential, and that in turn determines the 0:08:45.600 --> 0:08:50.400 voltage of the battery. Voltage is akin to pressure, how 0:08:50.480 --> 0:08:54.680 much force is there in the system pushing those electrons along. 0:08:55.200 --> 0:08:58.320 The force determines whether or not electrons flow. If there's 0:08:58.360 --> 0:09:01.000 not enough voltage, the electrons won't move. If there's a 0:09:01.040 --> 0:09:05.000 lot of voltage, they're gonna move too sweet. So if 0:09:05.040 --> 0:09:07.720 the weight is too heavy, if the load on the 0:09:07.760 --> 0:09:11.000 circuit is too great, then it's going to require greater 0:09:11.120 --> 0:09:14.400 force or voltage to do that work with the same 0:09:14.480 --> 0:09:18.720 amount of electrons. Alternatively, you might be able to do 0:09:18.800 --> 0:09:22.640 that work if you had more electrons a larger volume 0:09:22.920 --> 0:09:27.120 of electrons moving through at that lower voltage. This would 0:09:27.160 --> 0:09:30.960 be a description of current or amperage. But one or 0:09:31.080 --> 0:09:33.960 the other needs to go up. If the electrons are 0:09:33.960 --> 0:09:36.480 going to be able to move that weight to to 0:09:36.679 --> 0:09:40.079 power that load on the circuit, there needs to either 0:09:40.200 --> 0:09:42.200 be more of the electrons, or they need to be 0:09:42.240 --> 0:09:45.920 pushed harder, or you know both. It all depends on 0:09:45.920 --> 0:09:48.680 what the circuit can handle and things like that. So 0:09:49.520 --> 0:09:51.880 you can have a high voltage and a low amperage, 0:09:52.040 --> 0:09:53.840 which means you've got a lot of pressure behind a 0:09:53.880 --> 0:09:57.679 relatively small volume of electrons. Or you could have low 0:09:57.800 --> 0:10:01.840 voltage and high amperage, in which a relatively small amount 0:10:01.880 --> 0:10:05.880 of force is moving a relatively large volume of electrons. 0:10:06.400 --> 0:10:09.319 Or you could have any combination. So your typical household 0:10:09.360 --> 0:10:12.520 batteries have a voltage of one point five and these 0:10:12.520 --> 0:10:15.280 would be your classic double A or triple A batteries 0:10:15.320 --> 0:10:18.880 for example. They're all at one point five volts. Okay, 0:10:18.880 --> 0:10:20.679 But let's say you've got a job and it's going 0:10:20.720 --> 0:10:23.600 to be too much for the battery to handle based 0:10:23.640 --> 0:10:28.400 on that batteries voltage, what are your options. Well, you 0:10:28.440 --> 0:10:31.480 could use a different type of battery if your system 0:10:31.559 --> 0:10:35.760 allowed for that battery that had greater electrochemical potential between 0:10:35.760 --> 0:10:38.880 the two electrodes. But the other option is to stack 0:10:38.960 --> 0:10:43.120 the batteries together in series. This has an additive effect 0:10:43.280 --> 0:10:46.000 on the batteries voltage. Now if you were to connect 0:10:46.040 --> 0:10:50.080 the batteries in parallel instead of in series, So in series, 0:10:50.120 --> 0:10:52.680 you can think of them as one right behind the other. 0:10:52.920 --> 0:10:55.760 In parallel, they're all kind of linked up in their 0:10:55.800 --> 0:10:59.480 own individual pathways into the main circuit. Well, if you 0:10:59.520 --> 0:11:02.080 go in PA Hello, you increase the amperage, you increase 0:11:02.160 --> 0:11:05.720 the current, but not the voltage, so it all depends 0:11:05.760 --> 0:11:09.320 on what you need to do. Now, some batteries can 0:11:09.480 --> 0:11:13.480 only do this process one time through all the way 0:11:13.520 --> 0:11:15.880 through it. So once the cathode nightclub gets full of 0:11:15.960 --> 0:11:20.920 enough electrons, it will lose its positive charge. The electrochemical 0:11:20.920 --> 0:11:24.680 potential between the anode and the cathode will decrease. The 0:11:24.720 --> 0:11:27.679 population of electrons at the anode, entrance of the nightclub 0:11:27.679 --> 0:11:32.040 will diminish, and so even if you have a pathway 0:11:32.120 --> 0:11:34.320 that gives electrons a free and clear entry point to 0:11:34.360 --> 0:11:39.199 the cathode with no load to to work, it won't 0:11:39.240 --> 0:11:42.840 matter because there won't be enough electric potential difference for 0:11:43.000 --> 0:11:46.280 there to be any voltage to be any flow of current. 0:11:46.640 --> 0:11:49.160 So essentially the cathode nightclub has reached kind of a 0:11:49.200 --> 0:11:51.520 neutral charge and no electrons are gonna want to go 0:11:51.559 --> 0:11:54.679 there now because it's some lame spot no one cares about. 0:11:55.000 --> 0:11:58.160 The battery is dead and it needs to be discarded 0:11:58.440 --> 0:12:04.080 or preferably recycled. But other batteries are rechargeable, and putting 0:12:04.080 --> 0:12:07.280 them into a charger means that you're actually introducing an 0:12:07.320 --> 0:12:11.200 incoming electric current into the battery, and it forces this 0:12:11.280 --> 0:12:15.560 reaction to reverse itself. The electrons will bail on the 0:12:15.600 --> 0:12:19.880 Cathode nightclub and return to the anode end, and when 0:12:19.920 --> 0:12:22.960 you remove the battery from the charger, it's back to 0:12:23.000 --> 0:12:27.680 where it was before you used it the first time. Mostly, typically, 0:12:27.679 --> 0:12:31.680 rechargeable batteries recapture only a percentage of the full charge 0:12:31.760 --> 0:12:34.600 they once held, which in our analogy would mean some 0:12:34.720 --> 0:12:37.199 of those electrons were just too much in the groove 0:12:37.320 --> 0:12:40.520 and the Cathode nightclub, so they didn't leave when everyone 0:12:40.559 --> 0:12:44.040 else got kicked out. So over time, even a rechargeable 0:12:44.040 --> 0:12:48.319 battery will lose its ability to store energy. The electrochemical 0:12:48.320 --> 0:12:50.720 potential will become too low for the battery to do 0:12:50.800 --> 0:12:52.920 any useful work. I mean, you might be able to 0:12:52.920 --> 0:12:55.000 hook it up to a meter and say, yes, technically 0:12:55.080 --> 0:12:59.319 current is flowing, but it's at such a small amperage 0:12:59.559 --> 0:13:02.800 that it's not useful for anything. I can't do it 0:13:02.840 --> 0:13:05.880 to light a light bulb or whatever. So that's your 0:13:05.880 --> 0:13:09.800 classic battery. There's another energy storage method we should cover 0:13:09.880 --> 0:13:12.080 as well, as it's going to be useful. When we 0:13:12.120 --> 0:13:15.560 talk about redox flow batteries and that would be fuel cells. 0:13:16.280 --> 0:13:20.800 Fuel cells are similar to, but distinct from batteries. Sir 0:13:20.840 --> 0:13:25.320 William Robert Grove, a Welsh judge, generally gets credit for 0:13:25.400 --> 0:13:28.400 inventing the first fuel cell all the way back in 0:13:28.480 --> 0:13:31.800 eighteen thirty nine. I guess this tells us that Welsh 0:13:31.880 --> 0:13:33.880 judges had a lot of spare time on their hands 0:13:33.920 --> 0:13:37.760 in the mid nineteenth century. Basically, Sir Willie found out 0:13:37.800 --> 0:13:41.599 that by mixing hydrogen and oxygen in the presence of 0:13:41.640 --> 0:13:45.400 an electro light would end up with some interesting byproducts. 0:13:45.720 --> 0:13:48.360 He would get water, you know, good old H two 0:13:48.360 --> 0:13:53.320 O two hydrogens to one oxygen and electricity. But this 0:13:53.480 --> 0:13:57.920 particular incarnation of a fuel cell, well interesting, wasn't practical 0:13:58.080 --> 0:14:01.040 because it wasn't producing enough like tricity to do anything 0:14:01.080 --> 0:14:05.160 of use. However, we're gonna skip way ahead. Fuel Cells, 0:14:05.360 --> 0:14:10.280 like batteries, convert chemical energy into electric energy. There are 0:14:10.280 --> 0:14:12.480 many different kinds, but the ones you and I would 0:14:12.559 --> 0:14:15.760 most likely encounter are those that use hydrogen and oxygen, 0:14:16.000 --> 0:14:18.520 much like Sir Williams fuel cell from more than a 0:14:18.600 --> 0:14:22.600 century ago. In a fuel cell, you've essentially got a 0:14:22.640 --> 0:14:27.360 couple of chambers separated by a semi permeable membrane. In 0:14:27.440 --> 0:14:31.280 one chamber you pump in hydrogen and in the other 0:14:31.360 --> 0:14:35.920 chamber you pump in oxygen. The semi permeable membrane is 0:14:36.000 --> 0:14:39.680 an electrolyte, typically paired with a catalyst, and a catalyst 0:14:39.800 --> 0:14:43.240 is something that facilitates a reaction. It doesn't cause a 0:14:43.240 --> 0:14:47.560 reaction on itself, but it makes reactions easier. It reduces 0:14:47.640 --> 0:14:52.640 the the energy requirement for a reaction to happen. So 0:14:52.800 --> 0:14:56.120 the hydrogen atoms, which consist of one electron and one 0:14:56.200 --> 0:14:59.720 proton that's a hydrogen atom, they react with this electrolyte 0:14:59.720 --> 0:15:03.160 and the catalyst. This causes the hydrogen atoms to say 0:15:03.280 --> 0:15:06.880 bone voyage to that electron. So you get a positively 0:15:07.040 --> 0:15:12.520 charged hydrogen ion or the cat ion, and that would 0:15:12.560 --> 0:15:17.880 be the positive hydrogen uh anions are then negatively charged ions, 0:15:17.920 --> 0:15:21.520 thus like cathode and anode, and we have another word 0:15:21.560 --> 0:15:24.880 for hydrogen ions that would be a proton, because that's 0:15:24.920 --> 0:15:28.160 all a hydrogen nucleus really is. It's one proton, so 0:15:28.360 --> 0:15:33.040 positively charged sub atomic particle. The semipermeable membrane allows the 0:15:33.040 --> 0:15:36.280 proton to pass through it, but not the electron. So 0:15:36.360 --> 0:15:39.400 like our previous example, the electrons really want to get 0:15:39.440 --> 0:15:41.720 to that other side of the membrane because that's where 0:15:41.760 --> 0:15:45.160 a positive charge exists. So you can connect the fuel 0:15:45.200 --> 0:15:48.120 cell to a circuit and the electrons will travel through 0:15:48.160 --> 0:15:51.880 that path and head toward the opposite chamber and they'll 0:15:51.920 --> 0:15:54.600 do work. They'll do work on an electric load along 0:15:54.640 --> 0:15:58.560 the way. How much depends again upon the electrochemical potential 0:15:58.840 --> 0:16:02.720 between the two electrodes, the anode and the cathode. And 0:16:02.760 --> 0:16:05.040 then they'll get over to where all the oxygen and 0:16:05.120 --> 0:16:11.080 hydrogen uh nuclei, the protons, those cat ions all happen 0:16:11.160 --> 0:16:13.240 to be. Now, I have a little bit more to 0:16:13.320 --> 0:16:15.920 say about fuel cells, but before I get into that, 0:16:16.040 --> 0:16:26.720 let's take a quick break. So before we left off, 0:16:27.040 --> 0:16:29.760 I mentioned that the hydrogen in a fuel cell gets 0:16:29.880 --> 0:16:34.760 stripped of its electron. The hydrogen cation or proton, passes 0:16:34.800 --> 0:16:38.560 through this semi permeable membrane. The electron goes through a circuit, 0:16:38.720 --> 0:16:41.800 doing work along the way before finally making its way 0:16:41.800 --> 0:16:44.480 to the other chamber in the fuel cell. In that 0:16:44.520 --> 0:16:49.480 opposite chamber, the protons, electrons, and oxygen combined to form water. 0:16:50.080 --> 0:16:53.800 This is also an exothermic reaction, meaning it gives off heat, 0:16:53.920 --> 0:16:58.520 So your byproducts of this reaction are electricity, heat, and water. 0:16:59.120 --> 0:17:02.480 The fuel cell only generates electricity so long as there 0:17:02.600 --> 0:17:06.920 is hydrogen and oxygen a k a. The fuel that's 0:17:07.000 --> 0:17:09.840 in the cell, and that means that once it runs 0:17:09.840 --> 0:17:12.919 out of those, you have to refuel it. This is 0:17:12.960 --> 0:17:16.520 not something that just stays contained within the fuel cell. 0:17:16.760 --> 0:17:19.080 You're refueling it, just as you would have to refuel 0:17:19.160 --> 0:17:21.920 something like a car, you know, to top it off. 0:17:22.359 --> 0:17:25.440 And it is a clean process within the fuel cell 0:17:25.480 --> 0:17:29.880 itself because the byproduct is pure water. People have advocated 0:17:29.920 --> 0:17:32.959 for fuel cells to replace stuff like gasoline or diesel 0:17:33.000 --> 0:17:36.479 powered vehicles. So what's stopping us? What is in the 0:17:36.520 --> 0:17:40.320 way of doing that? Well, there are a few challenges, 0:17:40.520 --> 0:17:43.679 and one is that hydrogen is actually not that easy 0:17:43.720 --> 0:17:46.040 to come by. Now what do I mean by that? 0:17:46.280 --> 0:17:49.440 I mean, we know hydrogen is the most plentiful stuff 0:17:49.440 --> 0:17:52.280 in the universe, so you figure it would be the 0:17:52.320 --> 0:17:54.679 easiest stuff in the world to get hold of. But 0:17:54.880 --> 0:17:59.200 hydrogen also tends to bond with other stuff. In its 0:17:59.240 --> 0:18:03.120 pure form, hydrogen is a gas and it's lighter than air, 0:18:03.160 --> 0:18:06.720 so it floats off beyond our reach. We typically get 0:18:06.800 --> 0:18:11.600 hydrogen through some other process which involves breaking the molecular 0:18:11.640 --> 0:18:15.800 bonds that hold hydrogen to other elements. But that means 0:18:15.840 --> 0:18:19.040 you have to actually pour energy into this process. In 0:18:19.119 --> 0:18:21.320 order to get to the hydrogen, you have to break 0:18:21.359 --> 0:18:25.280 those molecular bonds. That requires using energy. So to swap 0:18:25.320 --> 0:18:28.240 out to a hydrogen based system, you have to take 0:18:28.359 --> 0:18:31.480 that part into account. Now, if it turns out you're 0:18:31.560 --> 0:18:35.200 using more energy to get the hydrogen, then you would 0:18:35.680 --> 0:18:40.600 get energy by harnessing that hydrogen. You're playing a losing game, right. 0:18:40.640 --> 0:18:43.399 If you're spending more energy just to get the fuel, 0:18:43.840 --> 0:18:47.360 then you are being able to use the fuel. Why 0:18:47.400 --> 0:18:49.800 are you doing that? You should just choose some other method. 0:18:50.119 --> 0:18:54.080 Or if the method you're using to break those molecular 0:18:54.119 --> 0:18:59.320 bonds doesn't depend upon an environmentally friendly method, then really 0:18:59.320 --> 0:19:03.080 you're just shifting pollution to a different part of the system. Now, 0:19:03.160 --> 0:19:05.840 you can get hydrogen out of water by running an 0:19:05.840 --> 0:19:09.520 electric current through the water. In fact, this is essentially 0:19:09.720 --> 0:19:13.440 the same process we see in fuel cells, but in reverse, right, 0:19:13.840 --> 0:19:18.400 because in fuel cells we see hydrogen and oxygen binding 0:19:18.440 --> 0:19:23.000 together and the byproduct in this is electricity and some heat. 0:19:23.440 --> 0:19:26.080 By running an electric current through water, we can break 0:19:26.160 --> 0:19:29.040 up oxygen and hydrogen, and you know, we break that 0:19:29.119 --> 0:19:32.520 molecular bond, so again the same process, but in reverse. 0:19:32.840 --> 0:19:36.240 It's actually called electrolysis. But in order to do that, 0:19:36.320 --> 0:19:39.320 you have to have access to suitable water. You need 0:19:39.359 --> 0:19:42.760 a clean method to generate electricity, maybe use solar power 0:19:42.920 --> 0:19:46.360 or wind power, And all of this starts raising questions 0:19:46.359 --> 0:19:48.920 about why would you not just use solar or wind 0:19:48.920 --> 0:19:52.800 power directly, So you couldn't really do that for like 0:19:53.000 --> 0:19:56.040 an onboard system on a car, and the counter argument 0:19:56.119 --> 0:19:57.480 is that you still have to have a way to 0:19:57.600 --> 0:20:01.000 store energy. Fuel cells would be a way to help 0:20:01.119 --> 0:20:05.520 store energy, but there are other challenges besides the access 0:20:05.600 --> 0:20:09.240 to hydrogen. Another big one is that most fuel cells 0:20:09.280 --> 0:20:13.000 have a band of temperatures within which they can operate, 0:20:13.560 --> 0:20:16.600 and if you get outside that band of temperatures, if 0:20:16.600 --> 0:20:18.680 you go too high or too low, the fuel cell 0:20:18.760 --> 0:20:21.920 will not perform as well and it might even suffer damage, 0:20:22.119 --> 0:20:26.000 which means it will have a much shorter life cycle. Anyway, 0:20:26.160 --> 0:20:29.520 most fuel cells don't operate very well below a certain 0:20:29.560 --> 0:20:34.080 threshold temperature. The specific temperature threshold really depends upon the 0:20:34.119 --> 0:20:37.200 type of fuel cell, and this makes them a little 0:20:37.359 --> 0:20:40.399 less reliable if you want to, I don't know, have 0:20:40.560 --> 0:20:44.399 a fuel cell powered car in Alaska in the middle 0:20:44.440 --> 0:20:47.680 of winter, the temperatures can actually get low enough where 0:20:47.720 --> 0:20:51.840 it's below the real operating temperatures for that fuel cell, 0:20:52.240 --> 0:20:54.760 and it might even do damage to the fuel cells membrane. 0:20:54.960 --> 0:20:57.720 So this is a tricky problem to get around. And 0:20:57.800 --> 0:21:01.320 yet another challenge is that many fuel cells rely on 0:21:01.600 --> 0:21:06.600 rare and expensive materials to act as catalysts, such as platinum. 0:21:06.640 --> 0:21:09.680 And yet another challenge is that many fuel cells rely 0:21:09.880 --> 0:21:14.320 on rare and expensive materials to act as catalysts such 0:21:14.320 --> 0:21:19.119 as platinum. Platinum is expensive stuff, and that drives up 0:21:19.160 --> 0:21:22.119 the cost of manufacturing. As much as I wish we 0:21:22.119 --> 0:21:26.000 could all ignore the impact of money, we can't. If 0:21:26.040 --> 0:21:28.960 you have two ways to store energy, and one is 0:21:29.000 --> 0:21:34.040 relatively cheap but environmentally it's harmful, the other is expensive 0:21:34.240 --> 0:21:38.960 but has no real negative environmental impact, some people, perhaps 0:21:39.040 --> 0:21:42.960 most people, are going to go with the less expensive option, 0:21:43.240 --> 0:21:45.600 even though in the long run you could argue that 0:21:45.680 --> 0:21:50.200 it's more expensive and to have a true hydrogen based economy, 0:21:50.640 --> 0:21:52.760 you would also have to invest in building out a 0:21:52.800 --> 0:21:56.960 new infrastructure, which can run into the billions of dollars, 0:21:57.000 --> 0:22:00.960 so it's another big challenge. Also, I should point out 0:22:01.000 --> 0:22:05.320 that while the actual chemical reaction within a hydrogen based 0:22:05.440 --> 0:22:08.640 fuel cell is a clean one, there can be other 0:22:08.720 --> 0:22:13.480 factors that cause a negative environmental impact, including the mining 0:22:13.560 --> 0:22:15.800 methods that you have to rely on to get the 0:22:15.840 --> 0:22:19.400 materials for the catalyst. You always have to take a 0:22:19.440 --> 0:22:22.120 big picture look at these things and not just look 0:22:22.160 --> 0:22:25.600 at the mechanism of the fuel cell itself. You gotta 0:22:25.600 --> 0:22:28.960 look at the whole ecosystem and say, does this make 0:22:29.000 --> 0:22:32.800 more sense than fossil fuels. I would argue it does, 0:22:33.640 --> 0:22:36.200 but you have to take the whole picture into account 0:22:36.240 --> 0:22:39.120 before you can actually say something like that. And I'm 0:22:39.119 --> 0:22:41.920 not saying all of this to completely dismiss fuel cells, 0:22:41.960 --> 0:22:45.520 because I happen to love fuel cell technology, but I 0:22:45.600 --> 0:22:48.680 also believe we have to acknowledge the obstacles that are 0:22:48.720 --> 0:22:50.919 in our way if we ever are to have a 0:22:50.960 --> 0:22:56.120 hope of surmounting those obstacles. Now, let's finally move on 0:22:56.240 --> 0:22:59.639 to redox flow batteries. Now, luckily, with the grounding we 0:22:59.760 --> 0:23:02.960 have of in traditional batteries and with fuel cells, we 0:23:03.000 --> 0:23:06.760 can tackle this concept a bit more easily. Lawrence H. 0:23:06.960 --> 0:23:11.160 Thaller filed a patent for an electrically rechargeable redox flow 0:23:11.200 --> 0:23:15.160 cell back in nineteen. The Patent Office in the United 0:23:15.160 --> 0:23:19.080 States granted that patent the following year. The abstract gives 0:23:19.119 --> 0:23:22.080 us a really useful starting points, so I'm gonna read 0:23:22.119 --> 0:23:25.840 it in full. Also, this patent expired in so this 0:23:25.920 --> 0:23:28.680 is about as fair use as it gets. But here's 0:23:28.720 --> 0:23:33.600 the abstract. There is disclosed a bulk energy storage system 0:23:33.680 --> 0:23:40.280 including an electrically rechargeable reduction oxidation redox cell, divided into 0:23:40.320 --> 0:23:45.000 two compartments by a membrane. Each compartment containing an electrode 0:23:45.359 --> 0:23:48.560 and anode fluid is directed through the first compartment at 0:23:48.560 --> 0:23:51.920 the same time that a cathode fluid is directed through 0:23:51.920 --> 0:23:55.600 the second compartment, thereby causing the electrode in the first 0:23:55.640 --> 0:23:59.119 compartment to have a negative potential while the electrode in 0:23:59.160 --> 0:24:03.040 the second compart mint has a positive potential. The electrodes 0:24:03.160 --> 0:24:07.280 are inert with respect to the anode and cathode fluids used, 0:24:07.480 --> 0:24:11.840 and the membrane is substantially impermeable to all except select 0:24:11.920 --> 0:24:15.560 ions of both the anode and cathode fluid. Whether the 0:24:15.600 --> 0:24:19.080 cell is fully charged or in a state of discharge. 0:24:19.560 --> 0:24:23.440 Means are provided for circulating the anode and cathode fluids, 0:24:23.600 --> 0:24:26.639 and the electrodes are connected to an intermittent or non 0:24:26.720 --> 0:24:31.399 continuous electrical source, which, when operating, supplies current to a 0:24:31.480 --> 0:24:34.119 load as well as to the cell to recharge it. 0:24:34.600 --> 0:24:39.000