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more on fuel cells and electrolysers

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Cross section of a PEMEL(polymer exchange membrane electrolyte?) stack comprising four cells, according to Science Direct

Jacinta: So continuing with Philip Russell’s simple video of a small hydrogen fuel cell (in the previous post), he explains that when the electrolysis process reverses itself, powering the fan, hydrogen is entering the cathode where it reacts with the palladium catalyst. The reaction with palladium is described as complex and weird, so he puts the matter off to a future video. In any case the hydrogen is split, producing electrons and hydrogen ions. Those electrons travel around the circuit which powers the fan, or a light bulb or some other electrical device, and the hydrogen ions travel through/across the PEM, where they react with the electrons in the circuit, and the oxygen, to produce water, which escapes from the anode side. 

Canto: So what they’re after in all this is the electrons, in sufficient abundance and in continuous supply to power whatever, without the use of carbon-based fuels. Frankly I’m not even sure how fossil fuels, hydrocarbons etc produce electricity, but hopefully I’ll learn something about this along the way.

Jacinta: You mean how does coal, oil or gas get transformed into high-energy electrons bumped along in a circuit? Yes, we have a lot to learn. 

Canto: And how do electrons in a wire make an air-conditioner work? But let’s stick with hydrogen for now. An older video, from 2012, from the excellent Fully Charged series, provides some other insights. I won’t go into too much detail with it, as the fuel cell described is very similar to Russell’s, but it does highlight some problems, at least from 2012. First, the interviewee, James Courtney from Birmingham University, uses the term proton-exchange membrane (PEM) rather than Russell’s PEM – a polymer exchange membrane. They mean the same thing, as the membrane is made of a polymer, and the key is that it’s an ‘electron insulator’, allowing protons to pass through. The polymer is usually nafion, a synthetic polymer created sixty years ago. It’s described as an ionomer for its ionic properties. But the most important thing I learned from Courtney is about the issue of platinum/palladium. It’s very very expensive, and its price is rising. Courtney – nine years ago – was experimenting with solid oxide electrolytes.

 Jacinta: From Wikipedia: 

solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.

Canto: An organisation called Bloom Energy, self-described as ‘a leader in the SOFC industry’, has a bit to say about the technology. So, again we have the negative anode and the positive cathode, and the electrolyte in between which undergoes ‘an electrochemical reaction’…

Jacinta: That’s when the miracle occurs.

Canto: Yes, and this produces an electrical current. So here’s something to think about re electrolytes: 

The electrolyte is an ion conductor that moves ions either from the fuel to the air or the air to the fuel to create electron flow. Electrolytes vary among fuel cell types, and depending on the electrolyte deployed, the fuel cells undergo slightly different electrochemical reactions, use different catalysts, run on different fuels, and achieve varying efficiencies.

Does that help?

Jacinta: Yes, it helps to complicate matters. 

Canto: So the Bloom Energy website reckons that SOFCs have the best potential for fuel cell technology, and promises they’ll bear fruit in the next six years – instead of the usual five. Here’s their diagram of an SOFC.

 

Note that they’re using natural gas (methane) in a process called methane reformation, also mentioned by James Courtney. So, not exactly a clean technology, but also, as the illustration mentions, no precious metals, corrosive acids or molten materials. 

Jacinta: But apparently this isn’t a hydrogen fuel cell. Barely a mention of hydrogen. 

Canto: Yes, the illustration presents oxygen ions reacting with ‘fuel in the fuel cell’ to produce electricity. The cleanness comes from the fact that there’s no combustion, making it more sustainable and of course more green than combustion-based tech. Apart from a partial reduction in greenhouse gases, this tech does away with the emission of harmful sulphur dioxide and nitrogen oxide. And their ‘Bloom box’ fuel cell packs can run on hydrogen, with net zero carbon emissions. They see their technology being well suited to distributed networks and mini-grids, which may provide the power supplies of the future.

Jacinta: We shall see – if we live long enough. Meanwhile let’s look at another video, featuring Dr Stephen Carr, of the H2 Centre, University of South Wales, on how a hydrogen fuel cell works. Eventually it’ll all come together.

Canto: And then fall apart again. This video is more recent than the previous two, but I’m not sure that there have been any new developments in the interval. So Dr Carr presents ‘a demonstration kit of a renewable hydrogen energy storage system’, in which the hydrogen is produced by solar power…

Jacinta: Another magical moment?

Canto: Well, apparently. Anyway, he represents the sun with a lamp – so I suppose it’s a demonstration, not the real thing. The lamp shines on a PV (photovoltaic) panel which produces electricity.

Jacinta: Grrr, they never explain that bit.

Canto: How do you produce annoyance? Bet you can’t explain that either. Anyway, the electricity runs through an electrolyser, which splits water into oxygen and hydrogen, which is stored for times when we can’t directly produce power from the sun. At such times we can run the hydrogen and oxygen through a fuel cell (which seems to operate oppositely to an electrolyser) to produce electrical power. As he says (and this is new) the photons from the lamp (in lieu of the sun) are converted by the panel into electrical energy or power (but I think those are two distinct things). This is of course referring to how solar energy/power works, which is an entirely different thing. We’ll leave that aside for now, along with the big heap of other things.

Jacinta: Yes let’s just focus on what Dr Carr says. The electrical power powers an electrolyser. The electrons are used to drive an electrochemical process which splits water into hydrogen and oxygen. On one side of this electrolyser the water is ‘split into hydrogen’ and on the other side it produces oxygen (magic happens). Then the hydrogen and oxygen can be stored until required, when we can somehow convert these elements into electricity. We can observe, as in the Philip Russell video, bubbles of hydrogen and oxygen forming on either side of the electrolyser, and being collected and stored. 

Canto: So we’re again not going to discover the detailed physics/chemistry of all this, but apparently we now have stored power. And this gets run backwards through the fuel cell. In the fuel cell, the released oxygen and hydrogen, in a reverse process to electrolysis (I think), produces pure, apparently drinkable water, and electricity. So the two gases are released from the electrolyser into the fuel cell, oxygen at one electrode, hydrogen at the other, and they’re combined and subjected to electrochemical processes (more magic), producing water and electricity sufficient in this tiny demo model to power a fan or small light. So far, precisely as enlightening as the Philip Russell video.

Jacinta: So next we’re taken to a big electrolyser, something like the new one at Tonsley, South Australia. It uses a stack of some 80 fuel cells to produce stacks of hydrogen. The electrolyser takes in about 50kw of power and produces about 1 kilogram of hydrogen per hour – which means very little to me. 

Canto: It’s good that they know this I suppose. So they have an electrolysis stack, and they feed in ‘pure de-ionised water’ – I bet we could do a whole post on that – and apply DC electric power – another post’s worth – which splits the water into hydrogen and oxygen.

Jacinta: When I think of AC and DC I think of Tesla v Edison. History is so much easier than science. I think we need to do a basic course in electricity. But continuing with Dr Carr, for what it’s worth to us, he says that ‘everything else in this unit is gas clean-up’. The hydrogen is ‘de-watered’ to make sure it’s completely dry, and it’s also de-oxygenated, in other words thoroughly purified. Then, for storage, it’s compressed to 200 bar, meaning 200x atmospheric pressure.

Canto: The bar, presumably for barometric pressure, is commonly used in Europe but not accepted by the US, centre of arseholedom with regard to weights and measures. 

Jacinta: The trouble is that ‘atmosphere’ for measures of atmospheric pressure, is highly contestable. Anyway, we’ll finish this off next time, for now I’ll just say that Elon Musk is still not much impressed with hydrogen technology, saying that hydrolysis is way too energy-intensive-expensive, that methane or propane etc extraction defeats the purpose, that hydrogen is too light to store easily, that it’s very volatile etc, but maybe it could work for aircraft in the future… So why is so much money being expended on it, in so many countries? Why is it suddenly such a big deal? That’s a ‘mystery’ we’ll have to investigate… 

References

https://www.sciencedirect.com/science/article/pii/S0360319919312145

The Hydrogen fuel cell explained, clean energy, by Philip Russell, youtube video

Hydrogen Fuel Cells | Fully Charged, youtube video

https://en.wikipedia.org/wiki/Solid_oxide_fuel_cell

https://www.bloomenergy.com/blog/everything-you-need-to-know-about-solid-oxide-fuel-cells/

https://www.sciencedirect.com/science/article/pii/S1369702103003316

How does a hydrogen fuel cell work, with Dr Stephen Car, video

Elon Musk about Hydrogen Cars, video

Written by stewart henderson

July 7, 2021 at 9:27 pm

on fuel cells and electrolysers and other confusions

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Canto: So it seems the more you look towards future technologies, the more future technologies there are to look at. Funny that. Two future developments we want to focus on in these next few posts are the graphene aluminium ion batteries being researched and developed in Queensland for the world, and the whole field of green hydrogen technology, a topic we’ll start on today.

Jacinta: Yes and the two key terms which we’re hoping might enlighten us if we can get a handle on them are fuel cell and electrolyser.

Canto: But first, I’ve just watched a brief video, admittedly five years old, a lifetime it seems in nuevo-tech terms, in which Elon Musk, who I’ve generally considered a hero, describes hydrogen fuels as silly, and seems at the end to be lost for words in expressing his contempt for the technology.

Jacinta: Yes, and the video appears to have been unearthed recently because all the comments, mostly well-informed (as far as I can discern) are only months old, and contradict Musk’s claims. But let’s not dwell on that. What is a fuel cell?

Canto: Well, we’re looking at the possibility of fuel cell electric vehicles (FCEVs), which presumably will operate in direct competition with Tesla’s EVs. Interestingly, one of the claimed deficits of EVs is their long charging times, which the new graphene-aluminium ion technology should greatly reduce. If FCEVs become a thing, the ‘old’ battery driven things will become known as BEVs, even before the EV term has really caught on.. Anyway, fuel cells produce electricity. You don’t have to plug them in, according to BMW.com (which may have a bias towards hydrogen in terms of investment). However, they don’t really show how the hydrogen is produced, and their image, shown above, presents a hydrogen tank without explaining where the hydrogen comes from.

Jacinta: Yes, so here’s how BMW.com begins its explanation:

In fuel cell technology, a process known as reverse electrolysis takes place, in which hydrogen reacts with oxygen in the fuel cell. The hydrogen comes from one or more tanks built into the FCEV, while the oxygen comes from the ambient air. The only results of this reaction are electrical energy, heat and water, which is emitted through the exhaust as water vapor. So hydrogen-powered cars are locally emission-free…

Canto: Which explains nothing much so far. Hydrogen reacts with oxygen. How? By reverse electrolysis. What’s that? The name implies splitting by electricity (but in reverse?), but I’d like more detail.

Jacinta: Yeah we’ll have to go elsewhere for that. In the image above you see a battery pack, much smaller than those in EVs, and an electric engine or motor. The BMW site reckons that the generated electricity from the fuel cell can either flow directly to the electric motor, powering the vehicle, or it can go to the battery, called a ‘peak power battery’, which stores the energy until needed by the motor. Being constantly recharged by the fuel cell, it’s only a fraction of the size of an EV battery.

Canto: Okay, that’s the BMW design, but I want the science nitty-gritty. I’ve heard that fuel cells go back a long way.

Jacinta: Yes, and we may need several posts to get our heads around them. I’ll start with the English engineer Francis Thomas Bacon (illustriously named), who developed the first alkaline fuel cell, or hydrogen-oxygen fuel cell, also known as the Bacon fuel cell, in the 1930s. This type of fuel cell has been used by NASA since the sixties. But the Wikipedia article again skips some steps.

Canto: So alkaline is the opposite of acidic, sort of, and car batteries require acid, but I don’t know what the difference is, in electrical terms.

Jacinta: Hopefully all will be revealed. One basic thing I’ve learned is that a fuel cell requires a cathode, an anode (collectively, two electrodes) and an electrolyte. So let’s take this slowly. The cathode is the one from which the conventional current departs – CCD, cathode current departs. Conventional current is defined as the direction of the positive charge. In the case of hydrogen, that’s just protons. The electrons go in the opposite direction. The anode, which maybe I should’ve mentioned first, is the electrode through which a conventional current enters the fuel cell or device. Think ACID, anode current into device. Now, the cathode and anode must be made of particular materials, which presumably relate to the fuel you’re trying to split, or electrolyse.

Canto: Hmmm, I’m wondering if a fuel cell and an electrolytic cell are the same thing, or one is a subset of the other. Apparently not, according to Wikipedia.

For fuel cells and other galvanic cells, the anode is the negative terminal; for electrolytic cells (where electrolysis occurs), the anode is the positive terminal. Made from, with, or by water.

So, shit, what’s a galvanic cell and how does it differ from an electrolytic cell? From the above description, it sounds like an electrolytic cell (anode positive) is the opposite of a fuel/galvanic cell (anode negative). We need to know what electrolysis actually means – not to mention galvanisis. And I believe reverse electrolysis is a thing.

Jacinta: Shit indeed. So at least from the above we know that electrolysis always involves water. Or does it? Okay, a galvanic cell, also known as a voltaic cell (Luigi Galvani, Alessandro Volta) combines two metals and an electrolyte (in Galvani’s case, a frog’s leg). Galvani and others thought the frog, or some other creature, was necessary for the current – ‘animal electricity’ became a thing for a while. Volta showed that this was not the case, though there was much argy-bargy for a while. But enough easy history, we need to tackle tough science.

Canto: So I don’t know if the currently titled hydrogen fuel cells are correctly described as alkaline fuel cells, but there are some videos, such as one by Philip Russell, describing very simple hydrogen fuel cells, driving a small fan. Russell explains the process very carefully, and I’ll go through it myself for my understanding. He has a tiny blue fuel cell connected by two tubes to two glasses of water. In one glass, hydrogen will be collected from one side of the cell, and oxygen from the other side in the other glass. He connects the fuel cell to a small solar panel via two wires, one red one black. He says that ‘to the negative side [holding the black wire] I’m going to connect to the side [of the cell] that produces hydrogen and the positive side [red] I’m going to connect to the side that produces hydrogen’. And now I’m confused. Both sides will produce hydrogen? How? What does that even mean?

Jacinta: In DC circuitry, black is conventionally negative and red positive. The difference between AC and DC may have to be explored because I think it’s relevant to all this nuevo-tech. Now, considering that Russell plugged the wires into opposite sides of the cell and said twice ‘the side that produces hydrogen’, the logical conclusion is that he made a mistake, but I can’t be sure. After all, what does he want to produce other than hydrogen?

Canto: Actually he said that one of the glasses will be collecting oxygen, so clearly he should’ve said oxygen for one of those two sides. But which one? Let’s continue with the video. So he’s connected the solar panel to the cell and he says ‘now we can collect solar energy and turn it into hydrogen and oxygen’. So the mistake hypothesis seems right, and that might have to be clarified with other videos. We plan to look at about a hundred of them, because our skulls are thick. So Russell next takes us inside the fuel cell. The outside is of blue-tinted glass or plastic. Inside we see ‘a perforated metal sheet’ (at least on one side). Apparently this is a hydrogen flow field, which ‘allows the hydrogen gas to escape from the fuel cell’. This again makes little sense to me. How did the hydrogen get in there in the first place? Hopefully all will be explained – or not. Next to, or behind this flow field is an anode consisting of a palladium catalyst. And in a fuel cell, the anode is negative.

Jacinta: According to Britannica, palladium is a type of platinum metal which makes an excellent catalyst:

Because hydrogen passes rapidly through the metal at high temperatures, heated palladium tubes impervious to other gases function as semipermeable membranes and are used to pass hydrogen in and out of closed gas systems or for hydrogen purification.

Canto: Good, so between the two electrodes is our electrolyte, consisting of a polymer electrolyte membrane (PEM) which ‘allows the transfer of the hydrogen gas and hydrogen ions’. Again this isn’t particularly enlightening but we’ll explore it later. Next to the the electrolyte membrane is the cathode (positive), and then comes the oxygen flow field, ‘which allows the oxygen to come in and escape from the fuel cell’. Again unclear.

Jacinta: It’s a start, sort of. We’ll glean what we can from this little video and supplement it from other videos and info sites. So electricity is coming into the fuel cell which breaks down the water coming from the two glass jars. I’m confused, though, about the glass jars and the tubes leading to, or from, the fuel cell. They’re filled with water (which I’m presuming is highly purified) and they’re delivering water to either side of the fuel cell, via these tubes, which are attached, in each of the glasses, to something like a suction cup, which will, it seems, have something to do with gas coming from the fuel and being sent through the tube to the bottom of the glass jars – hydrogen along one tube, oxygen along the other. So the water is presumably being depleted from the jars and the two gasses are being collected at the bottom of the jars, to judge from the look of the setup. But how are these tubes able to deliver water one way and collect gas in the other direction at the same time?

Canto: Haha and we’re only halfway through this teeny video. And we next go to a diagram which again upsets our thinking, as it shows the anode as positive, whereas Wikipedia says the anode is negative in fuel cells. It seems we’re being stumped by nomenclature. What Philip Russell is demonstrating appears to be an electrolytic cell or an electrolyser, but it’s being called a fuel cell. A website from energy-gov, linked below, has a diagram of a fuel cell/electrolyser very similar to Russell’s. They call it an electrolyser. They’re conspiring to confuse us!

Illustration of a PEM electrolyzer

 

Jacinta: Anyway, Russell explains his thingummmy, and I quote: ‘We have, in the middle, this polymer electrolyte membrane [PEM] surrounded by the electrodes, and on either side, the anode and cathodes[!]. When we start, water enters through the anode, and here, when it reaches the cathode and anode [!] things start to happen. The water is broken down into hydrogen ions by the electrons in the battery, and this then produces oxygen gas. The hydrogen ions travel across/through the PEM where they are reacted with electrons and this forms hydrogen gas which escapes through to the cathode side of the fuel cell’.

Canto: Yes, clear as far as it goes. So this is electrolysis he’s talking about isn’t it? Is it really this simple? Probably not, in scaled up versions. Anyway, Russell finishes up by disconnecting his wires from the solar panel and connecting them to a small fan, which immediately starts to function. The fuel cell has reversed, according to Russell, and is producing electricity from H2 and O2. 

Jacinta: Yes, the way he presents it, it’s all very simple. But I don’t think so. We’ve scratched the surface of this technology, and informed ourselves in very small part, but there’s a long way to go. We need to struggle on, in our brave, heroic way.

 

References

https://www.bmw.com/en/innovation/how-hydrogen-fuel-cell-cars-work.html

https://en.wikipedia.org/wiki/Alkaline_fuel_cell

https://en.wikipedia.org/wiki/Galvanic_cell

https://www.britannica.com/science/palladium-chemical-element

https://www.energy.gov/eere/fuelcells/hydrogen-production-electrolysis

 

Written by stewart henderson

July 3, 2021 at 11:50 am