🧪 Solutions 110 | What your raincoat and a hydrogen fuel cell have in common

A good nonstick pan can be your best friend in the kitchen. Frying an egg, getting crunchy skin on a piece of fish or making a beautiful pancake, it's all easier if you don't have to worry about scraping food off the skillet. But nonstick cookware has only been around since the 1950s. It was originally made possible by an accidental discovery in the late 1930s when chemists created a polymer called PTFE or Poly tetrafluoroethylene. To act sexy and water resistant, you might know it better by another name, Teflon. In 1969, a scientist attempting to stretch PTFE made a discovery. If he heated PTFE rods to high temperatures and slowly stretched them apart, they broke. But when he grabbed the two ends of a rod and gave it a fast hard yank, it expanded to 10 times its original size. This new material called EPTFE for expanded poly tetrafluoroethylene can be up to 95% air. It can be formed into all kinds of shapes, from threads and pipes to thin fabric-like membranes. Under a microscope, it looks like a dense spider web, with sinewy tendrils of polymer stretching out between thick nodes. Not only does this make it light and flexible, but it also means the air pockets and pores in the structure can be filled with other materials, allowing for a seemingly endless number of composites. It can be filled with graphite to help clean up oil spills, or combined with silicone to make medical devices and implants. It's also water resistant, strong, and inert, making it useful and outdoor gear like ski jackets and camping tents. But today, we're going to be talking about a more unusual application. EPTFE, the same material found in your raincoat, is also an integral component of hydrogen fuel cells, a potential method of powering cars that produces nothing but water as they're exhaust. I'm Alex Danes, this is Solutions, and today we're going to talk about hydrogen fuel cells, how they're powering a new generation of cars, and how a simple, strong membrane makes them possible. And we're also going to talk about some of the reasons why, despite being a clean and emission-free technology, you probably don't have a hydrogen powered car in your driveway just yet. Hydrogen fuel cells have been around for a long time, though it took a while to reach their full potential. The first fuel cell experiment was performed in 1839 by Sir William Robert Grove, though it didn't create much electricity at all. His gas battery, as he called it, had one electrode sealed in a container of oxygen and another in a container of hydrogen. And while it wasn't exactly useful, it did produce current and a visible amount of water as a byproduct. In 1959, a 20-horsepower tractor became the first fuel cell powered vehicle, and hydrogen fuel cell prototype car existed as early as 1966. Hydrogen powered vehicles hit the consumer market in 2013, and today there are just over 11,000 of them on the road in the US. But how do they work? The fuel cell cars filling up at rest stops in California, they're not just burning straight hydrogen to make energy. A fuel cell works a bit like a battery. For having fuel cell to work, you will need to convert hydrogen into proton and electrons. This is Dr. Wen Liu. She's a research scientist who works on fuel cell technology, and fuel cell technology relies on moving protons and electrons around in specific ways. Imagine that the fuel cell is a sandwich, with two pieces of bread and a big piece of meat in the middle. On one side of the sandwich is an anode or negative electrode. On the other side is a cathode or positive electrode. These are your two pieces of bread. In between is a PEM or proton exchange membrane. This is the meat of your sandwich. The PEM is made up of a sturdy matrix full of pores and an ionomer, a polymer that allows protons to flow through it, that fills those pores. It's kind of like a pimento loaf with pickles and pimento filling space between the meat. The PEM becomes a solid barrier to the hydrogen that flows over the anode side of the sandwich and the oxygen containing air that flows over the cathode. At the anode, a catalyst, usually something like platinum, splits hydrogen apart into a proton and an electron. The protons can flow through the ionomer and the PEM to the other side of the sandwich, the cathode. The electrons, however, need to take a different path. They leave the anode and go through a circuit that powers your car before reaching the cathode side of the sandwich. But now, both the proton and the electron have reached the cathode. Here they combine with oxygen flowing over that cathode to form water. So rather than the dirty exhaust flowing out of something like combustion engine, hydrogen fuel cells produce water as their end product, releasing just water vapor through the tailpipe of the car. Hydrogen and oxygen in, water and energy out. It's a pretty clean system. Now, back to those protons. There are many very important functions this fuel cell needs to carry. One of them is to transport proton through a polymer matrix. That polymer and ionomer matrix that allows the protons to flow from one side of the fuel cell sandwich to the other, our meat, remember, is called the PEM or proton exchange membrane. The PEM has to do a number of things well. It needs to be strong to last many thousands of hours of running the fuel cell. It has to be light so that the fuel cell doesn't get too heavy. And it needs to be a nerd so that it won't react with any reactive byproducts in the system. And what did we learn is strong light and a nerd? EPTFE. EPTFE play a very important role within this proton exchange membrane. It can reinforce the actual functional polymer to be very strong so that it can conduct the proton through years of operating time while it able the membrane to be seen enough proton can transport very fast. The same material that keeps your raincoat dry and helped make nonstick cookware possible is the same thing keeping automotive fuel cells working. As we mentioned before, EPTFE looks like a spider web when zoomed in close. But if we went even closer to the molecular level, PTFE is a long chain of carbons, each with two fluorines hanging to the sides. EPTFE is just that, except stretched out and expanded. It can be thick, it can be very thin, it can be very high in its density, or it can be so light that once you wave it and let it go, it can get even dancing the air. So it's a very versatile, porous film that can be used in many applications. All of those different potential properties come from exactly how you stretch the EPTFE. In the fuel cell, those porers are important because they can both hold the ionomer, the ion conducting polymer, and capture water, which is essential for creating paths for protons to travel from one side of the fuel cell to the other. I always remind myself of a wetland, like a marshland. You have water channels that are connected. You also have dry channels that are connected. So this mixed phase structure is very essential to maintain mechanical integrity and it can conduct proton in the water channels. But despite these important pores, it's important that the PEM stays sturdy and strong. As the car drives faster, drawing more power, the fuel cell will dry out slightly, cutting off some of those wet channels. This change in moisture level can cause the PEM to expand and shrink, and it has to do that over and over without breaking. So when this polymer works, it will have lots of water inside of it. It will expand in its volume. While when we're driving a car in accelerating conditions, the environment will become drier. This polymer will need to shrink. So it needs to expand and shrink, expand and shrink many hundreds of thousands of times throughout this lifetime. To do it durably, EPTFE as a mechanical reinforcement becomes very essential. What EPFE does is it can constrain the swelling of this ionic conducting polymer. As the PEM swells and shrinks over time, it can start to wear out, crack and break. But the EPTFE holds it in place, preventing that swelling and keeping it stable for longer. This means the fuel cell can power a car without breaking for years, not months. Now there is a potential downside to having a material that's so durable, and if you've heard of PTFE before, you might already be thinking about it. It could last forever. Not just longer than cars, but also the people driving them. EPTFE is part of a class of molecules called PFAS or PER and polyfluoral alcohol substances. This label encompasses more than 5,000 different chemicals, some of which can get into the environment, stay there a long time, and have been increasingly linked to health risks like cancer and adverse developmental effects. The Environmental Protection Agency recently announced a multi-year strategy for "tackling PFAS." That includes doing more research into which PFAS may pose environmental and health risks and which may not. How does this relate to fuel cell technology? Well, what we know right now is that once it's in the polymerized form used to make the membranes, EPTFE's stability, water and solubility, and inert nature means that it's unlikely to break down and release harmful molecules into the environment. And we don't have too many other options to make long-lasting fuel cells right now. Part of proton exchange membranes are still under development or not widely used. EPTFE/PEMs are currently one of the better solutions on the market to keep fuel cells running long enough to make them worthwhile and have the potential to help the environment by reducing emissions from combustion engines. In short, it's complicated. There are a number of factors to balance. Well, I think that we all realize it is important for us to look at how can we do carbon ionize our economy. Transportation such as passenger vehicles, commercial vehicles, trains or freight, they do contribute significantly to carbon emission. Utilizing fuel cell as the main power source instead of combustion engine, since the byproduct is only water, you can significantly cut the carbon emission of transportation sector. But, just like how the upstream power source for electric vehicles could still be a carbon rich source like coal or oil, the current methods we have of making hydrogen can also be pretty fossil fuel heavy. There are many ways to produce hydrogen and what are the economically feasible and clean ways to produce hydrogen. If you want to cut down the carbon emissions for the whole economy, we would really have to consider source of hydrogen, whether it's green or not. So all of these are big, challenging, mega questions that require the government industries and people to come together to solve those issues. Hydrogen fuel cells are one part of a larger equation that can get us to lower emission transportation. If, we can find clean sources of hydrogen, and build an infrastructure to support it. Now, here's the deal. Consumer hydrogen fuel cell cars have been on the road for nearly 10 years, but they're nowhere near as common as something like a battery-powered electric vehicle. There are a number of reasons for this. First, there isn't a big refueling infrastructure yet. Right now, you see gas stations everywhere. You start to see charging stations popping up, right? You don't see many fuel cell fuel stations. Well, it's a chicken lag scenario. If you don't have fuel stations, people are not going to buy cars with those hydrogens. Hydrogen fuel cell cars are also more expensive than comparable electric combustion options, and their efficiency falls right in between those two as well. More efficient than a combustion engine, but less efficient than a standard electric vehicle. So, in the future, I do think both battery, vehicle, and fuel cell vehicles would play key roles in driving down the carbon emission of the transportation section. For cars that only drive short range, can be charged every night, certainly battery vehicle would be very popular. But for things that require a very long-time operation or very fast charge time that maybe fuel cell vehicles would play a major role in the future. These long-run time fast-refuel situations are where hydrogen fuel cells may have even bigger future impacts on the transportation and industrial sector than in consumer cars. Fuel cells are great for applications with defined travel, built-in infrastructure, and a need to refuel quickly. For example, public transit like trains and buses, which run on fixed routes and know exactly where they will refuel, could be a perfect fuel cell use case. A fuel cell trained debuted on German rail lines in 2018, and a concept boat powered by the same fuel cells tucked into Toyota's Marais hit the ocean this year. Forklifts powered by fuel cells have also started filling Amazon's warehouses, places where you don't want to be running an emissions-bueing vehicle indoors, and want a fast recharge time. Hydrogen fuel cell cars may not be in everyone's driveway quite yet, and they may be just one part of a future that strives for lower carbon emissions from all parts of our economy. But we need lots of different solutions to pour ourselves out of the carbon-filled present day we've created for ourselves. I think in the next five to ten years is where you will see very competitive fuel cell vehicle options come on the market, and I even met a bat with one of our Gore technical leaders. That was in 2019, and I told him, "You bet, in five years, I'll be driving the fuel cell car to work." I think that that was if I win or take everybody out for lunch, I'd love to take everybody out for lunch too, but I also would like to win that bat. This is made with funding and featuring scientists from 3M, Ascend Performance Materials, Baker Hughes, B-I-S-F, Dow, DuPont, Proctor and Gamble, PPG, Royal DSM, Sabaq, Solve, and WL Gore and Associates, none of whom influenced any editorial decisions. Solutions is hosted by me, Dr. Alex Daneus, and produced by the American Chemical Society with charts and leisure.