If we asked you to think of a device that converts a chemical reaction into electricity, you’d probably say we were thinking of a battery. That’s true, but there is another device that does this that is both very similar and very different from a battery: the fuel cell.
In a very simple way, you can think of a fuel cell as a battery that consumes the chemicals it uses and allows you to replace those chemicals so that, as long as you have fuel, you can have electricity. However, the truth is a little more complicated than that. Batteries are energy storage devices. They run out when the energy stored in the chemicals runs out. In fact, many batteries can take electricity and reverse the chemical reaction, in effect recharging them. Fuel cells react chemicals to produce electricity. No fuel, no electricity.
Superficially, the two devices seem very similar. Like batteries, fuel cells have an anode and a cathode. They also have an electrolyte, but its purpose isn’t the same as in a conventional battery. Typically, a catalyst causes fuel to oxidize, creating positively charged ions and electrons. These ions move from the anode to the cathode, and the electrons move from the anode, through an external circuit, and then to the cathode, so electric current occurs. As a byproduct, many fuel cells produce potentially useful byproducts like water. NASA has the animation below that shows how one type of cell works.
History
Sir William Grove seems to have made the first fuel cell in 1838, publishing in The London and Edinburgh Philosophical Magazine and Journal of Science. His fuel cell used dilute acid, copper sulphate, along with sheet metal and porcelain. Today, the phosphoric acid fuel cell is similar to Grove’s design.
The Bacon fuel cell is due to Francis Thomas Bacon and uses alkaline fuel. Modern versions of this are in use today by NASA and others. Although Bacon’s fuel cell could produce 5 kW, it was General Electric in 1955 that started creating larger units. GE chemists developed an ion exchange membrane that included a platinum catalyst. Named after the developers, the “Grubb-Niedrach” fuel cell flew in Gemini space capsules. By 1959, a fuel cell tractor prototype was running, as well as a welding machine powered by a Bacon cell.
One of the reasons spacecraft often use fuel cells is that many cells take hydrogen and oxygen as fuel and put out electricity and water. There are already gas tanks available, and you can always use water.
Types of Fuel Cells
Not all fuel cells use the same fuel or produce the same byproducts. At the anode, a catalyst ionizes the fuel, which produces a positive ion and a free electron. The electrolyte, often a membrane, can pass ions, but not the electrons. That way, the ions move towards the cathode, but the electrons have to find another way — through the load — to get to the cathode. When they meet again, a reaction with more fuel and a catalyst produces the byproduct: hydrogen and oxygen form water.
Most common cells use hydrogen and oxygen with an anode catalyst of platinum and a cathode catalyst of nickel. The voltage output per cell is often less than a volt. However, some fuel cells use hydrocarbons. Diesel, methanol, and other hydrocarbons can produce electricity and carbon dioxide as a byproduct, along with water. You can even use some unusual organic inputs, although to be fair, those are microbial fuel cells.
Common types include:
Alkaline – The Bacon cell was a fixture in space capsules, using carbon electrodes, a catalyst, and a hydroxide electrolyte.
Solid acid – These use a solid acid material as electrolyte. The material is heated to increase conductivity.
Phosphoric acid – Another acid-based technology that operates at hotter temperatures.
Molten carbonate – These work at high temperatures using lithium potassium carbonate as an electrolyte.
Solid oxide – Another high temperature that uses zirconia ceramic as the electrolyte.
In addition to technology, you can consider some fuel cells as stationary — typically producing a lot of power for consumption by some power grid — or mobile.
Using fuel cells in stationary applications is attractive partly because they have no moving parts. However, you need a way to fuel it and — if you want efficiency — you need a way to harness the waste heat produced. It is possible, for example, to use solar power to turn water into gas and then use that gas to feed a fuel cell. It is possible to use the heat directly or to convert it to electricity in a more conventional way.
Space
Fuel cells have a long history in space. You can see how alkaline Bacon cells were used in early fuel cells in the video below.
Very early fuel cells — starting with Gemini in 1962 — used a proton exchange membrane. However, in 1967, NASA started using Nafion from DuPont, which was improved over the old membranes.
However, alkaline cells had vastly improved power density, and from Apollo on, these cells, using a potassium hydroxide electrolyte, were standard issue.
Even the Shuttle had fuel cells. Russian spacecraft also had fuel cells, starting with a liquid oxygen-hydrogen cell used on the Soviet Lunar Orbital Spacecraft (LOK).
The shuttle’s power plant measured 14 x 15 x 45 inches and weighed 260 pounds. They were installed under the payload bay, just aft of the crew compartment. They drew cryogenic gases from nearby tanks and could provide 12 kW continuously, and up to 16 kW. However, they typically were taxed at about 50% capacity. Each orbiter’s power plant contained 96 individual cells connected to achieve a 28-volt output.
Going Mobile
There have been attempts to make fuel cell cars, but with the difficulty of delivering, storing, and transporting hydrogen, there has been resistance. The Toyota Mirai, for example, costs $57,000, yet owners sued because they couldn’t obtain hydrogen. Some buses use fuel cells, and a small number of trains (including the one mentioned in the video below).
Surprisingly, there is a market for forklifts using fuel cells. The clean output makes them ideal for indoor operation. Batteries? They take longer to charge and don’t work well in the cold. Fuel cells don’t mind the cold, and you can top them off in three minutes.
There have been attempts to put fuel cells into any vehicle you can imagine. Airplanes, motorcycles, and boats sporting fuel cells have all made the rounds.
Can You DIY?
We have seen a few fuel cell projects, but they all seem to vanish over time. In theory, it shouldn’t be that hard, unless you demand commercial efficiency. However, it can be done, as you can see in the video below. If you make a fuel cell, be sure to send us a tip so we can spread the word.
This articles is written by : Nermeen Nabil Khear Abdelmalak
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