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What are fuel cells, which types exist and how do they work?


At Umicore, we believe fuel cell electric vehicles are part of the way forward for cleaner mobility. That is why we have been working hard on developing Proton Exchange Membrane (PEM) fuel cell catalysts, doing our part to lead the charge. Now, we want to do more: we also want to spread the word about their technology benefits in a series of 6 episodes on fuel cells.

In episode 1: What are fuel cells, which types exist and how do they work?

What are fuel cells?

Fuel cells are devices that generate electricity through electrochemical redox reactions, not combustion. In short, they convert the chemical energy of fuels, such as hydrogen or methane, directly into electrical energy by combining them with oxygen. 

Because the chemical energy does not need to be converted into thermal energy and mechanical energy first, fuel cells are extremely efficient. Besides minimizing energy losses, fuel cells are also less polluting than classic combustion: carbon emissions are much lower. If green hydrogen – hydrogen created using renewable energy sources - is fueling the cell, they only emit vapor and warm air. 

On top of that, fuel cells are allrounders. They can provide power for systems as large as utility power stations and as small as a laptops. Consequently, fuel cells are used in a wide range of sectors, including marine, aviation and railway. At Umicore, we are focusing on their added value for the automotive industry.

Which types of fuel cells exist? 

There are several types of fuel cells, differentiated by the type of electrolyte separating the fuel from the oxygen. This classification determines the kind of electro-chemical reactions that take place in the cell, the required catalysts, the operating temperature, the required fuel, and other factors. 

These are 4 common categories of fuel cells:

  • Proton Exchange Membrane (PEM) fuel cells
  • Alkaline fuel cells
  • Solid oxide fuel cells
  • Phosphoric acid fuel cells

The characteristics each category entails determine which type of application they’re most suitable for. For example, PEM fuel cells are particularly interesting for the automotive industry, since they deliver high power density, operate at relatively low temperatures, and are lighter and more compact than other fuel cells.

What's the difference between fuel cells and batteries? 

The redox reactions that take place in fuel cells lead people to think that they are not that different from batteries. Although the similarities in how both devices work are undeniable, there is also a very clear distinction.

Batteries are used to store energy. You fill them up with electrical energy, which you then consume. If they are rechargeable, you can fill them up again and repeat the process. 

Fuel cells produce energy and don’t run down or need recharging. They produce electricity as long as fuel is available. In other words, the reagents are not stored in a closed system (like batteries), but can be continuously supplied.

How do fuel cells work?

Every fuel cell consists of two electrodes – a negative electrode (or anode) and a positive electrode (or cathode) – which are wrapped around an electrolyte. The general principle for this setup: a fuel is fed to the anode, while oxygen is fed to the cathode.

Let’s take the example of PEM fuel cells to illustrate the process:

  1. Hydrogen molecules enter the anode

  2. The anode catalyst separates the hydrogen molecules into protons and electrons

  3. The protons and electrons travel to the cathode via different paths

  4. The protons pass through the membrane, where they unite with oxygen and the electrons to produce water and heat

  5. The electrons go through an external circuit, generating electricity

Types of PEM fuel cell catalysts

Depending on the design of the fuel cell, different catalysts may be required:

  • Platinum nanoparticles supported on carbon black: the most common catalysts.
  • Platinum alloy catalysts: platinum is additionally alloyed with nickel or cobalt to modify the electric properties improving the catalytic activity.
  • Iridium-oxide based catalysts: these catalysts are used as protective additives in the anode electrode, which they prevent from being damaged in critical operating conditions, such as fast load changes or system start-ups at low temperatures.

Why work with Umicore's fuel cell catalysts: 

  1. Umicore has over 30 years of experience in precious metals and fuel cell development, focusing on PEM fuel cell catalysts. 
  2. We have a strong R&D department and produce fuel cell PEM catalyst on a large industrial scale
  3. We have qualified our catalysts at more than 10 OEMs and our catalyst technology is being considered as a benchmark in the industry.

Eager to find out more about Umicore’s fuel cell catalyst activities?

Discover how we can accelerate your fuel cell technology