How Do Hydrogen Fuel Cells Work?

After so many successes in recent weeks, it feels like there is electricity in the air at COP26 – and on the minds of its attendees. All throughout the exhibition floors and lecture theatres, the prospects of fully-electric transport are being considered and displayed. But among the myriad questions that all of these speeches and showcases raise, one is unavoidable: how are we going to cleanly and efficiently generate all of this electricity?

Many, including Tesla, Inc. CEO Elon Musk, have been evangelical about the potentials of lithium batteries, pouring millions into mining and manufacturing operations in hopes of mastering this scarce resource. But a persistent, long-standing fringe have a different obsession. And this time, they’re after the most abundant element in the universe.

What’s the Big Idea?

In recent years, hydrogen fuel cells have proven immensely scalable and have come to be used in growing numbers of planes, trains and automobiles (if you’d like more information on this, take a look at our articles on each of these developments). For many, however, these fuel cells remain misunderstood, causing a great deal of hesitation in up-take.

Perhaps, then, it is worth going back to basics and learning the secrets of this simple but potentially world-changing technology. So, let’s start at the beginning: what’s a fuel cell?

Well, the simple answer is that it’s a particular type of component on an electrical circuit which uses a chemical reaction to produce an electrical current. It’s not a battery, which stores all that it needs internally and thus, runs out. Instead, a fuel cell receives material from outside for its chemical reaction, so it doesn’t – in principle – need to be replaced.

Now, chemical reactions are complicated, to say the least, but the basic facts in the case of fuel cells are relatively intuitive. Firstly, you have your fuel, the reactants whose electrons will produce a current in the circuit – in the case of a hydrogen fuel cell, these are hydrogen (H2) and oxygen (O2). Then, you’ve got your electrodes – two per cell, to be exact – which rob your reactants of electrons and pump them into and out of the circuit. In a hydrogen fuel cell, hydrogen enters the cell at an electrode which maintains a positive charge, thereby attracting to itself the hydrogen’s electrons and repelling its protons. The opposite happens to oxygen, which meets the cell where the electrode is negatively charged, as its electrons are repelled, and protons attracted. These repelled electrons are then pulled through the circuit towards the positively-charged electrode - it is this movement, from cathode (the negatively-charged electrode) to anode (the positively-charged electrode), which constitutes the circuit’s electrical current.

And last but certainly not least, you have your electrolyte solution in which your electrodes are submerged. It is by means of this solution that your electron-less hydrogen atoms move from cathode to anode, there to become water (H2O) with oxygen. Indeed, that’s the kicker: the singular chemical by-product of a hydrogen fuel cell is water. Not carbon dioxide, not methane – just water.

From these humble beginnings, hydrogen fuel cells get more complicated and more targeted in their application. But they retain these basic principles, which ensure that they are not only totally emission-free, but convenient and almost limitless in capacity. For just a taste of where hydrogen fuel cells might take us,  take a look at the studies collated below and read through our article on What is Sustainable Aviation Fuel (SAF)?