How does a fuel cell work?

The concept of a fuel cell was demonstrated in the early nineteenth century by a number of scientists, including Humphry Davy and Christian Friedrich Schönbein. William Grove, a chemist, physicist and lawyer, is generally credited with inventing the fuel cell in 1839.

Rather than relying on combustion to drive pistons and a mechanical driveline, a fuel cell uses electro-chemistry to generate electricity.

That electrical current can be used directly, to power a motor, but is generally fed into a battery bank that then powers a motor or motors.

The battery bank is used to supplement fuel-cell output during acceleration or hill-climbing and also to absorb and store ‘regenerative’ electrical power produced by the electric motor when the truck is running downhill and braking.

Although a fuel cell uses highly flammable hydrogen gas as its fuel, in the presence of air which contains mainly nitrogen and oxygen, there is no hot combustion in a fuel cell, so no nitrogen oxides are formed. Because there is no carbon in the fuel there is no hydrocarbon, carbon monoxide or carbon dioxide emitted either.

A fuel cell generates no emissions, other than water vapour and needs no after-treatment of its exhaust.

Military interest in fuel cells began many years ago and not because of pollution reduction. The attraction of a fuel cell is its lack of ‘heat signature’, making fuel cell generators and vehicle motors less likely to show up on thermal imaging, or infra-red cameras.

The US military already uses fuel-cell electricity generators in large numbers and has been evaluating vehicle propulsion fuel cells since 2016.

Those who want the full electro-chemical explanation of fuel-cell operation have several scientific sources they can check out. However, for those brought up a rough understanding of the ‘suck-squeeze-bang-blow’ operation of a four-stroke diesel engine, suffice to say that hydrogen enters one side of the fuel-cell ‘stack’ and air enters the other. The result, after electrical-ion-transfer, is electric current flowing from the fuel cell.

Here’s a diagram of the fuel-cell principle:

Of course, the real world is somewhat more complicated than this simple atmospheric-pressure fuel cell suggests. Production fuel cells gain efficiency by having moist air, rather than dry air, enter the stack and there’s also the need to circulate hydrogen through the stack under some pressure.

A cooling system maintains optimum temperature and, of course, there are several electronic control modules involved. A production fuel cell diagram shows more complexity and a real-word cell doesn’t look entirely different from a combustion engine, especially given it has an electrically-driven turbo for air induction.

The typical fuel cell being evaluated in early production FCEV trucks around the world has an output of 110kW to 150kW and weighs around 230kg. These fuel cells are dimensioned to fit in the engine bays of trucks that were originally designed for diesel power – single cells for small and medium trucks and twin cells for heavies.

Together with the Volvo Group, Daimler Truck is committed to hydrogen-based fuel cells. Both companies founded their joint venture Cellcentric in 2021, with the goal of becoming one of the world's leading manufacturers of fuel-cell systems. To this end, the company plans to set up one of the largest series production facilities in Europe, starting in 2025.

Daimler Truck is developing Mercedes-Benz FCEV heavy trucks for release in the second half of the 2020s and the company acknowledges that liquid hydrogen fuel will have to be available, to maximise vehicle range. With twin tanks, carrying 80kg of ‘sub-cooled’ liquid hydrogen, the company expects 1000-plus kilometre range.

With less-energy-dense gaseous hydrogen in its tanks an FCEV truck would have no more range than a battery-electric (BEV) truck and that negates one of the FCEVs perceived advantages over a BEV.

Tesla developer, Elon Musk, has referred to the fuel cell as a ‘fool cell’, because he reckons the electricity consumed in the production of hydrogen gas should be used directly in a battery-electric vehicle, rather than being stored, transported, stored again and then pumped into a fuel cell electric vehicle (FCEV). In terms of efficiency, he’s absolutely right, but there are other issues involved.

For a start, in the case of heavy BEVs, we’re talking about high-current, megawatt charging, to bring the ‘refuelling’ time down to well under an hour. The electrical supply infrastructure for that is massive, especially if several B-Double BEVs need to be recharged at the same time.

Also, given that a BEV heavy truck will have a range of only around 500km, at the 2022 level of battery technology, there would need to be twice as many BEV recharging stations as 1000km-range FCEV charging stations.

In contrast, an FCEV B-Double can be refilled with hydrogen in 20 minutes, from storage tanks in a filling station that’s an expanded version of today’s diesel station.

However, there’s still considerable infrastructure required for hydrogen production, liquefaction, transport and storage. Also, if hydrogen is produced from a hydrocarbon such as natural gas, there is carbon dioxide pollution at the source.

It’s important to note the difference between gaseous hydrogen refilling and liquid hydrogen refilling. There are already several hundred hydrogen gas refueling stations around the world and more are coming on stream every week.

However, there’s not a yet a single commercial liquid hydrogen refuelling station for vehicles, although Daimler Truck and Linde Gas are building an ‘sLH2’ prototype station, scheduled to open in 2023.

Mercedes- Benz Trucks and its partners are planning for a high level of transparency and openness around the relevant interfaces of the jointly-developed sLH2 technology. The goal is to collaborate with as many additional companies and associations as possible, to develop refuelling and vehicle technologies to a new new liquid-hydrogen standard and thereby establish a global mass-market for the process.

Related reading:
1000km hydrogen truck?
'Hydrogen highway' to link eastern states
Mercedes-Benz's hydrogen truck options
Hyundai's hydrogen heavy-duty trucks to hit the road in Germany

When it comes to infrastructure for hydrogen filling stations along important transport routes in Europe, Daimler Truck is planning to work with Shell, BP and TotalEnergies. Daimler Truck is also a shareholder in hydrogen filling station operator H2 Mobility Deutschland.

In addition, Daimler Truck, IVECO, Linde, OMV, Shell, TotalEnergies and the Volvo Group have committed to work together to help create the conditions for the mass-market roll-out of hydrogen trucks in Europe as part of the H2Accelerate (H2A) interest group.

Australian hydrogen refueling infrastructure is likely to be several years behind European and US developments.

There has been much written about the dangers of hydrogen transport and storage, and memories of the pre-WWII Hindenburg airship disaster revived. However, every fuel handling and refuelling operation involves hazards.

It’s quite likely that if we tried to implement vehicle refuelling as it’s now practised around the world in roadside service stations – done by all of us untrained, unskilled people – it wouldn’t pass current OH&S regulations!

In contrast to liquid hydrocarbon fuels and LPG, hydrogen is much lighter than air and doesn’t ‘pool’ if leaked. It rapidly dissipates upwards.

At present, most hydrogen is produced in plants, then transported and stored, but it’s possible in the future that hydrogen filling stations will simply electrolyse mains water – extracting the hydrogen end emitting oxygen – in real time.

The technology isn’t far away and several streams are being pursued, including the use of sunlight to split water and ‘particle spin’ to eliminate the by-production of electrode-poisoning hydrogen peroxide during electrolysis.

Another possible means of hydrogen storage is chemically bonded hydrogen. In June 2008 we came across an article in the Royal Society of Chemistry journal Energy & Environmental Science. The story reported that chemists in the US had developed a simple reaction to make ammonia borane – a hydrogen-dense powder.

We’d almost forgotten about ‘hydrogen powder’ until Deakin University researchers made a breakthrough in July 2022. The new process was first described by nanotechnology researchers from Deakin’s Institute for Frontier Materials (IFM) in the journal, Materials Today.

“Right now, Australia is experiencing an unprecedented gas crisis and needs an urgent solution,” Alfred Deakin Professor Ying (Ian) Chen, IFM’s Chair of Nanotechnology, said.

“More efficient use of cleaner gaseous fuels, such as hydrogen, is an alternative approach to reduce carbon emissions and slow global warming.”

The special ingredient in the Deakin Uni process is boron nitride powder, which has a large amount of surface area for gas adsorption.

“The boron nitride powder can be re-used multiple times to carry out the same gas separation and storage process again and again,” said Deakin’s Dr Mateti.

“Boron nitride is classified as a level-0 chemical that is deemed perfectly safe to have in your house – meaning you could store hydrogen anywhere and use it whenever it’s needed,” he said.

At trucksales.com.au we’ll keep updating hydrogen-fuel developments as they occur. We’re certainly living in ‘interesting times.’