Hydrogen motorcycles: MCN explores the wonder gas billed as the green way to power the planet

We’re constantly promised that better, lighter, faster-charging batteries are just over a horizon as a viable alternative to combustion engines in motorcycles, but what about hydrogen?

• Latest news: Kawasaki test hydrogen H2 SX at Suzuka ciruit

Genuinely high-performance, long-range battery-powered bikes remain a pipedream for most – leading Japanese giants Yamaha and Kawasaki to join forces on a hydrogen-fuelled combustion engine project, and tying in with car giant Toyota.

Meanwhile, Honda and Suzuki also have long histories with hydrogen fuel cell electric vehicles, and Honda have partnered with General Motors’s subsidiary Isuzu to develop a next-generation fuel cell system for a truck due in 2027.

Pooling their expertise, the Japanese ‘Big Four’ have now joined forces to develop ‘Hydrogen Small Mobility Engines’ for motorcycles in a grouping dubbed ‘HySE’. But how does the technology work, and how difficult is it to achieve?

While both hydrogen combustion engines and fuel cells use on-board hydrogen tanks, allowing rapid refuelling as a huge advantage over batteries, and both have emissions that are almost entirely harmless water vapour, the two technologies couldn’t be further apart.

Hydrogen combustion engines

Hydrogen combustion engines look familiar to all of us: they’re essentially the same as petrol-powered four-strokes, but turbo or supercharging and direct fuel injection are vital. Petrol engines need an air/fuel ratio of 14.7:1, hydrogen engines need a 34:1 air/fuel ratio and can run at up to 180:1, with higher ratios helping ensure a clean, complete burn.

So, even though hydrogen is nearly three times as power-dense as petrol, you need much more air in the cylinder to get equivalent performance.

The solution to this problem is to compress the air with a supercharger before it enters the cylinder, then to use direct fuel injection to add the hydrogen after the inlet valves have closed.

Hydrogen fuel cells

A hydrogen fuel cell is more akin to a battery. The fuel cell turns hydrogen and air into electricity, which is then fed to a conventional electric motor. A fuel cell has an anode (negative electrode) and cathode (positive electrode) separated by an electrolyte, just like you would see in a battery.

Hydrogen is fed to the anode, where it meets a catalyst that splits its protons and electrons. Air goes to the cathode where it hits another catalyst, causing an oxygen reduction reaction with those protons and electrons to form water as an end product.

The protons can get through the electrolyte (called the proton exchange membrane) to the cathode, but the electrons have to travel through an external circuit, creating an electric current. For most purposes, including bikes, several of these fuel cells are layered together to form a fuel cell stack.

The pros and cons of using hydrogen to power vehicles

Hydrogen-powered combustion engines have the benefit that they convert the fuel and air directly into heat and motion, without the need for a separate electric motor, and they can be manufactured using similar techniques and materials as petrol engines, leading to huge savings in the supply chain. They can also run on relatively impure hydrogen while fuel cells will be contaminated, causing expensive damage, if the hydrogen that is fed into them isn’t completely pure.

On the downside, they’re less efficient – around 40-45% of the energy in the hydrogen is turned into power in a combustion engine, while fuel cells can be up to 60% efficient.

They also emit some harmful polluting gasses, such as NOx, despite being carbon-neutral, while fuel cells emit only heat and water.

The challenges facing hydrogen powered motorbikes

Although hydrogen has the potential to allow carbon-neutral power, it’s still hamstrung by problems. Getting it is one of them.

It can be derived from water via electrolysis, but you need clean electricity to do it without pollution. It can also be separated from natural gas or created by heating coal into a gas, but these solutions create carbon emissions of their own.

Transporting it is also fraught, requiring extremely high pressures and cryogenic temperatures to get into tankers, while the small hydrogen molecules mean pipelines are prone to leaks.

Once it reaches your bike, the problems don’t end. A typical 15-litres tank of petrol weighs around 12kg. Hydrogen is nearly three times as energy dense, so you could get a similar amount of power/range from about 4kg, but at atmospheric pressure 4kg of hydrogen would fill 44,000 litres of space. That would be a cube around 3.5 metres along each edge.

To address this problem, Kawasaki favour the idea of pre-filled, swappable hydrogen canisters rather than a single high-pressure tank but that still requires large panniers full of fuel as seen on their concept drawings.

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Hydrogen filling stations

Another drawback with hydrogen is a lack of refuelling infrastructure, but tech giants Bosch have big plans in place for that issue, too, 4000 filling stations in the works by 2030.

Bosch, which supplies a vast swathe of the motorcycle industry with components – notably electronics and ABS – are already leading the way when it comes to green credentials. The firm became carbon-neutral back in 2020, and already has its own electrolyser to produce green hydrogen at its ‘Industry 4.0’ plant in Homberg, Germany.  

The firm intends to invest nearly 500 million euros into electrolysis by 2030 – by which time it expects the market for electrolyser components to be worth 14 billion euros – and wants to have its hydrogen generation systems on the market by 2025.