Is hydrogen key to accelerating the road to zero?

By Professor Sam Akehurst, IAAPS Deputy Academic Director.

The automotive industry is facing unprecedented change to meet zero CO2 emissions regulations by 2050, ideally earlier. But the transportation sector is hard to decarbonise due to the need for high power density and high energy density energy sources on the vehicles. Effectively, governments are mandating electrification as the chosen technology solution to address the challenge. However, this may not be the only solution. If indeed rapid decarbonisation is the overarching goal, then we must look at other, parallel alternatives and consider a holistic, mixed technology approach, especially in transport sectors which are particularly hard to electrify, such as aviation, marine, heavy-duty haulage and off-highway. Hydrogen, ammonia and net zero replacement fuels must be considered as appropriate solutions and part of a diversified strategy.

Challenges around electric vehicle adoption

The current challenges around electric vehicle adoption are well documented, dominated not least by the time it will take to change the existing fleet of traditionally fuelled cars. Even if we all started buying electric cars now, the historical fleet of ICE powered vehicles is significant and will take many years to disappear. The UK government has announced a ban of the ICE by 2030. This will be done in two stages; firstly, a ban on conventional ICE without hybridisation by 2030, followed by hybrids by 2035. To achieve this transition to a zero CO2 economy, we need alternative drop-in replacement fuels that are carbon neutral and will offer quick decarbonisation in both existing and future fleets.

Furthermore, there are multiple challenges around the cost of adoption: significant investment in infrastructure is needed; batteries are still expensive relative to conventional powertrains, and there are legitimate concerns around supply constraints, production volumes and resources. In addition, there is the question of consumer acceptance. While some people are happy to adopt electric vehicles, the vast majority are still reluctant due to issues around purchase price and ‘perceived’ range anxiety.

We also need to invest in a greener grid. There’s no point charging all these electric vehicles with a highly polluting, highly CO2 intensive grid. We need more renewables, and while these are excellent solutions and we are moving in the right direction, these, too, cause significant diversity of grid supply.

The question remains: How do we support the baseload? Are governments investing in things like nuclear power stations and other solutions to manage the baseload when wind energy and solar energy are not delivering? Global solar capacity and therefore power generation is inconsistent and vastly depends on geographical location and factors such as cloud cover, which can have a considerable adverse effect. It’s a similar story with global wind generation capacity – it is evident that areas of high generation are dominated by coastal areas, and there is very limited capacity inland. So, we need backfill solutions for when not enough energy can be generated from these sources.

One option is clearly green hydrogen. This is hydrogen manufactured from electrolysis, so using the electricity spare in the grid, to electrolyse water and generate the hydrogen. This is water resource intensive, and we have to be careful about its application, but we can then store that hydrogen under pressure in its gas form, or we can convert it, either into e-fuels by attaching carbon atoms to it, or into ammonia, by connecting nitrogen atoms to it. Both gaseous and liquid fuels have one key advantage: their viable long term seasonal storage capability, both in gaseous and liquid state, and they can also be transported to point of use and can be applied in conventional transport methods or pumped along pipelines. They also have high specific gravimetric and volumetric energy density that we require for road transport, aviation and other transport sectors.  

Hydrogen fuelled ICEs

It is relatively straight forward to convert an existing gasoline or diesel ICE into a hydrogen fuelled ICE in a short time frame and with relatively simple technology. If, however, we want to optimise it to be the best hydrogen engine we can, with good efficiency, then there are some research questions that need to be answered. But they are not relying on scientific breakthroughs as such, rather on good engineering processes. Therefore, potentially this is a good starting point, because these engines may be dual fuelled, which would allow us to transition from conventional fuels to H2 as the infrastructure develops. The clear benefit is that if hydrogen is unavailable, the vehicle can still run on conventional fuel. In terms of performance, a direct injected hydrogen fuelled engine is competitive with existing engine technologies. However, one of the downsides of hydrogen is that on vehicles storage is still a challenge; normally it is stored at 300-700bar. Although one solution we are actively researching at IAAPS is hydrogen from ammonia, where ammonia itself offers a potential improved storage solution and waste heat energy may be used to reform the ammonia to hydrogen before combustion.

Hydrogen fuelled IC engines can be a low cost compared to fuel cell technology, and can have good efficiency, especially if they are deployed as an auxiliary power unit or dedicated hybrid engine. There is also a lack of cold start issues with hydrogen fuelled engines relative to fuel cell technology and an internal combustion engine can work on a lower purity of hydrogen than that required by a fuel cell. Fuel cells are also liable to air contamination, which is not a problem for H2ICE. Our research has shown that hydrogen powered ICEs can be near zero emissions capable due to the lean limit of combustion that hydrogen fuelling enables. They also build on decades of experience of ICE development and low cost of production, so we can adapt existing factories to manufacture hydrogen engines while fuel cell technology matures.

Conclusion

Hydrogen, and other e-fuels for that matter, have specific merits. Use of these fuels in internal combustion applications can not only support and accelerate the decarbonisation of transport, but also act as an important pathway to further fuel cell adoption as the technology and price evolves. Rather than mandating a single solution, let’s use all the technologies available simultaneously to achieve the goal of a net zero economy.

Multiple solutions applied in parallel will get us there faster and will continue to be at the forefront of our work at IAAPS. If you would like to discuss any of the research or technologies being developed at IAAPS, please feel free to drop me a line on enssa@bath.ac.uk.

Photo of Professor Sam Akehurst

Professor Sam Akehurst, IAAPS Deputy Academic Director