The fuel cell technology behind Toyota’s Mirai has been in development for two decades. The car is built on a solid hybrid platform and years of know-how Toyota has built up with the hybrid Prius. ‘This car is exactly like a Prius, except that you are replacing the Prius engine with a fuel cell [system],’ says Julien Roussel, Mirai project manager, Europe.
The Mirai’s fuel cell is a PEM (proton-exchange membrane)-type, consisting of around 300 separate electrochemical cells stacked like CDs, and runs below 100°C. Hydrogen passes through to each anode where it is oxidised by a catalyst to hydrogen ions and the electrons released in the process follow a circuit to generate electrical power. The hydrogen ions pass across an electrolyte – the PEM membrane – to the cathode where they combine with oxygen to form water as the only byproduct.
The fuel cell generates 114kW (144 horse power) of electric power with an extra boost available for acceleration from a nickel hydride battery; the battery also collects energy from regenerative breaking and will power the car in city traffic. ‘If you are at a crawl, there is no need to start your fuel cell. You can just get the 30 or 40 horse power you need from the battery,’ explains Roussel.
A real challenge of the technology has been cost, but Toyota has driven this down significantly. ‘The fuel cell itself has been made dramatically more compact. Now 114kW of power can be packed into 37L,’ says Roussel. ‘Our previous model in 2008 had 110kW in 64L.’ Toyota has also introduced new catalyst structures, cutting the amount of platinum required by a factor of three; improved the electrolyte so it can harvest more voltage per cell; and made the materials between cells thinner and lighter.
The Mirai is fuelled by 5kg of hydrogen, giving the sedan a range of 300 miles and thus offering a real alternative to petrol or diesel cars. And unlike pure electric vehicles, which can take 8 hours to charge, these hydrogen-fuelled cars can be topped up in 3-5 minutes.
The hydrogen gas is stored under 700 atmospheres in two 60L tanks, which are made from a carbon-fibre composite that is chemically similar to Kevlar; the tanks weigh around 100kg. ‘The tanks are still too expensive,’ says Roussel, ’but on the other hand, critics said this would be the showstopper so we have proved them wrong.’
An average family petrol/diesel car has a fuel tank of 70L, whereas the Mirai holds 120L, reflecting the favourable energy density of the former over compressed hydrogen. But hydrogen fuel cells have their own powerful attractions. Not only will these cars be more efficient than those powered by internal combustion engines but they promise zero emissions. Moreover, the hydrogen could be obtained from water using natural renewable energy sources like solar and wind power, or from man-made byproducts such as sewage sludge or agricultural waste
‘You wouldn’t want to bet against Toyota. This is a serious attempt to introduce a new technology,’ says Alan Lloyd, former secretary of the Environmental Protection Agency (EPA) in California, US, and a current member of the Hydrogen and Fuel Cell Advisory Committee at the US Department of Energy. The company has, after all, a proven track record – 5m Prius have been sold since their launch in the mid-1990s.
Not surprisingly, Toyota is not alone in gearing towards hydrogen. Hyundai and Honda have fuel cell vehicles close to market, as have Ford, Mercedes and Nissan, and even sceptics like Volkswagen seem to have had a change of heart. The firm unveiled a fuel cell powered Golf at the Los Angeles Motor Show in November 2014.
But fuel cells cars are still very expensive. In Europe, the Mirai will retail at around €60,000 plus or minus added taxes, incentives and tax breaks. In Japan, they are selling at ¥7m (ca £40,000), although with a hefty government subsidy of about ¥3m.
A major obstacle for hydrogen fuel cell cars is the need for a new infrastructure for re-fuelling – unlike electric cars, you can’t plug into an existing energy network. And in the US at least, all eyes are on the state of California. ‘Everyone is waiting to see what happens here. To see if we can prove the model works,’ says Keith Malone of the California Fuel Cell Partnership, a collaboration of automakers, energy providers and government agencies.
California has eight hydrogen stations operational and expects to have 50 plus by mid-2016, allowing any road trip north to south California on hydrogen. ‘We realised that we needed a network of about 68 stations to launch the market,’ says Malone.
In 2013, the state passed a series of clean transportation laws, which included investment of over $100m for new hydrogen stations and for adding pumps to existing gas stations at a cost of $2-3m each. While many car companies have been reluctant to hand over cash for stations, Toyota and Honda announced millions of dollars in loans to station provider First Element in 2014. This followed an investment of around $27m to the provider by the California Energy Commission in the same year.
‘This has given confidence to everyone. Consumers know there will be a network, early adopters know they can go to California with their vehicles, and industrial gas producers know there will be a market here,’ says Malone.
The Mirai is expected to cruise along California’s Big Sur before it hits Europe, with 200 cars expected in the Golden State this year and 3000 by 2017. One hundred cars are marked down for Europe; Germany, Denmark and the UK are the most likely first markets, says Toyota.
UK interest
In 2014, the UK government announced funds for a network of 15 refuelling stations by the end of 2015, with £2m to upgrade around eight existing stations and £3.5m, which will be matched by industry, to fund new stations. The move was supported by the UK H2Mobility project, an industry-government partnership that has been tasked with setting out a business plan for fuel cell electric vehicles. There are 12 industry partners, but many are not UK-based, placing the UK at a disadvantage, say some.
‘The UK is probably in second place [in terms of exploitation of this technology] in Europe, behind Germany, but it is a long way back,’ explains Paul Dodds at University College London’s Energy Institute, UK. Germany is planning for around 100 stations by 2017 – from 16 today – and hosting key industries within its own H2Mobility consortium.
Dodds contrasts the UK’s tepid approach with that of the German government: ‘Half of the UK H2Mobility group are not UK companies, which makes it more difficult for the government to justify subsidising their products. The German government support has been stronger, but that is not surprising as they see this as an area of national industrial strength.’
Nonetheless, the UK does have much technical expertise in the field and is keen not to miss out on potential opportunities – there are several medium-sized companies that make the engines not only for cars but also for buses, for example. Intelligent Energy is a UK fuel cell company, part of the H2Mobility consortium, which provides PEM fuel cells to some automakers and works on a joint venture (SMILE) with Suzuki on its Burgman fuel cell motorbike. In 2011, this was the first fuel cell vehicle to achieve European Wide Vehicle Type Approval, based on environmental, safety and security standard tests, allowing the vehicle to be sold in all member states. ‘There are opportunities for the UK in terms of the supply chain and engineering for fuel cell vehicles,’ notes Chris Dudfield, director of technology and development at Intelligent Energy.
Dudfield points to a £6.3m grant from the UK’s Advanced Propulsion Centre (APC), announced in March 2015, for a hydrogen fuel cell range extender for electric light commercial vehicles in a joint £12m plus project by Intelligent Energy. In the same month, ITM Power received a grant of £2.89m to build two new hydrogen stations in London.
Robert Steinberger-Wilckens, who heads the Centre for Hydrogen and Fuel Cell Research at Birmingham University, UK, however, criticises UK funding for hydrogen fuel as being split between too many agencies, with institutions receiving occasional massive amounts of funding and then nothing for years. Policy, he says, is muddled. ‘I don’t see any sort of strategy, but perhaps that will change with a growth in understanding of the importance of fuel cells and hydrogen for securing innovation and long-term competitiveness for the UK.’
‘The lure of hydrogen vehicles for the UK,’ adds Dodds,’ is that it could improve the UK balance of payments by billions of pounds, by avoiding the import of petrol and diesel.’ There is also energy security, an issue of rising in importance for Europe given geopolitical tensions with Russia, he says.
Meanwhile, Japan – a country without adequate fossil fuel reserves and an understandable hesitancy for nuclear power – is committed to fuel cell technology, having already successfully introduced fuel cells for domestic heating (C&I, 2015, 4, 32).
‘Japan is looking at hydrogen as a driver for its economy,’ explains Lloyd. Honda and Toyota are said to be collaborating to ensure at least 6000 fuel cell cars on the road by 2020, in time for the summer Olympics, while Tokyo bureaucrats are looking for 100,000 fuel cell vehicles by 2025.
Generating green hydrogen
Today’s hydrogen is mostly made from natural gas through steam reformation. Companies like Air Liquide, Linde and small local companies are interested in supplying the new fuel, but a requirement in the US since 2006 has been that 33% of hydrogen sold through publicly funded stations has to come from renewable sources, such as electrolysing water using wind or solar power or extracting from biomass or agriculture waste. California has great potential at least, given it opened the largest solar power facility in the world in February 2015 – the 550MW Desert Sunlight solar farm.
Basic science research is now looking to a future where huge quantities of green hydrogen can be produced instead of digging up fossil fuels.
‘We need to transition from sources that make carbon dioxide to sources where we simply split seawater into hydrogen and oxygen and then combine them back in a fuel cell to get pure water and electricity,’ says Harry Gray, professor of chemistry at Caltech and director of the US National Science Foundation’s Center for Chemical Innovation (CCI) in Solar Fuels Program. He explains that there are potentially three paths to green hydrogen.
One would be to generate electricity using cheaper, more efficient photovoltaics and then use that to electrolyse water and produce hydrogen. A second way would be to design an artificial leaf to split water and evolve hydrogen and oxygen in separate photoanode and photocathode compartments. ‘You would have a membrane separating these two compartments that would conduct electrons and protons, so the device would oxidise water to oxygen at the photoanode, and conduct electrons and photons through the membrane to the photocathode, where they would be converted to hydrogen,’ explains Gray.
Another way would be to use a polymer matrix with the components embedded in it; this is much cheaper, but risks hydrogen and oxygen recombining and exploding: attractively inexpensive, but with a glaring downside’
‘The big technical challenge is to find robust systems that are made of Earth-abundant elements that are actually stable over long periods of irradiation and don’t decompose,’ Gray explains, referring to artificial photosynthesis, but he is in no doubt that a hydrogen economy is on the horizon.
‘What people don’t understand is that hydrogen is useful, not only for fuel, but for making ammonia and many other chemicals. We need to replace all the natural gas used in Haber plants now to make ammonia for fertiliser with water splitting devices. The hydrogen business is for everything. Once we have hydrogen we can combine it with carbon dioxide and carbon monoxide to make liquid fuels, so splitting water is key to so many problems.’
Anthony King is a freelance writer based in Dublin, Ireland
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