Buses spewing diesel fumes have long been recognised as a major cause of urban air pollution, and the increased use of “zero carbon” vehicles is an obvious means to counter it. One of the most attractive technologies to achieve that goal is fuel cells, in which hydrogen gas is passed over a platinum catalyst to react with oxygen from the atmosphere in a process that generates electricity to drive a motor and produces only water as a tailpipe emission.
There are 100 fuel-cell electric buses in operation worldwide – a number likely to triple over the next two to three years. London’s fleet of eight single-decker electric buses is due to be joined by at least 20 more over that period. In addition, this year will see trials on the city’s streets of the world’s first double-decker fuel-cell electric bus. But how do companies supplying the technologies for these developments view the situation?
A major supplier of platinum is mining company Anglo American. According to Andrew Hinkly, executive head of its platinum marketing division, two thirds of the company’s output of the metal already goes to the automotive industry. Almost all of it is used in catalytic converters that help clean up the exhaust fumes from internal combustion engines. But the company believes that the tiny proportion – perhaps 1% or 570kg – of global supply that is currently used in automotive hydrogen fuel cells represents the initial step in what could become a major market.
“The electrification of the powertrain represents a significant opportunity if it relies on fuel cells,” he says, adding that a 25-fold increase over the next five to 10 years is quite feasible.
That is a future which Anglo American is seeking to foster through external investment. Hinkly says the organisation has committed $110 million over the past three-and-a-half years, of which 50% has been invested in companies developing “new applications for precious metals”. Two thirds of that has gone directly into fuel cells, while some of the rest has gone into what he terms the supporting “value stream” – such as techniques to facilitate the bulk transport of hydrogen necessary for a distributed refuelling network.
That last point underscores Hinkly’s belief that the basic technology of fuel cells is now fairly mature and that the main impediment to their adoption lies in the creation of supporting infrastructure, most obviously for refuelling.
Hinkly says other factors are beginning to militate strongly in favour of the wider adoption of fuel-cell technologies. One that he identifies is their increasing use, particularly in the US, in a niche area – powering forklift trucks in factories and warehouses. He says this constitutes a “sweet spot” in which all the advantages fuel cells can provide – zero emissions and obviation of the need for lengthy or frequent refuelling stops – are demonstrated. It provides a microcosm of how the use of fuel cells could easily be practicable on a wider level.
Another factor relates to what Hinkly terms the “balance of plant”, the ancillary technologies that help form the complete fuel-cell propulsion system. He points out that the only one that is unique to a fuel-cell system is the on-board tank for the storage of hydrogen fuel – a task that is demanding since the fuel may well be stored as a gas at a pressure as high as 700bar – but that otherwise the technologies involved are in many cases identical to those used in hybrid and battery-powered vehicles.
Batteries are a case in point since fuel-cell vehicles will use one to support acceleration phases but other technologies include overall control and regenerative braking systems. This means that fuel-cell propulsion systems can now increasingly use proven, off-the-shelf technologies, the cost of which will be amortised by their wider use in other forms of low- or zero-carbon emission systems.
An example of that ability to use existing technologies to mitigate the problem of constructing an economical and effective means of transporting and storing hydrogen is provided by a company in which Anglo American has invested. This is Hydrogenious Technologies, which was spun-off from the University of Erlangen-Nuremburg in Germany to bring to the market an ingenious technique for hydrogen transport and storage that dispenses with any need for pressurisation of the gas up to the 50bar or so at which it is normally transported or for it to be subjected to cryogenic freezing.
Instead, as chief executive Dr Daniel Teichmann explains, the company is offering a “chemical” method called Liquid Organic Hydrogen Carriers in which the gas is made to form a compound with a carrier liquid through a process that involves using platinum as one of a number of catalyst materials. The resulting liquid can be transported “just as easily as if it were a conventional liquid fuel” such as diesel oil.
The liquid used in the process, he explains, is a commercially available toluene-based product marketed under the name Marlotherm. It is, he says, “non-toxic and non-explosive” and can be transported using existing tanker systems. In the event of a spillage and exposure to the atmosphere the compound remains stable.
Precise details of how the initial hydrogenisation process and its reversal at the point of use work remain confidential, but it does not require a sizeable installation. Instead, Teichmann says, a “container-sized” package of hardware will suffice, which at the front-end of the whole cycle will have to be co-located with the plant for producing the hydrogen, though again that is a standard industrial process.
He says an installation capable of releasing “a few hundred kilograms” of hydrogen per day – such as for an urban refuelling station for fuel-cell cars – might cost
“¤0.5 million”.
The interim economics – those governing the transport of the hydrogen from the point of hydrogenisation to the point of use – are also attractive despite the fact that they involve transporting the seemingly much heavier load of a liquid rather than a gas, even one that is highly compressed. Teichmann explains that the containers required to transport pressurised gas are much heavier than those required to carry the unpressurised liquid and that in practice the two factors cancel each other out.
For any given volume, he adds, the Hydrogenious technique can store five times as much hydrogen. According to the company’s figures 57kg of hydrogen can be stored in 1m3 of the carrier liquid, which would provide 1.9MWh of energy. Finally, after the hydrogen has been extracted the carrier liquid can be returned to the source location and used again.
Meanwhile one manufacturer of fuel cells is Ballard Power Systems, which makes the units used in those London buses in British Columbia in Canada. According to marketing director Nicolas Pocard, the company manufactures 8,000 stacks a year. Each stack comprises 50-150 cells, each of which is built around a core membrane electrode assembly (MEA), having a total power output in the range 20-200kW depending on the final use. A bus, he says, might typically employ a module comprising a number of stacks with a total power output of 80-100kW.
Pocard says the major focus now is on cost reduction, not least through minimising the use of expensive materials such as platinum. He says Ballard has achieved a “drastic” reduction in the use of the material in its products, although he will not give a precise figure. He does say that the cost to a user of a complete module is at least 50% less now than it was five years ago.
Another key benchmark is that of durability – how long the MEAs will perform reliably. Pocard says that five years ago 10,000 hours would have been a reasonable expectation for the company’s products. But that has already been at least doubled, with some of the units in London buses having clocked up “20,000 hours without changing the stack”.
He adds that the cost of renewing the MEAs so that the stack can continue in service has also gone down from the 70-80% of the initial outlay that was the case a few years ago to less than 50% now. Another benefit of fuel cells comes into play in these circumstances – their high recyclability and the fact that they contain no toxic materials. So the optimistic projections for the uptake of fuel-cell powertrains seem well-founded.