REALITY BECKONS

Are we any closer to fuel cell commercialisation? And if so,
how close?

After years of reporting on the promise of fuel cells, it seems we could soon be giving news of their commercial launch and everyday use. Nowhere is that day nearer than in the micro fuel cell sector, as George Marsh reports.

Delegates at the recent fuel cells in paradise Fuel Cell Seminar in Honolulu, Hawaii – which marked the 30th anniversary of this now annual event – had their attention drawn to an innocuous-looking 1000 foot (300 m) long roll of transparent film material displayed by California-based PolyFuel. Far from innocuous, however, this roll was something special – a new hydrocarbon-based membrane material, continuously producible as a thin film, that brings closer the era of fuel
cell commercialisation.

Jim Balcom, PolyFuel’s president, is predicting that cells incorporating the material could be out in the marketplace within 18 months. And he subsequently told FC Focus, “we have developed a material architecture that offers far greater flexibility than fluorocarbon, the present industry standard [DuPont’s Nafion being the best known example], which has been around since the 1960s and has changed little. Our starting point is a hydrocarbon backbone on which you can locate the various functional and conducting groups etc. where you want, in order to optimise the membrane material to particular application needs. We use similar sulphonate conducting groups [to the industry standard competitor], but there the similarity ends.”

Given the ability to manipulate its membrane microstructure, PolyFuel was able to explore almost 200 architectural variations before alighting on a candidate for final development.

Although different variants of the material hold promise for stationary and automotive applications in the future, explains Balcom, the formulation chosen was judged to be best suited to the needs of the direct methanol fuel cell (DMFC), the type of fuel cell likely to achieve commercial status first.

PolyFuel’s novel and proprietary hydrocarbon material emerged from work carried out at the Stanford Research Institute, an offshoot of Stanford University, from the mid-1980s. Seven years ago, the company was formed to further
develop this promising technology and set it on a path to commercialisation.

Among the attributes of the current second-generation material, it is notably stable in methanol and water. It is therefore unaffected by DMFC fuel, which is known to cause fluorocarbon membranes to swell, with consequent pore expansion allowing methanol molecules to migrate through – accounting for the well known fuel ‘crossover’ problem.

The hydrocarbon material is also thermally tolerant, being able to operate anywhere in the range from 30 to 70°C.

“Different customers run their fuel cells at different temperatures,” says Jim Balcom. “Smaller handheld systems are typically designed to run at temperatures lower in the range. Large, laptop-type systems are operated at the higher end, and employ a small fan for cooling, similar to what is used to cool laptop processor chips.”

Most of the world’s leading battery producers are experimenting with the PolyFuel material. Each producer takes the membrane material and incorporates it into membrane-electrode assemblies developed by itself or with other partners.

The electrochemical performance for the hydrocarbon formulation is said to be more than adequate for DMFCs. A proprietary process step used in manufacturing the material has helped deliver an energy density which, for a fuel cell stack and system overall, approaches that delivered by lithium-ion batteries, the present standard for powering laptop computers and other portable electronic devices (PEDs), where long-running – independently of mains power – is highly prized. Achieving such parity is a key developmental aim.

A major advantage of the material microstructure is that it is permeable to water molecules, facilitating back-diffusion of the
water that collects on the cathode side of the cell as a by-product of the electrochemical reaction. In previous cells, this has had to be pumped away, necessitating a pumping sub-system. Since in the PolyFuel solution enough moisture diffuses back through the membrane internally, the need for a pump to remove it externally is avoided, so reducing complexity, cost and volumetric space requirement while also enhancing system reliability. Another factor simplifying the water management issue is that the hydrocarbon answer produces less moisture in the first place. This is because the electroosmotic drag – which exacerbates moisture production in fluorocarbon-based cells – is significantly lower with the hydrocarbon alternative. Dry running greatly reduces the possibility of nuisance leakage of water.

In terms of material durability, the PolyFuel solution again shines, having demonstrated over 7,000 hours of run-time, says Balcom. He points out that this is ample for PEDs where 3,000 hours would normally be considered acceptable. On the other hand, he concedes, it would not yet be sufficient for automotive or stationary power applications, where designers might look for nearer 10,000 hours and 40,000 hours, respectively.

“This is one reason that DMFC micro power is likely to be the first fuel cell application to reach the market,” says Balcom. “The parameters that have to be targeted are less extreme. Another favourable factor is that, in micro fuel cell stacks, the amounts of expensive membrane, catalyst and other materials used are tiny, so that material cost is not the big issue as it is in higher power applications. Performance and size, rather than cost and durability, are the primary drivers in this sector.”

At 20 μm, PolyFuel’s present membrane is its thinnest yet, previous materials having been 45 and 62 μm thick. Twenty microns gives a good trade-off between the back-diffusion that simplifies water management and other properties like power,
efficiency, robustness and durability. As Fuel Cell Seminar delegates were able to verify with their own eyes, it is perfectly possible to manufacture the membrane as a continuous film, roll to roll. PolyFuel is refining its capacity to accomplish this in quantity, reliably and economically.

Launch

In 2007, PolyFuel expects that test market trials will see several hundred PED users, selected for a variety of device types and usage profiles, issued with fuel cell power packs manufactured by PolyFuel and its fuel cell producing customers. Depending on the results, full product launches should follow in 2008–2009. Balcom and his team are confident that, by the end of the decade, micro fuel cell technology will be delivering, on a commercial scale, the holy grail for advanced PED users – extended run-times on feature-rich, power-hungry devices.

The team expects a considerable pent-up demand from a proportion of users wishing to run their latest laptops, 3G phones, combined DVD-TVs etc. for up to eight hours between charges – about double what the best batteries can deliver at present. The ability then to stay independent of ‘mains’ electricity simply by slipping in a replacement liquid methanol cartridge costing a dollar or two will, they calculate, be sorely
tempting to keen users. This ‘hot swapability’ could justify an initial price premium relative to batteries.

Jim Balcom does not propose fuel cells as battery substitutes, but rather as a run-time augmenter in hybrid systems combining both types of power source.

“Batteries are great for delivering peak loads instantly and for following highly fluctuating demand,” he says. “Fuel cells are
better for delivering energy over a prolonged period. We believe that consumers will welcome power packs that combine both sources, with battery recharge being available
from the fuel cell output. Outside the consumer sector there are some applications, in Homeland Security for instance, where DMFCs raise the possibility of making more sensing and screening devices truly portable.

Without fuel cells, they would need unduly large and cumbersome batteries.” Balcom declares, “even as the market takes off, our R&D team will continue to focus on enhancing power and efficiency. The high product turnover typically found in the PED market will give us the opportunity to innovate continually as the generations rapidly succeed each other, a luxury denied to colleagues in the automotive and stationary sectors. All in all, we can expect great things in the micro fuel cell power sector over the next few years.”

Stationary

The commercialisation of scientific research dating back over 15 years promises to make small-scale combined heat and power (CHP) an everyday reality, according to Bob Flint, commercial director of UK pioneer Ceres Power. In particular, he predicts that compact fuel cell powered CHP, substituting for conventional domestic boilers, will be in homes by the end of the decade, in parallel with other applications.

In the early 1990s scientists in the Materials Department of London’s Imperial College were working on an unusual electrochemistry, which they thought might transform the prospects for solid oxide fuel cells (SOFCs) – by enabling them to run at far lower temperatures than hitherto, and thus bringing SOFC technology into the reaches of mass markets.

As Flint explains: “They were experimenting with using cerium gallium oxide (CGO) electrolytes on stainless steel. The resulting fuel cell was able to operate robustly at intermediate
temperatures of 500–600°C, rather than the 800°C or so of the more conventional yttrium-stabilised zirconium (YSZ)-based high temperature cells (HT-SOFCs).

This significant reduction in operating temperature greatly boosts the prospects for small-scale distributed power generation and CHP.”

The rare earth element cerium had been all but written off as a suitable candidate for fuel cell application, until the Imperial College team, headed by the world-renowned Professor Brian Steele (since deceased), decided to combine the remarkable properties of cerium gadolinium oxide with stainless steel to make a winning intermediate-temperature solid oxide fuel cell (IT-SOFC) combination. Engineering cells to operate at less than 600°C, they realised, would avoid many of the engineering, manufacturing and cost issues associated with high-temperature SOFCs.

The steel substrate makes them tough with good electrical conductivity, as well as being cheaper to produce. Simpler sealing used throughout the fuel cell stack provides an ideal solution for rapid and continuous thermal cycling, without the risk of seal failure. Together, these features open up a wide range of commercial possibilities. For example, the cells’ ability to warm up to operating temperature in minutes rather than many hours, and to switch on and off repeatedly so as to follow load demand, make them a candidate for use in domestic and small business applications.

In 2001, Ceres Power was spun out from Imperial College with all the key intellectual property rights to take the nascent technology forward. Ceres still maintains an active working relationship with Imperial College and its academic founders.

Compact IT-SOFCs can be made using non-exotic materials and components that are widely available and affordable.
Deriving their strength from metal rather than ceramic materials brings down bulk material and manufacturing costs, while making the cells less brittle. Ceres screenprints the constituent cell materials onto thin stainless steel. Moreover, it is able to use both weld and compression seals rather than the more expensive glass seals conventionally used in HT-SOFCs. The resulting cells are both mechanically robust and thin, so that cells can be combined into stacks that are surprisingly light and compact. Last year the company announced a compact stack producing 1 kW of electrical power
– that is smaller and lighter than a typical car battery – and anticipates packaging multiple stacks together into power units offering 20 kWe or more.

Rare metals do not have to be used in the stack, while cerium and other cell constituents are inherently cost-effective. The part count is designed to be low, and most of the parts used in associated systems – heatexchangers, fuel processing etc. – are drawn from the white goods and automotive supply
chains. Ceres produces core fuel cell components in-house and also creates reference designs for complete systems, such as domestic CHP. The company works with partners to assemble finished products in volume for end users. As a result, Ceres is confident it will be able to achieve unit prices close to those of conventional products at the leading edge of the market today.

The technology’s characteristics are highly desirable in tackling the large domestic boiler market. “One should bear in mind,” Bob Flint points out, “that customers may want a CHP system to completely replace an existing boiler. Such systems will need to combine conventional boiler modules with a fuel cell stack and its associated components. However, the cost of buying and installing the unit will be balanced against substantial fuel cost savings. You’re not looking into the dim and distant future for payback, as can happen with other micro generation technologies.”

The Ceres fuel cell is expected to be highly durable, with a product design life similar to that of an average domestic boiler, currently around 10,000 hours. Durability also gains from the fact that the various layers of the cell have similar coefficients of thermal expansion, so that the internal stresses that would otherwise occur in the stack under conditions of frequent thermal cycling are absent. The structure is carefully engineered to avoid hot spots, and the movement of gas through the stack prevents the temperature from rising excessively.

Ceres is working towards integrated CHP units that can be free-standing but will also be light and compact enough for wall mounting. These are essentially ‘plug and play’ replacements for conventional domestic boilers, and are expected to be straightforward to install and operate. The electrical power can be used for a range of domestic purposes,
and the heat output can provide hot water or space heating via a heat-exchanger. A heatto-power ratio of approximately 1:1 makes the Ceres unit highly flexible, avoiding the
generation of too much heat, and meaning that the unit can still operate during the summer or in smaller properties.

Domestic CHP units will normally be operated in parallel with the mains electrical supply, and Ceres is therefore developing appropriate electronics to interface with the grid. However,
independent operation is also possible, providing remote or backup power in areas where the grid is unavailable or unreliable.

Progress

Two years ago, Ceres and industrial gases group BOC (now part of Linde) agreed to run joint development trials on the use of various cylinder gases, including liquefied petroleum gas (LPG), to generate electricity via Ceres fuel cells. Subsequent deals have transitioned the work from technical feasibility to the assessment of products aimed at specific market sectors and locations.

In early 2006 British Gas, a Centrica company, agreed to partner Ceres in a drive to develop domestic CHP boilers. A £2.7m (US$5.3m) programme was initiated to design, build and evaluate fuel cell-based CHP units for the UK residential market.

This work is part sponsored by the UK’s Department of Trade and Industry (DTI). In early 2006, Ceres successfully tested its
1 kW stack, a key technical milestone. By May 2006, the company had announced a CHP system design sufficiently light and compact to be wall-mountable, a prerequisite for installation in the majority of UK homes as a replacement for standard gas boilers. Frost & Sullivan recognised the company’s achievements in the European micro CHP market with its 2006 Excellence in Technology Award.

Other applications are in view. One prime prospect is auxiliary power for ambulances, military vehicles, aircraft and other platforms. Although predicted to start first in commercial and specialist vehicles, auxiliary power units (APUs) are expected to move into mass market vehicles including, over time, passenger cars.

Ceres is already preparing for manufacture. A new facility has been secured for the assembly of complete products, and plans are advanced for a ‘mother plant’ that will manufacture core fuel cell components in volume. Recently, the South East England Development Agency (SEEDA) agreed to fund one third of a £600,000 (US$1.2m) programme to support the scale-up of key processes for fuel cell production.

It seems that Ceres Power could be on the brink of bringing micro CHP to the market. Delivering IT-SOFC based domestic boilers will be just the start.

Automotive

Although we will not be driving fuel cell cars quite so soon, leading automakers are working hard to make it happen. One of these is European/US giant DaimlerChrysler, which has placed more than 100 fuel cell vehicles on public roads, more than any other OEM. Those vehicles are being used daily in worldwide locations, under diverse driving conditions.

As Dr Christian Mohrdieck, the company’s director of Fuel Cell Drive System Development told Fuel Cell Focus, “we embarked on our fleet programme in 2003, starting with our Mercedes-Benz A-Class Fuel Cell cars and fuel cell Citaro city buses.

There are 60 equipped cars out there, along with three Sprinter vans and 36 buses. By the middle of November, the buses had covered nearly 1.6 million kilometres (1 million miles), their fuel stacks having operated for over 3,000 hours
cumulatively. The Fuel Cell cars have been driven nearly a million kilometres (620,000 miles) and the Sprinter vans about 63,000 km (39,000 miles).”

Every day each vehicle sends data automatically via radio and internet to evaluation centres at Nabern and Ulm in Germany. Up to 60 parameters, including driving speed, fuel cell voltage characteristics, fuel tank pressure and so on, are analysed.
Bus operations are supported locally or regionally. Those in Europe are running under the European Commission-supported Clear Urban Transport for Europe (CUTE) and Ecological City Transport System (ECTOS) programmes, and now the followon HyFLEET-CUTE programme. “We’re now in the second phase of our bus programme,” confirms Mohrdieck, “and have another year to run. At the same time we have begun to build a next-generation bus, which will start rolling towards the end of 2008 or early 2009.”

The new design will benefit from experience gained with the existing buses in cities throughout Europe, but also in China and Australia. Cities were selected for the variety of driving conditions they offer: London for slow, stop-start running for
instance, Stockholm for its cold winter climate, Barcelona and Madrid for heat, and Stuttgart for its hilly nature. Three buses
in Perth, Western Australia cover longer distances at higher speeds, while another three have been coping with Beijing’s busy traffic for a year now. Experience has generally been positive, although certain issues of efficiency, harshness and vibration are being addressed for the next generation of vehicles.

The Fuel Cell car fleet is operating in the US, Europe, Singapore and Japan. Among the 35 vehicles in the United States, some are in Michigan but most are in California, a state noted for its support of alternative power concepts. Half a dozen cars are being trialled in Japan under the Japan Hydrogen& Fuel Cell Demonstration Project (JHFC). Europe has the rest – including 10 in Berlin– with support from the city’s Clean Energy Programme.

DaimlerChrysler is working with BP, Shell, Total and others to develop the necessary hydrogen fuel infrastructure. Each city where Citaro buses operate now has at least one hydrogen fuelling station, although mobile fuelling units were fielded initially. Motorists in Berlin have two options: a Total station, and one under the banner of Aral (a German subsidiary of BP). At the Aral station, a hydrogen dispenser is lined up alongside those for gasoline/petrol and diesel, setting a pattern for future refuelling stations. In the US, DaimlerChrysler and BP
are joining forces for a refuelling network being set up as part of a US$80m fuel cell demonstration programme, which is 50%
funded by the Department of Energy. Several stations are being established around San Francisco Bay and Los Angeles in California.

Although the US authorities currently restrict hydrogen access to approved users, one hopes they might eventually follow the example of Japan, where 10 or so stations in the Tokyo area offer full public access.

Mohrdieck accepts that the motoring public, conditioned by past history, will need reassuring about the safety of hydrogen. “In fact,” he points out, “hydrogen, given correct
engineering and handling, is no more dangerous than any other type of fuel in general use today.” And he adds that had gasoline not already been discovered and become an everyday transportation fuel, safety concerns would probably prevent its introduction now. Hydrogen fuel stations must be appropriately designed and dispensers constructed so that a gas-tight connection is formed between vehicle and dispenser – before fuel can be transferred. Vehicle fuel tanks specified
by DaimlerChrysler are strong, lightweight, filament-wound composite cylinders able to withstand both high internal hydrogen pressure and the forces exerted in a crash. Tanks
designed for 700 bar (10,000 psi), the pressure now favoured by the company to give the next generation of vehicles adequate range– have passed stringent crash tests required by the German state and federal authorities.

A good drive

Mohrdieck’s own recollections of first driving one of the Fuel Cell cars are illuminating. “It’s a good drive,” he says. “You get a smooth, quiet ride free of engine and gear noise and without the usual gear shifts. Electric drive gives you immediate high
torque, right from zero revs. So, when the lights change, you’re ahead for the first 20 metres or so, and to get that kind of kick from a car that produces zero emissions is most satisfying.”

Top speed is adequate for general motoring, at some 140 kph (about 85 mph). On the negative side, the range between fuel
stops is currently limited to about 160 km (100 miles), though a careful driver can obtain 200 km (125 miles). Improvements
intended for the next vehicle, the planned B-Series, will extend this range to 400 km (250 miles) – comparable to that of a typical gasoline-powered car. A recently produced precursor for the B-Series, the F600 HYGENIUS concept car first shown at the Tokyo Motor Show in October 2005, paves the way, running 400 km on a full 4 kg charge of hydrogen at 700 bar pressure.

Show visitors to Tokyo were intrigued by the futuristic placing of the PEMFC and its associated systems within the vehicle’s sandwich floor, although they could equally be engineered into a regular engine compartment or trunk/boot.

The powertrain on the F600 benefits from a number of improvements. The fuel cell stack is 40% smaller than its predecessor, for similar power. It is also 43–45% efficient,
tank to wheel, in standardised driving cycles, compared with 37–38% previously. And associated systems have been redesigned. For instance, active humidification on present
vehicles has given way to a passive system relying on gas-to-gas humidification taking place in hollow fibre bundles. Avoiding the formation of liquid moisture means that water cannot collect and freeze. Accordingly, cold ‘freeze’ starts are possible down to –25°C.

An electric turbocharger delivers air to the powertrain’s double-pack stack. Improved lithium-ion batteries are used, along with a permanent magnet electric motor rather than the asynchronous type employed on the present A-Class vehicles.

Challenge

There is still some way to go before a fuel cell car can be marketed commercially. DaimlerChrysler has a road map to
get there, however, based on evolutionary improvement. For example, reducing the platinum content of the latest fuel cell has resulted in bipolar plates a mere 0.15 mm thick, thereby reducing cell cost (see ‘Bipolar plates: Cutting costs’, on page 28). Even so, cost remains a critical issue, especially when
it is compounded with that of membrane durability.

As Mohrdieck explains, “it is possible to make cells cheaper or to make them more durable, but achieving both these things at once is a real challenge. We need an advanced, affordable cell that will operate for 5,000 to 6,000 hours, giving the average car owner about 10 years of motoring.”

The company is supporting efforts to develop alternative membrane materials, especially high-temperature membranes
like hydrocarbons and polybenzimidazole (PBI)-phosphoric acid, but sees such solutions as taking at least a decade to mature. Meanwhile it continues to evolve standard fluorocarbon membranes, in particular Nafion.

“We know it works and understand its characteristics,” says Mohrdieck. “We can work it harder, further raising the operating temperature, for instance, to increase electrochemical efficiency.”

Daimler Chrysler collaborates with Ballard Power Systems in Canada and Ford Motor Company, its partners in a Fuel Cell Alliance formed eight years ago. The partners are keen to further reduce PEMFC platinum loading relative to stack power density, as well as aiming to raise power density so that less
area of expensive active membrane is needed. Mohrdieck suggests that the cost of the membrane-electrode assembly (MEA) on the B-Class vehicle can be halved relative to that
of the existing A-Class solution. Other intended enhancements concern the ancillary systems and the final electric motor drive. For example, it should be possible to both improve the power electronics for permanent magnet motors while also incorporating them into the motors themselves. Overall efficiencies in excess of 50% are envisaged, since engineers see no sharp cut-off analogous to the theoretical Carnot efficiency limit that applies to internal combustion engines.

The next most critical issue, after the MEA, is that of hydrogen storage. Although 700 bar pressurised hydrogen – preferably
produced from renewable sources – is the preferred option at present, the company carefully monitors whether other storage solutions are emerging. Another development focus is to simplify the controls.

Currently controls are needed for the hydrogen tank, battery, electric motor drive and fuel cell. The aim is to rationalise the
control architecture and make the process virtually autonomous. Despite the substantial obstacles still to be overcome, Christian Mohrdieck is confident that the present road map, alongside the parallel development of the necessary hydrogen delivery infrastructure, addresses them all.

“Sometime between 2012 and 2015,” he predicts, “we will have matured the technology sufficiently to launch a marketable fuel cell car able to compete with conventionally
powered vehicles.”