Environmentally sound exhaust: Fuel-cell powered cars emit pure water vapor
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Automobiles with absolutely no pollutant emissions offer exciting prospects for manufacturers, customers, and the environment. EMD is developing new types of catalysts that will help pave the way for mass production of fuel cell vehicles.
Fuel cells are the great hope of the automotive industry. The technology transforms chemical energy into environmentally friendly electricity that can power a vehicle.
The mobile electricity sources run on gas or liquid hydrogen generated from water in a climate-neutral process that utilizes energy from solar or wind power facilities. The only emission they produce is pure water vapor. In terms of protecting the environment, there’s no better way to drive.
In combination with batteries that temporarily store braking energy and can be recharged at an electric socket, fuel cells are therefore playing a key role in the development of electrically powered zero-emission vehicles. The batteries provide the electricity on short trips, while the fuel cells supply energy over longer distances. Experts say zero-emission vehicles can travel up to 600 kilometers without having to refuel, which makes them attractive for the mass market.
“This development will help us develop fuel cells for the mass market.“
As a result, the Korean automaker Hyundai, for example, has announced plans to put 1,000 zero-emission vehicles on the road by 2015. Current zero-emission prototypes still cost € 80,000 to manufacture at the beginning of 2013. One reason for this high price is that around 60 grams of platinum are needed in a fuel cell to produce an electrical output of 100 kilowatts, which is the power required by a typical mid-range passenger car. The platinum catalyst material alone currently costs around € 5,000, which makes the price of a fuel cell vehicle too high to compete with a vehicle powered by a combustion engine.
EMD is working on developing a new and much less expensive catalyst-coating method for fuel cells. “This catalyst coating method enables us to reduce the platinum requirement to only ten grams,” says Project Manager Zeeshan Mahmood. “That will help us develop fuel cells for the mass market.” A fuel cell basically functions as follows: Hydrogen (from a tank) and oxygen (from the ambient air) are channeled into two chambers. The two gases are separated by an ultra-thin polymer electrolyte membrane (PEM) to prevent them from mixing.
Such a mixture would trigger an uncontrolled reaction and explosion. The two chambers are connected by electrodes coated with platinum catalysts, as well as by an electrical conductor. The electrode in the hydrogen chamber is the anode, the electrode in the oxygen chamber is the cathode. The catalyst helps split each hydrogen molecule at the anode into two positively charged protons and two negatively charged electrons. Only the protons pass through the membrane to the cathode side, which leads to a surplus of protons there, and conversely a surplus of electrons at the anode.
This generates a voltage between the electrodes, which causes electrons to travel to the cathode via the electrical conductor. The result is an electrical current that powers the electric drive system. When the electrodes reach the cathode, four of them always join with four protons and then bond with an oxygen molecule to produce pure water, which emerges from the fuel cell as water vapor.
The high platinum requirement pushes up the cost of today's fuel cells. Researchers at EMD are working on lowering this requirement
The fuel cell’s efficiency depends almost exclusively on the structure of the catalyst surface, whereby the more contact area the platinum offers the reacting substances, the faster the reactions will be, and the greater will be the amount of electricity that can flow. Mahmood and his research team are focusing on improving the cathode side. “We’re increasing the surface area of the catalyst we use here by incorporating the platinum as tiny nano-sized spheres that nevertheless can’t be too small, otherwise they'll clump together like damp flour,” Mahmood explains.
He and his team of experts from various EMD divisions are on a good track to demonstrate the feasibility of their approach. The researchers are developing catalysts whose platinum content is just one-sixth of the amount normally used to achieve the same fuel cell electrical output. What’s more, the decline in output over 5,000 operating hours is in the direction of only 20 percent, which corresponds to 13.7 years of service life given one hour of driving each day.
Two automotive industry customers have already positively assessed the new method's proof of concept, which previously had been tested only in a laboratory. Mahmood now plans to develop an industrial manufacturing process for the components that meets the stringent quality requirements of the automotive sector. “The first sample systems will be delivered to customers in 2013,” he says.
Other functional improvements are now being considered, such as raising the fuel cell operating temperature from the current value of approximately 90 degrees Celsius to 130 degrees Celsius. This would allow automakers to kill two birds with one stone, as it would both simplify cell cooling and increase the protons’ freedom of movement, which in turn would increase the efficiency of the electricity source.
It might even be possible one day to do away with artificial cell humidification, which is still needed today in order to prevent the membranes from drying out and becoming damaged. “If we could do that,” says Mahmood, “we could reduce the total cost of a fuel cell by a further ten percent.”
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