Brown team studying new fuel-cell catalyst

FUELED UP: Brown University professor Shouheng Sun, forefront, with students, from left: Sen Zhang, Shojun Guo and Liheng Wu. / PBN PHOTO/BRIAN MCDONALD
FUELED UP: Brown University professor Shouheng Sun, forefront, with students, from left: Sen Zhang, Shojun Guo and Liheng Wu. / PBN PHOTO/BRIAN MCDONALD

Imagine a future where almost all cars and houses are powered by a fuel cell, an electrical generator – not a battery – that has no pollutant emissions and does not use petroleum-based fuel. It’s been an idea for years, but difficult to make a mass-production reality due to certain constraints, including costs.
Scientists have worked on perfecting the technology to find an inexpensive way to mass-produce hydrogen fuel cells. Over the last year Brown University professor of chemistry Shouheng Sun and his research team have been encouraged by their efforts to make it a commonplace reality.
Fuel cells work by chemical reaction. They have two poles, an anode and a cathode, and each cell also has an electrolyte that carries charged particles from one electrode to the other, and a catalyst, which speeds the reaction. Hydrogen is the commonly used fuel. Rather than smoke, its byproduct is usually water. The cells generate direct current – DC – power but need to be stacked to generate enough power to be useful. The power must also be converted from DC to AC, the country’s electrical standard.
The field is still in its infancy but steadily growing. On Oct. 21, Toyota Motor Sales USA announced the activation of a new 1.1-megawatt hydrogen fuel-cell generator at its Torrance, Calif. facility. Believed to be the largest of its kind, the cell generates enough electricity to power 765 homes. The cell, consisting of thousands of stacks of individual cells, is the size of two tractor-trailer trucks.
Many other similar stationary units have been installed throughout the country. The units, however, are large and heavy and paid for through a variety of federal grants. Those using hydrogen as a fuel provide less than 1 MW of energy.
In 2002, Toyota manufactured its first fuel-cell vehicle, and has promised a mass-produced fuel-cell vehicle by 2015. Prototypes, however, have thus far resulted in a very compact automobile that could cost upwards of $50,000. The company admits there are still issues to be resolved and mass production could mean only 100 or so vehicles. Other car manufacturers are looking into similar automobiles. Hydrogen fuel-cell vehicles include the Hyundai Tucson and Honda FCX Clarity as well as other cars, trucks, buses and military vehicles. Unfortunately the same obstacles still exist; cost, weight, durability, range between fuel stops, ability to mass produce and a lack of fueling stations. The first fueling station in the country was opened on May 10, 2011 by Toyota, in Torrance, Calif. At Brown, Sun and his team are hot on the trail of a better technology.
“Basically, we used our chemical knowledge,” Sun told Providence Business News. “We are talking about an oxygen-reduction reaction. Traditionally people always use platinum to catalyze the oxygen reduction, to make oxygen gain an electron much more easily. The platinum stays in its original form.” The problem, said Sun, is a matter of money; platinum is very expensive and there is a very limited supply, facts that have essentially ground fuel-cell technology advancement to a halt. The price of platinum fluctuates because it is traded as a commodity.
“If we cannot find a catalyst that is much cheaper than platinum and more available, there is no future for fuel cells,” he said. Recognizing the bottleneck, Sun and his team of student researchers have investigated possible solutions for years. In fact, teams of researchers across the world have searched for a nonplatinum substitute for use as a catalyst. Sun’s team has been able to reduce the amount of platinum but is striving to eliminate it altogether. On Oct. 16, they announced that they might be on the right track by using a substance called graphene. Scientists have been aware of graphene for 50 years but it was only in 2010 that it was brought to the forefront of the scientific community, when exploration of the substance resulted in awarding the Nobel Prize in physics. At an atomic level it is a thin honeycomb of carbon, and a great conductor with a large surface area.
In recent trials the group began using cobalt and cobalt-oxide coated with a graphene sheet that reacts almost as well as platinum. It is also more durable, more plentiful and more importantly, cheaper.
It is the first catalyst not made from a precious metal that approximates platinum’s properties.
According to postdoctoral researcher Shaojun Guo and Shaojun Dong, part of Sun’s team, their trial has the best performance for any nonplatinum catalyst, and their work has been published in the journal Angewandte Chemie International Edition.
After one 17-hour test, the graphene-cobalt system performed at about 70 percent of its initial capacity, the platinum system at less than 60 percent. In that test, the former proved more durable.
The news is exciting because if given enough time to solve difficulties with the cell, an almost unlimited source of nonpolluting, nonpetroleum-based power is foreseeable, Sun said. “Each cell creates a little more than one volt so they have to be stacked to achieve a practical use. Right now they are not commonly used. If the problems with platinum are not resolved it will make it very difficult for fuel cells to become a practical solution to generate electricity.”
Ultimately, Sun said, finding a suitable nonplatinum catalyst is the key to getting fuel cells “out of the laboratory phase and into common production as power sources for cars and other devices.” •

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