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Hydrogen: The slow slog to zero emission energy

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An artist's conception of a commercial hydrogen production plant that uses sunlight to split water in order to produce clean hydrogen fuel. (Photo: University of Colorado Boulder)

Around three years ago, a doctoral student, somewhat by accident, made a small discovery that could one day change the entire energy economy: a unique thermal reaction between two compounds.

The student, under professor Alan Weimer at the University of Colorado, Boulder, then went a step further, outlining a way that two of the processes for extracting hydrogen, reduction and oxidation, could be run at the same temperature through this reaction. With this blueprint, the team made designs for a manufacturing plant with a series of mirrors that direct sunlight to a single point atop a central tower. Solar rays deliver a temperature of 2,500°F (1,371°C) to a thermal reactor, where the metal oxides release their oxygen molecules. As steam, heated by the solar energy, passes across the compounds, oxygen molecules separate from the water, having been sucked into the void left on the compounds. What rises from this is a sustained stream of hydrogen, created only by water and sunlight.

The most abundant fuel source in the universe, hydrogen, has the potential to charge cities and fuel cars while producing zero emissions. On Earth most hydrogen is found either in the upper atmosphere or coupled with carbon in fossil fuels. Hydrogen production, meanwhile, typically requires more energy than is produced. The promise of extracting hydrogen from water has had scientists scrambling for new ways to develop this process into a renewable resource.

Weimer's water splitting technique, which he announced last year, comes at a time when hydrogen fuel cells are gaining attention, as three major automakers recently unveiled a new 2015 line of fuel cell vehicles, with at least two more companies working on their own models. According to the Environmental Protection Agency, fossil fuels for transportation accounted for 28% of the country's greenhouse gas emissions in 2011.

These sorts of hydrogen energy breakthroughs have until now remained mainly novelties. Yet a cultural change in the way consumers are looking to renewable technologies is happening at the same time hydrogen energy is facing the valley of death, where early adopters will determine whether hydrogen makes it as a viable energy source anytime soon. Hybrid electric vehicles and photovoltaic solar panels have crossed that valley before, which gives hope to hydrogen proponents. Yet a slew of obstacles still stand in the way of hydrogen entering the mainstream marketplace.

A number of AAAS members, like Alan Weimer, are working tirelessly to solve each of these technological hurdles that now separate hydrogen from the larger energy economy.

A competitive market

"Nobody's going to do that," shouted a colleague, adding: "You're losing it, Weimer!" He stood, shaking his head and rotating his finger around his ear—the universal gesture for "crazy"—in the back row of a seminar Weimer was giving on solar thermal reactors at his former company. 

"But clearly it's possible to do this," says Weimer, now that he has a proof of principle experiment, "and there are a number of researchers in the world, not just us here, that are developing the materials that can make this happen."  

Weimer's single-temperature process is faster than the standard approach to manufacturing hydrogen, which is to heat compounds up to nearly 3,000°F (1,500°C), cool them and then reheat them again to nearly 2,000°F. This requires a tremendous amount of energy, often supplied cheaply and efficiently by natural gas, which diminishes the sustainability goal for hydrogen energy. The hydrogen molecules, meanwhile, are often extracted from natural gas in a process called methane reforming. This is how hydrogen for refining gasoline and for hydrogenated oil is processed.

If scaled to an industrial level, Weimer's hydrogen plant would occupy about 60% of the space needed to run the equivalent photovoltaic solar farm, due to the fact that hydrogen could be produced at a greater efficiency than either photovoltaic or wind power. Sunlight could also be substituted by waste heat emitted from industrial plants already running at high temperatures.

Yet there's a hitch.

"Realistically, with the price of natural gas as cheap as it is," says Weimer, "being clean, not putting out carbon, is at a competitive disadvantage."

The valley of death

Cars in America have a difficult life.

Typically, they go from ambient temperature in the morning to turning on, operating at high power for 30 minutes to an hour a day and sitting the rest of time. They get wet, hot and frozen and yet are expected to survive this abuse for at least 5,000 hours, or 150,000 miles. Compared to stationary power systems, which operate at constant rates, cars are the workhorses of American culture.

On top of this, consumers expect cars to refuel in three to five minutes, with a tank that lasts around 300 miles. "It's turning out to be a considerable challenge," says AAAS member Tom Gennett, a scientist specializing in hydrogen storage at the National Renewable Energy Laboratory (NREL), under the Department of Energy. "You can get one. You can't get the other."

The performance, look and cost for combustion engine cars, meanwhile, have put even more pressure on engineers to develop a fuel cell vehicle that regular consumers will choose over a gasoline vehicle.

"It's a free for all when you're doing science at this level," Gennett says of the progression of hydrogen storage research over the last 15 years. Several thrusts have possibilities and gradually the science has focused on the material sets for storage that are the most promising for controlling issues like the amount of heat generated from the electrochemical reactions in fuel cells. Once they define key measurements like temperature and pressure ranges in fuel cells, laboratories like NREL put out best practices guidelines for those materials. NREL also tests some of the technology car manufacturers are working on. This collaborative research focuses the workable materials down to an even finer set, though no single material has yet to meet all of the ideal metrics for storing hydrogen.

The new fuel cell cars introduced by Honda, Hyundai and Toyota (which boasts its car can also

Author

Brad Hooker

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