Among the many daunting challenges to replacing fossil fuels with hydrogen is how to make hydrogen cheaply in ways that don't pollute the environment. Splitting water molecules into hydrogen and oxygen using electricity from energy sources such as wind turbines is one possibility -- but it's still far too expensive to be widely practical.
Now researchers at GE say they've come up with a less expensive, easy-to-manufacture apparatus that can directly produce hydrogen via electrolysis for about $3 per kilogram -- a quantity roughly comparable to a gallon of gasoline -- down from today's $8 per kilogram. That could make it economically practical for future fuel-cell vehicles that run on hydrogen.
Electrolyzers are fairly simple technologies: water is mixed with potassium hydroxide electrolyte and made to flow past a stack of electrodes. Electricity causes the water molecules to crack into hydrogen and oxygen gases, which bubble out of the solution. The chemistry makes a good high-school science experiment -- but commercial-scale quantities of hydrogen are extracted far more cheaply from natural gas.
The core problem in improving electrolyzers for hydrogen manufacture is not how to improve the fundamental conversion efficiency, says Richard Bourgeois, an electrolysis project leader at GE Global Research in Niskayuna, NY. "You can only make it so much more efficient; there isn't a lot you can do. So we've attacked the capital costs," he says.
Today's electrolyzers are made of metal plates bolted together manually, with gaskets between them, and the whole unit is typically housed in a chamber made of the same metals used in the electrodes, says Bourgeois. The materials are expensive and assembly requires costly labor.
Bourgeois' research team came up with a way to make future electrolyzers largely out of plastic. They used a GE plastic called Noryl that is extremely resistant to the highly alkaline potassium hydroxide. And because the plastic is easy to form and join, manufacturing an electrolyzer is relatively cheap.
Inside the plastic housing, metal electrodes still do the same job. But because GE is using less electrode material, the reactivity of the electrodes' surfaces is improved. To do this, the researchers borrowed a spray-coating process -- normally used to apply coatings for parts on jet engines -- to coat the electrodes with a proprietary nickel-based catalyst with a large surface area.
GE has demonstrated the technology in a prototype, and is now building a larger production module -- one that can produce 1 kilogram of hydrogen per hour -- for testing in its labs later this year. A machine of that scale could be attached to small electricity sources to produce hydrogen on the side. The technology also has the potential to be massively scaled up to create a hydrogen gas station.
GE's new electrolyzer could be ready for production in a few years. "You can talk about transitioning to a hydrogen economy, but really these things don't move unless the economics are there," Bourgeois says. "This takes enough capital cost out of the whole electrolyzer system, so when you buy this and amortize it over so many years, you compete with gasoline."
Paul Bakke, an electrical engineer and program manager at the U.S. Department of Energy in Golden, CO, says a cheap electrolyzer could be a key component of the future hydrogen economy. "As far as I know, GE is the only one who has tried to tackle this problem," he says. "Assuming GE is successful in being able to produce these things with a high level of reliability and low cost, it will break through the barrier that has traditionally been there for electrolyzers -- namely, the capital cost barrier."
Bakke adds: "I would say it's an important piece; it may not be the only way to make hydrogen, but it's an important piece. Natural-gas reforming may be a near-term bridge, but in order to get away from the environmental concerns, we will have to go to electrolysis, derived from wind turbines and solar panels and so forth."