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 prototype version of an easy-to-manufacture apparatus that they believe could lead to a commercial machine able to 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 split 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.