A team of scientists from the US Department of Energy’s Idaho National Laboratory earlier this month reached a major milestone with the successful production of hydrogen through High-Temperature Electrolysis (HTE). (Earlier post.) The milestone was reached when the Integrated Laboratory Scale experiment started producing hydrogen at a rate of 5.6 cubic meters per hour—a major scale-up from earlier INL experiments on a smaller scale.
|A HTE system with a high-temperature nuclear reactor. Click to enlarge. Source: INL|
Conventional electrolysis splits water into its components—hydrogen and oxygen—by charging water with an electrical current. The charge breaks the chemical bond between the hydrogen and oxygen and splits apart the atomic components. The main drawbacks of conventional electrolysis for large-scale hydrogen production are the amount of electricity required for the process and the high cost of membrane production. It takes about 142 MJ to produce 1 kilogram of hydrogen—about 40-50 kWh of electricity per kilogram of hydrogen.
High-temperature electrolysis (HTE) adds in some of the energy needed to split the water as heat—from a source such as high-temperature steam from an advanced nuclear reactor system or an adapted solar energy system—instead of electricity. Because the conversion efficiency of heat to electricity is low compared to using the heat directly, HTE reduces the overall energy required.
HTE uses a device very similar to an Solid Oxide Fuel Cell (SOFC). Essentially, the electrolytic cell consists of a solid oxide electrolyte with conducting electrodes deposited on either side of the electrolyte. A high-temperature mixture of steam and hydrogen is supplied to the anode side of the electrolyte.
Combined with a power source such as a next-generation nuclear plant, HTE could produce hydrogen at 45 to 55% efficiency, according to the INL team.
There are several potential applications of hydrogen from high-temperature electrolysis, all of which are closer to being actualized now that HTE has proven itself capable of producing hydrogen at such an advanced level.
Hydrogen is commonly used to help produce liquid fuels. INL Laboratory Fellow Steve Herring, who heads the HTE project, said it could also prove helpful in upgrading fuel from the Athabasca Tar Sands in Alberta, Canada, because producing gasoline and diesel fuel from such heavy oil deposits requires extensive amounts of hydrogen and steam. Eventually, HTE could provide pure hydrogen for fuel cell-powered cars, Herring said, “but that’s a long way off.”