Idaho National Laboratory

High-Temperature Electrolysis

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Efficient production of hydrogen without increased 

greenhouse gas emissions 

is the key to achieving the “hydrogen economy” envisioned by the 

Nuclear Hydrogen Initiative. As 

the lead laboratory for the Department of Energy’s Office of Nuclear 

Energy, the Idaho National Laboratory is assuming a major role 

in developing technologies to 

produce hydrogen using nuclear 

energy. One of the most promising 

of these technologies is called hightemperature electrolysis.

What Is High-Temperature 

Electrolysis?

One way to produce hydrogen is 

electrolysis – using electricity to 

separate hydrogen from water. By 

performing electrolysis at high 

temperatures, its overall efficiency 

increases considerably. In a hightemperature electrolysis system using 

nuclear energy, a nuclear reactor 

supplies thermal energy that both 

generates the electricity and heats 

the steam needed for the electrolysis 

process. A high-temperature heat exchanger supplies steam superheated 

to about 850 degrees Celsius. Heat 

from the reactor is also used to generate electricity. The combination 

of electric power and high temperature splits the H2O molecules into 

hydrogen and oxygen in a stack of 

ceramic electrolysis cells.

The Advantages of 

Nuclear-Powered HighTemperature Electrolysis

Nuclear-powered high-temperature 

electrolysis is the key to efficient, 

clean production of hydrogen.

Unlocking Hydrogen’s Potential with Nuclear Energy

In a high-temperature electrolysis system 

using nuclear energy, a nuclear reactor 

supplies thermal energy that both 

generates the electricity and heats the 

steam needed for the electrolysis process.

Power for Electrolysis

Power to Grid

Electricity

Very High

Temperature

Reactor

HighTemperature

Steam

Electrolysis

Unit

Electrolyte

Electrodes

Steam/Hydrogen

Mixture Helium

Helium

Steam/Hydrogen Mixture

Steam

Gas Turbine

Compressor

Compressor

Generator

Heat Sink

Heat Sink

Recuperator

Water Heat Exchanger

Steam/Hydrogen

Separator

Hydrogen

Oxygen

Membrane
Idaho National Laboratory

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•	 High-temperature systems reduce the amount of electricity 

needed for hydrogen production, and generate the necessary 

electricity more efficiently.

•	 A high-temperature advanced

nuclear reactor coupled with a 

high-efficiency high-temperature 

electrolyzer would be extremely 

efficient, with a thermal-tohydrogen conversion efficiency 

of 45 to 55 percent.

•	 Using nuclearenergy ratherthan

fossil fuels for electrolysis would 

allow hydrogen production with 

no associated greenhouse gas 

emissions.

•	 High-temperature electrolysis

plants could serve an important 

balancing function, supplying 

electricity to the power grid when 

electricity demand is high or 

drawing electricity from the grid 

when demand is low to produce 

extra hydrogen.

It’s Happening at INL

INL is leading research on using 

nuclear energy for high-temperature 

electrolysis. INL is already testing the 

use of solid-oxide cells – used mainly 

for power production in fuel cells – 

for electrolysis. In fuel cells, hydrogen 

and oxygen are combined electrochemically to produce water, and, in 

the process, heat and electricity. INL 

is experimenting with reversing the 

process – using solid-oxide cells to 

split water into hydrogen and oxygen 

while consuming electricity and heat. 

A new generation of nuclear reactor 

under development at INL, the 

Very High Temperature Reactor, 

will eventually supply both electricity and high-temperature heat to 

the electrolyzer.

Conceptual design and analysis for 

hydrogen production facilities is 

underway at INL.

•	 The high temperatureelectrolysis

Integrated Laboratory Scale experiment started operation with 

one module (5 kW) in August 

2007 and will operate with three 

modules in September 2008. 

•	 A pre-conceptual design for a

pilot-scale (500 kilowatts) hightemperature electrolysis facility is 

complete. The Nuclear Hydrogen 

Initiative’s Research and Development Plan calls for the facility 

to be deployed around 2013.

•	 The plan callsforalarger 5megawatt engineering demonstration 

facility to be developed at INL 

around 2019.

In fuel cells, hydrogen and oxygen 

are combined electro-chemically 

to produce water, and, in the 

process, heat and electricity. INL 

is experimenting with reversing 

the process – using solid-oxide 

cells to split water into hydrogen 

and oxygen while consuming 

electricity and heat. 

INL is already testing the use of 

solid-oxide cells – used mainly 

for power production in fuel cells 

– for electrolysis. 

The INL is one of the U.S. Department of Energy’s 

multiprogram national laboratories, and is 

managed by Battelle Energy Alliance, LLC.

08-GA50044-06

For More Information

Technical Contact:

Steve Herring

208-526-9497

J.Herring@inl.gov

Communications

Contact:

Teri Ehresman

208-526-7785

Teri.Ehresman@inl.gov