High Temperature Electrolysis system coupled with Gas-cooled Reactor.

High-Temperature Electrolysis for Hydrogen 

Production from Nuclear Energy

A research and development program is under way at the INEEL on high-temperature 

electrolysis for hydrogen production from steam. When coupled to an advanced 

reactor and power cycle, this process has the potential to achieve high efficiency (45-

50% vs. ~30% for conventional electrolysis), with no greenhouse gas emissions and 

no consumption of fossil fuels. This work is supported by the Department of Energy, 

Office of Nuclear Energy, under the Nuclear Hydrogen Initiative (NHI).

High-Temperature Electrolysis 

High-temperature electrolytic water-splitting

supported by nuclear process heat and electricity has 

the potential to produce hydrogen with an overall 

system efficiency near those of the thermochemical 

(e.g., Sulphur-Iodine) processes, but without the 

challenging corrosive conditions of the 

thermochemical processes and without the fossil fuel 

consumption and greenhouse gas emissions 

associated with hydrocarbon processes. 

Specifically, a high-temperature advanced nuclear 

reactor coupled with a high-efficiency hightemperature electrolyzer could achieve a competitive 

thermal-to-hydrogen conversion efficiency of 45 to 

55%. 

A schematic of a nuclear hydrogen plant using high

temperature electrolysis is shown below. The 

reactor (in this case a High Temperature Gas-cooled 

Reactor, HTGR) supplies thermal energy to drive 

the power cycle and to heat steam for the 

electrolysis process. The hightemperature heat exchanger supplies 

superheated steam to the cells at a 

temperature of ~850oC, and a

pressure of 5 Mpa (725 psi). The 

input gas contains both steam and

hydrogen in order to maintain

reducing conditions at the 

electrolytic cathode. There are no 

moving parts within the steam

electrolysis unit. While the HTE 

plant would be devoted primarily to

the production of hydrogen, it is

important to note that output of the 

electrical generator could be sent to

the grid, if demanded. Conversely, 

the steam flow rate could be

increased and the electrolyzer could 

be operated at a higher current

density to profitably accept power from the grid for 

increased hydrogen production in times of low 

electrical demand. Thus HTE can play an important 

role in matching the constant output of future

reactors to varying electrical demands. 

Research on Solid-Oxide Electrolysis Cells 

A research and development program is under way 

at INEEL to develop materials and techniques for 

high-temperature electrolytic production of

hydrogen using solid-oxide cells. Solid-oxide cells

have been developed primarily for power production 

in the fuel-cell mode of operation. In the fuel-cell 

mode, hydrogen and oxygen are combined electrochemically to produce water, liberating heat and

electricity. Operated in reverse, solid-oxide cells can 

achieve water splitting to produce separate streams 

of hydrogen and oxygen, while consuming electrical

power and heat. The efficiency of this simple 

process increases with increasing temperature for 

reasons related to both thermodynamics and 
materials behavior. Thermodynamically, operation 

at high temperature reduces the electrical energy 

requirement for electrolysis and also increases the 

thermal efficiency of the power-generating cycle. In

terms of materials, ohmic losses are reduced at high 

temperature. Ohmic losses can also be reduced by 

minimizing the thickness of the electrolyte and/or 

by using higher ionic conductivity electrolytes. In

planar stack configurations, special attention must 

also be given to the design of the bipolar 

interconnect plates to minimize contact resistance. 

We are working with Ceramatec, Inc. of Salt Lake

City to address these materials and design issues. 

Technical Point of 

Contact 

Steve Herring 

Phone - 208-526-9497 

E-mail - sth@inel.gov

We have developed a solid-oxide electrolysis test

capability at INEEL. To date, we have acquired

detailed performance characterization data on

individual button cells manufactured by Ceramatec, 

Inc. A close-up photo of one of these “button cells” 

is shown above. The button cell is cemented to a 

zirconia tube and the apparatus is suspended in the 

furnace. A steam-hydrogen mixture is introduced

into the interior of the zirconia tube with a sweeping 

flow of air on the exterior of the tube inside the 

furnace. The active electrode area is 2.5 cm2

, with a 

small additional inactive area serving as a reference 

electrode. The button cell temperature is measured

by the thermocouple (TC) shown. The cathode (in

electrolysis mode) is a nickel zirconia cermet and 

the anode (visible in the photograph) is strontiumdoped lanthanum manganite. A platinum wire mesh 

is used on the button cell electrodes for optimal 

current distribution. The wire mesh would not be 

included in a stack configuration since the 

interconnect plate serves as a current distributor in

that case. These are electrolyte-supported cells with

an electrolyte thickness of approximately 125 μm, 

fabricated from either yttria-stabilized zirconia or 

scandia-stabilized zirconia. Electrode-supported

cells with very thin electrolytes (~10 μm) are also

under development. In this case, advanced chemical

vapor deposition (CVD) techniques are used to 

deposit the electrolyte material. 

Instrumented electrolysis button cell.

Electrolysis stack testing has already been 

performed at Ceramatec as part of this program. A

six-cell electrolysis stack was operated for over 

1100 hours, producing 35 normal liters of hydrogen 

per hour (Nl/hr), a rate equal to the largest 

operational S-I thermochemical experiment to date. 

Systems Analysis and Scale-Up 

Conceptual design and systems analysis for largeand intermediate-scale facilities for the production 

of hydrogen via planar solid-oxide electrolysis 

technology is also under way. The Research and 

Development Plan for the NHI calls for the

deployment of a Pilot-Scale (500 kW) demonstration 

facility for HTE in the 2008 time frame. A preconceptual design for this facility has been

completed. It would be capable of achieving a 

hydrogen production rate of 2780 Nl/min. The NHI

R&D plan also calls for a larger 5 MW engineering 

demonstration facility to be developed in the 2013

time frame.

Assembled 10-cell electrolysis stack. High temperature electrolysis research at the INEEL.