|View of the edge of one high-temperature electrolysis cell while operating at 830º C (1,525º F). The arch-like openings carry air and the oxygen produced for the electrolysis. Source: INEEL
Researchers at DOE’s Idaho National Engineering and Environmental Laboratory (INEEL) ran a high-temperature electrolysis stack to produce hydrogen for 1,000 hours in the longest and largest experiment to date on processes that could lead to the production of hydrogen using nuclear energy.
The stack, operating at 830º C (1,525º F), produced 177 normal liters of hydrogen each hour, or 4.248 normal cubic meters in a 24-hour period—an amount (0.36 kg) equivalent to about half of a driver’s average daily gasoline usage.
INEEL has previously estimated that a single next-generation nuclear plant will be able to produce in hydrogen the energy equivalent of 200,000 gallons of gasoline each day. The US consumes about 9 million barrels of gasoline per day, or 378 million gallons.
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 resulting ions form at two poles: the anode, which is positively charged, and the cathode, which is negatively charged. Hydrogen ions gather at the cathode and react with it to form hydrogen gas, which is then collected. Oxygen goes through a similar process at the anode.
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.
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Oxygen ions are drawn through the electrolyte by the electrical potential and combine to O2 on the cathode side. The steam-hydrogen mixture exits and the water and hydrogen gas mixture is passed through a separator to separate hydrogen.
Such a high-temperature system has the potential to achieve overall conversion efficiencies in the 45% to 50% range, compared to approximately 30% for conventional electrolysis. Added benefits include the avoidance of both greenhouse gas emissions and fossil fuel consumption.
We’ve shown that hydrogen can be produced at temperatures and pressures suitable for a Generation IV reactor. The simple and modular approach we’ve taken with our research partners produces either hydrogen or electricity, and most notable of all—achieves the highest-known production rate of hydrogen by high-temperature electrolysis.—Steve Herring, lead INEEL researcher
This demonstration is seen as a necessary first step toward large-scale production of hydrogen from water rather than fossil fuels.
INEEL has been working with Ceramatec, a private-sector company, on the project for several years.
We’re pleased that the technology created over the nearly two decades dedicated to high-temperature fuel cell research at Ceramatec is directly applicable to hydrogen production by steam electrolysis.
In fact, both fuel cell and hydrogen generation functionality can be embodied in a single device capable of seamless transition between the two modes. These years of investment, both public and private, in high temperature fuel cell research have enabled the Ceramatec-INEEL team to move quickly and achieve this important milestone toward establishing hydrogen as a part of our national energy strategy.—Ashok Joshi, Ph.D., Ceramatec CEO
Secretary of Energy Spencer Abraham recently announced a grant of nearly $2 million to a Ceramatec-led effort teaming with the INEEL, the University of Washington and Hoeganaes Corp. to continue work in the broad area of high-temperature electrolysis and fuel cell development.