high temperature electrolysis

High temperature electrolysis (HTE) is a method of generating hydrogen from water, utilising high temperatures.

What is high-temperature electrolysis? (HTE)

High temperature electrolysis is more efficient than lower temperature methods as energy is already supplied as heat, a bi-product of another process. At over 2500 °C, water breaks down to hydrogen and oxygen through thermolysis, not requiring the electrical input. However, these temperatures are impractical. HTE systems realistically operate up-to 850 °C. At 100 °C, it is 41% efficient and at 850 °C, 225 this rises to 64% efficiency.

 

Hydrogen economy

Alternative hydrogen production methods are possible, such as the thermochemical sulfur-iodine cycle. Thermochemical production might reach higher efficiencies than HTE because no heat engine is required but mass production will require advances in materials that can withstand high-temperature and pressure.

The market for hydrogen is rapidly expanding and growing at about 10% per year. Hydrogen vehicles, fulfilling the global net zero remit are an example. Pyrolysis of hydrocarbons to produce the hydrogen, which results in CO2 emissions is the main process. The two major consumers are oil refineries and fertiliser plants.

 

 

Thermodynamics (hydrogen electrolysis fuel cells)

During electrolysis, the amount of electrical energy that must be added equals the change in Gibbs free energy of the reaction plus the losses in the system. The losses can be close to zero, so the maximum thermodynamic efficiency of any electrochemical process is 100%.

In most cases, such as room temperature water electrolysis, the electric input is larger than the enthalpy change of the reaction, so some energy is released as waste heat. In the case of electrolysis of steam into hydrogen and oxygen at high temperature, the opposite is true. The maximum theoretical efficiency of a fuel cell is the inverse of that of electrolysis at the same temperature.

Applications for hydrogen

HTE is an inefficient way to store energy as conversion losses of energy occur both in the electrolysis process, and in the conversion of the resulting hydrogen back into power.

HTE is of interest as a more efficient route to the production of hydrogen, to be used as a carbon neutral fuel and general energy storage. It may become economical if cheap non-fossil fuel sources of heat (solar, nuclear, geothermal) can be used in conjunction with non-fossil fuel sources of electricity (solar, wind and nuclear).

Possible supplies of cheap high-temperature heat for HTE are all non-chemical, including nuclear reactors, concentrating solar thermal collectors, and geothermal sources.

 

Nuclear electrolysis projects

The Department of Energy, US, awarded $3.5 million to three hydrogen nuclear production research and development projects. Their technologies aim to produce hydrogen at less than $4/kg.

According to the International Atomic Energy Agency (IAEA), in the high temperature range of 800–1000 °C, electricity input could be about 35% lower than that of conventional electrolysis.

 

Hydrogen electrolysis for MARS mission

High temperature electrolysis with solid oxide electrolyser cells has also been proposed to produce oxygen on Mars from atmospheric carbon dioxide, using zirconia electrolysis devices.

 

 

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References

  1. Hauch, A.; Ebbesen, S. D.; Jensen, S. H.; Mogensen, M. (2008). “Highly Efficient high temperature electrolysis”. J. Mater. Chem18: 2331–2340. doi:10.1039/b718822f.
  2. ^ Badwal, SPS; Giddey S; Munnings C (2012). “Hydrogen production via solid electrolytic routes”WIREs Energy and Environment2 (5): 473–487. doi:10.1002/wene.50.
  3. ^ Hi2h2 – High temperature electrolysis using SOEC
  4. ^ WELTEMP-Water electrolysis at elevated temperatures
  5. ^ Kazuya Yamada, Shinichi Makino, Kiyoshi Ono, Kentaro Matsunaga, Masato Yoshino, Takashi Ogawa, Shigeo Kasai, Seiji Fujiwara, and Hiroyuki Yamauchi “High Temperature Electrolysis for Hydrogen Production Using Solid Oxide Electrolyte Tubular Cells Assembly Unit”, presented at AICHE Annual Meeting, San Francisco, California, November 2006. abstract
  6. ^ “Steam heat: researchers gear up for full-scale hydrogen plant” (Press release). Science Daily. 2008-09-19.
  7. ^ “Nuclear hydrogen R&D plan” (PDF)U.S. Dept. of Energy. March 2004. Archived from the original (PDF) on 2013-06-22. Retrieved 2008-05-09.
  8. ^ Wall, Mike (August 1, 2014). “Oxygen-Generating Mars Rover to Bring Colonization Closer”Space.com. Retrieved 2014-11-05.
  9. ^ The Mars Oxygen ISRU Experiment (MOXIE) PDF. Presentation: MARS 2020 Mission and Instruments”. November 6, 2014.
  10. https://en.wikipedia.org/wiki/High-temperature_electrolysis
  11. https://www.greencarcongress.com/2018/05/20180525-hte.html