4.7 Article

Parameter optimization of ZrCo-H system for durable tritium storage and delivery system of ITER

Journal

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Volume 46, Issue 11, Pages 8067-8077

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2020.11.279

Keywords

ZrCo alloy; Hydrogen storage; Cycling stability; Disproportionation

Funding

  1. National key research and development program [2017YFE0301505]
  2. Foundation of president of China Academy of Engineering Physics [YZJJLX2017008]
  3. Foundation for Distinguished Talents from Institute of Materials of CAEP
  4. National Natural Science Foundation of China [51901213, 21573200]

Ask authors/readers for more resources

The cycling stability of the ZrCo-H system is influenced by various parameters including hydrogen pressure, temperature, composition, and stoichiometric ratio of H atoms. Maintaining a stoichiometric ratio of H atoms above 1 in the ZrCo alloy can prevent disproportionation reaction and improve cycling performance.
Cycling stability of ZrCo-H system is extremely important for the long-term operation of the storage and delivery system (SDS) in ITER. Herein, the optimal cycling operation parameters were systematically investigated. It indicates that various parameters, such as hydrogen pressure, temperature, composition, and stoichiometric ratio of H atoms, will all affect the cycling performance of the ZrCo-H system significantly. The decline rate of the hydrogen capacity of the ZrCo-H system is positively correlated with the hydrogen pressure. The experimental result shows that 54% of hydrogen capacity decreases under 28.1 kPa hydrogen pressure, while 30% of attenuation is obtained when the pressure is decreased to 8.1 kPa after 14 cycles. In terms of temperature, the lowest cycling attenuation can be maintained at about 25% after 14 cycles when the dehydrogenation temperature at 550 degrees C. The effects of doping elements, Hf and Ti, on the cycling stability of ZrCo-H system are also compared. The Zr0.8Ti0.2Co sample exhibits higher cycling capacity than ZrCo and Zr0.8Hf0.2Co samples. The extremely excellent behavior can be achieved when all ZrCo alloys are continuously evacuated during the hydrogen release process, and the attenuation of only 1.1% is observed for Zr0.8Ti0.2Co after 15 cycles. Besides, the cycling attenuation is related to residual stoichiometric ratio of H atoms in ZrCo alloy during the cycling test. When the residual H atoms proportion exceeds 1 in ZrCo during dehydrogenation, hydrogen cycling capacity hardly fades. The XRD results reveal that the disproportionation of ZrCo is directly associated with the cycling degradation, yielding the more stable products of ZrCo2 and ZrH2, However, the disproportionation can be avoided during the cycling process by controlling the stoichiometric ratio of H atoms remained in ZrCo above 1. This study demonstrates that the cycling performance of ZrCo can be substantially improved when the operation parameters are properly adjusted, which provides a significant important reference for durable running of SDS in ITER. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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