Acta Phys. -Chim. Sin. ›› 2019, Vol. 35 ›› Issue (3): 284-291.doi: 10.3866/PKU.WHXB201804171

• ARTICLE • Previous Articles     Next Articles

Effect of Oxygen Partial Pressure on Solid Oxide Electrolysis Cells

Quan HOU1,3,Chengzhi GUAN1,2,3,Guoping XIAO1,2,Jian-Qiang WANG1,2,*(),Zhiyuan ZHU1,2   

  1. 1 Department of Molten Salt Chemistry and Engineering, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, P. R. China
    2 Key Laboratory of Interfacial Physics and Technology, Chinese Academy of Sciences, Shanghai 201800, P. R. China
    3 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2018-03-21 Published:2018-08-28
  • Contact: Jian-Qiang WANG E-mail:wangjianqiang@sinap.ac.cn
  • Supported by:
    the "Strategic Priority Research Program" of the Chinese Academy of Sciences(XDA02040600)

Abstract:

High-temperature (700–900 ℃) steam electrolysis based on solid oxide electrolysis cells (SOECs) is valuable as an efficient and clean path for large-scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steam methane reforming or coal gasification. The operation parameters, in particular the feeding gas composition and pressure, significantly affect the performance of the electrolysis cell. In this study, a computational fluid dynamics model of an SOEC is built to predict the electrochemical performance of the cell with different sweep gases on the oxygen electrode. Sweep gases with different oxygen partial pressures between 1.01 × 103 and 1.0 × 105 Pa are fed to the oxygen electrode of the cell, and the influence of the oxygen partial pressure on the chemical equilibrium and kinetic reactions of the SOECs is analyzed. It is shown that the rate of increase of the reversible potential is inversely proportional to the oxygen partial pressure. Regarding the overpotentials caused by the ohmic, activation, and concentration polarization, the results vary with the reversible potential. The Ohmic overpotential is constant under different operating conditions. The activation and concentration overpotentials at the hydrogen electrode are also steady over the entire oxygen partial pressure range. The oxygen partial pressure has the largest effect on the activation and concentration overpotentials on the oxygen electrode side, both of which decrease sharply with increasing oxygen partial pressure. Owing to the combined effects of the reversible potential and polarization overpotentials, the total electrolysis voltage is nonlinear. At low current density, the electrolysis cell shows better performance at low oxygen partial pressure, whereas the performance improves with increasing oxygen partial pressure at high current density. Thus, at low current density, the best sweep gas should be an oxygen-deficient gas such as nitrogen, CO2, or steam. Steam is the most promising because it is easy to separate the steam from the by-product oxygen in the tail gas, provided that the oxygen electrode is humidity-tolerant. However, at high current density, it is best to use pure oxygen as the sweep gas to reduce the electric energy consumption in the steam electrolysis process. The effects of the oxygen partial pressure on the power density and coefficient of performance of the SOEC are also discussed. At low current density, the electrical power demand is constant, and the efficiency decreases with growing oxygen partial pressure, whereas at high current density, the electrical power demand drops, and the efficiency increases.

Key words: Solid oxide electrolysis cell, Interface, Oxygen partial pressure, Theoretical model, Computational fluid dynamics

MSC2000: 

  • O646