Potentiostatic operation of solid oxide electrolysis cells (SOECs) at the thermoneutral voltage enables operation of the SOECs close to 100% electrical efficiency and simplifies the heat management at the stack and system level. In this work, we investigate the long-term durability of Ni/yttria-stabilized zirconia (YSZ) fuel electrode supported SOECs operated for electrolysis of steam at the thermoneutral voltage of 1290 mV, by testing cells at 800, 750, and 700 ℃ for periods exceeding 1000 h each. The cells show different initial performance due to different operating temperatures, but all experience a significant degree of initial degradation within the first 300 h, with a degradation rate of 2.80, 1.93, and 1.77 A cm−2 kh−1 (~1.80, 1.51 and 1.90% kh−1) for the cells tested at 800, 750, and 700 ℃, respectively. Hereafter the cells show stable performance or even slight activation. After 300 h of operation, the cell tested at 750 ℃ exhibits performance comparable to the cell tested at 800 ℃ and more than 74% higher than the cell tested at 700 ℃, and this is maintained until the end of the test, suggesting that among three operating temperatures 750 ℃ is the optimum one. The different degradation behavior of the cells is further investigated by electrochemical impedance spectroscopy (EIS) analysis and post-test microstructural characterization. The cause of degradation is discussed in terms of electrode overpotential. Our findings highlight the significance of operating temperature optimization on the long-term durability of SOECs when operated in potentiostatic mode.
Bibliographical noteFunding Information:
This work was supported by the project “ Efficient Power2Gas Combining SOEC and Biomass Gasification ” (EUDP no. 64017–0011 ). The authors would also like to acknowledge colleagues at DTU Energy, especially Henrik Henriksen and Søren Koch for technical assistance. Y. R. Yang acknowledges the financial support from the China Scholarship Council ( CSC201604910912 ).
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- Operating temperature
- Solid oxide electrolysis cells
- Thermoneutral voltage