Tracing Resistances of Anion Exchange Membrane Water Electrolyzer during Long-term Stability Tests

Abstract

In this study, an anion exchange membrane water electrolysis (AEMWE) cell was operated for ~1000 h at a voltage bias of 1.95 V. Impedance spectra were regularly measured every ~ 100 h, and changes in the ohmic and non-ohmic resistance were traced as a function of time. While there was relatively little change in the I-V curves and the total cell resistance during the long-term test, we observed various electrochemical phenomena in the cell: 1) initial activation with a decrease in both ohmic and non-ohmic resistance; 2) momentary and non-permanent bubble resistance (non-ohmic resistance) depending on the voltage bias, and 3) membrane degradation with a slight increase in the ohmic resistance. Thus, the regular test protocol used in this study provided clear insights into the performance degradation (or improvement) mechanism of AEMWE cells.

Stability Tests on Anion Exchange Membrane Water Electrolyzer under On-Off Cycling with Continuous Solution Feeding

“…The difference in ASRs was 0.026 Ω cm 2 . In the present study, the difference in ASRs (0.038 Ω cm 2 ) between the tested membrane and the new membrane was comparable to the differ-ence in ASRs (0.026 Ω cm 2 ) in a previous study for a stable and undegraded membrane [34]. However, this difference in ASRs contrasted with a study in which the membrane was degraded [19].…”

“…Polarization resistance (non-ohmic ASR) is the difference between the total and ohmic ASRs; its value was 0.793 Ω cm 2 . The initial ohmic ASR of the cell was slightly higher than that in our previous studies [19,34,36] because of the lower operating temperature (40 o C). However, this value was comparable to those reported in previous studies [22,28,37].…”

“…Impedance was measured using a testing fixture developed in-house. Previous work has described the details of the testing fixture and measurement technique [34]. Initially, the ASR of the KOH solution was obtained from the high-frequency intercept (30 kHz) of the real axis and was found to be 0.835 Ω cm 2 .…”

“…The electrolyzer was operated at 40 o C in the on-off cycling mode with an applied electrical bias for ~800 h. For this purpose, a protocol in which the electrolyzer cell was operated under a current density of 500 mA cm -2 for 5 h and then left under an open circuit condition for 12 h was designed. The KOH solution was provided to the cell continuously at a rate of 2 mL min -1 (this flow rate is sufficient to prevent degradation) whether the cell was under bias or open circuit conditions [19,28,29,34]. This protocol continued until the cells reached approximately 800 h. The operation under a constant current density is called the constant current test.…”

“…However, the introduction of Li-ion batteries further complicates the system, making it even more complex. Our previous study found that when the electrolyzer cell was subjected to opencircuit conditions (for 12 h without solution feeding) once in ~100 h of operation, it did not affect the stability of AEMWE [34]. However, degradation is more likely to occur when the cell is subjected to an open-circuit condition > 5 times in 100 h of operation [19].…”