Impact of Intermittent Operation on Lifetime and Performance of a PEM Water Electrolyzer

Abstract

The aim of this study is to provide a better understanding of performance degrading mechanisms occurring when a proton exchange membrane water electrolyzer (PEM-WE) is coupled with renewable energies, where times of operation and idle periods alternate. An accelerated stress test (AST) is proposed, mimicking a fluctuating power supply by operating the electrolyzer cell between high (3 A cm −2 geo) and low current densities (0.1 A cm −2 geo), alternating with idle periods during which no current is supplied and the cell rests at open circuit voltage (OCV). Polarization curves, periodically recorded during the OCV-AST, reveal an initial increase in activity (≈50 mV after 10 cycles) followed by a significant decrease in performance during prolonged OCV cycling due to an increasing high frequency resistance (HFR) (≈1.6-fold after 718 cycles). These performance changes can clearly be related to the OCV periods, since they are not observed in a reference experiment where the OCV period is replaced by a potential hold at 1.3 V. The origin of the phenomena, which are responsible for the initial performance gain as well as the subsequent decay are analyzed via detailed electrochemical and physical characterization of the MEAs, and an operating strategy to prevent performance degradation is proposed.

Current Challenges in Catalyst Development for PEM Water Electrolyzers

“…Note that the here advanced hypothesis is different from that proposed by Cherevko et al , who on the basis of half‐cell experiments in an aqueous sulfuric acid electrolyte proposed that the intrinsic dissolution rate of hydrous iridium oxide is higher than that of crystalline IrO 2 . Owing to the high iridium loading in the here shown OCV‐AST, the effect of iridium dissolution on the OER activity is very small (< 20 mV ) and the vast majority of the observed performance losses after 718 OCV‐AST cycles (red diamonds Fig. b) are due to an increase of the HFR (red diamonds Fig.…”

“…b), where the anode potential was always kept positive of 1.3 V RHE . Both the increase in HFR as well as the formation of a hydrous Ir(OH) x phase clearly shown by cyclic voltammetry are both related to cycling the anode potential between ≈ 0 V RHE during the OCV‐periods and high potentials when current is applied to the electrolyzer. The main cause for an increasing HFR along with the observed performance decrease over the course of the OCV‐AST can be related to the formation of an additional interfacial resistance on the anode side of the MEA.…”

“…The main cause for an increasing HFR along with the observed performance decrease over the course of the OCV‐AST can be related to the formation of an additional interfacial resistance on the anode side of the MEA. This additional resistance is the result of a higher contact resistance due to the passivation of the Ti‐PTL (porous transport layer) in combination with the less electrically conductive Ir(OH) x . In summary, significant degradation of an electrolyzer MEA can occur during extended OCV periods during which the anode potential is allowed to decay to ≈ 0 V RHE , a situation which should be avoided in a PEM‐WE, at least when using non‐coated Ti‐PTLs.…”

Electrodeposition at Highly Negative Potentials of an Iron‐Cobalt Oxide Catalyst for Use in Electrochemical Water Splitting

“…This will have implications in a commercial sense for electrolysers that are connected to intermittent renewable energy sources that may be subjected to rapid start up and shut down conditions. It has been shown that a reverse current can flow in the electrolyser if a base level of power is not provided . This has significant implications for the stability of the anode.…”

“…It has been shown that a reverse current can flow in the electrolyser if a base level of power is not provided. [86][87] This has significant implications for the stability of the anode. This degradation in performance may be related to structural transitions such as this occurring during reverse current flow in the electrolyser.…”