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

A Weiß,M Bernt,A Siebel,T.-H Shen,H A Gasteiger,V Tileli

doi:10.1149/2.0421908jes

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−2geo) and low current densities (0.1 A cm−2geo), 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.

Highlights

While it is well known that alkaline water electrolyzers must be operated with a so-called protective current in stand-by/idle conditions in order to avoid a substantial performance degradation,[4,7,9,10] very little is known about the gravity of this effect in polymer electrolyte membrane water electrolyzer (PEM-WE), even though it will be an important consideration for coupling PEM-WEs with renewable energy sources.[6,11]
First a high (3 A cm−2geo) and a low (0.1 A cm−2geo) current density are drawn from the cell, followed by a current interrupt during which the cell is left to rest at the open-circuit voltage (OCV), simulating shut-off periods of a PEM-WE operated with intermittent renewable energy
An accelerated stress test (AST) protocol was designed comprising periods of operation at two current densities (3 A cm−2geo and 0.1 A cm−2geo), alternating with idle periods where the cell is left at the OCV in order to simulate the discontinuous power output of renewable energy sources

Summary

Introduction

The concomitant increase in gas permeation leads to an unacceptably large, safety-critical H2 concentration in the O2 anode compartment, as the H2 oxidation activity of iridium based anode catalysts is very poor (contrary to the O2 reduction activity in the H2 anode). This is described in an early study by Stucki et al, who showed that the failure of a dynamically operated 100 kW PEM-WE plant after only ≈15,000 h was mostly related to thinning of the PFSA membrane, caused by chemical degradation.[12] Here, it should be noted that the chemical durability of today’s PFSA membranes is dramatically better. The authors observed a reduction of the anodic exchange current density, which they attribute to a contamination with titanium from either the anode catalyst itself (iridium oxide coated onto a titanium oxide support) or the anodic Ti-PTL

Objectives

Results

Conclusion