Durability Analysis on PEM Water Electrolyzers against the Voltage Fluctuation of Wind Power
Authors: Honsho Yusuke , Nagayama Mayumi , Sasaki Kazunari , Hayashi Akari 
Published: December 2020

Introduction

Utilizing of hydrogen as an energy carrier is drawing attention as one of the efficient uses of renewable energy. Water electrolysis becomes a key technology. Polymer electrolyte membrane (PEM) water electrolyzers can be operated from room temperature and can be compact owing to the thin electrolyte membrane, leading to low ohmic resistance. Such characteristics will be advantages when water electrolyzers are combined with renewable energy power plants.
While the combination between renewable energy and water electrolyzers is important, one of the problems on renewable energy is the fluctuation of the output voltage. Durability of PEM water electorlyzers against such voltage fluctuation has not been well studied. In our previous study, our group have tried durability analyses of a PEM water electrolysis cell against the voltage fluctuation simulating the wind and solar power fluctuation.[1] As a result, degradation of the water electrolysis cell according to the change in the anode catalyst layer was found. In this study, in order to further understand the durability against the voltage fluctuation of renewable energy, an actual voltage fluctuation of wind power was applied a PEM water electrolysis cell, and changes in electrochemical characteristic were analyzed.

Experimental method

A PEM water electrolysis cell was prepared using a method of preparing a membrane electrode assembly (MEA). MEAs were made with IrO2 anode, Pt/KB cathode, and Nafion117 membrane. The size of electrode was 1 cm2, and the anode loading and cathode loading were 0.5 mg IrO2/cm2 and 0.3 mg Pt/cm2, respectively. The actual 24-hour voltage fluctuation of wind power used in this study is shown in Figure 1. Since a single water electrolysis cell was tested in this study, the voltage was reduced into one hundredth and applied to a MEA. MEAs were electrochemically evaluated before and after applying the voltage fluctuation using impedance and current-voltage (I-V) measurements. Then, each overvoltage was separately analyzed. In addition, for the purpose of evaluating the change in the anode individually, CV measurements were conducted using the cathode as a reference electrode.

Results and discussion

The change in the current density at 2.0 V before and after every 24 hours of the voltage fluctuation is shown in Figure 2. In Figure 2, the current density increased in the initial term of the durability test, which means I-V performance was improved. After 96 hours, where the current density reached the highest value, the current density declined. Regarding to the initial improvement in I-V performance, each overvoltage was separately analyzed. As a result, ohmic overvoltage, concentration overvoltage, and activation overvoltage were all reduced. In order to study the decrease in activation overvoltage more deeply, the change in the electric double layer of the anode was evaluated by obtaining CV on the anode side. Accordingly, the increase in the electric double layer, leading to increase in active surface area was observed. Regarding to the decrease in I-V performance after 96 hours, it was just temporary decline and not owing to the degradation of a water electrolysis cell. The difference in results in our previous study and this study will be deeply discussed.

Reference

[1] Marika Muto et al, ECS Transactions, 13, 719-726 (2018).

Figure 1