Characterisation of a proton exchange membrane electrolyser using electrochemical impedance spectroscopy

Abstract

Hydrogen is a promising energy carrier and a possible replacement for fossil fuel energy sources in the future. Hydrogen has the highest energy content per unit weight of any known fuel. The proton exchange membrane (PEM) electrolyser is a promising technology to produce hydrogen by splitting water into hydrogen and oxygen. A fundamental characterisation study of the PEM electrolyser is necessary to improve the technology. The aim of this study is therefore to characterise a PEM electrolyser using electrochemical impedance spectroscopy (EIS). EIS is a non-invasive technique which measures the response of a system by applying a small sinusoidal disturbance signal. The advantage of using EIS is that the technique has the ability to distinguish between the different electrochemical processes. The EIS technique can be applied while the PEM electrolyser is operated at normal conditions. Models found in the literature were used to develop an equivalent circuit model in such a way that each component in the equivalent circuit model represents a process or component in the PEM electrolyser. The EIS experimental results are fitted to the equivalent circuit model using a non-linear least squares method. The equivalent circuit model was verified by using other electrochemical techniques such as the polarisation curves and Tafel plots. The polarisation curve was used to verify the ohmic resistance of the PEM electrolyser. Tafel plots showed the same trend as the EIS results for the activation losses. Mass transfer losses were verified by changing the anode gas diffusion media. The most significant findings which forms part of the validation of the equivalent circuit model are that the equivalent circuit model is capable of characterising different membrane electrode assemblies (MEAs), it can indicate the optimum operating area and it can facilitate component optimisation.