Development and testing of an anion exchange membrane electrolyser

https://doi.org/10.1016/j.ijhydene.2015.04.149Get rights and content

Highlights

  • NiWTiOx and CoNiMoW alloys show excellent properties as cathodes for AAEMWE.

  • The developed AEM show better chemical stability than the commercially available.

  • An OH conducting ionic binder is a necessary condition for AAEMWE.

Abstract

In the context of energy policy and the use of renewable energies, our research institute collaborates with other partners on the development of a compact, environmental-friendly and effective electrolyser for efficient power storage. This electrolyser combines the positive properties of the alkaline water electrolysis and the proton exchange membrane (PEM) electrolysis. On the cathode side on porous current collectors were electrodeposited in one step multi-component non-precious alloys. New cross-linked anion-exchange membranes have been developed to achieve high ionic conductivity. The anode side was coated with the sol–gel method. The catalytic activity of the electrodes was investigated by electrochemical studies. Current collectors have been tested under real conditions of electrolysis. For the construction of a corresponding single cell, media supply was taken into consideration and appropriate materials for current collectors, the bipolar plates and gaskets were selected.

Introduction

In the recent years the renewable energy sources got an increasing significance. A disadvantage of these sources is the fact that the produced electricity is not constant. Alkaline water electrolysers (AWE) may store the excess electricity, produced from solar or wind power sources, converting it into chemical energy via H2 production. The present effective AWE are based on large-scale concepts of limited current densities, using KOH as electrolyte. These caustic solutions are not quite eco-friendly and require a complex system design.

Therefore it would be an advantage to abandon the caustic solution like in a PEM electrolyser but without using platinum group metals (PGM). In order to do this, there have to be developed new anion conducting membranes and a new type of current collectors – substrates with a distinct and well developed porous surface [1], [2] covered with multiple component non-precious metal catalysts [3], [4]. In one previous work we presented the three alloys NiWTiOx, CoMn and CoNiMoW and their positive effect on the Hydrogen Evolution Reaction (HER) [5]. The usage of such reasonably priced substrate and catalyst materials for both current collectors will reduce the costs of the electrolyser.

Water electrolysers based upon alkaline anion exchange membranes (AAEM) give the opportunity to replace the KOH in AWE with solid polymer electrolyte [6], [7], [8], [9]. This will make them environmentally friendly and compact, which means user-friendly and suitable also for small and medium-sized enterprises.

The goal of this project was to develop an anion exchange membrane electrolyser with separate fabrication of the different components of the electrolyser with a subsequent membrane electrode assembly (MEA). This technique offers certain advantages: a high variability is possible by using several different substrates, combined with various methods of layer deposition and different layer types; a treatment of the layers (for example thermal activation) is possible; the used anodic and cathodic current collectors could be composed of different materials.

In this work we want to sum up the different aspects of the development of such electrolysers and the difficulties in the early stages by assembling the alkaline cell. The main targets were as follows: producing economically priced electrodes with low hydrogen and oxygen overpotential, which are stable at the electrolysis conditions; development of a cross-linked AAEM with high ionic conductivity; testing the different components assembling a real alkaline cell.

The fundamental design of an alkaline anion exchange membrane water electrolyser cell (AAEMWE) is shown in Fig. 1. The cell contains an AAEM which separates two electrode compartments. Both electrodes consist of a bipolar plate with a flow field and a substrate covered with a catalyst layer. The purpose of the channels in the flow fields is the conduction of water and produced gases. The two bipolar plates are separated by a gasket, which defines the electrode compartment with the facing sides of anode and cathode assemblies (Fig. 1) and seals the cell against the environment in order to run the cell safely.

In this study, we demonstrate the electrochemical deposition of three alloys with different structures on various substrate materials, the production of AAEM and first operations of MEAs containing the new developed current collectors.

Section snippets

Experimental setup

The surface morphologies of the anode and cathode current collectors were investigated by EDX-analysis, X-Ray fluorescence spectrometer (XDAL, Helmut Fischer GmbH & co. KG) and scanning electron microscopy (SEM) with a Leo Supra 55VP microscope from Carl Zeiss AG.

The electrodes with a geometrical surface of about 2 cm2 were tested for HER and for OER in 1 M KOH (p.A., Sigma Aldrich) in a classical 3-electrode electrochemical cell using electrochemical workstation IM 6 (Zahner). Ti–Pt mesh was

Cathode electrodes

At first different nickel meshes were used as substrates. It was estimated that the presence of TiOx-particles improve the electrocatalytic activity of the sample in comparison with the pure substrate by 300 mV [5]. In brief, the reason for this influence of the TiOx on the decrease of the H2 evolution polarization could be found in the following mechanism of water adsorption and dissociation on TiO2 surfaces. It is known, that on point defects (O vacancies) in the TiO2 water adsorbs, interacts

Conclusion

  • 1)

    Different alloy and composite coatings of non-precious metals have been prepared as electrocatalyst by electrodeposition on stainless steel non-woven fabrics for anion exchange membrane electrolysers. NiWTiOx and CoNiMoW alloys show excellent properties for reduction the hydrogen overpotential in wide temperature and current region.

  • 2)

    The sol–gel method is not appropriate for covering the stainless steel non-woven fabrics.

  • 3)

    The novel membranes proved to show better chemical stability in high

Acknowledgements

The project 402 ZN of the Research Association “Association of the Research Institute for Precious Metals and Metals Chemistry e.V.” was financed by the AiF within the program to promote the Industrial Research Collective (IGF) from Federal Ministry of Economics and Technology (BMWi) according to a decision of the German Federal Parliament. The Federal Ministry of economics and Technology used ‘Kapitel 0905; Title 68601; IGF Vorhaben N. 402 ZN’. Translated: Section 0905; Title 68601; Project

References (29)

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