Electrochemical deposition and characterization of protective coatings for PEM electrolyzer components
Martin Leimbach, Mario Kurniawan, Christopher Zimmermann, Christian Höß, Carlos Aziz, Mathias Fritz, Michael Stich, Andreas Bund
Technische Universität Ilmenau is launching the StacIE research project, which aims to make hydrogen an environmentally friendly and more cost-effective energy carrier. Currently, around 96 percent of hydrogen is produced from fossil fuels, resulting in the release of environmentally harmful carbon dioxide. If, on the other hand, renewable energies are used, hydrogen can be produced without CO2. But the production of green hydrogen is still expensive. The StacIE project is part of the flagship H2Giga project funded by the German Federal Ministry of Education and Research, which aims to mass-produce electrolyzers for the production of hydrogen on an industrial scale. The goal: large quantities of the clean energy carrier and drastically reduced manufacturing costs.
Hydrogen is seen by many as the energy carrier of the future. The most abundant chemical element in the universe, it is readily available and clean because it is found in water. And it can be used in many ways: as a fuel for fuel cell vehicles and in heavy-duty transport, in rail and shipping, or as a raw material for the chemical or steel industries.
One of the most important processes used to produce CO2-free hydrogen is proton exchange membrane electrolysis (PEM). In this process, water is broken down into hydrogen and oxygen with the aid of an electric current. The advantages of PEM electrolysis are that it is flexible and can respond within milliseconds to the large jumps in electricity production from wind and solar plants. The big disadvantage is the high price. Due to the complexity to produce the individual components which are time-consuming and labor-intensive. This expensive production cost leads to a high hydrogen price. In addition, the precious metals used as catalyst materials raise the price further.
In the StacIE project ("Stack Scale-up - Industrialization PEM Electrolysis"), the TU Ilmenau, together with nine other project partners from industry and research institutions, is striving to upscale PEM electrolysis to the giga-watt scale. The aim is to simplify the manufacturing process and make the components for the electrolyzers more efficient.
As an alternative to using titanium-based materials, Electrodeposition offers several advantages within the manufacturing process. The metallic components of the electrolyzer, like bipolar plates and porous transport layers, can be made from relatively cheap and easy-to-manufacture materials (e.g. stainless steel). These components are plated electrochemically with thin layers to protect the components from corrosion under the harsh conditions during the electrolysis process. The coatings have to withstand high anodic potentials and low acidic conditions. Furthermore, electroplating processes can be upscaled and provide industrial-scale production at a low cost.
The metallic components are plated with several materials, particularly noble metals, nickel alloys, and multilayer coatings, and are tested in a specially designed corrosion cell to do a pre-selection of the materials and plating parameters. Special focus was given to the pretreatment of the stainless-steel substrate to provide sufficient adhesion of the electroplated layers. The corrosion resistance of selected coating systems will be further evaluated in a five-cell test stack electolyzer (Fig. 1).
The custom made five-cell stack electrolyzer is assembled in a test station with a periphery for performance monitoring, electrochemical characterization and process media analysis (Fig. 2). Components can be exchanged easily to evaluate the stability of various materials and coatings. Different test protocols can be applied on the stack electrolyzer while monitoring the electrochemical performance (e.g. corrosion products) of each cell simultaneously with a multi-channel potentiostat. The liquid media from anode and cathode side of each cell is captured separately to measure pH, conductivity and metal ion content. These parameters are strong indications of corrosion during operation of the stack.
Finally, the results of all partners within the StacIE project are collected to setup a reference stack with the optimum coating systems in matters of stability, performance, availability and cost. This fully optimized reference stack will serve as an example for future large-scale production of PEM electrolyzers.