High performance coatings for PEM electrolyser metallic bipolar plates

Background Bipolar plates (BPP) for PEM (Polymer Electrolyte Membrane) electrolysers account for more than ¼ of the total system costs. Precious materials and high cost processing contribute to the approximately EUR 600 / kW. The goal of both the EU and the DoE is to reduce this cost by at least 50% over the next 10 years, thus large cost reductions must also be see in the bipolar plate technology. The 2030 target states BPP cost just over EUR 200 / kW. The objective of the project was to reduce this significantly (up to 80%), while the coatings and application methods must be suitable for mass production. This was done by using thin steel plates as substrates where the required structure is stamped. The coating must be corrosion-resistant to protect against the acidic environment of the electrolyzer while providing low current and low contact resistance to the other components. Actors COATELY was an ERA-NET project with partners from Spain and Norway. The funding in Norway was given by the Research Council of Norway. The conductive oxide materials were developed by CERPOTECH, while further processing for coating and testing of these was performed by SINTEF. Development of PVD coatings based on tantalum and indium tin oxide (ITO) was mainly carried out by Tekniker, as sub-contractor to Kendu / Sendotu. The latter focused on scaling up for mass production of the process and materials. These plates were also tested at SINTEF, in situ in an electrolysis cell and ex situ in a controlled environment that mimics the conditions in a cell. The cooperation between the partners has worked very well. Status web-meetings have been conducted once a month. Results The production cost of BPP using steel (material and stamping) is below the EU and US target for 2030. That is, the plates themselves can be manufactured for less than EUR 20 per piece. Ta-ITO coating by PVD (physical vapor deposition) is calculated to cost less than EUR 10 per plate. Two plates must be welded per cell and with an average performance of 3.5 W / cm2 the total cost will be less than EUR 20 / kW. The proposed process and materials are thus very promising, but some work remains to be done before the technical qualifications of the concept are good enough. The experiments with Ta-ITO on titanium show that the coating on the anode side degrades faster than platinum coatings, which appears to be due to the fact that some of the coating has disappeared during the test. The results are nevertheless promising to lower the contact resistance of the Ta-ITO material itself. Coating on steel plates has also been attempted, but these have not been tested in-situ in a cell. The results after testing in simulated electrolysis environment show that full coverage of the coating on steel is required. Small holes where the steel is exposed to acidic environment leads to relatively severe corrosion and leaching of corrosion products / ions to the rest of the electrolysis cell. The strategy for solving this has been to work with multilayer coatings with different materials and properties. Optimum materials were not found during the project. The composite materials showed high conductivity, but in combination with different binders and solvents the contact resistance in the coating became too high. Further work with these must first focus on optimizing the choice of materials that fit well together. Throughout the project, the partners have developed further expertise in testing components for PEM electrolysers. In order to reduce the cost and time of such attempts, ex-situ experiments are often used where the environment and test conditions mimic what actually happens in a cell. Test protocols have been adjusted and improved along the way, so they are now more representative for the investigation of relevant material properties. The market study conducted showed that the global market potential for BPP for PEM electrolyzers could be up to 0.5 billion EURO in 2030 and a ten-fold increase can be seen by 2050. Impact Despite the fact that not all technical goals were achieved, the research was carried out with the planned activities and according to the budget. The materials and process development achieved in the project are not commercially exploitable at present. On a general basis, work has attracted great interest from both academia and industry. There has not been so many similar public funded projects before, so the interest in the topic has been high. The results and test protocols will be used as input in further work. Further improvement is still required for both PVD and composite coatings before they can be used commercially in electrolyzers. For both, there is a need for additional financial support to further develop and improve the materials. CERPOTECH and Tekniker have already been granted a new project, but on another topic.

In order to be able to take full advantage of intermittent renewable energy sources, the energy needs to be stored. This energy can be stored as hydrogen, and later be converted to energy in fuel cells. The desired way to produce hydrogen is by water elec trolysis, and the most energy efficient system is the polymer electrolyte membrane electrolyser. A major obstacle for commercialization of PEM electrolysers is the expensive bipolar plates, which nowadays are made of titanium. The bipolar plate for a PEM electrolyser is very challenging compared to a PEM fuel cell because of the fact that the anodic potential is twofold. The proposed project has acknowledged the problem, and two highly innovative ways to both reduce cost and increase the total system perf ormance of the electrolyser is suggested. The COATELY project aims at developing a new generation of high performance coatings for cost-effective stainless steel BPP for PEM technology deposited by advanced coating techniques.