Methodological insights of defining material criticality by assessing different electrolysis and fuel cell stacks

Shifting economic sectors to a resource-efficient economy with zero net greenhouse gas emissions by 2050 faces major challenges for the European Union, which is highly dependent on material imports. Critical raw materials play a key role in a wide range of emerging technologies. In times of increasing demand, the assessment of critical raw materials is therefore of utmost importance. This study addresses methodological principles of various materials criticality indicators on product-level. Using the example of manufacturing different electrolysis and fuel cell stacks, these criticality indicators are applied, and the results are discussed. The case study demonstrated that alkaline electrolysis has the lowest criticality among the electrolyzers in seven out of nine criticality indicator evaluations. For fuel cells, the heavier stack concept shows lower criticality compared to the light-weight concept. One reason is the higher demand of rare earth elements and cobalt needed for manufacturing compared to heavier stack. Various rare earths are identified as critical in the manufacture of solid oxide electrolysis and fuel cell stacks. Iridium and nickel contribute most to criticality in the construction of proton exchange membrane electrolysis and alkaline electrolysis stacks, respectively. Five of nine indicators point to the same or similar criticality hotspots and can therefore set priorities for action in materials research for hydrogen and fuel cell systems. Nevertheless, when deciding for or against a material, one has to be aware that the criticality indicators use different sensitive sub-indicators which have an impact on the ranking of materials.