Hydrogen production via solid oxide electrolysis: Balancing environmental issues and material criticality

• Multi-criteria assessment based on joint technology definition. • Mathematical model provides reliable data on energy flows. • Prospective life cycle assessment of solid oxide electrolysis. • Quantitative material criticality of solid oxide electrolysis at product level. • Optimization of operational current density in terms of minimum impacts. Hydrogen is considered an essential component in mitigating climate change. Water electrolysis technologies present the potential for generating environmentally friendly hydrogen. The solid oxide water electrolysis attracts attention due to its high-temperature operation, leading to an unsurpassed efficiency. Nevertheless, high-temperature operation requires special materials, raising material criticality concerns. This study aims to determine the optimum current density for future solid oxide water electrolysis operation. To this end, the energetic performance of solid oxide electrolysis is assessed under different current densities with a numerical simulation. Consequently, prospective life cycle assessments and product-level material criticality assessments are performed. These dimensions are combined in a multi-criteria optimization. The environmental impacts strongly depend on electricity and heat generation, whereas manufacturing and the feed water supply play a minor role. Heat integration, a unique feature of solid oxide water electrolysis, is beneficial if heat carries less environmental impact than electricity. Then, the solid oxide electrolysis should be operated at relatively low current densities. In contrast, the material criticality decreases with increasing current densities. The multi-criteria optimization reveals that if minimizing environmental impacts and material criticality is equally vital, solid oxide water electrolysis should be operated at 0.955 A/cm 2 , whereas a focus on environmental impacts leads to lower current densities. In conclusion, the energy supply situation affects the operational current density from an environmental perspective. In contrast, the material criticality favors high current densities for solid oxide water electrolysis. When combining both, medium current densities lead to minimum environmental and material criticality issues.