The PEPPER project is paving the way for the scale-up of next-generation steam electrolysis technology. As simple as a water splitting reaction can look, the production of green hydrogen by electrolysis remains an electro-intensive process. In this context, high-temperature steam electrolysis technologies appear as the most promising ones, because a significant share of the energy needed to split the water molecule is supplied in the form of heat rather than electricity. This makes high-temperature steam electrolysis especially advantageous when low-cost heat can be used to generate steam, for example by recovering waste heat from industrial processes. The dominance of solid oxide cell technology Today, the landscape for high-temperature technologies is dominated by solid oxide electrolysis technology, relying on the ability of certain oxides — often zirconia-based — to conduct oxygen ions at temperatures typically above 700°C. These transport properties in zirconia-based materials have been known for a long time: at the end of the 19th century, Walther Nernst made use of this feature to use zirconia as glowing rod in an early form of incandescent …