The penetration of fuel cells and electrolyzers in energy systems calls for their scale-up to the gigawatt (GW) level. High temperature solid oxide cells (SOC) offer unrivaled efficiencies in both electrolysis and fuel cell operation. However, they are made of ceramics and are brittle by nature. Consequently, a high mechanical strength to avoid failure during stacking is essential to achieve a high manufacturing yield. Here, we show that without changing the materials of the state-of-the-art cells, thin and dense ceria interlayers enable comparable power densities and durability in fuel cell operation. The sole tuning of the morphology and processing of the interlayers reduce the residual stress in the cell significantly which increases its mechanical strength by up to 78%. These results promise performance gains of similar magnitude by enabling a substantial decrease of the electrolyte thickness while maintaining robustness. This stress engineering approach presents a way to increase the volumetric power density and material efficiency of SOC systems.

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