Benchmark study of performances and durability between different stack technologies for high temperature electrolysis

Abstract In the current landscape of high temperature electrolysis, mainly two solid oxide cell (SOC) technologies are being used: electrolyte‐supported and cathode‐supported SOCs. The geometrical differences, namely the thickness of the electrolyte, can lead to vastly different operating temperatures. Since most phenomena affecting performance and durability remain thermally activated, comparing stack technologies can be a difficult endeavor at best. While the most visible goal of the European project MultiPLHY consists of Sunfire GmbH building the first multi‐megawatt solid oxide electrolyzer, a work package is being dedicated to stack testing in a laboratory environment. A harmonized protocol was first elaborated to allow comparing different stack technologies. It includes the recording of performance maps, several galvanostatic steps in thermoneutral conditions, as well as load point and thermal cycles. Subsequently, Sunfire operated a pile‐up of two 30‐cell electrolyte‐supported stacks for over 8200 h, while a 25‐cell cathode‐supported stack was tested at CEA for 6800 h. The present article aims at presenting the findings gathered during the implementation of the protocol. This benchmark study puts forward performance maps as well as voltage and stack temperature profiles over time, and discusses some of the difficulties inherent to long‐term testing.