2D transient electro-chemical model of steam electrolysis with Ni/Gd-Doped Ceria (CGO) fuel electrode

Abstract

The advantages of solid oxide electrolysis cells (SOECs), such as high electrical efficiency and long-term stability, make them a promising candidate for conversion of electrical energy into chemical compounds. The presence of the active double phase boundary (DPB) [1] between CGO surface and gas phase in Ni/Gadolinium doped ceria (CGO) electrodes improves the performance compared to other types of Ni/cermet electrodes, where the active area is limited to the triple phase boundary (TPB) between nickel, oxygen ion conducting ceramics and gas phase. Detailed understanding of underlying physical processes within SOEC in general and within the Ni-CGO fuel electrode in particular is crucial for cell optimisation and understanding of cell degradation. In the current study a 2D dynamic multiphase model of a commercial electrolyser cell is presented. The model spatially resolves cell composite layers as well as the gas channels. The following aspects are included: detailed surface kinetics, charge transport, as well as gas transport/conversion in the channels and porous electrodes. The main accent is made on understanding of electro-chemical processes in the fuel electrode. The model is parametrised and validated by electrochemical impedance measurements of an incremental 1 cm² electrolyte-supported symmetrical cell with Ni-CGO electrodes fueled with different compositions of H2, H2O and N2 [2]. A spatial extension of the model and subsequent validation is successfully done for 16 cm² full cells exhibiting lateral temperature and gas concentration gradients. Furthermore, using this cell model as a building block, the development of a transient 2D model of a SOEC short stack will be discussed in this contribution.