The Stress Engendered by Oxygen Bubble Formation in the Electrolyte of Solid Oxide Electrolysis Cells

Abstract

It has been reported that running a Solid Oxide Electrolysis Cell above a critical current degrades the cell very quickly. This degradation has been linked to oxygen bubble formation in the electrolyte near the oxygen electrode. The applied current in the presence of charge transfer resistances is responsible for a high oxygen potential under the oxygen electrode which translates into a large driving force for the formation of oxygen gas in the electrolyte and can lead to the nucleation of oxygen gas bubbles. When such a bubble nucleates, local equilibrium at the interface between the bubble and oxide leads to an extremely high pressure inside it introducing, in return, significant stresses in the oxide. In this paper, the stress field surrounding the oxygen bubbles in the electrolyte is treated and the resulting elastic energy is determined.

Degradation of (La0.8Sr0.2)0.98MnO3−δ–Zr0.84Y0.16O2−γ composite electrodes during reversing current operation

“…3i,l,m This high effective oxygen pressure can drive the observed nucleation of oxygen bubbles in the region near the electrode-electrolyte interface. 3m In one case, a critical h required to nucleate oxygen bubbles in YSZ was predicted to be 0.28 V. 12 The present results, where the h value sufficient to cause degradation was between 0.18 V and 0.33 V, are consistent with this predicted value. Other models are based on La 2 Zr 2 O 7 formation 3i and LSM lattice contraction 3l due to the high oxygen potential, but these do not predict potential values where degradation is expected.…”

High Temperature Electrolysis in Alkaline Cells, Solid Proton Conducting Cells, and Solid Oxide Cells

“…Modeling has been used to study the degradation of SOECs, − and the observed bubble formation/delamination at the oxygen electrode observed when operating the SOECs at high current densities. It has been suggested that the delamination is a result of an increased oxygen pressure within the electrolyte close to the oxygen electrode/electrolyte interface , or being related to the temperature gradients across the cell and the different thermal expansion coefficients (TEC) for the electrode and electrolyte . It has to be mentioned that delamination is not only observed at the interface, which TEC differences might account for, but also inside the electrolyte, which TEC differences cannot account for.…”