Investigation of oxygen permeation enhancement with He/O₂ plasma and SOEC interaction

High temperature solid-oxide electrolysis cells (SOECs) using oxygen-selective conducting membrane in combination with plasma has shown high conversion efficiencies in nitrogen fixation and CO₂ conversion, which provides a promising method for renewable energy usage and gas conversion. But the underlying kinetics and limiting rates of the plasma-assisted oxygen conducting membrane remain not clear. The plasma-activated species (e.g., by plasma-excitation, dissociation and ionization) may promote the reduction kinetics on the ion-conducting membrane surface. The effects of plasma-induced surface charging and local fields on the exchange kinetics may also play a significant role in the improvement of the oxygen permeation fluxes of the ion-conducting membrane. To understand the interaction of the plasma and the oxygen-conducting membrane, we develop a dedicated plasma-SOEC reactor to investigate the plasma enhanced oxygen permeation mechanism.

In this contribution, we will present the experimental results of the enhancement of the oxygen permeation fluxes owing to the presence of the oxygen radicals and electrons from He/ O₂ low pressure (~1 Torr) plasma. Langmuir probe measurements and optical emission spectrometry and actinometry will determine the plasma properties (electron density, electron temperature and O radical densities etc.) and provide inputs for the plasma-kinetic modelling of the plasma bulk and wall region. The characterizations of the SOEC with different plasma conditions and membrane temperature are conducted to determine the pumping rates (current density) of the oxygen permeation process. Ultimately, the plasma effects on SOEC performance will be quantified, and novel insights into the ion-conducting rate-limiting kinetics will be discussed.