Plasma-Enhanced High Temperature Solid-Oxide Electrolysis Cells: The Search for Synergy

Abstract

High temperature solid-oxide electrolysis cells (SOECs) are a promising conversion technology to produce energy-rich molecules such as CO from CO2 [Song2019]. The high energy efficiency and separation of product streams intrinsic to oxygen ion-conducting electrolyte materials are desirable for renewable synthetic fuel and value-added chemical production at industrial scale. While most improvement in SOEC performance in recent years has been achieved by advancements in electrode materials and cell design, the use of plasmas to enhance SOEC performance also shows potential [Mori2017, Patel2019]. It is reported that the oxygen exchange rate for yttria-stabilized zirconia (YSZ) is 100 times higher simply by exposure to plasma [Rohnke2004]. Despite the apparent synergy in such plasma-SOEC approaches, the underlying mechanisms of plasma and surface processes are presently not well understood. A common explanation is that plasma-activated species (e.g., by vibrational excitation, plasma-dissociation and ionization) support the reduction kinetics on the surface. The effects of plasma-induced surface charging and local fields on, for instance, the vacancy concentration and exchange kinetics may also play a significant role. Dedicated experiments aimed to distinguish between these underlying mechanisms are essential to reveal the true nature of the synergy. In this contribution, we will present our novel hybrid plasma-SOEC reactor aimed at investigating fundamental aspects of SOEC-plasma synergy. The plasma is generated in a brushed electrode discharge in the quiescent region [Ratynskaia2015], which provides a highly stable, homogeneous and field-free plasma environment well suited for a controlled exposure of the SOEC. Langmuir probe measurements will help to obtain insights into the plasma properties, complemented with 1D plasma-kinetic modelling of the plasma bulk and wall region. With this combined experimental-modeling approach, we intend not only to quantify the plasma-effect on SOEC performance, but also to develop insights into the rate-limiting kinetics. We will share our first experimental results on plasma-enhanced oxygen pumping in an O2/He plasma environment. Song, Y., Zhang, X., Xie, K., Wang, G., & Bao, X. (2019). High-Temperature CO2 Electrolysis in Solid Oxide Electrolysis Cells: Developments, Challenges, and Prospects. Advanced Materials Mori, S., & Tun, L. L. (2017). Synergistic CO2 conversion by hybridization of dielectric barrier discharge and solid oxide electrolyser cell. Plasma Processes and Polymers, 14(6), 1600153. Patel, H., Sharma, R. K., Kyriakou, V., Pandiyan, A., Welzel, S., Van De Sanden, M. C. M., & Tsampas, M. N. (2019). Plasma-Activated Electrolysis for Cogeneration of Nitric Oxide and Hydrogen from Water and Nitrogen. ACS Energy Letters, 4(9), 2091–2095. Rohnke, M., Janek, J., Kilner, J. A., & Chater, R. J. (2004). Surface oxygen exchange between yttria-stabilised zirconia and a low-temperature oxygen rf-plasma. Solid State Ionics, 166(1–2), 89–102. Ratynskaia, S., Dilecce, G., & Tolias, P. (2015). BABE – a brush cathode discharge for thermal fluctuation measurements. J. Plasma Physics, 81(2), 345810202.

Enhancing CO2 conversion with plasma reactors in series and O2 removal

“…Furthermore, the electrode stability is much better compared to the conventional CO2 electrochemical conversion. In-situ plasma-SOEC reactors show promising results as well, [59,60] although this is not applicable for all types of plasma reactors depending on the required temperatures, plasma properties, etc.…”