Redox Stability of Co-Doped Barium Niobate Thin Films in Reducing Conditions Analyzed Using Cyclic Voltammetry Measurements
Authors: Denoyer Luke H , Ramaiyan Kannan , Benavidez Angelica , Ferlauto Andre Santarosa , Fonseca Fabio Coral , Garzon Fernando H. 
Published: December 2024

Perovskite anodes (general chemical formula ABO3) for the high temperature (>750 °C) electrolysis of methane to ethylene in a ceramic solid oxide electrolysis cell require both high activity, chemical and mechanical stability as well as durability for future commercialization efforts. We have previously shown co-doped barium niobate perovskites as stable anode materials for electrochemical oxidation of methane (E-OCM)1 . The mechanism for the excellent chemical stability is highly connected to the flexible oxidation state switching of Nb4+/Nb5+ cations associated with changes in lattice oxygen concentration2
,3. To further evaluate their chemical stability in highly reducing conditions to understand their applicable potential window , this work utilizes the Ca and Fe codoped perovskite BaCa0.33Nb0.67-xFexO3-δ (BCNF). BCNF has shown very good methane activation properties and higher activities in E-OCM operation via increased conductivity and ethylene selectivity4. We deposited BCNF thin films utilizing pulsed laser deposition on various substrates such as quartz glass and yttria stabilized zirconia (YSZ) and analyzed their electrical properties using electrochemical impedance spectroscopy (EIS) in various oxygen partial pressures and cyclic voltammetry (CV) in a homemade test setup that allow for redox stability under controlled gas environments to be examined. This advanced screening methodology allows for holding at desired operating temperatures while altering the applied potential bias to simulate electrode reduction in various gas environments (for a single test). The results of these measurements along with physical characterization of the thin films by TEM, SEM, AFM will be presented to demonstrate the utility of BCNF perovskites in E-OCM applications.

References:

(1) Denoyer, L. H.; Benavidez, A.; Garzon, F. H.; Ramaiyan, K. P. Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene. Adv. Mater. Interfaces
2022, 9 (27), 2200796. https://doi.org/10.1002/admi.202200796.

(2) Denoyer, L. H.; Benavidez, A.; Brearley, A.; Ramaiyan, K.; Garzon, F. H. Chemical Stability of BaMg0.33Nb0.67-XFexO3-δ in High Temperature Methane Conversion Environments. ECS Trans.
2023, 111 (6), 587. https://doi.org/10.1149/11106.0587ecst.

(3) Denoyer, L. H.; Benavidez, A.; Brearley, A.; Ramaiyan, K.; Garzon, F. H. Electrochemical oxidative coupling of methane: deciphering the exceptional properties of BaMg0.33Nb0.67-xFexO3-δ for enhanced electrocatalysis and durable operation Energy and Fuels.
2024, Accepted. https://doi.org/10.1021/acs.energyfuels.4c00720

(4) Ramaiyan, K.; Denoyer, L. H.; Benavidez, A.; Garzon, F. H. Role of Dopants in Fine-Tuning the Electrical and Catalytic Properties of Barium Niobate Perovskites Towards High-Temperature Electrolyzer Application. ECS Trans.
2023, 111 (6), 1139. https://doi.org/10.1149/11106.1139ecst.