Electrochemical Conversion of Methane to Ethylene Utilizing Highly Durable Barium Niobate Perovskites

Abstract

Efficient conversion of methane to value added products such as olefins and aromatics has been in pursuit for the past several decades. The demand has increased further due to the recent discoveries of shale gas reserves. Electrochemical methane conversion is gaining attention due to its ability to control the oxide ion flux that will help reduce the over-oxidation of methane while also help activate methane via applied potential. High temperature electrolysis further benefits this process due to improved kinetics. Unfortunately, high temperature operation also leads to materials degradation via sintering, crystal structure disproportion to thermodynamically more stable phases, and interfacial reactions that reduces the performance. For example, lifetime requirements for energy conversion technologies often times exceed 10 years of usage with no more than 20% degradation.[1] Similarly, we demonstrated the chemical instability of Sr2Fe1.5Mo0.5O6- d (SFMO) perovskite that was reported to show good methane activation properties.[2] [3] SFMO formed carbonates and coke upon exposure to CH4. Hence, the durability measurement results are often not reported for these catalysts under the extremely reducing or oxidizing high temperature environments. We have developed an exciting class of barium niobate perovskite materials with varying levels of Mg/Ca and Fe co-doping that show good catalytic activity towards methane activation in the electrochemical and conventional heterogeneous oxidative coupling environment.[4] These catalysts further demonstrate durable electrochemical activities over five days of continuous operation. We have performed thermogravimetric, FT-IR and electrochemical linear sweep voltammetry methods to rapidly determine their stability under operationally relevant conditions and these results are compared to stability calculations. Stability determinations of our perovskite oxide electrocatalysts for EC-OCM offer an excellent example of our approach towards evaluation of materials durability under challenging temperature and reducing conditions. These perovskite materials could also serve as a support for a wide variety of catalyst materials for high temperature applications thus opening up new possibilities. References [1] A. Hauch, S. D. Ebbesen, S. H. Jensen, and M. Mogensen, “Highly efficient high temperature electrolysis,” J. Mater. Chem., vol. 18, no. 20, pp. 2331–2340, 2008, doi: 10.1039/B718822F. [2] K. P. Ramaiyan, L. H. Denoyer, A. Benavidez, and F. H. Garzon, “Selective electrochemical oxidative coupling of methane mediated by Sr2Fe1.5Mo0.5O6-δ and its chemical stability,” Commun. Chem., vol. 4, no. 1, p. 139, 2021, doi: 10.1038/s42004-021-00568-1. [3] C. Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., vol. 10, no. 1, p. 1173, 2019, doi: 10.1038/s41467-019-09083-3. [4] F. H. G. Kannan P. Ramaiyan, Luke H. Denoyer, Angelica Benavidez, “Highly Stable Doped Barium Niobate Based Electrocatalysts for Effective Electrochemical Coupling of Methane to Ethylene,” ACS Catal. Under Rivsion.