Pursuing efficient conversion of methane to value-added products such as olefins and aromatics is a prospective use of natural methane feedstocks. The demand for on-site methane conversion has further increased due to the recent discoveries of shale gas reserves. Electrochemical methane conversion provides a means to control the surface oxide ion concentration, aiming to eliminate the over-oxidation of methane while also aiding in methane activation via applied potential. High temperature electrolysis processes provide improved reaction kinetics. Unfortunately, high temperature operation also leads to material degradation via sintering, crystal structure disproportion to thermodynamically more stable phases, and interfacial reactions that reduce performance. We demonstrated that the Sr2Fe1.5Mo0.5O6-d (SFMO) perovskite which was reported with desirable methane activation properties had poor chemical and electrochemical stability as it formed carbonates and coke under methane rich environments.[1][2] Here we present an exciting class of barium niobate perovskite materials with varying levels of Mg and Fe co-doping that show promising catalytic activity towards methane activation in the electrochemical and conventional heterogeneous oxidative coupling environment. The perovskite material was prepared by conventional solid-state methods and by microwave synthesis methods to compare the role of surface area. Thermogravimetric analysis and temperature programmed reaction measurements under methane show superior chemical stability in comparison to SFMO perovskites. These catalysts’ electrochemical properties are evaluated by cyclic voltammetry, impedance spectroscopy, and chronoamperometric measurements coupled with mass spectra analysis that demonstrate durable operation for five continuous days. A maximum ethylene production of 277 mmolcm-2h-1 with a faradaic efficiency of 20% at 1V was obtained. Stability determinations of our perovskite oxide electrocatalysts for EC-OCM offer an excellent example of our approach towards evaluation of materials durability under the highly carburizing environments. These perovskite materials could also serve as a support for a wide variety of catalyst materials for high temperature applications thus opening new possibilities.
References
[1] 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.
[2] 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.