High-Temperature Solid Oxide Cells and Membrane Reactors for Oxidative Coupling of Methane-to-Ethylene: Recent Advances and Future Outlook

Methane is a highly abundant, low-cost hydrocarbon; hence, effective conversion of methane toward value-added products such as olefins has been a highly researched field for over 40 years. Oxidative coupling of methane (OCM) is one of the most studied methods for direct methane conversion due to favorable thermodynamics; however, at industrially relevant methane conversion rates, the overoxidation to CO 2 inhibits the selectivity toward desired C 2 products. Electrochemical OCM (E-OCM) using high-temperature solid oxide electrolyzer cells (SOECs) has recently gained attention, as it can alter product selectivity by catalyst selection and externally applied potential. However, the material requirements for E-OCM applications are seldom addressed. For example, the anode of an E-OCM cell must possess high electronic and ionic conductivity while showing tolerance toward coke or carbonate formation under methane-rich conditions under applied potentials for successfully activating methane toward C 2 products. This paper reviews the E-OCM literature to provide a perspective on materials’ properties governing catalytic activity, electrical conductivity, and chemical stability under E-OCM conditions. Methane coupling in SOECs utilizing oxide ion conductors, proton conductors, and catalytic membrane reactors is reviewed in detail. An outlook for future directions for material development and catalytic requirements is provided.