title: Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition-Metal Spinels.
abstract: Exploring efficient and low-cost electrocatalysts for the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) is critical for developing renewable energy technologies such as fuel cells, metal-air batteries, and water electrolyzers. A rational design of a catalyst can be guided by identifying descriptors that determine its activity. Here, a descriptor study on the ORR/OER of spinel oxides is presented. With a series of MnCo2O4, the Mn in octahedral sites is identified as an active site. This finding is then applied to successfully explain the ORR/OER activities of other transition-metal spinels, including MnxCo3-xO4(x = 2, 2.5, 3), LixMn2O4(x = 0.7, 1), XCo2O4(X = Co, Ni, Zn), and XFe2O4(X = Mn, Co, Ni). A general principle is concluded that the egoccupancy of the active cation in the octahedral site is the activity descriptor for the ORR/OER of spinels, consolidating the role of electron orbital filling in metal oxide catalysis.
authors.affiliation: School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: Chao
authors.initials: C
authors.lastname: Wei
authors.affiliation: School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, 97331, USA.
authors.forename: Zhenxing
authors.initials: Z
authors.lastname: Feng
authors.affiliation: TUM-CREATE, One Create Way, 138602, Singapore.
authors.forename: Günther G
authors.initials: GG
authors.lastname: Scherer
authors.affiliation: Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK.|Solar Fuels Laboratory, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: James
authors.initials: J
authors.lastname: Barber
authors.affiliation: Materials Science and Engineering Department, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.|Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Shao-Horn
authors.affiliation: School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.|Solar Fuels Laboratory, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.|Energy Research Institute @ Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
authors.forename: Zhichuan J
authors.initials: ZJ
authors.lastname: Xu
keywords: descriptors; electron orbital filling; octahedral coordination; oxygen electrocatalysis; spinel