Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition-Metal Spinels

Chao Wei; Zhenxing Feng; Günther G Scherer; James Barber; Yang Shao-Horn; Zhichuan J Xu

doi:10.1002/adma.201606800

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition-Metal Spinels

Adv Mater. 2017 Jun;29(23). doi: 10.1002/adma.201606800. Epub 2017 Apr 10.

Authors

Chao Wei¹, Zhenxing Feng², Günther G Scherer³, James Barber^{4

5}, Yang Shao-Horn^{6

7}, Zhichuan J Xu^{1

5

8}

Affiliations

¹ School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
² School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, 97331, USA.
³ TUM-CREATE, One Create Way, 138602, Singapore.
⁴ Department of Life Sciences, Imperial College London, London, SW7 2AZ, UK.
⁵ Solar Fuels Laboratory, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
⁶ Materials Science and Engineering Department, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
⁷ Electrochemical Energy Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
⁸ Energy Research Institute @ Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.

PMID: 28394440
DOI: 10.1002/adma.201606800

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 MnCo₂ O₄ , 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 Mn_x Co_3-_x O₄ (x = 2, 2.5, 3), Li_x Mn₂ O₄ (x = 0.7, 1), XCo₂ O₄ (X = Co, Ni, Zn), and XFe₂ O₄ (X = Mn, Co, Ni). A general principle is concluded that the e_g occupancy 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.

Keywords: descriptors; electron orbital filling; octahedral coordination; oxygen electrocatalysis; spinel.