Tuning the electrocatalytic water oxidation properties of AB2O4 spinel nanocrystals: A (Li, Mg, Zn) and B (Mn, Co) site variants of LiMn2O4

Clyde W. Cady, Graeme Gardner, Zachary O. Maron, Maria Retuerto, Yong Bok Go, Shreeda Segan, Martha Greenblatt, G. Charles Dismukes

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Transition metal oxides containing cubic B4O4 subcores are noted for their catalytic activity in water oxidation (OER). We synthesized a series of ternary spinel oxides, AB2O4, derived from LiMn2O4 by either replacement at the tetrahedral A site or Co substitution at the octahedral B site and measured their electrocatalytic OER activity. Atomic emission and powder X-ray diffraction confirmed spinel structure type and purity. Weak activation of the OER occurs upon A-site substitution: Zn2+ > Mg2+ > A-vacancy > Li+ = 0. Zn and Mg substitution is accompanied by (1) B-site conversion of Mn(IV) to Mn(III), resulting in expansion and higher symmetry of the [Mn4O4]4+ core relative to LiMn2O4 (inducing greater flexibility of the core and lower reorganization barrier to distortions), and (2) the electrochemical oxidation potential for Mn(III)/IV) increases by 0.15-0.2 V, producing a stronger driving force for water oxidation. Progressive replacement of Mn(III/IV) by Co(III) at the B site (LiMn2-xCoxO4, 0 ≤ x ≤ 1.5) both symmetrizes the [Mn4-xCoxO4] core and increases the oxidation potential for Co(III/IV), resulting in the highest OER activity within the spinel structure type. These observations point to two predictors of OER catalysis: (1) Among AMn2O4 spinels, those starting with Mn(III) in the resting lattice (prior to oxidation) result in longer, weaker Mn-O bonds for this eg1 antibonding electronic configuration, yielding greater core flexibility and a higher oxidation potential to Mn(IV), and (2) a linear free energy relationship exists between the electrocatalytic rate and the binding affinity of the substrate oxygen (OH andOOH) to the B site.

Original languageEnglish
Pages (from-to)3403-3410
Number of pages8
JournalACS Catalysis
Volume5
Issue number6
DOIs
Publication statusPublished - Jun 5 2015

Keywords

  • cobalt oxide
  • manganese oxide
  • photosystem II
  • spinel
  • water oxidation catalyst
  • water splitting

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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