Uncovering correlations of surface reactivity and electron transport in oxide spinels

Redox reactions over transition metal oxide structures benefit from bulk charge transport and surface mass exchange, both of which depend on anion-cation interactions. This literature review is aimed at discussing the dual functionality of anions in tuning bulk electron transport and surface reactivity of spinels. As a result of this literature review, we discovered a new correlation between electron hopping activation energy in the materials and the rate constant of oxygen electrocatalysis over transition metal oxides crystallized in spinel structures. This review also provides information that can be used for tuning the chemical and physical properties of spinels via manganese incorporation. Additionally, both single and multi-phase approaches of manganese incorporation and their impact on catalysis, electrocatalysis, energy storage, and sensor applications are reviewed. We discovered that the variability of manganese oxidation states and the Jahn-Teller active Mn3+O6 have the most significant impacts on the bulk properties and surface reactivity of these materials. We have also answered for the first time why Mn-doped spinels are suitable as electrodes for oxygen evolution reactions, and why Mn3O4 does not perform optimally as a gas sensor based on the dual functionality of anionic oxygens in these spinels.