Superoxide (Electro)Chemistry on Well-Defined Surfaces in Organic Environments

Efficient chemical transformations in energy conversion and storage systems depend on understanding superoxide anion (O₂^-) electrochemistry at atomic and molecular levels. Here, a combination of experimental and theoretical techniques are used for rationalizing, and ultimately understanding, the complexity of superoxide anion (electro)chemistry in organic environments. By exploring the O₂ + e^- ↔ O₂^- reaction on well-characterized metal single crystals (Au, Pt, Ir), Pt single crystal modified with a single layer of graphene (Graphene@Pt(111)), and glassy carbon (GC) in 1,2 dimethoxyethane (DME) electrolytes, we demonstrate that (i) the reaction is an outer-sphere process; (ii) the reaction product O₂^- can "attack" any part of the DME molecule, i.e., the C-O bond via nucleophilic reaction and the C-H bond via radical hydrogen abstraction; (iii) the adsorption of carbon-based decomposition products and the extent of formation of a "solid electrolyte interface" ("SEI") increases in the same order as the reactivity of the substrate, i.e., Pt(hkl)/Ir(hkl) ≫ Au(hkl)/GC > Gaphene@Pt(111); and (iv) the formation of the "SEI" layer leads to irreversible superoxide electrochemistry on Pt(hkl) and Ir(hkl) surfaces. We believe this fundamental insight provides a pathway for the rational design of stable organic solvents that are urgently needed for the development of a new generation of reliable and affordable battery systems.