Fig. 3: Driving forces, kinetics and ¹O₂ formation during Lewis-acid-induced superoxide disproportionation.

a, Thermodynamics of relevant redox couples for Li⁺-induced superoxide disproportionation as a function of the fractions of Li⁺ and TBA⁺ salt. The gradient boxes and short arrows indicate increasing superoxide solvation with potentials between values relevant for solid LiO_2(s) (dark colour), solvated \({({{\rm{Li}}}^{+}{{{\rm{O}}}_{2}}^{-})}_{n\ge 1,({\rm{sln}})}\) clusters, and solvated \({({{\rm{Li}}}^{+}{{{\rm{O}}}_{2}}^{-})}_{({\rm{sln}})}\) (faded colour). LiO₂ is in all relevant electrolytes at least somewhat soluble as \({({{\rm{Li}}}^{+}{{{\rm{O}}}_{2}}^{-})}_{n\ge 1,({\rm{sln}})}\) clusters. The nature of superoxide shifts from \({({{\rm{Li}}}^{+}{{{\rm{O}}}_{2}}^{-})}_{n\ge 1,({\rm{sln}})}\) towards \({({{\rm{TBA}}}^{+}{{{\rm{O}}}_{2}}^{-})}_{({\rm{sln}})}\) as the cation changes from pure Li⁺ towards pure TBA⁺. The inclined lines indicate the associated shift of the potentials. \({E}_{{\genfrac{}{}{0ex}{}{1}{}{\rm{O}}}_{2}/{\rm{superoxide}}}={E}_{{\genfrac{}{}{0ex}{}{3}{}{\rm{O}}}_{2}/{\rm{superoxide}}}+0.84\,{\rm{V}}\). The driving force \(\Delta G=-\,({E}_{{\rm{superoxide}}/{\text{Li}}_{2}{\text{O}}_{2}}-{E}_{{\genfrac{}{}{0ex}{}{3}{}{\rm{O}}}_{2}/{\rm{superoxide}}})F\) grows with the shift of the O₂/superoxide and superoxide/Li₂O_2(s) potentials. Note that the O₂ reduction potential changes nonlinearly with the Li⁺:TBA⁺ ratio³². b, Normalized 1,270 nm NIR emission as a function of Li⁺ mole fraction, which determines the driving force. The markers show superoxide disproportionation kinetics as measured by pressure evolution. The dotted line is a guide to the eye. Glyme served as the electrolyte solvent. Data are presented as mean ± s.d. (n ≥ 3).

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