Thermodynamic Assessment of Sacrificial Oxidant Potential, H₂O/O₂ Potential, and Rate–Overpotential Relationship to Examine Catalytic Water Oxidation in Nonaqueous Solvents

The water oxidation reaction (WOR), which is pivotal to storing energy in chemical bonds, requires a catalyst to overcome its inherent kinetic barrier. In bulk solutions, sacrificial oxidants (SOs) can regenerate the catalysts to ensure that the homogeneous WOR can be operated with long-term consistent performance. To implement this strategy for organic WOR systems, we modified four common SOs with tetra-<i>n</i>-butylammonium ([NBu₄]⁺)─[NBu₄]₂[Ce(NO₃)₆], [NBu₄][IO₄], [NBu₄][HSO₅], and [NBu₄]₂[S₂O₈]─and examined their chemical stability and electrochemical behaviors in various organic solvents. We also derived the organic-solvent-associated redox potential of H₂O/O₂ in organic media (<i>E</i>_{H₂O/O₂(org)}) using open-circuit potential measurements of the H⁺/H₂ redox couple and the related thermochemical cycle. Our findings indicate that the <i>E</i>_{H₂O/O₂(org)} varies with solvent identity and can be adjusted by changing the [H₂O], [acid], and [base] levels; thus, the SO should be carefully selected for WOR, because the innate redox potentials of SOs are not always higher than <i>E</i>_{H₂O/O₂(org)} under the studied conditions. Lastly, we obtained catalyst-performance-related insights via a rate-overpotential free-energy relationship by calculating the overpotentials of previously studied WOR systems in organic media.