Fig. 6: Overview of insights into alcohol oxidation catalysis by surface-immobilized nitroxide from operando FE-EPR.

The mechanism of alcohol oxidation by surface-bound oxoammonium (yellow) is an EC′ mechanism described by the Michaelis–Menten model, with k_cat and K_M accessible from operando FE-EPR through the quantitative detection of the key STEMPO^• catalytic intermediate. k_s (also obtainable from electrochemistry alone) is slow, and the exact value is dependent on the electrode and experimental conditions, leading to n_app < 1 (Extended Data Fig. 7). The [Catalyst–Substrate] = [TEMPO⁺–RCH₂OH] adduct formation is characterized by the Michaelis–Menten constant K_M. Regeneration of the STEMPO^• catalyst in the steps following the rate-determining step (k_cat) occurs via PCET and/or comproportionation (main text and equations (1) to (6)). Rate constants and K_M are given for the substrate MBA at pH 8.0 (Extended Data Figs. 8 and 9 present values for glycerol at pH 8.0 and MBA at pH 7.3, respectively).