Electron transfer rate of pyrogenic carbon in aquatic environments: Establishment of analytical methods, structural drivers, and roles in pollutant degradation

Pyrogenic carbon (PyC) is a ubiquitous redox-active material in natural and engineered environments, yet its environmental reactivity is commonly evaluated by measuring static electron-accepting and electron-donating capacities, without explicit consideration of electron transfer kinetics. Here, we developed a mediated electrochemistry–kinetic modeling framework that enabled simultaneous quantification of both equilibrium electron transfer capacities and intrinsic electron transfer rate constants for PyC in the aqueous phase, including both electron-accepting ( k A ) and electron-donating ( k D ) processes. Application of this approach to PyC produced at different pyrolysis temperatures revealed a tradeoff between capacity and kinetics, with high-temperature PyC exhibiting substantially faster electron transfer despite lower redox capacity. Reanalysis of more than 110 mediated electrochemical datasets from the literature demonstrated a general and robust trend of k A >  k D across diverse PyC types. Structure–performance relationships integrating spectroscopic analyses and quantum chemical calculations identified carbon defects as the dominant drivers of electron transfer kinetics. Using p -nitrophenol as a model pollutant under anaerobic conditions, we showed that faster electron transfer kinetics enhanced degradation rates and favored oxidative transformation pathways. This study shifts the prevailing capacity-centric view of PyC redox reactivity toward a kinetics-driven framework and provides a mechanistic basis for predicting the role of PyC in aquatic environmental redox processes.