Center for Functional Nanomaterials Seminar

The role of pyridinium cations in electrochemistry has been believed known for decades, and their radical forms have been proposed as key intermediates in modern photoelectrocatalytic CO2 reduction processes. Using first-principles density functional theory and continuum solvation models, we have calculated acidity constants for pyridinium cations and their corresponding pyridinyl radicals, as well as their electrochemical redox potentials. Contrary to previous assumptions, our results show that these species can be ruled out as active participants in homogeneous electrochemistry. A comparison of calculated redox potentials for pyridinium with calculated and experimental redox potentials of related molecules indicates that pyridinium cations behave differently than previously thought. By contrast, some differently substituted pyridine molecules, such as such a 4,4’-bipyridine, have acidity constants and redox potentials comparable to those observed in CO2 reduction. This work substantially alters the mechanistic view of pyridinium-catalyzed photoelectrochemical CO2 reduction.