Electrocatalytic carbon dioxide activation: The rate-determining step of pyridinium-catalyzed CO₂ reduction

The reactivity of reduced pyridinium with CO₂ was investigated as a function of catalyst concentration, temperature, and pressure at platinum electrodes. Concentration experiments show that the catalytic current measured by cyclic voltammetry increases linearly with pyridinium and CO₂ concentrations; this indicates that the rate-determining step is first order in both. The formation of a carbamate intermediate is supported by the data presented. Increased electron density at the pyridyl nitrogen upon reduction, as calculated by DFT, favors a Lewis acid/base interaction between the nitrogen and the CO₂. The rate of the known side reaction, pyridinium coupling to form hydrogen, does not vary over the temperature range investigated and had a rate constant of 2.5M^-1s^-1. CO₂ reduction followed Arrhenius behavior and the activation energy determined by electrochemical simulation was (69±10)a kJmol^-1.