Overpotential Decomposition Analysis for the Impacts of Microchannel Flow on the Intensification of Kolbe Reaction

Abstract

A microchannel reactor is believed to be effective equipment to implement electrosynthesis for its short distance between electrodes to reduce the energy cost of ion transport in electrolytic solutions. However, many electrochemical reactions are also confined by the convective mass transfer of ionic reactants, such as the classical Kolbe reaction for realizing carbon–carbon coupling. In this research, an overpotential decomposition analysis is proposed to investigate a typical Kolbe reaction conducted by visualized microchannel reactors, which display both the multi-phase microchannel flow and the energy cost contributions of electromigration, electrochemical reaction kinetics, and convective mass transfer. The unique flow patterns in different sized and layout microchannels are summarized, and their effects on overpotential distributions and ohmic potential loss are synthetically summarized. The research shows that the microchannel reactors not only largely reduce the ohmic potential loss but also enhance the convective mass transfer of ionic reactants, whose overpotential is on the same level of the rotating-disk electrode reactor that owns tens of microns mass transfer boundary layer thickness. The mass transfer overpotential could occupy 40% anodic overpotential and has approximate linear relationships with the logarithm of current density. Properly controlling the Kolbe reaction under homogeneous flow or sparse bubble flow is useful for conducting mass transfer enhancement via microchannels.