TEMPO-Modified Polymethacrylates As Mediators in Electrosynthesis - Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity

Abstract

Compared to direct electrolysis, homogeneous electrocatalysis often gains better selectivity and higher yields with less energy consumption.[1] However, additional separation steps are necessary for product isolation and catalyst recycling increasing waste generation and adding expenses. Polymerized electrocatalysts (polymediators) can be separated and reused by membrane filtration and therefore simplify the separation process.[2] Tuning the molecular weight distribution represents a possibility for optimization of the overall reaction rate that is currently under investigation in our laboratory.We used cyclic voltammetry as a tool to analyze the electrochemical behavior of two model compounds (ACT and BTM) as well as TEMPO-modified polymethacrylates (TPMA) of different molecular weight (MW) distributions in view of anodic alcohol oxidation. The MW distributions were adjusted using the RAFT technique,[3] leading to well-defined polymediators with average MWs from 2.5 kDa to 126 kDa and monomodal weight distributions.While the electrochemical properties of all polymers (redox potential, current enhancements) are similar, the diffusion rate of the polymediators is curbed with increasing MW, also decreasing the overall reaction rate during electrolysis, and increasing reaction time.[4] The remaining task is to find an optimal operating range in which both reasonable filtration efficiencies and sufficient current densities are achieved.