Abstract

Polymer-supported molecular electrocatalysts offer an effective strategy to enhance catalytic performance while preserving well-defined redox properties. In this work, cobaloxime complexes immobilized on chitosan and chitosan oligosaccharide (COS) matrices are evaluated as heterogeneous electrocatalysts for the electrochemical reductive dechlorination of hexachloroethane. Covalent anchoring of an aldehyde-functionalized cobaloxime precursor onto amino-containing biopolymers affords stable hybrid materials without significantly affecting the Co(II)/Co(I) redox potential, which remains within a narrow range (-1.00 to -1.03 V vs Ag/AgCl). Marked differences are instead observed in the catalytic kinetics. Foot-of-the-wave analysis shows that the high-molecular-weight chitosan-supported cobaloxime displays the highest activity, with a catalytic rate constant (kcat = 1.50 & times; 105M-1 s-1), approximately one order of magnitude larger than those of the COS-supported and molecular counterparts. Tafel analysis further confirms enhanced turnover frequencies for polymer-supported systems at moderate overpotentials. The electrochemical and kinetic results are consistent with an Electrochemical-Chemical-Electrochemical-Chemical (ECEC) mechanism involving a supernucleophilic Co(I) intermediate responsible for C-Cl bond cleavage. The superior performance of the chitosan-based catalyst is attributed to biopolymer architecture effects, including substrate confinement, increased local substrate concentration, and stabilization of reactive intermediates. Overall, these findings highlight the key role of polymer architecture in controlling the kinetics of heterogeneous molecular electrocatalysts for electrochemical dechlorination processes.