Computational exploration of the electrochemical oxidation mechanism of thiocyanate catalyzed by cobalt-phthalocyanines†

Abstract

In this study, we focused on the mechanism of the electrocatalytic oxidation of thiocyanate, which in traditional electrodes typically requires high overpotentials. As models for reducing these overpotentials and catalyzing the reaction, we used a set of modified cobalt phthalocyanines (CoPc), known as electrocatalysts. Using DFT calculations, we explored how modifications to CoPc by adding electron-donating and withdrawing groups and the coordination of 4-amino thiophenol impact the oxidation process. The reaction mechanism for the electrooxidation of thiocyanate has remained elusive, where only the reaction products have been properly identified, including hydrogen cyanide and sulfate ions at pH 4. The approach for understanding the reaction was considering the formation of an (SCN)₂ dimer as an intermediate that is a suitable precursor of the products of the reaction. Our findings showed that electron-donating groups and 4-amino thiophenol coordination lowered oxidation potentials, enhancing electrocatalytic efficiency and promoting thiocyanate radical formation and release before dimerization occurs. In contrast, electron-withdrawing groups facilitated dimerization while attached to cobalt, albeit with lower electrocatalytic proficiency. This study highlights the crucial role of CoPc modifications in thiocyanate oxidation, demonstrating the potential for improved electrocatalytic processes through tailored catalyst design.