Unraveling the role of electrolytes during electrochemical oxidation by differential electrochemical mass spectrometry

Abstract

A fundamental understanding of the role of supporting electrolytes on the electrochemical oxidation of organics is essential to develop strategies for water treatment applications. This work completes research efforts of literature by evaluating directly the evolution of CO2 at the BDD electrode as a result of the mineralization of oxalic acid. The use of differential electrochemical mass spectrometry (DEMS) as an electroanalytical tool enables online measurement of engineering figures of merit of electrochemical advanced oxidation technologies and unravels the influence of coexisting ionic species in solution. Furthermore, the oxidation of CO is conducted to elucidate how different electrogenerated oxidants may be involved in oxidation reactions. CO2 current efficiencies calculated for the oxidation of CO were higher for electrolytes where more •OH radicals are available for the oxidation of CO which suggests the •OH radicals-mediated CO oxidation at BDD. Thereby, higher efficiency was observed in the perchlorate electrolyte than nitrate, sulfate, and chloride electrolytes. The decrease in the CO2 current efficiencies in the other electrolytes is explained by the competitive consumption of •OH due to the formation of other oxidants such as SO4•–, Cl•, other chlorine active species, and possibly also NO4−. CO2 was the predominant oxidation product during the oxidation of oxalic acid in all electrolytes with a higher oxidation capability in the perchlorate and chloride electrolytes than nitrate and sulfate. These results show that the oxidation of oxalic acid is mediated by •OH, direct charge transfer, as well as by other oxidants produced at the BDD at different electrolytes.