Cathodic electroorganic reaction on silicon oxide dielectric electrode

Abstract

The faradaic reaction at the insulator is counterintuitive. For this reason, electroorganic reactions at the dielectric layer have been scarcely investigated despite their interesting aspects and opportunities. In particular, the cathodic reaction at a silicon oxide surface under a negative potential bias remains unexplored. In this study, we utilize defective 200-nm-thick n+-Si/SiO2 as a dielectric electrode for electrolysis in an H-type divided cell to demonstrate the cathodic electroorganic reaction of anthracene and its derivatives. Intriguingly, the oxidized products are generated at the cathode. The experiments under various conditions provide consistent evidence supporting that the electrochemically generated hydrogen species, supposedly the hydrogen atom, is responsible for this phenomenon. The electrogenerated hydrogen species at the dielectric layer suggests a synthetic strategy for organic molecules.

Electrochemistry of the Silicon Oxide Dielectric Layer: Principles, Electrochemical Reactions, and Perspectives

“…An unusual, unique electrochemical phenomenon occurs within the silicon oxide dielectric layer in the EOS system: hydrogen atom mediated electrochemistry [13,20,21,36] . It was recognized from the asymmetric voltammetric behavior, with only the cathodic wave observed.…”

“…In particular, iridium was reduced, which is impossible via hydrogen gas reduction but is possible by hydrogen atoms under ambient conditions [13] . Moreover, electroorganic reactions of anthracene occurred when the applied voltage was lower than their reduction potentials [20] . In fact, oxidized products of anthracene and its derivatives were electrochemically generated when the silicon oxide layer was used as the cathode .…”

“…Shin et al . performed an electroorganic reaction using a silicon oxide dielectric layer as the cathode [20] . The electrolysis was performed in an H‐type divided cell by applying a voltage less than the reduction potentials of the organic compounds to demonstrate that the products were not formed due to electroreduction.…”

“…The electrochemical reaction was confirmed from various chemical analyses and control experiments, indicating that the silicon oxide dielectric layer generated reactive chemical species, likely hydrogen atoms, acting as a “chemical electrode.” Therefore, electrogenerated hydrogen atoms react with the C−H bonds of the organic compound via hydrogen atom abstraction, followed by chemical reaction with oxygen species in the solution, i. e., moisture (Scheme 3). The scope of this reaction was demonstrated using anthracene, its derivatives, and other classes of polycyclic aromatic hydrocarbons [20] . Nevertheless, a normal electrochemical reduction was exemplified by the reaction of nitrobenzene [20] …”

“…Even the formation of nanopores and further etching may be achieved at the silicon oxide [15,19] . Nevertheless, the fine current allows precise manipulation of metal electrodeposition and electroorganic reactions [13,20,21] …”