Is plasma electrochemistry just electrochemistry at plasma-liquid interfaces? Learnings from organic reactions

In plasma electrochemical synthesis, one of the electrodes of a traditional electrochemical cell is replaced by plasma. In this study, we tried to use plasma electrochemistry for the largest industrial organic electrosynthetic process, the electrohydrodimerization of acrylonitrile (AN) to adiponitrile (ADN), a precursor to Nylon 6,6. We used a DC pin-to-liquid Ar plasma where the liquid was aqueous AN. While we did not make ADN, we produced H₂, H₂O₂, propionitrile (PN), O₂, CO₂, C_2, and C₃ hydrocarbons and AN-derived polymers with amounts depending on the AN concentration, current, and polarity. When a negative potential was applied, H₂ was produced at amounts exceeding those expected from Faradaic currents, underscoring the importance of nonelectrochemical reactions. When the polarity was reversed, H₂ production was even higher, increasing with AN concentration. H₂O₂ was produced in both polarities but more under positive potentials; its production dropped rapidly with increasing AN concentration. Under negative potentials, PN was produced at rates commensurate with Faradaic currents, but its production rose to levels much higher when the polarity was reversed, suggesting that it, too, may be produced via nonelectrochemical pathways. Clearly, there is more than electrochemistry to plasma electrochemistry.