Semi-solid electrolyte with layered heterometallic low-valent electron-mediator enabling indirect destruction of gaseous toluene

The electrochemical degradation of air pollutants, particularly volatile organic compounds (VOCs), at their gaseous state is a promising method. However, it remains at an infant stage due to sluggish solid???gas electron transfers at room temperature. We established a triphase reaction condition using a semi-solid electrolyte layer between the electrode and membrane to enhance the electron transfer at room temperature. A polyvinyl alcohol (PVA) gel layer was inserted between a bimetallic layered CuNi(CN)4 complex coated Cu foam electrode (TCNi-Cu) and Nafion 324 membrane for the degradation of gaseous toluene. The cyclic voltammetry of TCNi-Cu using a sodium hydroxide-coated copper mesh electrode at a triphase showed Cu1+ and Ni1+ stabilization at-0.7 and-0.9 V, respectively, which was similar to the liquid phase electron transfer behavior. The degradation capacity of gaseous toluene without using electrogenerated TCNi-Cu + PVA gel was 0.54 mg cm2 min- 1, whereas that of TCNi-Cu + PVA gel layers was 1.17 mg cm- 2min- 1, which revealed the mediation effect at a triphase condition. Toluene was converted into oxygen-containing products, such as butanol, propanol, and acetone (without reduction products), which revealed that indirect oxidation occurred at the cathode using an in-situ generated oxidant, such as OH?? radical. As an electron-mediator, Cu1+ was used to form oxidants for the degradation of toluene at-0.7 V. The toluene removal rate reached 1.4 ??mol h-1, with an energy efficiency of 0.15 Wh L-1. This study is the first attempt to describe a liquid-electrolyte-free cathodic half-cell in electrochemical application to VOCs degradation, highlighting the electron transfer at room temperature.

Automated summary

The electrochemical degradation of gaseous air pollutants, such as volatile organic compounds (VOCs), is still in its early stages due to slow electron transfers at room temperature. This study proposes a triphase reaction condition using a semi-solid electrolyte layer to enhance electron transfer. By inserting a polyvinyl alcohol (PVA) gel layer between a bimetallic CuNi(CN)4 complex coated Cu foam electrode (TCNi-Cu) and a Nafion 324 membrane, the degradation capacity of gaseous toluene was significantly improved.