Electrochemical sequential reduction and oxidation facilitates the continual ambient temperature degradation of SF6 to nontoxic gaseous compounds

Abstract

An efficient process for the degradation of the potent greenhouse gas, SF6, into non-toxic gaseous products at ambient temperature is still desirable. In this study, consistently generable homogeneous low/high-valent metal ions were used to degrade SF6 to non-toxic gaseous products at ambient temperature. Two homogenous electron mediators, [Ni(I)(CN)4]3− (Ni(I) low-valent) and AgSO4 or Ag(NO3)2 (Ag(II) high-valent), were generated concurrently using a membrane-divided electrolytic cell and quantified by measuring the ORP (oxidation/reduction potential) variations along with a potentiometric titration. The variation of electrogenerated Ni(I) from 6.3 mM to 4.1 mM and Ag(II) from 4.8 mM to 4.3 mM during the removal of SF6 evidenced their concurrent generation, and SF6 removal followed a mediated electrocatalytic reduction (MER) and mediated electrocatalytic oxidation (MEO) process. FTIR online gas analyzer confirmed that using the MER process only, approximately 92% of the SF6 in a gas mixture containing 5 ppm of SF6 at a 0.2 L min−1 flow rate had decomposed to OF2 (7 ppm), SOF2 (2 ppm), and SO2 (2.9 ppm). At the same time, the MER-treated gas passed into Ag(II) generated anolyte solution resulted in the complete removal of SF6, SOF2, OF2, and SO2 by the MEO process. Also, the absence of fluoride containing gases and SO2 gas in the exit gas from the MEO process and the presence of fluoride ions in the anolyte solution demonstrates the aqueous soluble products fluoride and sulfate ions formation. The possible consistent generation of homogenous electrocatalysts and their combined use in SF6 degradation at ambient temperatures is a practical technology that can be scaled up to a more practical level.