Electrochemical Generation of Hydroxide and Hydrogen Peroxide for Hydrolysis of Sulfuryl Fluoride Fumigant.

The post-harvest fumigant, sulfuryl fluoride (SOF), is a >1000-fold more potent greenhouse gas than carbon dioxide and methane. Pilot studies have shown that SOF fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH) and hydrogen peroxide (HO) at pH ∼ 12 in a scrubber, producing SO and F as waste salts. To reduce the costs and challenges associated with purchasing and mixing these reagents onsite, this study evaluates the electrochemical generation of OH and HO within spent scrubbing solution, taking advantage of the waste SO and F as free sources of electrolyte. The study used a gas diffusion electrode constructed from carbon paper coated with carbon black as a catalyst selective for the reduction of O to HO. Under galvanostatic conditions, the study evaluated the effect of electrochemical conditions, including applied cathodic current density and electrolyte strength. Within an electrolyte containing 200 mM SO and 400 mM F, comparable to the waste salts generated by a SOF scrubbing event, the system produced 250 mM HO at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O reduction to HO. In a scrubbing-water sample from lab-scale fumigation, the system generated ∼200 mM HO at pH 13.5 within 4 h with a Faradaic efficiency of 75.6%. A comparison of the costs to purchase NaOH and HO against the electricity costs for electrochemical treatment indicated that the electrochemical approach could be 38-71% lower, depending on the local cost of electricity.