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

The post-harvest fumigant, sulfuryl fluoride (SO 2 F 2 ), is a >1000-fold more potent greenhouse gas than carbon dioxide and methane. Pilot studies have shown that SO 2 F 2 fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH - ) and hydrogen peroxide (H 2 O 2 ) at pH ∼ 12 in a scrubber, producing SO 4 2- 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 H 2 O 2 within spent scrubbing solution, taking advantage of the waste SO 4 2- 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 2 to H 2 O 2 . 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 4 2- and 400 mM F - , comparable to the waste salts generated by a SO 2 F 2 scrubbing event, the system produced 250 mM H 2 O 2 at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O 2 reduction to H 2 O 2 . In a scrubbing-water sample from lab-scale fumigation, the system generated ∼200 mM H 2 O 2 at pH 13.5 within 4 h with a Faradaic efficiency of 75.6%. A comparison of the costs to purchase NaOH and H 2 O 2 against the electricity costs for electrochemical treatment indicated that the electrochemical approach could be 38-71% lower, depending on the local cost of electricity.