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

The post-harvest fumigant, sulfuryl fluoride (SO₂F₂), is a >1000-fold more potent greenhouse gas than carbon dioxide and methane. Pilot studies have shown that SO₂F₂ fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH^–) and hydrogen peroxide (H₂O₂) at pH ∼ 12 in a scrubber, producing SO₄^2– 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 H₂O₂ within spent scrubbing solution, taking advantage of the waste SO₄^2– 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 O₂ to H₂O₂. 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 SO₄^2– and 400 mM F^–, comparable to the waste salts generated by a SO₂F₂ scrubbing event, the system produced 250 mM H₂O₂ at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O₂ reduction to H₂O₂. In a scrubbing-water sample from lab-scale fumigation, the system generated ∼200 mM H₂O₂ at pH 13.5 within 4 h with a Faradaic efficiency of 75.6%. A comparison of the costs to purchase NaOH and H₂O₂ against the electricity costs for electrochemical treatment indicated that the electrochemical approach could be 38–71% lower, depending on the local cost of electricity.