Rates of HO Electrogeneration by Reduction of Anodic O at RVC Foam Cathodes in Batch and Flow-through Cells.

The Electro-Fenton process for in-situ HO electrogeneration is impacted by low O utilization efficiency (<0.1%) and the need of acid for pH adjustment. An electrochemical flow-through cell can develop localized acidic conditions, coupled with simultaneous formation and utilization of O to enhance HO formation. Multiple electrode configurations using reticulated vitreous carbon (RVC) foam and Ti/mixed metal oxides (MMO) are proposed to identify the optimum conditions for HO formation in batch and flow-through cells. A pH of 2.75±0.25 is developed locally in the flow-through cell that supports effective O reduction. Up to 9.66 mg/L HO is generated in a 180 mL batch cell under 100 mA, at pH 2, and mixing at 350 rpm. In flow-through conditions, both flow rate and current significantly influence HO production. A current of 120 mA produced 2.27 mg/L HO under a flow rate of 3 mL/min in a 3-electrode cell with one RVC foam cathode at 60 min. The low current of 60 mA does not enable effective HO production, while the high current of 250 mA produced less HO due to parasitic reactions competing with O reduction. Higher flow rates decrease the retention time, but also increase the O mass transfer. Furthermore, 3-electrode flow-through cell with two RVC foam cathodes was not effective for HO production due to the limited O supply for the secondary cathode. Finally, a coupled process that uses both O and H from water electrolysis is proposed to improve the HO yield further.