"Floating" cathode for efficient H₂O₂ electrogeneration applied to degradation of ibuprofen as a model pollutant

The performance of the Electro-Fenton (EF) process for contaminant degradation depends on the rate of H₂O₂ production at the cathode via 2-electron dissolved O₂ reduction. However, the low solubility of O₂ (≈1×10^-3 mol dm^-3) limits H₂O₂ production. Herein, a novel and practical strategy that enables the synergistic utilization of O₂ from the bulk electrolyte and ambient air for efficient H₂O₂ production is proposed. Compared with a conventional "submerged" cathode, the H₂O₂ concentration obtained using the "floating" cathode is 4.3 and 1.5 times higher using porous graphite felt (GF) and reticulated vitreous carbon (RVC) foam electrodes, respectively. This surprising enhancement results from the formation of a three-phase interface inside the porous cathode, where the O₂ from ambient air is also utilized for H₂O₂ production. The contribution of O₂ from ambient air varies depending on the cathode material and is calculated to be 76.7% for the GF cathode and 35.6% for the RVC foam cathode. The effects of pH, current, and mixing on H₂O₂ production are evaluated. Finally, the EF process enhanced by the "floating" cathode degraded 78.3% of the anti-inflammatory drug ibuprofen after 120 min compared to only 25.4% using a conventional "submerged" electrode, without any increase in the cost.