The Surfactant-Promoted Electroreduction of Oxygen to Hydrogen Peroxide

Abstract

The two-electron reduction of O2O2 at pH 3 (1 M Na2SO4Na2SO4 acidified by glacial acetic acid) and 9.6 (mixture of 0.5 M Na2CO3Na2CO3 and 0.5 M NaHCO3)NaHCO3) was investigated in flow-by electrochemical reactors with three-dimensional cathodes, consisting of graphite felt (GF) or reticulated vitreous carbon (RVC). The cathode was operated with co-current upward gas/liquid flow and O2O2 pressures in the range of 200-700 kPa. A factorial design with four variables at two levels was employed to investigate the effects of superficial current density, liquid load, O2O2 pressure, and cationic surfactant concentration [i.e., trioctylmethylammonium chloride (Aliquat® 336, A336)] on H2O2H2O2 concentration, current efficiency, and reactor voltage. Among the investigated variables A336 exerted the strongest positive main effect on both H2O2H2O2 concentration and current efficiency. The beneficial effect of A336 was due to suppression of the H2O2H2O2 loss by both electroreduction and surface-catalyzed decomposition. However, A336 increased the pressure gradient through GF by up to 100%. The surfactant effect on the pressure gradient was estimated using the Herbolzheimer-Park model for the influence of surfactant on the motion of gas bubbles in liquid-filled capillaries. An O2O2 mass-transfer model in both GF and RVC was developed and correlated with the experimental results. © 2005 The Electrochemical Society. All rights reserved.