Cathodic generation of hydrogen peroxide sustained by electrolytic O2 in a rotating cylinder electrode (RCE) reactor

Abstract

This investigation reports the electrosynthesis of H2O2 from the two-electron reduction of dissolved O2 , provided by anodic water oxidation, in a rotating cylinder electrode (RCE) reactor. O2 evolved at six surrounding Ti|IrO2 anode plates, whereas the oxygen reduction reaction (ORR) occurred at a (C-PTFE)- coated carbon cloth covering a rotating steel cathode. The mass transport characterization of the ca- thodic ORR to yield H2O2 was carried out through limiting current measurements (-0.65 ≤E ≤-0.3 V vs. SHE). Peripheral velocities (U) between 11.9 and 79.6 cm s−1 (i.e., Reynolds ( Re ) numbers of 4537 ≤ Re ≤ 30243) were employed to ensure turbulent flow conditions. An apparent plateau was obtained in the studied potential range, in agreement with mass transport-controlled ORR. From the limiting cur- rent values obtained, the mass transport correlation kma = bUc , which describe the transport considering the geometrical aspects of the cell and the hydrodynamic regime, were obtained. Additionally, bulk elec- trolyses were executed to accumulate H2O2 , with no O2 feeding from any air pump. These trials were performed under mass transport control at a cathode potential of -0.46 V vs. SHE. Both, mass transport studies and bulk H2O2 electrogeneration, were performed in the presence and absence of atmospheric air on top of the RCE reactor to evaluate the potential contribution of additional O2 dissolution promoted by the electrolyte velocity and pressure gradients imposed by the RCE. Its contribution to H2O2 production depended on U . The best conditions for the self-sustained electrolytic H2O2 synthesis were U = 79.6 cm s−1 and cathode potential of -0.46 V, achieving 177.2 mg L−1 H2O2 with current efficiency and energy consumption of 23.3% and 0.013 kW h (g H2O2 )−1 after 180 min. The potential application of this RCE reactor to the degradation of organic pollutants is thus envisaged.