Effect of pressure on the electrochemical generation of hydrogen peroxide in undivided cells on carbon felt electrodes

Abstract

The electrochemical generation of H2O2can be performed in aqueous solutions by cathodic reduction at carbonaceous cathodes of oxygen coming from air. The performances of the process in terms of concentration of H2O2and current efficiency (CE) are limited by the low solubility of oxygen in water at atmospheric pressure. However, the solubility of oxygen can be increased upon enhancing the air pressure. The effect of pressure on the electrochemical generation of hydrogen peroxide was studied in undivided cells changing the pressure from 0 to 30 relative bar and the current density from 1 to 100 mA cm−2. Simple carbon felt and compact graphite cathodes were first used. A dramatic effect of the pressure was shown: at carbon felt a concentration of hydrogen peroxide slightly lower than 30 mM was obtained by working at 30 bar and 20 mA cm−2, about two orders of magnitude higher than that achieved at atmospheric pressure, as a result of mass transport intensification. The utilization of both a modified carbon felt (with carbon black and polytetrafluoroethylene) and relatively low pressures allowed to further enhance the generation of H2O2and the CE. Under the best conditions (30 bar and 100 mA cm−2), concentrations up to 225 mM together with the highest production rate (1.84 mmol H2O2cm−2 h−1and 98.9% CE) in an electrolytic system fed with air are reported.