Electrochemical extraction of oxygen from air via hydroperoxide ion

A novel electrochemical method for the extraction of pure oxygen from air is described. The system consists of an undivided cell with a nickel anode, a carbon-polytetrafluoroethylene (CP) air-fed cathode and a KOH+HO2- solution as electrolyte. In such a Ni-CP cell, oxygen from the air is reduced in the cathode to form HO2- via a two-electron process, whereas anodic generation of oxygen gas can take place by the two-electron oxidation of HO2- and/or the four-electron oxidation of OH- of the medium. Gas chromatography confirmed that the oxygen produced from cells operating up to 190 mA cm(-2) does not contain hydrogen, as expected if cathodic reduction of H2O does not take place. The presence of HO2- causes a decrease in energy consumption of the cell, since it is easier to oxidize than OH-. Ni-CP cells containing solutions with concentrations of OH- to 2.4 mol dm(-3) and HO2- from 0.1 to 0.5 mol dm(-3) are stable at 25 degrees C for voltages to about 1.0 V. These cells work in a steady state in which the same number of moles of HO2- ions electrogenerated at the cathode are also anodically decomposed at the anode, without OH- oxidation. In this state, the oxygen consumed in the cathode,is anodically generated and extraction of oxygen from air occurs by a two-electron process. Energy consumptions between 1.710kWhkg(-1) O-2 and 1.224kWhkg(-1) O-2 are obtained for bielectronic stable cells operating at 100 mA cm(-2) and at temperatures between 25 degrees C and 45 degrees C, which are significantly lower than those reported for previous electrochemical oxygen generators based on the anodic decomposition of OH-.