The generation of hydrogen peroxide by means of the cathodic reduction of oxygen at gas-diffusion electrodes with a near 100% current efficiency was achieved in concentrations sufficient for the mineralization of refractory organics in Fenton treatment. A decrease in current efficiency over time at high temperatures and high current densities was observed. The polarization study carried out in potentiostatic, potentiodynamic and galvanostatic modes in 0.5 M Na 2 SO 4 solution at pH 3 showed that the destruction of hydrogen peroxide at the cathode of the electrochemical reactor, as well as its chemical decomposition in the bulk solution, takes place at a significantly lower rate than the oxidation of H 2 O 2 at the Ti-IrO 2 anode. Preparative electrolysis in the membrane reactor showed much higher current efficiencies for H 2 O 2 electro-generation in comparison with tests carried out in an undivided cell. The performance of different proton-exchange membrane in this process was studied and a membrane cell with a heterogeneous MK-40 type PEM was found to be suitable. An optimized cell design, the appropriate selection of electrodes, supporting electrolytes, and a membrane resulted in a lower voltage in the membrane cell in comparison with the undivided cell.

A comparative study of phenol, 4-chlorophenol and aniline degradation with the electro-generation of H 2 O 2 at gasdiffusion electrodes was carried out under three different conditions: electro-Fenton Ò treatment in an undivided cell; electro-Fenton treatment in the catholyte of a membrane cell divided by a proton-exchange membrane (in-cell electro-Fenton membrane process); and a treatment of polluted solution in the cathode space of a membrane cell with the generation of H 2 O 2 , followed by the addition of Fe(II) salt in the other reactor (ex-cell electro-Fenton process). An optimized cell design with no gap between the membrane and the anode, along with the appropriate choice of supporting electrolytes, ensured a voltage reduction with a membrane cell in comparison with that of an undivided cell. The accumulation of hydrogen peroxide in concentrations sufficient for the almost complete destruction (90-98%) of aromatic organic pollutants was achieved in all cases but the ex-cell process with the preparative electrolysis in the pilot scale membrane reactor separated by the proton-exchange membrane MK-40 showed higher treatment efficiency and lower specific energy consumption in comparison with known technologies. Damage of the gas-diffusion layer was observed in some tests which could be caused by alkaline conditions in the pores of the gas-diffusion cathode (GDE). The pH indicator paper showed a color specific for alkaline media in contact with the GDE treated in the solution with pH 3 in the bulk. A possible explanation could be that even in acid media, hydrogen peroxide generation in pores of the gas diffusion layer proceeds with formation of HO 2 ) which is common for alkaline media and consecutive protonation occurs at the interface with the acid solution.

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The novel process of H2O2 generation in the direct methanol fuel cell (DMFC) composed from the "Black Pearls 2000" gas-diffusion cathode (GDE), washed by sodium chloride brine or sea water for O2 electro-reduction and the half-membrane-electrode assembly (MEA) with the Nafion 115® cation-exchange membrane (CEM), hot pressed on one side with the carbonic gas-diffusion anode impregnated by Pt/Ru catalyst for methanol oxidation, has been developed. The effect of NaCl concentration in the catholyte, methanol and the KOH concentration in the anolyte, electrolyte temperature and circulation flow rate on the generated cell voltage, current and H2O2 current efficiency have been studied in 2 hour trials. 87-95 % current efficiency for H2O2 generation with a 5.286 -9.44 mg h-1 cm-2 rate and at 15 mA cm-2 current density was achieved in the DMFC with 1 M CH3OH +7M KOH in the anolyte and 30 g L-1 NaCl in the catholyte.