2014 Volume 57 Issue 6 Pages 237-250
Direct synthesis of H2O2 aqueous solutions from O2 and H2 using a fuel cell reactor was reviewed. H2O2 can be catalytically produced by electrochemical reaction without external electrical supply. New electrocatalysts and four types of fuel cell reactors were designed and developed to achieve higher performance of H2O2 formation, ex. an Au-mesh cathode and a type-1 reactor for H2O2/HCl aq. solutions, a heat-treated Mn–porphyrin/activated-carbon cathode and a type-2 reactor for H2O2/H2SO4 aq. solutions, a vapor-grown-carbon-fiber (VGCF) cathode and a type-3 reactor for H2O2/NaOH aq. solutions, and a heat-treated Co–porphyrin/VGCF cathode and a type-4 reactor for pure H2O2 aq. solutions. These studies indicated that synergy of selective electrocatalysis of the cathode and three-phase boundary of O2 (gas phase), electrocatalyst (solid phase) and electrolyte (liquid phase) were essential for the efficient reduction of O2 to H2O2. Therefore, direct synthesis of a pure H2O2 aq. solution of over 4.0 mol dm−3 was achieved with a good current efficiency of 42 %.