Electrochemical generation of hydrogen peroxide from dissolved oxygen in acidic solutions

Hydrogen peroxide (H2O2) was electro-generated in a parallel-plate electrol yzer by reduction of dissolved oxygen (DO) in acidic solutions containing d ilute supporting electrolyte. Operational parameters such as cathodic poten tial, oxygen purity and mass flow rate, cathode surface area, pH, temperatu re, and inert supporting electrolyte concentration were systematically inve stigated as to improve the Faradic current efficiency of H2O2 generation. R esults indicate that significant self-decomposition of H2O2 only occurs at high pH ( > 9) and elevated temperatures (> 23 degreesC). Results also indi cate that the optimal conditions for H2O2 generation are cathodic potential of -0.5 V vs. saturated calomel electrode (SCE), oxygen mass flow rate of 8.2 x 10(-2) mol/min, and pH 2. Under the optimal conditions, the average c urrent density and average current efficiency are 6.4 A/m(2) and 81%, respe ctively. However, when air is applied at the optimal flow rate of oxygen, t he average current density markedly decreases to 2.1 A/m(2), while the aver age current efficiency slightly increases to 90%. The limiting current dens ity is 6.4 A/m(2), which is independent of cathode geometry and surface are a. H2O2 generation is favored at low temperatures. In the concentration ran ge studied (0.01-0.25 M), the inert supporting electrolyte (NaClO4) affects the total potential drop of the electrolyzer, but does not affect the net generation rate of H2O2. (C) 2001 Elsevier Science Ltd. All rights reserved .