Electrochemical generation of hydrogen peroxide from dissolved oxygen in acidic solutions

Hydrogen peroxide (H2O2) was electro-generated in a parallel-plate electrolyzer by reduction of dissolved oxygen (DO) in acidic solutions containing dilute supporting electrolyte. Operational parameters such as cathodic potential, oxygen purity and mass flow rate, cathode surface area, pH, temperature, and inert supporting electrolyte concentration were systematically investigated as to improve the Faradic current efficiency of H2O2 generation. Results indicate that significant self-decomposition of H2O2 only occurs at high pH ( > 9) and elevated temperatures (> 23 degreesC). Results also indicate 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 current density and average current efficiency are 6.4 A/m(2) and 81%, respectively. However, when air is applied at the optimal flow rate of oxygen, the average current density markedly decreases to 2.1 A/m(2), while the average current efficiency slightly increases to 90%. The limiting current density is 6.4 A/m(2), which is independent of cathode geometry and surface area. H2O2 generation is favored at low temperatures. In the concentration range 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.