Hydroxyl Radical Production via a Reaction of Electrochemically Generated Hydrogen Peroxide and Atomic Hydrogen: An Effective Process for Contaminant Oxidation?

An electrochemical advanced oxidation process (EAOP) is demonstrated with a catalytic cathode capable of simultaneously catalyzing the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) with resultant in situ generation of atomic hydrogen (H*) and hydrogen peroxide (H₂O₂). A palladium-coated carbon-PTFE gas diffusion electrode (Pd/C GDE) was used as a catalytic cathode with hydroxyl radical (^•OH) formed as a result of the reaction of electrogenerated H* with H₂O₂. As both the HER and ORR can be induced to occur at the same cathode, the H*/GDE process results in more effective degradation of organic contaminants than can be achieved by a conventional H*/H₂O₂ process involving direct addition of H₂O₂. At circumneutral pH, 82.7% of added formate was degraded after 2 h treatment at an applied potential of -1.0 V vs Ag/AgCl with relatively low concentrations of generated H₂O₂ remaining in the solution. We also show that H* and H₂O₂ (and thus ^•OH) can be electrogenerated effectively over a wide range of pH (3.2-7.0). These results suggest that by in situ generation of H* and H₂O₂, the H*/GDE process is able to produce significant amounts of ^•OH without external chemical addition and thus offers an alternative method for abatement of aqueous organic contaminants.