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)-O-center dot) 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)-O-center dot) 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)-O-center dot without external chemical addition and thus offers an alternative method for abatement of aqueous organic contaminants.

Automated summary

This study demonstrates an electrochemical advanced oxidation process (EAOP) that can simultaneously catalyze the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) to generate atomic hydrogen (H*) and hydrogen peroxide (H2O2) in situ. By using a palladium-coated carbon-PTFE gas diffusion electrode (Pd/C GDE) as a catalytic cathode, hydroxyl radicals ((OH)-O-center dot) can be formed by the reaction of electrogenerated H* with H2O2. The H*/GDE process is more effective in degrading organic contaminants compared to the conventional H*/H2O2 process.