Study of hydrogen gas production coupled with phenol electrochemical oxidation degradation at different stages

• Protons released from phenol electrochemical oxidation degradation form hydrogen.
• Three stages were observed in phenol electrochemical oxidation degradation at 3 V.
• Each stages could be well described by the first order kinetic model.
• ICE increased in first two stages while decreased dramatically in third stage.
• Hydrogen yield improved in first stage but reduced in second stage.

Hydrogen gas production coupled with phenol electrochemical oxidation was investigated in a novel two-region equipment. The phenol degradation, COD removal, hydrogen production, kinetic, Instantaneous Current Efficiency for COD removal (ICECOD), and hydrogen gas yield (YH2) of simulated phenol solution electrochemical oxidation degradation at 3 V applied voltage were surveyed. The results indicated that three stages were observed during the electrochemical oxidation of simulated phenol in this study. The kinetic study showed that first order model well described each stage of phenol electrochemical oxidation process. The ICECOD increased slightly at the initial stage, and dramatically at the second stage, while fell at the finally stage, indicating water molecules were finally participated in the formation of hydrogen due to the degradation of phenol and COD. Hydrogen products from redox reaction of H+ which release from the degradation of organics oxidation reaction at the anode. Furthermore, the mechanism was discussed and showed that phenol transformed into benzoquinone intermediate in the first step, then the ring was broken and further oxidized into organic compounds like muconic acid, maleic acid or oxalic acid as intermediates in the followed stage, and finally disintegrated into CO2 and H2O in electrochemical oxidation process, which demonstrated by the UV and LC–MS images analysis. It could be seen that hydrogen gas production coupled with organic wastewaters electrochemical oxidation would be an effective approach for energy recovery and wastewater reutilization.

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