Effect of flow mode of gas-liquid phase in graphite-felt cathode on electrochemical production of hydrogen peroxide

An electrochemical reactor has been developed for the on-site electrochemic al production of hydrogen peroxide. Comparison was made between a trickle-b ed mode where gas and liquid phases flowed downward cocurrently in the grap hite-felt cathode and a packed-bed mode where two phases flowed upward cocu rrently. At the same now condition of gas-liquid phase, the current efficie ncy Ce using the trickle-bed electrode was higher than that using the packe d-bed electrode with gas-sparging. Mathematical analysis based on a three-p hase bed model was made to fit the over-potential profiles in the cathode b y using electrode kinetics and mass-transfer parameters, gas and liquid hol dups in the bed, the effective conductivity of the solution phase and the e ffective surface area of electrode. The current efficiency Cc was affected by now rates of gas and liquid, and the current density, because of the cha nges in the effective specific surface area a(eff) of electrode and liquid- solid mass transfer coefficient k(mA) or oxygen onto the electrode. In this experiment, Ce was increased mainly by increasing a(eff) rather than k(mA) . Using the trickle-bed electrode, a(eff) and k(mA) were higher than that u sing the packed-bed electrode, because oxygen gas and catholyte were disper sed uniformly in the cathode compartment, thus leading to higher Ce.