Effects of holdups of gas and liquid phases in packed-bed electrode on current efficiency of electrochemical production of hydrogen peroxide

A packed-bed electrode of graphite felts sparged with oxygen gas was used for the on-site electrochemical production of hydrogen peroxide. The terminal voltage and the current efficiency were affected by operational conditions such as liquid and gas velocities in the packed-bed cathode. The holdups of gas and liquid phases, and the potential profiles of the solution phase in the cathode were measured to clarify the effects of the operational conditions on the electrolysis performance. The holdups of gas and liquid phases were determined as functions of superficial velocities of gas and liquid. The cathodic potential in the bed was shifted up by increasing liquid velocity at a certain velocity of gas. The reaction resistivity of oxygen reduction was increased by increasing liquid holdup, because of the increase in the diffusion length of the oxygen. Meanwhile the effective resistivity of the solution was decreased by increasing liquid holdup. Then the potential of the solution in the bed had a minimum profile at a certain holdup of the liquid phase. The optimum conditions for electrolysis were determined as follows: the current density was 300A . m(-2) holdups of gas and liquid phases, epsilon(G) = 0.85 similar to 0.90, and epsilon(L) = 0.04 similar to 0.05.