Carbon-based cathodes degradation during electro-Fenton treatment at pilot scale: Changes in HO electrogeneration.

Autopsy of carbon-PTFE cathodes was performed by addressing their degradation in a commercial plate-and-frame cell equipped with a Nb-BDD anode. Cell is arranged within an electrochemical pilot plant designed for treating wastewaters by electrochemical Fenton-like processes, thus an efficient electrocatalytic production of HO is necessary to guarantee Fenton's reaction. Significant decrease in HO electrogeneration occurred during pilot plant operation, hindering the efficient performance of Fenton-like processes. Two cathodes were studied, first was operated at pH 3 and second at neutral pH by using EDDS as complexing agent to maintain iron in solution. Electrogenerated HO decreased from 43 mg L to 16 mg L in the first cathode after 50 h of operation and from 49 mg L to 24 mg L in the second one after 26 h of operation. Both were cleaned with 30% (v/v) solution of HCl/water for 24 h and HO production was recovered only in the second cathode (able to generate 39 mg L). Autopsy of the cathodes was tackled by scanning electron microscopy (SEM) and X-ray energy dispersive (EDX), evidencing a strong degradation of first cathode surface and iron oxide inlays in second one due to the decomposition of Fe:EDDS and consequent iron precipitation at neutral pH.