Enhanced electrocatalytic production of H2O2 at Co-based air-diffusion cathodes for the photoelectro-Fenton treatment of bronopol.

Graphical abstract Highlights • Manufactured C cloth /(Co, S, P)-MWCNTs air-diffusion cathode enhanced H 2 O 2 production. • EO-H 2 O 2 : 15.7 mM vs. 7.4 mM H 2 O 2 with catalyzed and uncatalyzed cathodes of 20 cm2. • Up to 100% current efficiency for H 2 O 2 generation during first minutes at 10 mA cm−2. • Faster bronopol and TOC removals with catalyzed cathode in EO-H 2 O 2 , EF, PEF and SPEF. • Superiority of SPEF (94% TOC removal) and formation of formic acid, NO 3 –, Br– and BrO 3 –. Abstract (Co, S, P)-decorated multiwalled carbon nanotubes (MWCNTs) have been synthesized following a hydrothermal route as electrocatalysts to manufacture large surface area air-diffusion cathodes with carbon cloth as substrate. The enhanced electrocatalytic H 2 O 2 production as compared with Co-free MWCNTs cathodes was demonstrated in a 2.5-L pre-pilot plant with either a RuO 2 -based or boron-doped diamond (BDD) anode, accumulating between 2- and 3-fold greater H 2 O 2 contents with the catalyzed cathode. The good stability of this new material was ensured from the low Co leaching, with less than 9% Co released to solutions upon repeated usage. Aqueous solutions of the brominated organic preservative bronopol with 0.050 M Na 2 SO 4 at pH 3.0 were comparatively treated by electro-oxidation (EO-H 2 O 2), electro-Fenton (EF), UVA-assisted photoelectro-Fenton (PEF) and solar PEF (SPEF) at constant current density. SPEF with BDD anode and the catalyzed cathode showed the best performance, with total bronopol removal at 210 min and 94% mineralization after 360 min at 40 mA cm−2, thanks to the action of OH, BDD(OH) and sunlight. Formic acid was identified as main reaction by-product, whereas Br and N atoms were mainly converted to Br–, BrO 3 – and NO 3 –. Some unidentified organic by-product containing Br and N was formed as well. [ABSTRACT FROM AUTHOR]