Lignin combined with polypyrrole as a renewable cathode material for H2O2 generation and its application in the electro-Fenton process for azo dye removal

The development of renewable, low-cost, and high-efficiency cathode materials for oxygen reduction to H 2 O 2 is desirable for use in electro-Fenton systems for the oxidative treatment of wastewater. In the present study, we report the synthesis of a renewable biopolymer with lignin (lig) interpenetrated into a polypyrrole (PPy) framework via a simple one-step electropolymerization method. This allows the formation of PPy/lig composites that are uniformly coated on a graphite felt (GF) substrate, having large surface area, increased mechanical stability, and abundant C O (including quinone-type) groups. These features improved the electrocatalytic activity of the PPy/lig-GF cathode for oxygen reduction to H 2 O 2 when an optimal cathodic potential (−0.5 V vs. SCE) was applied, as evidenced by the observed higher H 2 O 2 electro-generation yield and efficiency compared to the raw GF and PPy/ClO 4 − -GF cathodes. Electro-Fenton systems equipped with the GF cathodes (either modified or unmodified) for the decolorization and mineralization of AO7 (an azo dye) followed a pseudo-first-order kinetic model . The PPy/lig-GF cathode achieved substantially higher rate constants and degradation efficiencies. In addition, the incorporation of lignin significantly improved the cycling stability of the cathode material.