Dramatic enhancement of organics degradation and electricity generation via strengthening superoxide radical by using a novel 3D AQS/PPy-GF cathode.

A dramatic enhancement of organics degradation and electricity generation has been achieved in a wastewater fuel cell (WFC) system via strengthening superoxide radical with radical chain reaction by using a novel 3D anthraquinone/polypyrrole modified graphite felt (AQS/PPy-GF) cathode. The AQS/PPy-GF was synthesized by one-pot electrochemical polymerization method and used to in-situ generate superoxide radical by reducing oxygen under self-imposed electric field. Results showed that methyl orange (MO) were effectively degraded in AQS/PPy-GF/Fe system with a high apparent rate constant (0.0677 min), which was 3.9 times that (0.0174 min) in the Pt/Fe system and even 9.4 times that (0.0072 min) in the traditional WFC system (without Fe). Meanwhile, it showed a superior performance for electricity generation and the maximum power density output (1.130 mW cm) was nearly 3.3 times and 5.0 times higher, respectively, when compared with the Pt/Fe system and traditional WFC. This dramatic advance was attributed to 3D AQS/PPy-GF cathode which produces more O via one-electron reduction process. The presence of O cannot only directly contribute to MO degradation, but also promotes the final complete mineralization by turning itself to OH. Additionally, O accelerates the Fe/Fe couple cycling, thus avoiding continuous addition of any external ferrous ions. Inhibition and probe studies were conducted to ascertain the role of several radicals (OH and O) on the MO degradation. Superoxide radicals were considered as the primary reactive oxidants, and the degradation mechanism of MO was proposed. The proposed WFC system provides a more economical and efficient way for energy recovery and wastewater treatment.