Sewage sludge biochar as an efficient catalyst for oxygen reduction reaction in an microbial fuel cell

Sewage sludge (SS) biochars have been prepared under an inert atmosphere at different temperatures. Morphologic and chemical analyses reveal that the surface of the biochar carbonized at 900 °C (SS900) has more abundant micropores, and higher nitrogen and iron contents as compared to those carbonized at 500 (SS500) and 700 °C (SS700). The electrochemical analyses display that the prepared biochars are active for catalyzing oxygen reduction reaction (ORR). However, more positive peak potential and larger peak current of ORR are found using the SS900 as compared to the SS500 and SS700. In MFCs, the maximum power density of 500 ± 17 mW m−2 was obtained from the SS900 cathode, which is comparable to the Pt cathode. The proposed cathode exhibited good stability and great tolerance to methanol. Given these results, it is expected that the SS-derived biochar cathode can find application in fuel cell systems.