Nitrogen-doped biochar derived from watermelon rind as oxygen reduction catalyst in air cathode microbial fuel cells

Cathodic electrocatalyst is critical to the performance of microbial fuel cells. Developing cost-effective and efficient catalyst for oxygen reduction reaction is therefore an important step towards wider application of microbial fuel cells. Herein, we report a cost-effective and environment-friendly strategy for synthesis of nitrogen-doped hierarchically porous carbon with watermelon rind as a nitrogen-rich and high stability precursor and the biochar is used as cathode catalyst in air cathode microbial fuel cells. In this study, the pyrolysis derivative, WRC-700, achieves a current density of redox peak of 0.19 mA cm−2, which is comparable to the Pt/C catalyst. There are more CN bonds and higher concentrations of pyridinic nitrogen and graphitic nitrogen in the carbon framework of WRC-700 catalyst resulting in an outstanding electrochemical active area of 658.90 m2 g−1, functioning through a four-electron pathway toward oxygen reduction reaction process. The charge transfer resistance of 20.63 Ω is achieved by WRC-700 cathode, which is slightly smaller than Pt/C cathode (37.56 Ω). With experimental validation, we find that carbon from watermelon rind biomass can be considered as a superior alternative to non-metal catalyst in microbial fuel cell applications and envisage an enhanced power output from microbial fuel cells using the catalyst-modified cathodes.