Hierarchically structured carbon materials derived from lotus leaves as efficient electrocatalyst for microbial energy harvesting.

Abstract Developing a highly efficient, cost-effective, easily scalable and sustainable cathode for oxygen reduction reaction (ORR) is a crucial challenge in terms of future "green" energy conversion technologies, e.g., microbial fuel cells (MFCs). In this study, a natural and widely available lotus leaf with intrinsically hierarchical structure was employed to serve as the single precursor to prepare the catalyst applied as the MFC cathode. The hierarchically particle-coated bio‑carbon was self-constructed from the lotus leaf, which yielded a large specific surface area, highly porous structure and superhydrophobicity via facile pyrolysis coupling hydrothermal activation by ZnCl 2 /(NH 4) 2 SO 4. Electrochemical evaluation demonstrated that these natural leaf-derived carbons have an efficient ORR activity. Specifically, the HC-900 catalyst with hydrothermal activation achieved an onset potential of −0.015 V vs. Ag/AgCl, which was comparable to the commercial Pt/C catalyst (−0.010 V vs. Ag/AgCl) and was more efficient than the DC-900 catalyst through direct pyrolysis. Furthermore, the HC-900 catalyst achieved an outstanding ORR activity via a one-step and four-electron pathway, exhibiting a potential alternative to Pt/C as electrocatalyst in ORR, due to its better long-term durability and methanol resistance. Additionally, the HC-900 catalyst was applied as an effective electrocatalytic cathode in an MFC system with a maximum power density of 511.5 ± 25.6 mW⋅m−2, exhibiting a superior energy harvesting capacity to the Pt/C cathode. Graphical abstract Unlabelled Image Highlights • Lotus leaf-based carbon (HC-900) with hierarchical micro/nanostructure was obtained. • HC-900 has a highly porous structure and super-hydrophobic property. • HC-900 has an efficient and stable ORR activity, outperforming 20 wt% Pt/C catalyst. • HC-900 can be used as effective cathode catalyst for microbial energy harvesting. [ABSTRACT FROM AUTHOR]