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

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 ZnCl2/(NH4)2SO4. 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.