Honeycomb-like hierarchical carbon derived from livestock sewage sludge as oxygen reduction reaction catalysts in microbial fuel cells

Cathode catalysts with excellent efficiencies, low costs and long-term durability in microbial fuel cell (MFC) applications have attracted considerable attention. Herein, hierarchically structured carbons with honeycomb-like interconnected macro-mesoporous frameworks and N, P, and Fe heteroatom doping have been successfully prepared through direct pyrolysis from livestock sewage sludge. In neutral media, the as-prepared activated livestock sewage sludge carbon (LSC-A) catalyst displayed great electrocatalytic activity for the oxygen reduction reaction (ORR), and a maximum power density of 1273 ± 3 mW/m2 was obtained when this catalyst applied in MFCs, which is comparable to that of commercial Pt/C (1294 ± 2 mW/m2). Furthermore, after 90 days of operation, the voltage output of the MFC with the LSC-A cathode decreased only 10.2%, which is considerably lower than the 28.4% decrease of the Pt/C cathode, indicating that LSC-A possesses a greater long-term stability than the Pt/C cathode. This study demonstrated that the N, P, Fe-doped honeycomb-like hierarchically structured carbon derived from livestock sewage sludge is a cost-efficient and promising cathode catalyst for scaling up MFCs.