Synthesis of Fe-NC catalysts derived from ZIF-8 encapsulating different Fe sources: Oxygen reduction activity and application in air-cathode microbial fuel cell

Oxygen reaction reduction (ORR) catalyst plays an important role on the electricity generation performance of microbial fuel cell (MFC). Fe-N-C materials have attracted extensive attention due to their low cost, simple synthesis procedure and excellent ORR activity. To evaluate the effect of Fe source on catalyst synthesis, three Fe-containing compounds including ferric acetylacetonate (Fe(acac)₃), ferrous phthalocyanine (FePc) and ferrous bisglycinate (Fe(Gly)₂) are employed as Fe source for preparation of Fe/ZIF-8 precursor. After pyrolysis, the obtained catalysts are named as Fe(A)-NC, Fe(P)-NC and Fe(G)-NC, respectively. The onset potential (E_onset) and half-wave potential (E_1/2) of Fe(A)-NC are 0.828 and 0.690 V, respectively, superior to commercial 20 % Pt/C (0.808 and 0.687 V), Fe(P)-NC (0.813 and 0.688 V) and Fe(G)-NC (0.816 and 0.664 V) in oxygen-saturated 50 mM PBS solution. Electrochemical analyses confirm a four-electron-transfer pathway of the ORR on Fe(A)-NC. Air-cathode (AC) MFCs are constructed to assess the application of the synthesized catalysts. The AC-MFC loaded with Fe(A)-NC exhibites excellent stability and efficient removal rate of chemical oxygen demand (COD) during cell operation over 24 days (6 cycles). The maximum power density of the MFC loaded with Fe(A)-NC is 1917 mW m⁻², higher than 20 % Pt/C (1428 mW m⁻²).