A facile synthesis of FeS/Fe3C nanoparticles highly dispersed on in situ grown N-doped CNTs as cathode electrocatalysts for microbial fuel cells

Abstract

A novel composite of iron sulfide, iron carbide and nitrogen carbides (Nano-FeS/Fe₃C@NCNTs) as a cathode electrocatalyst for microbial fuel cells (MFCs) is synthesized by a one-pot solid state reaction, which yields a unique configuration of FeS/Fe₃C nanoparticles highly dispersed on in situ grown nitrogen-doped carbon nanotubes (NCNTs). The highly dispersed FeS/Fe₃C nanoparticles possess large active sites, while the NCNTs provide an electronically conductive network. Consequently, the resultant Nano-FeS/Fe₃C@NCNTs exhibit excellent electrocatalytic activity towards the oxygen reduction reaction (ORR), with a half-wave potential close to that of Pt/C (about 0.88 V vs. RHE), and enable MFCs to deliver a power density of 1.28 W m⁻² after two weeks’ operation, which is higher than that of MFCs with Pt/C as the cathode electrocatalyst (1.02 W m⁻²). Theoretical calculations and experimental data demonstrate that there is a synergistic effect between Fe₃C and FeS in Nano-FeS/Fe₃C@NCNTs. Fe₃C presents a strong attraction and electron-donating tendency to oxygen molecules, serving as the main active component, while FeS reduces charge transfer resistance by transferring electrons to Fe₃C, synergistically improving the kinetics of the ORR and power density of MFCs.