Macroporous hollow nanocarbon shell-supported Fe-N catalysts for oxygen reduction reaction in microbial fuel cellss

Abstract

Abstract The properties of carbon supports play a significant role in the performance of the oxygen reduction reaction (ORR) catalysts for single-chamber microbial fuel cells (MFCs). In this study, sodium citrate was directly carbonized to prepare macroporous nanocarbon shells (CSs) with a shell thickness of ∼8\u202fnm, which were proposed as the carbon support for the Fe-N catalyst (FePc/CS) for ORR. The experiments showed that the thin-walled macroporous nanostructure of CSs remained unchanged after pyrolysis with Fe (II)-phthalocyanine (FePc). Electrochemical tests performed in 50\u202fmM phosphate buffer solution demonstrated that the catalyst pyrolyzed at 500\u202f°C (FePc/CS500) exhibited a 42\u202fmV higher half-wave potential than that of commercial 20\u202fwt% Pt/C catalyst under the same loading. This is due to the combine effects of the chemical functions (abundant Fe-N active sites) and the structural advantages (macropores and thin-walls, which facilitated the mass transfer in CS and increased the contact interface between the electrolyte and active sites, respectively). FePc/CS500 also exhibited a better durability than Pt/C, stemming from the four-electron reaction pathway that prevented the active sites from being degraded by the generated H2O2. The performance evaluation showed that the MFC with FePc/CS500 as the cathode catalyst delivered a maximum power density of 2.16\u202f±\u202f0.02\u202fW\u202fm−2, which was 50% higher than that of Pt/C (1.44\u202f±\u202f0.04\u202fW\u202fm−2). These results indicated FePc/CS500 was a cheap but effective alternative ORR catalyst to Pt/C for energy recovery from wastewater.