PtSnP/C and PtSn/C as efficient cathode catalysts for oxygen reduction reaction in microbial fuel cells

This study focused on reducing the catalyst cost and improving the performance of cathode in single chamber microbial fuel cell (SCMFC). Cost-effective Pt7Sn3P/C and PtSn (with different Pt/Sn atomic ratios) catalysts were investigated for the oxygen reduction reaction (ORR) in SCMFCs with air cathode. The morphology, surface composition and the structural properties of the catalysts were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The cyclic voltammetry (CV) analyses showed that, phosphorus substantially improved ORR compared to the conventional Pt/C catalyst, which was ascribed to the smallest average particle diameters (1.58 nm) and uniform size distribution on Pt7Sn3P/C. Moreover, the addition of phosphorus modified the electronic structure of Pt through the pathway of electron transfer from Pt to P, leading to the lower energy shift of d-band center for Pt atom in PtSnP ternary catalyst. Among three PtSn/C catalysts with different Pt/Sn molar ratios, Pt7Sn3/C showed the highest ORR catalytic activity, even better than Pt/C, indicating that the atomic ratio had a significant effect on the catalytic behavior. The performances of SCMFCs varied with the types of cathode catalysts, with Pt7Sn3P/C having the highest power density (361 ± 7.5 mW m−2), followed by Pt7Sn3/C (336 ± 11.8 mW m−2) and Pt/C (307 ± 11.5 mW m−2). Pt7Sn3P/C has a great potential as the cathode catalyst in SCMFCs due to high ORR activity, low cost and good stability.