Platinum-free catalysts for low temperature fuel cells

Introduction An efficiency of low temperature oxygen-hydrogen fuel cells is influenced by kinetic limitations of the oxygen reduction reaction (ORR). Platinum and its alloys with transition metals are usually used as cathodic... [ view full abstract ]

Introduction
An efficiency of low temperature oxygen-hydrogen fuel cells is influenced by kinetic limitations of the oxygen reduction reaction (ORR). Platinum and its alloys with transition metals are usually used as cathodic catalysts for the ORR. However, platinum-based catalysts have some drawbacks such as high cost and high extent of degradation. Such situation stimulated recent investigations aiming on developing of platinum-free or low platinum content catalyst for ORR. Metal-organic frameworks (MOFs) and MOF-derived porous carbon materials may constitute a promising solution. This research is focused on the preparation of the porous MOFs that can be used as catalysts for oxygen reduction reaction.
Methods
Fe3O4@MOFs (MOF = ZIF-8, ZIF-68, HKUST-1) composites were prepared by sonochemical, solvothermal and microwave-assisted syntheses. At the first stage magnetic iron oxides nanoparticles were prepared by microwave-assisted modified co-precipitation method. They were characterized with X-ray diffraction (XRD), Fourier transformed Infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS). Then, magnetic nanoparticles were covered with MOFs. Final composites were additionally investigated using vibrating magnetometer and surface area and porosity analyzer. Furthermore, fractions of the samples were heat treated at 900 C under argon atmosphere to obtain catalytic active carbons.
Results and Discussion
According to XRD data the final composites contain both spinel phase of nanoparticles and the MOF’s phase. It was shown that prepared materials are porous and magnetic; their surface area and porosity depends on synthesis conditions. To have an insight into applicability of obtained composites in ORR, they were investigated by cyclic voltammetry (CV) in three-electrode cell in phosphate buffered saline at pH = 6 (see Fig.1). In conclusion, we have obtained catalytic active composites, which might be suitable for applications in low temperature air-hydrogen fuel cells.

This work was supported by Russian Foundation for Basic Research (grant № 16-33-00854).