Tunable properties of PtxFe1-x electrocatalysts and their catalytic activity towards the oxygen reduction reaction

We present the controlled synthesis of bimetallic PtxFe1-x nanoparticles with tunable physical properties and a study of their catalytic activity towards the oxygen reduction reaction (ORR). Composition-induced variations in alloying extent and Pt d-band vacancies in Pt-Fe/C catalysts are systematically investigated. Density functional theoretical calculations are performed in order to realize the electronic effect caused by alloying Pt with Fe. The DFT computational observations revealed that iron donates electrons to platinum, when the Fe 3d and Pt 5d orbitals undergo hybridization. The PtxFe1-x catalysts with various Pt-to-Fe atomic ratios are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and X-ray absorption spectroscopy (XAS). TEM images indicate that the dispersion of the metal nanoparticles is uniform and the XAS technique provides significant insight on Pt d-band vacancies and the alloying extent of Pt and Fe in PtxFe1-x nanoparticles. Rotating-disk voltammetry of PtxFe1-x nanoparticle catalysts with various Pt : Fe atomic compositions (3 : 1, 1 : 1, and 1 : 3) revealed that the Pt1Fe1/C nanocatalyst showed a greater enhancement in ORR activity than platinum. The enhanced catalytic activity toward ORR is attributed to the higher alloying extent of platinum and iron as well as the promising electronic structure offered by the lower unfilled Pt d states in PtxFe1-x nanoparticles when compared to pure Pt.