High Durability of PtSn/Graphene Electrocatalysts toward the Oxygen Reduction Reaction Studied with In Situ QEXAFS.

To prevent the corrosion of carbon and to enhance corrosion resistance, charge transfer, and mass transfer, graphene, which exhibits a high surface area and good conductivity, was used as an electrocatalyst support for a fuel cell. PtSn/G electrocatalysts for the oxygen reduction reaction (ORR) were prepared with alcohol reduction. The characterization of synthesized catalysts was analyzed according to the energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and extended X-ray absorption fine structure (EXAFS). The electrochemical performance was analyzed with cyclic-voltammetry (CV), linear sweep voltammetry (LSV), and accelerated degradation test (ADT) measurements. The PtSn/G electrocatalysts showed more positive onset potential and larger ORR mass activity than commercial Pt/C catalysts after 5000 cycles of ADT, indicating that in an acidic environment, PtSn/G is more chemically stable than Pt/C. Graphene has effective acid tolerance, is more stable against corrosion, and shows increased stability through preventing PtSn nanoparticles from detaching from the surface. According to the in situ quick EXAFS (QEXAFS) under a CV test to clarify the potential-dependent state of the PtSn/G electrocatalyst, the results show that the electrode surface is reproducible; there is no perceptible change in the oxidation state of the PtSn/G electrocatalyst. The radial distribution function (RDF) of the EXAFS spectra shows that the adsorption and desorption of H and OH cause no structural change in the PtSn crystallites. This work provides insight into the reaction mechanism of proton electroreduction and hydrogen adsorption on a PtSn/G electrocatalyst surface.