Structure of carbon-supported Pt–Ru nanoparticles and their electrocatalytic behavior for hydrogen oxidation reaction

The electrochemical activity towards hydrogen oxidation reaction (HOR) of a high performance carbon-supported Pt–Ru electrocatalyst (HP 20 wt.% 1:1 Pt–Ru alloy on Vulcan XC-72 carbon black) has been studied using the thin-film rotating disk electrode (RDE) technique. The physical properties of the Pt–Ru nanoparticles in the electrocatalyst were previously determined by transmission electron microscopy (TEM), high resolution TEM, fast Fourier transform (FFT), electron diffraction and X-ray diffraction (XRD). The corresponding compositional and size–shape analyses indicated that nanoparticles generally presented a 3D cubo-octahedral morphology with about 26 at.% Ru in the lattice positions of the face-centred cubic structure of Pt. The kinetics for HOR was studied in a hydrogen-saturated 0.5 M H2SO4 solution using thin-film electrodes prepared by depositing an ink of the electrocatalyst with different Nafion contents in a one-step process on a glassy carbon electrode. A maximum electrochemically active surface area (ECSA) of 119 m2 g Pt−1 was found for an optimum Nafion composition of the film of about 35 wt.%. The kinetic current density in the absence of mass transfer effects was 21 mA cm−2. A Tafel slope of 26 mV dec−1, independent of the rotation rate and Nafion content, was always obtained, evidencing that HOR behaves reversibly. The exchange current density referred to the ECSA of the Pt–Ru nanoparticles was 0.17 mA cm−2, a similar value to that previously found for analogous inks containing pure Pt nanoparticles.