The Fabrication Of NPG-Pdx/Ptx Films And Their Electrocatalytic Activities

Atomic layer-by-layer construction of Pd on nanoporous gold (NPG) has been investigated through the combination of underpotential deposition (UPD) with displacement reaction. It has been found that the UPD of Cu on NPG is sensitive to the applied potential and the deposition time. Improper potential will result in deposition of either submonolayer or bulk Cu. The optimum deposition potential and time were determined through potential- and time-sensitive stripping experiments. The NPG-Pd electrode shows a different voltammetric behavior in comparison to the bare NPG electrode, and the deposition potential was determined through the integrated charge control for the monolayer UPD of Cu on the NPG-Pd electrode. Five layers of Pd were constructed on NPG through the layer-by-layer deposition.In addition, the microstructure of the NPG-Pdx (x=1,2,3,4 and 5) films was probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) with nano-beam energy dispersive X-ray analysis (NB-EDX). The microstructural observation demonstrates that the atomic layers of Pd form on the ligament surface of NPG through the epitaxial growth, and have no effect on the nanoporous structure of NPG. The ligaments also show relatively smooth surfaces. The NB-EDX analysis indicates that both the center and border of the ligament are covered by Pd atoms. The cyclic voltammograms (CVs) of NPG-Pdx show that the current of the Pd oxide reduction peaks gradually increases with increasing Pd layers on the NPG surface. In addition, the oxygen reduction reaction (ORR) properties of the NPG-Pdx electrodes have also been researched. Electrochemical tests demonstrate that NPG-Pdx exhibits better catalytic activities for ORR than the commercial PtC and NPG catalysts. Among the prepared NPG-Pdx catalysts, the NPG-Pdl electrode exhibits the best catalytic activities in both half-wave potential and electrochemically active surface areas (ECSA). The NPG-Pdl electrode also exhibits better catalytic activities for the oxygen evolution reaction (OER). All of the above demonstrate the feasibility of this method for fabricating ultrathin Pd films on NPG. The prepared NPG-Pdx can be used as cathodic catalysts in fuel cells and are potential catalysts for the OER in industrial applications.Using the same substrate (NPG) and similar method (UPD and displacement reaction), we fabricated the NPG-Ptx catalyst. The as-prepared NPG-Ptx were observed and analyzed through SEM, EDX, TEM, and HRTEM with NB-EDX. The results show that even for NPG-Ptl, Pt atoms tend to form an island-like or particle-like structure on the NPG surface, which is quite different from the scenario of Pd deposition. Moreover, with increasing deposition layer, the size of Pt nanoparticles becomes larger and the nanoparticle surface becomes rough. Electrochemical tests demonstrate that NPG-Ptx exhibits better catalytic activities for ORR than the commercial PtC and PtRuC catalysts. Among them the NPG-Pt3 exhibits the best catalytic acitivities in both half-wave potential and the ECSA.Moreover, the NPG-Ptl electrode exhibits better catalytic activities for OER than NPG catalyst.