X-ray photoelectron
spectroscopy (XPS) (Perkin-Elmer Phi 560 XPS/Auger System, Waltham, MA, USA) was adopted with Al as the source to explore the electronic structures on the NP surface. High-resolution transmission electronic microscopy (HRTEM) with 300 kV of Selleck PRI-724 accelerated voltage (Hitachi H-9500 HRTEM, Tokyo, Japan) was employed to study the NP size and structure. Ultraviolet–visible (UV–vis) spectra were obtained with a Perkin-Elmer Lambda 19 UV/VIS/NIR spectrometer at room temperature. The compositions (weight fractions of Pd to the total mass) of the Au/Pd catalyst determined by inductively coupled MRT67307 solubility dmso plasma mass spectrometry (Perkin-Elmer ELAN DRC II) are as follows: Au25Pd 36.4 wt.%, Au50Pd 32.5 wt.%, and Au100Pd 29.5 wt.%, respectively. Electrochemical measurements were conducted with a Princeton Applied Research 2273 potentiostat (Oak Ridge, TN, USA) in three-electrode configuration using a rotating disk electrode (Pine Instrument Company, Grove City, PA, USA) of glassy carbon (area, 0.19635 cm2). Pt mesh and normal hydrogen electrode (NHE) were used as the counter electrode and reference electrode, respectively. Preparation of catalyst inks and rotating disk electrodes followed the procedure described in our previous work [18, 24]. Typically, 15 mg of catalysts was SB-715992 research buy mixed with 12 ml of distilled water and 4.4 ml of 5 wt.% Nafion (Ion Power Inc., Newcastle, DE, USA) and then dried under an IR lamp.
During the CO-stripping measurement, CO was first adsorbed to the catalysts at 0.2 V for 900 s in CO-saturated 0.1 M HClO4 solution, and then cyclic voltammetry (CV) was conducted from 0.075 to 1.2 V at a rate of 10 mV s-1 after bubbling Ar for an hour. The FAO test was conducted in a mixed electrolyte (0.1 M HClO4 and 0.1 M HCOOH) from -0.03 to 1.4 V (vs. NHE) at 1,000 rpm. The catalytic durability was
tested by an accelerated stress test (AST) protocol with square-wave potential cycles between 0.6 V (5 s) and 0.95 V (5 s). Results and discussion Figure 1a shows the XRD reflection peaks of the Pd black (Alfa Aesar, Ward Hill, MA, USA) at 40.20°, 46.73°, 68.21°, and 82.17°, respectively, corresponding to Pd (111), (200), (220), and (311) planes in the fcc structure Fludarabine nmr (JCPDS no. 87–0639; 40.21°, 46.78°, 68.3°, and 82.34°). For the Au/Pd NPs, the peaks at 38.28°, 44.42°, 64.76°, and 77.81° correspond respectively to Au (111), (200), (220), and (311) planes (JCPDS no. 65–2870; 38.19°, 44.38°, 64.57°, and 77.56°). The very weak Pd signal in the XRD pattern is attributed to the highly dispersed Pd nanocrystallites embedded at the Au surface (shown in the TEM images in Figure 2). There is no identifiable Cu signal in the spectra, suggesting that Cu has been completely replaced by the Pd shell, which confirms our previous study [24]. Besides, Figure 1b displays the Pd 3d core-level XPS spectra of the Au/Pd NPs and Pd black. The Au25Pd NPs showing lower Pd 3d 5/2 binding energy (334.