Multimetallic Mesoporous Spheres Through Surfactant‐Directed Synthesis

Multimetallic mesoporous spheres are successfully synthesized with ultra‐large mesopores with the assistance of nonionic triblock copolymer (F127) as a structural directing agent. The kinetically controlled reduction rate of metal species and the concentration of F127 are critical to the formation of the large mesopores.

All solutions were prepared with deionized water treated with a Millipore water purification system (Millipore Corp.).
In the typical condition, the relative mole ratio of Pt/Pd species was 5.00. Then, the mixed solution was continuously sonicated in a water bath for 4 hours at 40 o C. Finally, the sample was collected by centrifugation at 14,000 rpm for 20 min and the residual Pluronic F127 was removed by three consecutive washing/centrifugation cycles with ethanol and water. Preparation of mesoporous trimetallic PdPtCu spheres. Firstly, 1.5 ml Na 2 PdCl 4 (20.0 mM), 1.5 ml H 2 PtCl 6 (20.0 mM), 1.5 ml CuCl 2 (20 mM), 0.2 ml HCl (6.0 M) and 50.0 mg Pluronic F127 were mixed. After F127 was dissolved under ultrasound condition, an aqueous solution of 2.0 ml ascorbic acid (0.1 M) was added to above solution, giving the final Na 2 PdCl 4 , H 2 PtCl 6 , CuCl 2 precursor amounts of 0.03, 0.03, and 0.03 mmol, respectively. Then, the mixed solution was kept in an oil bath for 4 hours at 95 o C. Finally, the sample was collected by centrifugation at 14000 rpm for 20 min and the residual Pluronic F127 was removed by several consecutive washing/centrifugation cycles with ethanol and water. The as-prepared sample was stored in ethanol until the time of use and then dried at room temperature.
Preparation of dendritic Pt nanoparticles. Firstly, an aqueous solution consisting of nonionic Brij58 surfactant was prepared under stirring. Then, K 2 PtCl 4 and ascorbic acid (AA) were added to the surfactant Brij58 solutions, making the final concentration of K 2 PtCl 4 and AA to be 5 mM and 12.5 mM, respectively.
The final concentration of Brij58 in solution was 0.5 %. Then, the reaction solution was incubated without any external treatment for 12 h at room temperature. Finally, the sample was collected by centrifugation at 14000 rpm for 20 min and the residual Brij58 was removed by several consecutive washing/centrifugation cycles with ethanol and water. The as-prepared sample was stored in ethanol and then dried at room temperature.

Materials characterization. Scanning electron microscope (SEM) observation was carried out using a
Hitachi SU-8000 microscope operated at 5.00 kV. Transmission electron microscope (TEM) and high-angle annular dark-field scanning TEM (HAADF-STEM) observations were carried out using a JEOL JEM-2100F operated at 200 kV equipped with an energy-dispersive spectrometer. The samples for TEM study were prepared by depositing a drop of the diluted colloidal suspension on a carbon-coated copper grid. A wide-angle powder X-ray diffraction (XRD) pattern was recorded with a Rigaku Rint 2500 diffractometer with monochromated Cu Kα radiation. Low-angle XRD patterns were recorded by using a NANO VIEWER (Rigaku, Japan). Both CV and chronoamperometric experiments were performed using a CHI 842B electrochemical analyzer (CHI Instruments, USA). A conventional three-electrode cell was used, including an Ag/AgCl (containing saturated KCl) electrode as a reference electrode, a platinum wire as a counter electrode, and a modified glassy carbon electrode (GCE) as a working electrode. The modified GCE was coated with as-produced samples (5.0 μg) and dried at room temperature. Then, 5.0 μL of Nafion (0.05 wt %) was coated on the surface of the modified GCE and dried before electrochemical experiments. Prior to electrochemical experiments, the GCEs modified with the samples were activated electrochemically by cycling the electrode potential between -0.2 V and +1.5 V (vs. Ag/AgCl) in 0.5 M H 2 SO 4 until CVs that were characteristic for a clean Pt electrode were obtained.