Study On Controllable Synthesis And Electrocatalytic Activity Of Ruthenium - Based Nanostructures

In this dissertation, discoid Ru-Co alloy nanocrystals, chain-like Ru nanocrystals, platelike Pd-Ru nanocrystals and spherical Se-RuSe2 nanocomposites have been successfully synthesized in the system of ethylene glycol or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-py-rimidinone (DMPU). The samples are characterized by X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), etc. The major conclusions are as follows:(1) Chain-like Ru nanocrystals are prepared in the ethylene glycol solution using hydrated ruthenium chloride (RuCl3’nH2O) as the precursor and the polyvinyl pyrrolidone (PVP) and cetyltrimethyl ammonium bromide (CTAB) as surfactants. The chain-like Ru nanocrystals are assembled by many small Ru particles. The average diameter of chains is about 2.8 nm. HRTEM analysis shows clear lattice and the lattice spacing is 0.23 nm, corresponding to the (100) plane of hexagonal (hcc) Ru. The growth direction of Ru nanocrystals is along (100). It is found that PVP and CTAB play important roles in the formation of chain-like Ru. The PVP controlls the sizes of Ru nanoparitcles and the CTAB induces them to form the chains. The chain-like Ru nanocrystals exhibit excellent electrocatalytic activity in the hydrogen evolution reaction in comparison with the commercial platinum black. The polarization curve (i-V plot) recorded with the chain-like Ru nanocrystals on glassy carbon electrodes shows a small overpotential (η) of ～0.06 V for the HER.(2) DMPU is a kind of high boiling solvent, which is easily deliquescent in both water and oil. Discoild Ruthenium-Cobalt alloy nanocrystals are prepared in the mixed solvents of water and DMPU through the co-reduction of ruthenium chloride and cobalt chloride with hydrazine and using oleylamine (OLA) as structure directing regent. XRD results exhibit that the diffraction peak positions (40°< 20< 50°) of the obtained products are located in the middle of that of the hexagonal (hcc) Ru and hcc Co, indicating the products are Ru-Co alloy. TEM, SEM and AFM analysis reveal that the particles are irregular discoid structure. The average diameter of the particles is about 38 nm. HRTEM analysis shows that the d-spacings are 0.23 nm and 0.20 nm, which correspond to the value of the (100), (101) planes of hexagonal (hcc) Ru and hcc Co, respectively. The Ru-Co alloy nanocrystals exhibit superior electrocatalytic activity in the hydrogen evolution reaction.The polarization curve (i-V plot) recorded with the Ru-Co alloy nanocrystals on glassy carbon electrodes shows a very small overpotential (η) of～0.1 V for the HER, indicating the higher catalytic activity than that of the commercial Pt catalytic. After 5000 cycles in HER measurements, the i-V curves almost unchanged, suggesting the negligible loss of the cathodic current. So, the Ru-Co alloy catalyst has a very good stability for the HER.(3) Pd-Ru alloy nanocrystals are prepared in the ethylene glycol solution by using ruthenium chloride (RuCl3·nH2O) and palladium (Pd(NO3)2·2H2O) as precursors, PVP and CTAB as surfactants under appropriate conditions. XRD results exhibit that the positions of diffraction peaks are located between that of pure face-centered cubic phase (fcc) Pd NCs and fcc Ru NCs, displaying that the obtained sample is Pd-Ru alloy NCs with fcc phase structure. It is a rare case for Ru metal. The TEM analysis reveals that the obtained Pd-Ru nanocrystals have triangular and hexagon sheet structures with small Pd particles attached to the surfaces. Based on some control experiments, the formation mechanism is proposed. It can be speculated that at 110℃, most of Pd2+ ions and relatively little Ru3+ ions in the system are reduced to form sheet Pd-Ru alloy. Further raising the reaction temperatrure to 185℃, the remaining Ru3+ ions are reduced and enter into the sheets, and some small Pd particles appear at the alloy surfaces due to the surface segregation. The electrocatalytic tests of the Pd-Ru alloy for the oxidation of formic acid and oxygen reduction reaction are in progress.(4) Se-RuSe2 nanocomposites have been prepared by using ethyl ene glycol as solvent, PVP and CTAB as surfactants, and ruthenium chloride (RuCl3·nH2O) and Se as source materials. XRD analysis indicates the Se-RuSe2 are composed of amorphous RuSe2 and hcc Se. The TEM analysis reveals that the Se-RuSe2 composites are spherical structure with the average diameter of about 300～500 nm. These spherical structures are assembled by small particles. Mapping and Elements Linear-scan analyses display that Ru and Se atoms are distributed uniformly over the entire particle and the proportion is about 1:3 (Ru:Se). The electrocatalytic activities of the Se-RuSe2 nanocrystals for the oxygen reduction reaction in 0.5 M NaOH with and without 5 M methanol are investigated. The results show that they have high catalytic activity (the Onset potential is about -0.21 V) and superior endurance of methanol, implying the potential application in fuel cells.