Wen-Hung Chung

Pt–Ru and Pt–Mo electrodeposited onto Ir–IrO2nanorods and their catalytic activities in methanol and ethanol oxidation

Pt–Ru and Pt–Mo electrocatalysts are prepared via pulse electrodeposition of Pt, Ru, or Mo on a reduced IrO2nanorod (Ir–IrO2NR) array. High-resolution TEM analysis shows the 3–6 nm Ir nuclei are preferentially aligned, with Ir(110) lattice fringes parallel to the growth direction of the IrO2 rod. XPS analysis indicates Pt, Ru and Ir on the catalytic surface exist in the metallic state, and Mo is in the 4+ and 6+ oxidation states. The grains of Ir, nucleated by IrO2reduction, initiate the catalytic activity, as evidenced in the emergence of a prominent COadsoxidation peak in a broad potential range (0.36–0.90 V). The COadsoxidation activity is strongly influenced by the later electrodeposited Pt–Ru and Pt–Mo, and so are the activities toward methanol and ethanol oxidation. The Ru decoration narrows down the broad COadsoxidation potential range and shifts the peak to a lower potential so that PtRuIr– (at high voltage) and RuPtIr–IrO2NR (at low voltage) exceeds the performance of a commercial catalyst. The Mo decoration changes the activity such that PtMoIr– and MoPtIr–IrO2NR catalysts are more suitable for ethanol oxidation, even though the Mo promotion on COadsoxidation is moderate.

Structures and catalytic properties of PtRu electrocatalysts prepared via the reduced RuO2 nanorods array.

Structures and properties of PtRu electrocatalyts, derived from the aligned RuO2 nanorods (RuO2NR), are investigated using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry toward COads and methanol oxidation. The catalytic activity of methanol oxidation and the CO tolerance are promoted significantly by reducing RuO2 into Ru metal before decorating with Pt. Reduction of RuO2NR was carried out by either thermal decomposition at 650 degrees C in vacuum or H2-reduction at 130 degrees C in low-pressure hydrogen. Reduction assisted by hydrogen allows infiltrating decomposition at low temperature and produces an array of nanorods with rugged walls featuring small Ru nuclei and larger surface area. Pt-RuNR, whose surface Pt:Ru ratio=0.58:0.42 was prepared by decorating with 0.1 mg cm(-2) Pt on the H2-reduced array containing 0.39 mg cm(-2) Ru, demonstrates a favorable combination of CO tolerance and high methanol oxidation activity superior to other RuO2NR-derived catalysts. When compared with a commercial electrocatalyst of PtRu (1:1) alloy (<4 nm), the activity of Pt-RuNR in methanol oxidation is shown to be somewhat lower at potential<0.48 V and higher at potential>or=0.48 V.

Miniature asymmetric ultracapacitor of patterned carbon nanotubes and hydrous ruthenium dioxide

A symmetric ultracapacitor CNT_CNT and an asymmetric ultracapacitor CNT_hRuO(2) of mini size have been prepared with patterned carbon nanotubes (CNT) and hydrous ruthenium dioxide. Galvanostatic charge/discharge results indicate that CNT_hRuO(2) is the superior one in both power and energy densities. In a potential window 2.0 V, the CNT_hRuO(2) cell displays an energy density of 24.0 W h kg(-1) at a power density of 22.9 kW kg(-1). Its power density can be raised to 41.1 kW kg(-1) at the expense of the energy density, which drops to 6.8 W h kg(-1). On the other hand, CNT_CNT performs at a lower level, delivering 5.2 W h kg(-1) at 5.5 kW kg(-1). The favorable charge/discharge performance of CNT_hRuO(2) is attributed to hydrous RuO(2), whose pseudocapacitance drives the other electrode of the vertical CNT array to work harder and makes more use of its double-layer capacitance. The analysis of individual electrode capacitance indicates that the high capacitance of hRuO(2) also causes a disproportion in voltage partition, which restricts the low limit of cycling current in an extended potential window. On energy cycling, CNT_hRuO(2) demonstrates sufficient stability in 10,000 cycles, after an initial 13% drop in capacitance.