Yun-Min Chang

Pulse Electrodepositions of PtRu on Large-Area Carbon Nanotubes for Enhancement of Methanol Electro-Oxidation

We employed an electroless deposition technique to prepare Ni seeds uniformly on a carbon cloth, followed by carbon nanotube CNT formation at an elevated temperature. Subsequently, a pulse electrodeposition was used to impregnate PtRu nanoparticles on the CNT structure. Similar procedures were performed on carbon supports including Vulcan XC72R, BP2000, and carbon nanocapsules CNCs for comparison purposes. Diffraction patterns from an X-ray confirmed a PtRu alloyed phase. An analysis from inductively coupled plasma-mass spectrometry indicated that the PtRu composition was relatively unchanged. Images from scanning and transmission electron microscopes revealed dense CNTs throughout the carbon cloth with nanoparticulate PtRu evenly impregnated. Considerable PtRu aggregations were found on the CNCs and BP2000. We observed a significantly improved coulomb efficiency and an electrochemically active surface area for the CNT-grown carbon cloth. In both apparent current density and mass activity for methanol electro-oxidation, the CNT-grown carbon cloth revealed the largest values. We attribute the performance enhancement to the large-area CNT structure that allowed facile access of electrolytes.

Displacement Reaction in Pulse Current Deposition of PtRu for Methanol Electro-Oxidation

Galvanostatic depositions in rectangular pulses and nitrosol precursors were employed to prepare PtRu nanoparticles on carbon clothes in various sizes and compositions. Variables including current on-time Ton, current off-time Toff, and current density were explored to identify the optimized catalytic performances for methanol electro-oxidation. Electrochemical characterizations including cyclic voltammetry and hydrogen desorption were carried out. Images from a transmission electron microscope on the PtRu nanoparticles revealed a moderate size distribution. Signals from X-ray patterns indicated a slight shift of diffraction peaks, suggesting that the Ru was alloyed successfully in the Pt lattice. In addition, the amount of alloyed Ru was found to decrease with reduced duty cycles. Composition determinations from inductively coupled plasma mass spectrometry and analysis on the oxidation states from X-ray photoelectron spectroscopy suggested a displacement reaction in which the Ru was alternately deposited and dissolved during Ton and Toff, while the Pt was deposited continuously. As a result, we observed substantial enrichment of Pt in the PtRu nanoparticles when the duty cycle was shortened.

Mechanical Alloying Preparation of La0.6Ca0.4CoIr0.25O3.5 − δ as a Bifunctional Electrocatalyst in Alkaline Electrolyte

La 0.6 Ca 0.4 CoIr 0.25 O 3-5-δ was prepared by a mechanical alloying process from mixtures of La 0.6 Ca 0-4 CoO 3 and IrO 2 . Scanning electron microscopy images on the resulting powders exhibited particles with irregular shape at 300-500 nm in size. X-ray diffraction analysis confirmed formation of a perovskite with complete disappearance of rutile signals from IrO 2 , indicating successful incorporation of Ir 4+ at the Co 3+ sites. Supported on carbon nanocapsules, the La 0.6 Ca 0.4 CoIr 0.25 O 3.5-δ demonstrated superior performance over those of La 0-6 Ca 0.4 CoO 3 in both charging and discharging current density-voltage polarizations. In addition, galvanostatic charging and discharging measurements at 25 and 100 mA/cm 2 indicated that the electrocatalytic abilities of La 0.6 Ca 0.4 CoIr 0.25 O 3.5-δ are stable and sustainable.

Synthesis and Characterization of La0.6Ca0.4Co0.8Ru0.2O3 for Oxygen Reduction Reaction in an Alkaline Electrolyte

We employed an amorphous citrate precursor (ACP) method to synthesize stoichiometric La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 powders. Result from X-ray diffraction demonstrated a perovskite La 0.6 Ca 0.4 CoO 3 lattice, indicating the incorporation of Ru 3+ at the Co 3+ sites. Image from the scanning electron microscope revealed a foamlike microstructure with various pores at 0.5-3 μm. La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 exhibited a higher H 2 O 2 decomposition rate in KOH solution as opposed to that of ACP-derived La 0.6 Ca 0.4 CoO 3 , which suggested an improved catalytic ability for oxygen reduction reaction (ORR). A similar behavior was observed during the ORR current-potential polarization using La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 supported on Black Pearl 2000 as a gas diffusion electrode. In addition, impedance spectra at the open-circuit voltage and selective cathodic overpotentials also confirmed a smaller charge-transfer resistance for La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 . In galvanostatic measurements and lifetime evaluation, La 0.6 Ca 0.4 Co 0.8 Ru 0.2 O 3 demonstrated steady voltage profiles with negligible degradation.

Controlled Synthesis of Silver Particles Supported on Carbon Nanocapsules as Electrocatalysts for Oxygen Reduction Reaction in Alkaline Electrolyte

Synthesis of various sizes particulate Ag supported on carbon nanocapsules (CNCs) were conducted in typical impregnation and wet chemical approach for physical characterization and electrochemical analysis in alkaline electrolyte. XRD of the as-synthesized powders indicated Ag in FCC phase. In i-V polarizations, the nano Ag/CNCs derived wet chemical route exhibited much enhanced oxygen reduction reaction capabilities than those of Ag/CNCs from impregnation method. Similar behaviors were recorded in galvanostatic discharging measurements between 10 and 200 mA/cm2.

Galvanostatic Pulse Plating of PtRu Nanoparticles for Direct Methanol Fuel Cells

A galvanostatic pulse electrodeposition technique of preparing nanoparticulate PtRu electrocatalyst for direct methanol fuel cells has been demonstrated. After extensive cyclic voltammetric analysis, we determined the optimized parameters for the methanol oxidation to be current on-time on 50 ms, current off-time of 400 ms, current density of 50 mA/cm, and total charge of 8.0 C/cm. In addition, the catalyst loading was measured at 68 μg/cm,