Yu-Chi Hsieh

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.

Facile Surface Functionalization of Carbon/Nafion for Enhancement of Methanol Electro-Oxidation

We report a facile electrochemical method to produce functional groups on the carbon surface in which multiple cyclic voltammetric (CV) sweeps are imposed in 0.5 M H2SO4 electrolyte on the samples containing carbon cloth, Vulcan XC72R, and Nafion ionomer. With supply of ambient O2, the generation of radicals from the oxygen reduction and Nafion ionomer degradation enables an accelerated formation of oxygenated functional groups on the carbon surface. Raman analysis reveals structural variation for the carbon electrodes after CV modifications. X-ray photoelectron spectroscopy confirms the alteration of carbon structure in conjunction with notable increase of oxygenated groups and reduction in fluorine amount. The functionalized electrodes allow a 250% increment for PtRu electrodeposition as compared to the reference sample. We carry out electrochemical measurements on methanol electro-oxidation for the PtRu samples. The functionalized electrode demonstrates significant improvement in apparent current density and mass activity as opposed to the reference sample.

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,