Browsing by Author "Lu, Tzu-Hsiang"

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Synergistic-Effect-Controlled CoTe2/Carbon Nanotube Hybrid Material for Efficient Water Oxidation
(2016-12-15)
Lu, Tzu-Hsiang
;
Chen, Chih-Jung
;
Lu, Ying-Rui
;
Dong, Chung-Li
;
Liu, Ru-Shi
In anode, electrocatalytic water splitting involves oxygen evolution reaction (OER), which is a complex and sluggish reaction, and thus the efficiency to produce hydrogen is seriously limited by OER. We report that CoTe2 exhibits optimized OER activity for the first time. Multiwalled carbon nanotube (MWCNT) is utilized to support CoTe2 in generating a synergistic effect to enhance OER activity and improve stability by tuning different loading amounts of CoTe2 on CNT. In 1.0 M KOH, bare CoTe2 needed overpotential of 323 mV to produce 10 mA/ cm(2) with Tafel slope of 85.1 mV/dec, but CoTe2/carbon nanotube (CNT) with optimized loading amount of CoTe2 required only 291 mV to produce10 mA/cm(2) with Tafel slope of 44.2 mV/dec. X-ray absorption near edge structure (XANES) was applied to prove that an electron transfer from e(g) band of CoTe2 to CNT caused a synergistic effect. This electron transfer modulated the bond strength of oxygen-related intermediate species on the surface and optimized OER performance. In situ XANES was used to compare CoTe2/CNT and pristine CoTe2 during OER. It proved the transition state of CoOOH more easily existed by adding CNT in hybrid material during OER to enhance the efficiency of OER. Moreover, bare CoTe2 is unstable under OER, but the CoTe2/CNT hybrid materials exhibited improved and exceptional durability by time dependent potentiostatic electrochemical measurement for 24 h and continuous cyclic voltammetry for 1000 times. Our result suggests that this new OER electrocatalyst for OER can be applied in various water-splitting devices and can promote hydrogen economy.
Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution
(2016-03-02)
Chen, Chihjung
;
Yang, Kai-Chih
;
Basu, Mrinmoyee
;
Lu, Tzu-Hsiang
;
Lu, Ying-Rui
This study employed silicon@cobalt dichalcogenide micro wires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co(OH)(2) MWs were utilized as precursors to synthesize Si@CoX2 (X = S or Se) photocathodes. Si@CoS2 and Si@CoSe2 MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co(OH)(2), respectively. The CoX2 outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX2 layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS2 photocathode showed a photocurrent density of -3.22 mA cm(-2) at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe2 MWs revealed moderate photocurrent density of -2.55 mA cm(-2). However, Si@CoSe2 presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX2 MWs. Si@CoS2 electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe2 MWs gradually increased to -5 mA cm(-2) after chronoamperometry characterization owing to the amorphous structure generation.