Cobalt Ditelluride for Electrocatalytic Water Splitting
Date Issued
2016
Date
2016
Author(s)
Lu, Tzu-Hsiang
Abstract
Electrocatalytic water splitting to produce hydrogen is one of the effective ways to solve the energy crisis and environmental pollution. Noble metal catalysts show high activity to carry out water splitting, but their problem of low abundance and high costs limits their large-scale application. Therefore, the research focuses on looking for and improving non-noble metal catalysts in recent years. Electrocatalytic water splitting involves two half reaction. One is hydrogen evolution reaction (HER) in cathode: 2H+ + 2e- → H2, and the other is oxygen evolution reaction (OER) in anode: 2H2O → O2 + 4H+ + 4e-. We must not only enhance the catalytic activity of cathodic HER but also that of anodic OER, so looking for and improving non-noble metal catalysts are important not only in HER but also OER. In recent years, the direction of improving non-noble metal catalyst is decrease in overpotential, increase in current density, increase in kinetics of reaction and enhancement of stability. We synthesize cobalt ditelluride nanoparticles (CoTe2 NPs) and cobalt ditelluride/carbon nanotube (CoTe2/CNT) hybrid material by hydrothermal reaction in this study. And then we adhere these two catalysts on glass carbon electrode to perform electrochemical measurement. We apply them to HER and OER respectively to explore their activity and mechanism of HER and OER. X-ray diffraction was carried out to determine the crystallinity and the crystal structure. The morphology of the samples was investigated by using scanning electron microscopy and transmission electron microscopy. The X-ray absorption near edge structure of Co K- and L-edge was conducted to determine valence state and d orbital electron-filling rate of metal ion in samples. Finally, electrochemical measurements of linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy and amperometry were performed to determine overpotential, active surface area, charge transfer resistance and stability. During the hydrogen evolution reaction was in 0.5 M sulfuric acid (H2SO4), we confirmed that the CoTe2 NPs with smaller particle size generates more active site on the surface so they show better performance of HER. These nanoparticles can generate 10 mA/cm2 at an overpotential of 246 mV without any decay up to 48 h of continuous reaction. When oxygen evolution reaction was in 1.0 M potassium hydroxide (KOH), we confirmed that the CNT can enhance the catalytic activity of CoTe2, the main reason is the phenomenon of charge transfer at the interface between CoTe2 and CNT. The electron transfers from CoTe2 to CNT, which changes the electronic structure of Co in CoTe2. It achieves synergistic effect to improve activity and kinetics of OER. The hybrid material can generate 10 mA/cm2 at an overpotential of 291 mV with enhanced stability of 24 h compared with pure CoTe2.
Subjects
transition metal
telluride
carbon nanotube
electrocatalytic
water splitting
Type
thesis
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