Browsing by Author "Cheng, I-Kai"

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Acetone sensing mechanism of PdO at temperatures below 250 degrees C
(2017-04-02)
Tsai, Cheng-Yu
;
Chen, Yi Sheng
;
Cheng, I-Kai
;
Pan, Fu-Ming
;
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Correlation of surface processes with characteristic sensing responses of PdO thin films to ethanol
(2019-04-15)
Cheng, I-Kai
;
Wang, Jeng-Han
;
Tsai, Cheng-Yu
;
Chen, Yi-Sheng
;
Pan, Fu-Ming
Gas sensing characteristics of PdO nanoflake thin films exposed to ethanol (EtOH) at temperatures below 250 degrees C was studied. The PdO thin film responses distinctly to 0.15 ppm EtOH in dry air at temperatures above 100 degrees C. A characteristic valley-shaped response feature develops in the early stage of the exposure to EtOH at 150 degrees C and above. Formation of the valley feature is a result of the combined effects of two types of surface processes, which successively modify the sensor conductance in the opposite way. Dehydrogenation of adsorbed EtOH induces reduction of preadsorbed oxygen anions and the PdO substrate, resulting in the drop of the conductance. On the other hand, subsequent adsorption of EtOH and oxygen on newly growing Pd nanoclusters, which develop due to the reduction of the PdO substrate, causes the increase in the conductance. The Pd nanoclusters can be later reoxidized in the EtOH gas mixture, thereby modifying the sensing behavior of the PdO sensor. X-ray photoelectron spectroscopy (XPS), diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) were used to study adspecies and gaseous species formed in the EtOH gas sensing reactions. On the basis of the characteristic electrical response and chemical characterizations, we proposed the formation mechanism for the characteristic response feature.
Electrocatalytic performance of Pt nanoparticles sputter-deposited on indium tin oxide toward methanol oxidation reaction: The particle size effect
(2017-09-15)
Ting, Chao-Cheng
;
Chao, Chih-Hsuan
;
Tsai, Cheng Yu
;
Cheng, I-Kai
;
Pan, Fu-Ming
We sputter-deposited Pt nanoparticles with an average size ranging from 2.0 nm to 8.5 nm on the indium tin oxide (ITO) glass substrate, and studied the effect of the size of Pt nanoparticles on electrocatalytic activity of the Pt/ITO electrode toward methanol oxidation reaction (MOR) in acidic solution. X-ray photoelectron spectroscopy (XPS) reveals an interfacial oxidized Pt layer present between Pt nanoparticles and the ITO substrate, which may modify the surface electronic structure of Pt nanoparticles and thus influences the electrocatalytic properties of the Pt catalyst toward MOR. According to electrochemical analyses, smaller Pt nanoparticles exhibit slower kinetics for CO electrooxidation and MOR. However, a smaller particle size enables better CO tolerance because the bifunctional mechanism is more effective on smaller Pt nanoparticles. The electrocatalytic activity decays rapidly for Pt nanoparticles with a size smaller than 3 nm and larger than 8 nm. The rapid activity decay is attributed to Pt dissolution for smaller nanoparticles and to CO poisoning for larger ones. Pt nanoparticles of 5-6 nm in size loaded on ITO demonstrate a greatly improved electrocatalytic activity and stability compared with those deposited on different substrates in our previous studies. (C) 2017 Elsevier B.V. All rights reserved.
Ethanol gas sensing mechanism of PdO nanoflake thin film at temperatures below 250 degrees C
(2017-04-02)
Cheng, I-Kai
;
Wang, Jeng-Han
;
Tsai, Cheng-Yu
;
Chen, Yi-Sheng
;
Pan, Fu-Ming