Chen-Wei Liu

Pt–Au core/shell nanorods: preparation and applications as electrocatalysts for fuel cells

Carbon-supported Pt–Au nanorods with a core/shell structure and excellent oxygen reduction (ORR) activities have been prepared. The Pt shell nanorods exhibit high CO oxidation activity, while the PtAu shell nanorods benefits formic acid oxidation (FAO). The 1-D morphology of the nanorods enhances the electrochemical activity of ORR, FAO and CO oxidation.

Tomographic imaging of the ionosphere using the GPS/MET and NNSS data

Abstract The earlier experiments of ionospheric tomography were conducted by receiving satellite signals from ground-based stations and then reconstructing electron density distribution from measures of the total electron content (TEC). In June 1994, National Central University built up the low-latitude ionospheric tomography network (LITN) including six ground stations spanning a range of 16.7° (from 14.6°N to 31.3°N) in latitude within 1° of 121°E longitude to receive the naval navigation satellite system (NNSS) signals (150 and 400 MHz ). In the study of tomographic imaging of the ionosphere, TEC data from a network of ground-based stations can provide detailed information on the horizontal structure, but are of restricted utility in sensing vertical structure. However, an occultation observation mission termed the global positioning system/meteorology (GPS/MET) program used a low Earth orbiting (LEO) satellite (the MicroLab-1) to receive multi-channel GPS carrier phase signals (1.5 and 1.2 GHz ) and demonstrate active limb sounding of the Earths atmosphere and ionosphere. In this paper, we have implemented the multiplicative algebraic reconstruction technique (MART) to reconstruct and compare two-dimensional ionospheric structures from measured TECs through the receptions of the GPS signals, the NNSS signals, and/or both of the systems. We have also concluded the profiles retrieved from tomographic reconstruction showing much reasonable electron density results than the original vertical profiles retrieved by the Abel transformation and being in more agreement in peak electron density to nearby ionosonde measurements.

Preparation and characterization of carbon-supported Pt―Au cathode catalysts for oxygen reduction reaction

Alloy catalysts of Pt-Au/C with various Pt/Au ratios were prepared for an oxygen reduction reaction (ORR). The structure, surface species, surface compositions, and electrocatalytic activities of prepared alloy catalysts were characterized by XRD, TPR, XPS, and rotating disk electrode (RDE) techniques, respectively. It was observed that the ORR activity of the Pt(75)Au(25)/C alloy catalyst was enhanced significantly in comparison to the commercial Pt/C catalyst within the mixed kinetic-diffusion control region. The alloying with Au modified the oxophilicity of Pt-Au alloy catalysts. TPR characterization suggests that the enhancement of Pt(75)Au(25)/C was attributed to the formation of an alloy surface, having a moderate oxophilicity and a Pt-related alloy surface species.

Activity-Structure Correlation of Pt/Ru Catalysts for the Electrodecomposition of Methanol: The Importance of RuO2 and PtRu Alloying

Bimetallic catalysts: The effect of PtRu alloying and the influence of RuO(2) species on the methanol oxidation activity of PtRu/C catalysts is studied. Different heat treatments-utilizing either N(2) or air-are applied to the bimetallic materials to enhance the degree of alloying or produce RuO(2) [picture: see text]. The catalysts with the best performance are characterized by a small particle size, a high degree of PtRu alloying, and the presence of a Pt-related species on their surface.Herein, we study the effect of both PtRu alloying and the presence of RuO(2) species on the promotion of the methanol oxidation activity of PtRu/C catalysts. Bimetallic catalysts composed of 15 wt % PtRu/Ce(x)C (x=0 or 10) are prepared by using the precipitation-deposition method and activated through hydrogen reduction at 470 K. Different heat treatments, utilizing either N(2) or air, are applied to the as-prepared catalysts to enhance the degree of alloying or produce RuO(2), respectively. The electrocatalytic properties, the structure, and the surface composition of the alloys are investigated systematically by means of electrochemical measurements coupled with X-ray diffraction (XRD) and temperature-programmed reduction (TPR) experiments. We find that the N(2) heat treatment improves the catalytic activity of the alloys more significantly than the air heat treatment. Also, the current density and long-term durability toward methanol oxidation can be significantly enhanced by combining a loading of 10 % CeO(2) and N(2) with a heat treatment at 570 K. Physical characterization performed by means of TPR reveals that the surface of the N(2)-treated sample is covered with Pt, thereby presenting a higher methanol oxidation current than the air-treated sample whose surface is composed of RuO(2) and some alloy species. Moreover, a model for describing the physical structures of the deposited bimetallic crystallites obtained after the N(2) and air treatments is proposed. This model suggests that the catalysts with the best performance should have a small particle size and exhibit a structure characterized by a high degree of PtRu alloying and a Pt-related surface species. Therefore, we can conclude that the effect of PtRu alloying on the electro-oxidation activity of the catalysts is superior to that of the presence of RuO(2) species under practical conditions.

Improvement of Amperometric Biosensor Performance for H2O2 Detection based on Bimetallic PtM (M = Ru, Au, and Ir) Nanoparticles

Novel bimetallic nanoparticles have been synthesized via rapid microwave irradiation, leading to an improved sensitivity and a highly anti-interference property for amperometric biosensor in H2O2 detection. The material characterizations were performed by TEM, XRD, and EDX, which show the bimetallic formation of Pt-based catalysts and well-dispersed nanoparticles of 2–5 nm. The sensitivities for the detection of H2O2 of PtRu, PtAu, and PtIr as the biosensor working electrode catalysts are 539.01 (), 415.46 (), and 404.52 () μA·mM−1·cm−2, respectively, nearly twice higher than the pure Pt catalyst (221.77 μA·mM−1·cm−2, ), at a low applied potential of

The structure modification and activity improvement of Pd–Co/C electrocatalysts by the addition of Au for the oxygen reduction reaction

In this study, Pd75Co25−xAux/C ternary catalysts with varying x content are synthesized by the deposition–precipitation approach with hydrogen reduction at 390 K for the oxygen reduction reaction (ORR). The roles of Au in the modification of structures, surface species and electrochemical properties of PdCo/C catalysts are investigated. X-ray diffraction results reveal that although the low reduction temperature does not benefit the Co alloying with Pd, Pd–Au alloys are preferentially formed. Moreover, it confirms that the incorporation of Au into a Pd–Co system contributes to the generation of inhomogeneous alloy structure. Fine structural details determined by X-ray absorption spectroscopy indicate that Au addition improves the heteroatomic intermixing extent of alloy nanocatalysts, especially for Pd75Co10Au15/C (Au15) catalysts. Surface characterization by temperature programmed reduction suggests that a Pd-rich surface gradually changes to Pd, Au and alloy mixed surfaces when the Au content is larger than 15 at%. Regarding the electrochemical results, Au15 displays the superior ORR performance among all samples due to the improved heteroatomic intermixing extent, large electrochemical surface area and multiple coexisting surface species. Furthermore, it also displays a better stability than Pd/C and Pd75Co25/C catalysts after accelerated durability tests.

Promotion of PdCu/C Catalysts for Ethanol Oxidation in Alkaline Solution by SnO2 Modifier

The development of high performance PdCu/C catalysts through manipulation of reduction temperatures and addition of SnO2 promoter has been elucidated systematically in order to enhance ethanol oxidation reaction (EOR) performance. The structure, morphology, surface species, and electroactivity of the PdCu/C and SnO2‐modified PdCu/C catalysts are characterized by use of X‐ray diffraction, high resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and cyclic voltammetry. For the PdCu/C catalysts, the ratio of the forward anodic peak current density to that of the reverse, that is, the If/Ib ratio, the degree of alloying (Dalloy), grain size, and EOR performance increases as the reduction temperature increases to 570 K. However, severe sintering at 670 K deteriorates EOR performance. Therefore, 570 K is a suitable reduction temperature for the preparation of PdCu/C catalysts with fine alloy structure, small crystal size, good Dalloy, good anti‐poisoning ability, and excellent EOR performance. For the SnO2 modified PdCu/C catalysts, addition of 20 wt % Sn may cause a large amount of SnO2 to form on the surface and block the active site of the catalysts, thus decreasing EOR performance. However, addition of 10 wt % Sn promotes stability in EOR performance, attributable to the significant amount of PdSn phase in the bulk and SnO2 species on the surface, which enhance the CO oxidation ability and electrochemical surface area. Consequently, based on the chronoamperometric measurements after 1 hr, the EOR activity of PdCu/C catalysts with 10 wt % SnO2 modification is enhanced by approximately 230 % compared with the as‐reduced sample.