Kuan-Wen Wang

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.

The effect of alloying on the oxygen reduction reaction activity of carbon-supported PtCu and PtPd nanorods

In this study, we have investigated the effect of alloying on the modification of the d-band vacancies and oxygen reduction reaction (ORR) activity of PtPd and PtCu nanorods (NRs). PtCu and PtPd NRs with various ratios can be prepared successfully by a facile formic acid reduction method. The number of unfilled d-states (HTs) value of Pt nanoparticles is decreased due to the formation of NRs, and further decreased due to the alloying with different metals. For the Pt3Pd NRs, the HTs value is as low as 0.3056, suggesting that they have lower unfilled Pt d-states, and more d-band electrons transfer from Pd to Pt, leading to higher ORR activities than Pt/C. Besides, the electron transfer number (n) of Pt3Pd NRs towards the ORR is 3.7, meaning that they complete the O2 reduction to water and exhibit low hydrogen peroxide production during the ORR. As a result, the correlation between the HTs and ORR performance of PtPd and PtCu NRs highlights that the one-dimensional (1-D) structure and the electronic modification effect from Pd to Pt result in the excellent ORR activity and durability of Pt3Pd NRs synergistically.

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.

Promotion of Oxygen Reduction Reaction Durability of Carbon-Supported PtAu Catalysts by Surface Segregation and TiO2 Addition

Highly effective carbon supported-Pt75Au25 catalysts for oxygen reduction reaction (ORR) are prepared though titanium dioxide modification and post heat treatment. After accelerated durability test (ADT) of 1700 cycles, the ORR activity of PtAu/C catalysts modified by TiO2 and air heat treatment is 3 times higher than that of the commercial Pt/C. The enhancement of ORR activity is attributed to surface and structural alteration by air-induced Pt surface segregation and lower unfilled d states. On the contrary, for TiO2 modified and H2 treated PtAu/C catalysts, the deterioration of the ORR activity may be due to the loss of electrochemical surface area after ADT and the increase of d-band vacancy.

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.

Zn(x)Cd(1-x)S quantum dots-based white light-emitting diodes.

In this study, two kinds of colloidal ternary semiconductor white light-emitting quantum dots (WQDs), Zn(0.5)Cd(0.5)S and Zn(0.8)Cd(0.2)S, are prepared and used as nanophosphors in a UV light-emitting diode (UV-LED) pumping device. When the weight ratio of Zn(0.5)Cd(0.5)S WQDs is 9.1 wt. % in silicone and the drive current is set at 20 mA, the chromaticity coordinates (CIE), correlated color temperature (CCT), color rendering index (CRI), and luminous efficiency are (0.43,0.37), 2830 K, 90, and 0.94 lm/W, respectively. On the other hand, under the same weight ratio in silicone, the CIE, CCT, CRI, and luminous efficiency of Zn(0.8)Cd(0.2)S WQDs are (0.36,0.33), 4240 K, 86, and 4.12 lm/W, respectively. Based on the above results, we can conclude that WQDs-based LED can be obtained by controlling the compositions of Zn(x)Cd(1-x)S QDs due to the coexistence of band-edge and surface state emission.

Carbon nanotube-supported Cu3N nanocrystals as a highly active catalyst for oxygen reduction reaction

A controllable synthesis of a hybrid electrocatalyst consisting of copper(I) nitride nanoparticles (Cu3N) grown on carbon nanotubes (CNTs) by plasma enhanced atomic layer deposition (ALD) is presented. The island growth mechanism during ALD led to the formation of uniformly distributed Cu3N nanoparticles on the surface of CNTs. The size of copper nitride particles strongly influenced the electrocatalytic properties, and it could be precisely tuned by controlling the cycle number of ALD. The Pt-free non-precious nanocrystals coupling with CNTs exhibited pronounced electrocatalytic activity for oxygen reduction reaction (ORR). Koutecky–Levich analysis on the ORR current densities indicated that the Cu3N@CNT electrodes in alkaline media follow a mixed two- and four-electron transfer ORR pathway, whose mass activities are comparable to that of a typical Pt/C electrode. This report reveals a dry process to fabricate a well-dispersed metal nitride on a selected support material as an ORR catalyst that could enhance the catalytic activity by synergistic chemical coupling effects.

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.

Enhancement of oxygen reduction reaction performance of Pt nanomaterials by 1-dimensional structure and Au alloying

The effect of aspect ratios and Au alloying on the ORR performance of carbon-supported Pt nanorods (NRs) is investigated. The ORR activity of PtAu NRs after durability tests shows excellent stability due to the modification of electronic structure and surface composition.