Hong-Shuo Chen

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.

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.

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.

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.

Crystal growth of platinum–ruthenium bimetallic nanocrystallites and their methanol electrooxidation activity

This study investigates how the nucleation sequences of Pt and Ru crystallites affect the structure evolutions along with the methanol electrooxidation activity of bimetallic PtRu nanoparticles (BiNPs). We found that the BiNPs crystallites would transform from cubic to tetrakaidecahedron crystals on increasing the Ru content from 0 to 54 at%. This reduces the particle size and the size distributions during the nucleation-growth of the crystal. In the meantime, the unfilled d state and the heteroatomic intermixing of Pt atoms along with the MOR reactivity of the BiNPs will be enhanced. By increasing Ru >54 at%, the BiNPs would transform into an ellipsoid-like crystallite with a Ru rich core. This is because the Pt anions would replace the metallic Ru atoms and form a discrete sub-nano Pt nuclei at the NPs surface. Consequently, the surface MOR activity of the BiNPs is substantially suppressed.

The effect of surface structures and compositions on the quantum yields of highly effective Zn0.8Cd0.2S nanocrystals

We have synthesized white light emitting ternary Zn0.8Cd0.2S nanocrystals with high quantum yields of about 99%. Through detailed surface and structural characterization with the investigation of Cd and Zn coordination numbers, it can be found that besides surface state emission, the highly effective white light emission is strongly related to the surface chemical states of Zn and Zn–O/Cd–O bonding.

Correlation between surface state and band edge emission of white light ZnxCd1−xS nanocrystals

In this study, we have demonstrated a facile thermal pyrolyzed route to prepare ternary ZnxCd1−xS nanocrystals (NCs) with high quantum yield (QY) and white light emission. The detailed surface and structural characterizations based on the X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements have illustrated that by controlling the Zn content, the surface chemical states as well as the surface state emission of NCs can be manipulated, and their optical properties can be tuned accordingly The Zn shell of NCs may enhance the surface state emission, especially for Zn0.8Cd0.2S, thereby promoting the white light emission and increasing the QY to 56%. Moreover, the QY of Zn0.8Cd0.2S decreases from 56 to 49% after aging in hexane for 2 months, implying that the stability of NCs is excellent. The surface oxide-rich structure could be the reason that influences the surface state emission and stability of the ZnxCd1−xS NCs.

Oxidation triggered atomic restructures enhancing the electrooxidation activities of carbon supported platinum–ruthenium catalysts

This study demonstrated that the methanol oxidation reaction (MOR) activity of carbon supported platinum–ruthenium catalysts (Pt–Ru/C) could be enhanced 2.6-fold with adequate oxidation treatment. Our results show that such enhancement is triggered by the hetero-junction of Pt atomic layers on a tetragonal phased RuO2 crystal. In a freshly prepared sample, the nanocatalysts (NCs) were built on a Ru rich core capped by a PtRu alloy shell. The thermal treatment restructures the Pt and Ru atoms to form an ordered heterojunction at the core–shell interface and optimize the activity of the NCs at a temperature of 520 K. The higher temperature oxidizes the Ru into a crystallite rutile RuO2 phase. In such cases the Pt atoms were segregated to form individual crystallites by a substantial lattice mismatch between the metallic Pt and RuO2 phases. This work presents a systematic analysis with theoretical modelling and quantitative characterization, manipulating the structural evolution and thus optimizing the MOR activity of Pt–Ru/C catalysts.

The structure-dependent quantum yield of ZnCdS nanocrystals

In this study, we demonstrate the effect of atomic arrangement and valence band structures on the optical properties of ZnxCd1−xS nanocrystals (NCs) by controlling the Zn ratios. Our results indicate that the increase in coordination number of Zn–O bonding within the NCs and the structural changes in the valence band (VB) would enhance their quantum yield (QY) due to the influence of the surface states and charge recombination rate in VB, respectively. Consequently, the ZnxCd1−xS NCs with an optimal x = 0.4 have the highest QY of about 56%. By combining structural and optical analysis, we systematically elucidate the effect of composition on the local structure and the charge distribution in the VB of the ZnxCd1−xS NCs. Thus, this study provides mechanistic insight into the development of ZnCdS NCs with high QY.

Green light emission of Zn x Cd 1-x Se nanocrystals synthesized by one-pot method

We present a facile one-pot synthesis to prepare ternary ZnxCd1-xSe (x = 0.2, 0.5, 0.8, and 1) nanocrystals (NCs) with high emission quantumyield (QY, 45∼89%). The effect of Zn content (x) of ZnxCd...We present a facile one-pot synthesis to prepare ternary (x = 0.2, 0.5, 0.8, and 1) nanocrystals (NCs) with high emission quantum yield (QY, 45~89%). The effect of Zn content (x) of NCs on their physical properties is investigated. The NCs have a particle size of 3.2 nm and face centered cubic structure. However, the actual compositions of the NCs are Zn0.03Cd0.97Se, Zn0.11Cd0.89Se, and Zn0.38Cd0.62Se when Zn content is 0.2, 0.5, and 0.8, respectively. In terms of the optical properties, the emission wavelength shifts from 512 to 545 nm with increasing Zn content from 0 to 0.8 while the QY changes from 89 to 45, respectively. Partial replacement of Cd by Zn is beneficial to improve the QY of Zn0.2 and Zn0.5 NCs. The optical properties of ternary NCs are affected by compositional effect rather than particle size effect.