Wenyue Guo

Metallic Iron-Nickel Sulfide Ultrathin Nanosheets As a Highly Active Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media

We report on the synthesis of iron-nickel sulfide (INS) ultrathin nanosheets by topotactic conversion from a hydroxide precursor. The INS nanosheets exhibit excellent activity and stability in strong acidic solutions as a hydrogen evolution reaction (HER) catalyst, lending an attractive alternative to the Pt catalyst. The metallic α-INS nanosheets show an even lower overpotential of 105 mV at 10 mA/cm(2) and a smaller Tafel slope of 40 mV/dec. With the help of DFT calculations, the high specific surface area, facile ion transport and charge transfer, abundant electrochemical active sites, suitable H(+) adsorption, and H2 formation kinetics and energetics are proposed to contribute to the high activity of the INS ultrathin nanosheets toward HER.

Dithiafulvenyl unit as a new donor for high-efficiency dye-sensitized solar cells: synthesis and demonstration of a family of metal-free organic sensitizers.

This work identifies the dithiafulvenyl unit as an excellent electron donor for constructing D-π-A-type metal-free organic sensitizers of dye-sensitized solar cells (DSCs). Synthesized and tested are three sensitizers all with this donor and a cyanoacrylic acid acceptor but differing in the phenyl (DTF-C1), biphenyl (DTF-C2), and phenyl-thiopheneyl-phenyl π-bridges (DTF-C3). Devices based on these dyes exhibit a dramatically improved performance with the increasing π-bridge length, culminating with DTF-C3 in η = 8.29% under standard global AM 1.5 illumination.

Decomposition of ethanol on Pd(111): a density functional theory study.

Ethanol decomposition over Pd(111) has been systematically investigated using self-consistent periodic density functional theory, and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to follow the gas-phase bond order rules, wherein C is tetravalent and O is divalent with the missing H atoms replaced by metal atoms. Desorption is preferable for adsorbed ethanol, methane, and CO, while for the other species decomposition is preferred. For intermediates going along the decomposition pathways, energy barriers for the C-C, C(alpha)-H, and O-H scissions are decreased, while it is increased for the C-O path or changes less for the C(beta)-H path. For each of the C-C, C-O, and C-H paths, the Bronsted-Evans-Polanyi relation holds roughly. The most likely decomposition path is CH(3)CH(2)OH --> CH(3)CHOH --> CH(3)CHO --> CH(3)CO --> CH(2)CO --> CHCO --> CH + CO --> CO + H + CH(4) + C.

Strategies to enhance CO2 capture and separation based on engineering absorbent materials

Uncontrolled massive CO2 emission into the atmosphere is becoming a huge threat to our global climate and environment. Carbon capture and storage (CCS), starting with the crucial step of CO2 capture and separation, provides a promising approach to alleviate this issue. The major challenge for CO2 capture and separation is exploring efficient adsorbent materials with high storage capacity and selectivity. This review firstly summarized the significant advancement in a variety of state-of-the-art adsorbent materials. Then, particular attention was focused on the practical strategies to enhance CO2 capture and separation based on current adsorbent materials by topological structure design, chemical doping, chemical functionalization, open metal sites, and electric fields. These strategies paved constructive ways for the design and synthesis of novel adsorbent materials. Finally, we gave a perspective view on future directions in this rapidly growing field.

A NbO-type copper metal–organic framework decorated with carboxylate groups exhibiting highly selective CO2 adsorption and separation of organic dyes

A porous Cu metal–organic framework (1) based on a pentacarboxylate ligand and paddlewheel SBU was synthesized and structurally characterized. Complex 1 possesses a NbO-type framework with uncoordinated –COO− groups, resulting in its good selectivity for CO2/N2 (36) and CO2/CH4 (12) as well as a large CO2-uptake capacity of 140 cm3 g−1 at 273 K and 1 bar. Grand Canonical Monte Carlo (GCMC) simulations revealed that strong CO2 adsorption sites exist near the open CuII sites and the uncoordinated –COO− groups. Significantly, complex 1 exhibits water resistance and selective adsorption of cationic methylene blue (MB+) in aqueous solution and the adsorbed MB+ can be released in saturated NaCl solution, making it also a promising porous material for charge and pore-size dependent large-molecule capture and separation. The existence of coordinatively unsaturated metal sites as well as the exposed –COO− groups in the framework of 1 is responsible for its selective gas adsorption and dye separation.

Dehydrogenation of methanol on Pd(100): comparison with the results of Pd(111)

Dehydrogenation of methanol on Pd(100) is systematically investigated using self-consistent periodic density functional theory. The theoretical results are compared with those of the same reaction on Pd(111) published very recently [J. Phys. Chem. C, 2009, 113, 4188-4197]. Switching from (111) to (100), adsorptions are strengthened for most species except for CHO, CO and H at hollow sites. Moreover, Pd(100) affords relatively low energy barriers and higher rate constants for most elementary dehydrogenation steps as well as smaller desorption rates for the saturated adsorbates (methanol and formaldehyde), suggesting that the more open Pd surface indeed possesses the higher activity and selectivity for the complete dehydrogenation of methanol. At lower temperatures (e.g., 250 K), Pd(100) affords the same dehydrogenation path as Pd(111) for methanol, which is unchanged on the latter surface at both lower and higher temperatures; whereas at the typical steam re-forming (MSR) temperature (500 K), the path on Pd(100), i.e., CH(3)OH --> CH(3)O and/or CH(2)OH --> CH(2)O --> CHO --> CO, is different from the situation of Pd(111). In both cases, the initial bond scission process constitutes the rate-determining step.

Porous barium–organic frameworks with highly efficient catalytic capacity and fluorescence sensing ability

The current study describes the first barium–organic framework with permanent porosity, efficient catalytic capacity, and highly selective luminescence sensing of DMSO molecules and metal ions. Single-crystal-to-single-crystal transformations (from complex 1 to complexes 2 and 3) were used to thermally generate coordinatively unsaturated metal sites (CUSs) as catalytically active sites (CASs). Complex 3 exhibits efficient catalytic capacity for the cyanosilylation of aldehydes and ketones, and the cycloaddition of CO2 and epoxides. To the best of our knowledge, complex 3 keeps a record among the MOF-based catalysts for the cyanosilylation of aldehydes and ketones. The generation of Ba2+ CUSs with high catalytic activity in a SCSC fashion is responsible for the excellent properties of 3, which is further confirmed by the theoretical calculation. Besides, complex 2 can highly sense DMSO molecules through fluorescence enhancement.

Decomposition of methanthiol on Pt(111): a density functional investigation.

Decomposition of methanthiol on Pt(111) is systematically investigated using self-consistent periodic density functional theory (DFT), and the decomposition network has been mapped out. The most stable adsorption of the involved species tends to form the sp(3) hybridized configuration of both C and S atoms, in which C is almost tetrahedral and S has the tendency to bond to three atoms. Spontaneous dissociation rather than desorption is preferred for adsorbed methanthiol. Based on the harmonic transition state theory calculations, the decomposition rate constants of the thiolmethoxy and thioformaldehyde intermediates are found to be much lower than those for their formation, leading to long lifetimes of the intermediates for observation. Under the ultrahigh vacuum (UHV) condition, the most possible decomposition pathway for methanthiol on Pt(111) is found as CH(3)SH --> CH(3)S --> CH(2)S --> CHS --> CH + S --> C + S, in which the C-S bond cleavage mainly occurs at the CHS species. However, the decomposition pathway is CH(3)SH --> CH(3)S --> CH(3) + S under the hydrogenation condition; the C-S bond scission mainly occurs at CH(3)S. The Brønsted-Evans-Polanyi relation holds for each of the S-H, C-H, and C-S bond scission reactions.

Initial Hydrogenations of Pyridine on MoP(001): A Density Functional Study

The initial hydrogenations of pyridine on MoP(001) with various hydrogen species are studied using self-consistent periodic density functional theory (DFT). The possible surface hydrogen species are examined by studying interaction of H(2) and H(2)S with the surface, and the results suggest that the rational hydrogen source for pyridine hydrogenations should be surface hydrogen atoms, followed by adsorbed H(2)S and SH. On MoP(001), pyridine has two types of adsorption modes, i.e., side-on and end-on; and the most stable η(5)(N,C(α),C(β),C(β),C(α)) configuration of the side-on mode facilitates the hydrogenation of pyridine. The optimal hydrogenation path of pyridine with surface hydrogen atoms in the Langmuir-Hinshelwood mechanism is the formation of 3-monohydropyridine, followed by producing 3,5-dihydropyridine, in which the two-step hydrogenations take place on the C(β) atoms. When adsorbed H(2)S is considered as the source of hydrogen, slightly higher hydrogenation barriers are always involved, while the energy barriers for hydrogenations involving adsorbed SH are much lower. However, the hydrogenation of pyridine should be suppressed by the adsorption of H(2)S, and the promotion effect of adsorbed SH is limited.

Enhanced photovoltaic performance of dye-sensitized solar cells based on ZnO microrod array/TiO2 nanoparticle hybrid films

We report in this paper a simple and cheap method for the preparation of ZnO microrod array/TiO2 nanoparticle hybrid films for applications in dye-sensitized solar cells (DSCs), which is achieved by screen printing TiO2 paste into the interspace of low-density ZnO microrod arrays grown on FTO glass. The as-fabricated DSCs exhibit a remarkably enhanced power conversion efficiency of 7.76%, higher than 6.57% for standard TiO2 nanoparticle based DSCs. The electrochemical impedance spectroscopy analysis reveals that the electron transport, electron lifetime, effective diffusion length and the electron collection efficiency are increased, while the charge recombination is reduced, indicating that the ZnO microrod array/TiO2 nanoparticle hybrid film can be considered as a superior material to TiO2 nanoparticle in many respects.