Search

Nitrogen-doped graphene supported single metal atoms are expected to achieve high nitrogen reduction reaction (NRR) performance via the electroreduction process. Based on density functional theory (DFT) calculations, the application of three pyrrolic-N doped graphene (pyrrolic-N3–G) supported V1, Cr1, Mn1, Fe1, Nb1, Mo1, W1 and Re1 as electrocatalysts for NRR is evaluated from stability, limiting potential and ammonia selectivity points of view. Mo1(W1, Re1)/pyrrolic-N3–G are predicted to be potential candidates for NRR with high stability, less negative limiting potential (−0.49, −0.33 and −0.51 V) and high ammonia selectivity, which indicates that the catalytic performances are improved from both activity and selectivity aspects compared to the corresponding pyridine-N3–G supported ones. The identified descriptors indicate that the accumulated charges on metal atoms and the adsorbed hydrogen atoms have considerable impacts on limiting potential and selectivity, respectively. It is also suggested that the NRR activity can be tuned by changing the coordination environment and the response of changing coordination environments differs according to the type of transition metals.

The chemical coupling interaction has been explored extensively to boost heterogeneous catalysis, but the insight into how chemical coupling interaction works on CO2 electroreduction remains unclear. Herein we demonstrate how the chemical coupling interaction between porous In2O3 nanobelts and reduced graphene oxide (rGO) could substantially improve the electrocatalytic activity toward CO2 electroreduction. Such an In2O3-rGO hybrid catalyst showed 1.4-fold and 3.6-fold enhancements in Faradaic efficiency and specific current density for the formation of formate at -1.2 V versus reversible hydrogen electrode relative to the catalyst prepared by physically loading of In2O3 nanobelts onto rGO, respectively. The density functional theory calculations and electrochemical analysis together revealed that the chemical coupling interaction boosted CO2 electroreduction activity by improving electrical conductivity and stabilizing key intermediate HCOO-*. The present work not only deepens an understanding of chemical coupling effect but also provides an effective lever to optimize the catalytic performance toward CO2 electroreduction.

The electrochemical reduction of nitrogen to ammonia is a promising way to produce ammonia at mild condition. The design and preparation of an efficient catalyst with high ammonia selectivity is critical for the real applications. In this work, a series of transition metal (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, and Cd) atoms supported by gt-C3N4 (TM/gt-C3N4) are investigated as electrocatalysts for the nitrogen reduction reaction (NRR) based on density functional calculations. It is found that Mo/gt-C3N4 with a limiting potential of -0.82 V is the best catalyst for standing-on adsorbed N2 cases. While for lying-on adsorbed N2 cases, V/gt-C3N4 with a limiting potential of -0.79 V is better than other materials. It is believed that this work provides several promising candidates for the non-noble metal electrocatalysts for NRR at mild condition.

Searching for new types of electrocatalysts with high stability, activity, and selectivity is essential for the production of ammonia via electroreduction of nitrogen. Using density functional theo...

The chemical coupling interaction has been explored extensively to boost heterogeneous catalysis, but the insight into how chemical coupling interaction works on CO

As diversified reaction paths exist over practical catalysts towards CO2 hydrogenation, it is highly desiderated to precisely control the reaction path for developing efficient catalysts. Herein, we report that the ensemble of Pt single atoms coordinated with oxygen atoms in MIL-101 (Pt1@MIL) induces distinct reaction path to improve selective hydrogenation of CO2 into methanol. Pt1@MIL achieves the turnover frequency number of 117 h−1 in DMF under 32 bar at 150 °C, which is 5.6 times that of Ptn@MIL. Moreover, the selectivity for methanol is 90.3% over Pt1@MIL, much higher than that (13.3%) over Ptn@MIL with CO as the major product. According to mechanistic studies, CO2 is hydrogenated into HCOO* as the intermediate for Pt1@MIL, whereas COOH* serves as the intermediate for Ptn@MIL. The unique reaction path over Pt1@MIL not only lowers the activation energy for the enhanced catalytic activity, but also contributes to the high selectivity for methanol. Controlling the reaction path is instrumental for developing efficient catalysts for CO2 hydrogenation. Here, the authors report that the ensemble of Pt single atoms coordinated with oxygen atoms in MIL-101 induces distinct reaction path to improve selective hydrogenation of CO2 into methanol relative to nanocrystal counterparts.

As diversified reaction paths exist over practical catalysts towards CO2 hydrogenation, it is highly desiderated to precisely control the reaction path for developing efficient catalysts. Herein, we report that the ensemble of Pt single atoms coordinated with oxygen atoms in MIL-101 (Pt1@MIL) induces distinct reaction path to improve selective hydrogenation of CO2 into methanol. Pt1@MIL achieves the turnover frequency number of 117 h−1 in DMF under 32 bar at 150 °C, which is 5.6 times that of Ptn@MIL. Moreover, the selectivity for methanol is 90.3% over Pt1@MIL, much higher than that (13.3%) over Ptn@MIL with CO as the major product. According to mechanistic studies, CO2 is hydrogenated into HCOO* as the intermediate for Pt1@MIL, whereas COOH* serves as the intermediate for Ptn@MIL. The unique reaction path over Pt1@MIL not only lowers the activation energy for the enhanced catalytic activity, but also contributes to the high selectivity for methanol., Controlling the reaction path is instrumental for developing efficient catalysts for CO2 hydrogenation. Here, the authors report that the ensemble of Pt single atoms coordinated with oxygen atoms in MIL-101 induces distinct reaction path to improve selective hydrogenation of CO2 into methanol relative to nanocrystal counterparts.

The surface-induced ordering in thin films of asymmetric deuterated polystyrene (dPS)--poly(vinylpyridine) (PVP) diblock and triblock copolymers of comparable polymerization index and PVP volume fraction (f [approximately] 0.25) was studied using transmission electron microscopy, atomic force microscopy, secondary ion mass spectrometry, and neutron reflectivity. The morphology of both di- and triblock copolymer films was found to be cylindrical except for the layer adjacent to the silicon oxide surface, which due to the strong interaction of silica with PVP, was lamellar. The spacing between adjacent cylindrical layers was found to be consistent with mean field theory predictions. In the triblock copolymer films the cylindrical layers were oriented parallel to the silicon oxide surface, and no decay of the ordered structure was observed for at least 12 periods. If the total film thickness t[prime] deviated from t = [(n + 0.71)210 + 182] [angstrom], where n is an integer, islands or holes formed at the vacuum interface. The height of the holes or islands reached its equilibrium value, 210 [angstrom], after annealing 24 h at 180 C. In contrast, it was far more difficult to orient parallel to the silicon oxide surface the microphase-separated cylindrical domains in the diblock copolymer films. As amore » result no islands or holes were observed even after annealing for 5 days at 180 C. The authors concluded that the difference in ordering behavior was due to the ability of the triblock copolymer to form an interconnected micelle network while the diblock copolymer formed domains that were free to move with respect to each other. This conclusion was further confirmed by diffusion measurements which showed that the PS homopolymer penetrated easily into the ordered diblock copolymer films and was excluded from the ordered triblock copolymer films.« less

The authors have used atomic force microscopy (AFM) to study the lateral structure of end grafted poly(styrene) chains on a silicon substrate in air. As the grafting density is decreased, the chains are found to clump together into islands, resulting in a highly inhomogeneous monomer density with considerable portions of the substrate exposed to air. The transition from a stable homogeneous film to the clump formation is in agreement with recent theoretical simulations of polymer brushes in different solvent conditions. The islands are found to be interconnected by thin arms, which can be visualized as isolated chains stretching out on the substrate.

The conformation of polymer chains in the melt near an impenetrable boundary has recently been studied by molecular dynamics and off-lattice Monte Carlo simulations. Both types of calculations show an enhancement of the chain end density within a distance of approximately two polymer segment lengths of the interface relative to the bulk. In the absence of preferential interactions between monomers and the interface, the segregation arises from minimizing the loss of conformational entropy near an impenetrable boundary; i.e., by positioning an end near the surface, only one unit rather than two is reflected. In order to obtain an experimental measure of this effect, monodisperse polystyrene (PS) chains of molecular weight 63 000 with short blocks of deuterated polystyrene (dPS) at each end were prepared. The block length was kept as short as possible, while yet producing sufficient neutron scattering contrast in order to minimize any preferential surface segregation due to isotopic effects. The synthesis was carried out via living anionic polymerization of a purified styrene monomer in cyclohexane at 60 C, utilizing sec-butyllithium as the initiator. The process was terminated using degassed methanol.