High-efficiency Electroreduction of O2 into H2 O2 over ZnCo Bimetallic Triazole Frameworks Promoted by Ligand Activation.

Co-based metal-organic frameworks (MOFs) as electrocatalysts for two-electron oxygen reduction reaction (2e- ORR) are highly promising for H2 O2 production, but suffer from the intrinsic activity-selectivity trade-off. Herein, we report a ZnCo bimetal-triazole framework (ZnCo-MTF) as high-efficiency 2e- ORR electrocatalysts. The experimental and theoretical results demonstrate that the coordination between 1,2,3-triazole and Co increases the antibonding-orbital occupancy on the Co-N bond, promoting the activation of Co center. Besides, the adjacent Zn-Co sites on 1,2,3-triazole enable an asymmetric "side-on" adsorption mode of O2 , favoring the reduction of O2 molecules and desorption of OOH* intermediate. By virtue of the unique ligand effect, the ZnCo-MTF exhibits a 2e- ORR selectivity of ≈100 %, onset potential of 0.614 V and H2 O2 production rate of 5.55 mol gcat -1 h-1 , superior to the state-of-the-art zeolite imidazole frameworks. Our work paves the way for the design of 2e- ORR electrocatalysts with desirable coordination and electronic structure.

Group-VIII transition metal boride as promising hydrogen evolution reaction catalysts.

Searching for alternative catalysts for hydrogen evolution reaction (HER) under acidic conditions has been a major challenge in chemistry. Herein, we demonstrate that it is now feasible to identify unprecedented transition metal boride phases that are both stable and active for HER via stochastic global potential energy surface scanning. We show that B alloying alters the most stable crystal phase from face-centered (fcc) to hexagonal close packing (hcp) for both Pd and Rh. In particular, Pd2B, the thermodynamically most stable Pd boride with the highest B content, is predicted to exhibit an ultra-high intrinsic HER activity, ∼2 orders of magnitude higher than that of Pt nanoparticles at 0 V vs. NHE. The group VIII transition metal boride thus represents a promising HER catalyst to replace conventional Pt catalysts.

Engineering Carbon Nanotube Fiber for Real-Time Quantification of Ascorbic Acid Levels in a Live Rat Model of Alzheimer's Disease.

Ascorbic acid (AA) levels are closely correlated with physiological and pathological events in brain diseases, but the mechanism remains unclear, mainly due to the difficulty of accurately analyzing AA levels in live brain. In this study, by engineering tunable defects and oxygen-containing species in carbon nanotubes, a novel aligned carbon nanotube fiber was developed as an accurate microsensor for the ratiometric detection of AA levels in live rat brains with Alzheimer's disease (AD). AA oxidation is greatly facilitated on the fiber surface at a low potential, leading to high sensitivity as well as high selectivity against potential sources of interference in the brain. Additionally, an unexpected, separate peak from the fiber surface remains constant as the AA concentration increases, enabling real-time and ratiometric detection with high accuracy. The results demonstrated that the AA levels were estimated to be 259 ± 6 µM in cortex, 264 ± 20 µM in striatum, and 261 ± 21 µM in hippocampus, respectively, in normal condition. However, the overall AA level was decreased to 210 ± 30 µM in cortex, 182 ± 5 µM in striatum, and 136 ± 20 µM in hippocampus in the rat brain model of AD. To the best of our knowledge, this work is the first to accurately detect AA concentrations in the brains of live animal model of AD.

Subnano Pt Particles from a First-Principles Stochastic Surface Walking Global Search.

Subnano transition metal particles have wide applications in chemistry. For the complexity of their potential energy surface, it has long been a great challenge for both theory and experiment to determine the structure of subnano clusters and thus predict their physiochemical properties. Here we explore the structure configurations for 35 subnano PtN (N = 12-46) clusters using a first-principles Stochastic Surface Walking (SSW) global search. For each cluster, thousands of structure candidates are collected from a parallel SSW search. This leads to the finding of 20 new global minima in 35 clusters, which reflects the essence of a first-principles global search for revealing the structure of subnano transition metal clusters. PtN subnano clusters with N being 14, 18, 22, 27, 36, and 44 have higher stability than their neighboring size clusters and are characterized as magic number clusters. These PtN subnano clusters exhibit metallic characteristics with a diminishing HOMO-LUMO gap, much poorer binding energy (by 1-1.7 eV), and a much higher Fermi level (by 1-1.5 eV) than bulk metal, implying their high chemical activity. By analyzing their structures, we observe the presence of a rigid core and a soft shell for PtN clusters and find that the core-shell 3-D architecture evolves as early as N > 22. For these core-shell clusters, a good core-shell lattice match is the key to achieve the high stability.

Restructuring and Hydrogen Evolution on Pt Nanoparticle.

The restructuring of nanoparticles at the in situ condition is a common but complex phenomenon in nanoscience. Here, we present the first systematic survey on the structure dynamics and its catalytic consequence for hydrogen evolution reaction (HER) on Pt nanoparticles, as represented by a magic number Pt44 octahedron (∼1 nm size). Using a first principles calculation based global structure search method, we stepwise follow the significant nanoparticle restructuring under HER conditions as driven by thermodynamics to expose {100} facets, and reveal the consequent large activity enhancement due to the marked increase of the concentration of the active site, being identified to be apex atoms. The enhanced kinetics is thus a "byproduct" of the thermodynamical restructuring. Based on the results, the best Pt catalyst for HER is predicted to be ultrasmall Pt particles without core atoms, a size below ∼20 atoms.

Confined platinum nanoparticle in carbon nanotube: structure and oxidation.

A supported nanoparticle is dynamic in reaction conditions, but how this dynamic behavior is influenced by the support remains elusive. Using the stochastic surface walking global optimization method, herein, we report the structure, thermodynamics and catalytic properties of Pt nanoparticles inside and outside a carbon nanotube (CNT). We reveal that confined metal nanoparticles are, surprisingly, structurally more flexible at low temperatures but less likely to melt at high temperatures. By investigating the O2 interaction with a Pt15 cluster inside and outside the CNT, we find that the low temperature structure versatility facilitates the in situ creation of favorable reaction sites, and thus maintains the catalytic activity of O2 dissociation. The decrease of the population for the liquid-like structures (largely disordered) offers the higher stability of the confined nanocatalyst. The theoretical results are consistent with experimental findings for the enhanced antioxidation ability of the confined metal nanoparticles.

Quasi-planar aromatic B36 and B36(-) clusters: all-boron analogues of coronene.

Flat boron has recently emerged as a fascinating concept in cluster science. Here we present computational evidence for the quasi-planar all-boron aromatic B36 (C6v, (1)A1) and B36(-) (C2v, (2)A1) clusters, established as the global-minimum structures on the basis of Stochastic Surface Walking (SSW) searches. The energetics for low-lying isomeric structures are evaluated using the validated density-functional method at the PBE0/6-311+G* level. Our global-minimum structures are in line with a recent report (Z. A. Piazza et al., Nat. Commun., 2014, 5, 3113). These structures consist of two-dimensional close-packing boron with a perfect hexagonal hole at the center, which may serve as molecular models for the monolayer boron α sheet. Chemical bonding analysis indicates that B36 and B36(-) are all-boron analogues of coronene (C24H12), featuring concentric dual π aromaticity with an inner π sextet and an outer π sextet. The hydrogenated B36H6 (C6v, (1)A1) model cluster shows similar bonding properties, which possesses concentric triple aromaticity with inner π, outer π, and outer σ sextets.

Observation of an all-boron fullerene.

After the discovery of fullerene-C60, it took almost two decades for the possibility of boron-based fullerene structures to be considered. So far, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. Here we report the observation, by photoelectron spectroscopy, of an all-boron fullerene-like cage cluster at B40(-) with an extremely low electron-binding energy. Theoretical calculations show that this arises from a cage structure with a large energy gap, but that a quasi-planar isomer of B40(-) with two adjacent hexagonal holes is slightly more stable than the fullerene structure. In contrast, for neutral B40 the fullerene-like cage is calculated to be the most stable structure. The surface of the all-boron fullerene, bonded uniformly via delocalized σ and π bonds, is not perfectly smooth and exhibits unusual heptagonal faces, in contrast to C60 fullerene.

Optimum nanoparticles for electrocatalytic oxygen reduction: the size, shape and new design.

The electrocatalytic oxygen reduction reaction (ORR) on nanoparticles has attracted much attention in recent years for its significance in fuel cell applications. Here by combining density functional theory (DFT) calculations with the periodic continuum solvation model based on modified-Poisson-Boltzmann (CM-MPB) electrostatics, we analyzed the ORR activity on a set of differently sized Pt nanoparticles in order to identify the optimum particles for a better designed catalyst. We show that Pt nanoparticles of ∼2 nm size have the highest ORR mass activity, which is attributed to the variation of the effective reaction sites on the exposed {111} facet at the electrochemical conditions. We propose a type of a new nanocatalyst for the electrocatalytic oxygen reduction based on the knowledge from large-scale first principles simulations on Pt nanoparticles. The new catalyst has inert metal Au as the frame for the Pt nanoparticle and exposed Pt{111} sites are the active site for oxygen reduction. Such an architecture can not only prevent the initial O corrosion at the edge sites but also significantly improve the activity. The theoretical work provides a promising new direction for the rational design of a stable and active ORR catalyst via nano-structure engineering.

Periodic mesoporous organosilicas with controlled pore symmetries for peptides enrichment.

Periodic mesoporous organosilicas (PMOs) with controlled structures have been synthesized by using cetyltrimethylammonium bromide (CTAB) and sodium perfluorooctanoate (PFONa) as co-templates, 1,2-bis (triethoxysilyl)ethane (BTEE) as an organosilica precursor. By increasing the weight ratio of PFONa/CTAB, a structure transformation from a cubic (Pm-3n) to a two-dimensional hexagonal (p6m) mesostructure and then to multilamellar vesicles can be observed. The cubic and hexagonal samples have similar particle size (200-750 nm), pore size (2.6 and 2.8 nm, respectively), total pore volume (approximately 0.7 cm3/g), and surface area (approximately 900 m2/g), providing ideal candidates to study the peptide enrichment performance influenced simply by pore symmetries. Matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS) analysis indicates that PMO with a cubic (Pm-3n) structure is more effective in small molecular weight peptides enrichment compared with PMO with a hexagonal structure, showing the importance of mesostructural control for targeted applications. The phenomena can be attributed to the cage-type structure of the Pm-3n symmetry, which possesses cages with a relatively larger pore size and connectivity with a relatively smaller size. It is suggested that the pore entrances with small size are responsible for entrapping small molecular weight peptides. Our study may shed light on the designed synthesis of functional porous materials with controlled structures and enhanced performance in peptides enrichment.