Modulating Aluminum Solvation with Ionic Liquids for Improved Aqueous-Based Aluminum-Ion Batteries.

Aqueous-based Al-ion batteries are attractive alternatives to Li-ion batteries due to their safety, high volumetric energy density, abundance, and recyclability. Although aluminum-ion batteries are attractive, there are major challenges to overcome, which include understanding the nature of the passive layer of aluminum oxide on the aluminum anode, the narrow electrochemical window of aqueous electrolytes, and lack of suitable cathodes. Here, we report using experiments in conjunction with DFT simulations to clarify the role of ionic liquids (ILs) in altering the Al solvation dynamics, which in turn affects the aluminum electrochemistry and aqueous-based battery performance significantly. DFT calculations showed that the addition of 1-ethyl-3-methylimidazolium trifluoromethylsulfonate (EMIMTfO) changes the aluminum solvation structure in the aqueous (Al(TfO)3) electrolyte to lower coordinated solvation shells, thereby influencing and improving Al deposition/stripping on the Zn/Al alloy anode. Furthermore, the addition of an IL reduces the strain in manganese oxide during intercalation/deintercalation, thereby improving the Zn/Al-MnOx battery performance. By optimizing the electrolyte composition, a battery potential of >1.7 V was achieved for the Zn/Al-MnOx system.

Spectroscopic Identification of Active Sites of Oxygen-Doped Carbon for Selective Oxygen Reduction to Hydrogen Peroxide.

The electrochemical synthesis of hydrogen peroxide (H2 O2 ) via a two-electron (2 e- ) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst for H2 O2 electrochemical production. The optimized PCC900 material exhibits remarkable activity and selectivity, of which the onset potential reaches 0.83 V vs. reversible hydrogen electrode in 0.1 M KOH and the H2 O2 selectivity is over 95 % in a wide potential range. Comprehensive synchrotron-based near-edge X-ray absorption fine structure (NEXAFS) spectroscopy combined with electrocatalytic characterizations reveals the positive correlation between quinone content and 2 e- ORR performance. The effectiveness of chair-form quinone groups as the most efficient active sites is highlighted by the molecule-mimic strategy and theoretical analysis.

Periodic corner holes on the Si(111)-7×7 surface can trap silver atoms.

Advancement in nanotechnology to a large extent depends on the ability to manipulate materials at the atomistic level, including positioning single atoms on the active sites of the surfaces of interest, promoting strong chemical bonding. Here, we report a long-time confinement of a single Ag atom inside a corner hole (CH) of the technologically relevant Si(111)-7×7 surface, which has comparable size as a fullerene C60 molecule with a single dangling bond at the bottom center. Experiments reveal that a set of 17 Ag atoms stays entrapped in the CH for the entire duration of experiment, 4 days and 7 h. Warming up the surface to about 150 °C degrees forces the Ag atoms out of the CH within a few minutes. The processes of entrapment and diffusion are temperature dependent. Theoretical calculations based on density functional theory support the experimental results confirming the highest adsorption energy at the CH for the Ag atom, and suggest that other elements such as Li, Na, Cu, Au, F and I may display similar behavior. The capability of atomic manipulation at room temperature makes this effect particularly attractive for building single atom devices and possibly developing new engineering and nano-manufacturing methods.

Synthesis, Structural Investigation, Hirshfeld Surface Analysis, and Biological Evaluation of N-(3-Cyanothiophen-2-yl)-2-(thiophen-2-yl)acetamide.

In this study, a novel heterocyclic amide derivative, N-(3-cyanothiophen-2-yl)-2-(thiophen-2-yl)acetamide (I), was obtained by reacting 2-aminothiophene-3-carbonitrile with activated 2-(thiophen-2-yl)acetic acid in a N-acylation reaction and characterized by elemental analyses, FT-IR, 1H and 13C NMR spectroscopic studies, and single crystal X-ray crystallography. The crystal packing of I is stabilized by C-H···N and N-H···N hydrogen bonds. In addition, I was investigated computationally using the density functional theory (DFT) method with the B3LYP exchange and correlation functions in conjunction with the 6311++G(d,p) basis set in the gas phase. Fukui function (FF) analysis was also carried out. Electrophilicity-based charge transfer (ECT) method and charge transfer (ΔN) were computed to examine the interactions between I and DNA bases (such as guanine, thymine, adenine, and cytosine). The most important contributions to the Hirshfeld surface are H···H (21%), C···H (20%), S···H (19%), N···H (14%), and O···H (12%). An ABTS antioxidant assay was used to evaluate the in vitro antioxidant activity of I. The compound exhibited moderate antioxidant activity. The antimicrobial activity of the title molecule was investigated under aseptic conditions, using the microdilution method, against Gram-positive and Gram-negative bacterial strains, and it also demonstrated significant activity against yeasts (Candida glabrata ATCC 90030, Candida krusei ATCC 34135). The findings revealed that the molecule possesses significant antioxidant and antimicrobial properties.

A comparative study on the stability of the furfural molecule on the low index Ni, Pd and Pt surfaces.

We present a comparative density functional theory investigation of the furfural (Ff) molecule on the low index Ni, Pd and Pt surfaces to understand its geometrical and electronic properties to gain mechanistic insights into the experimentally measured catalytic reactivities of these metal catalysts. We show that the number of metal d-states, which hybridize with the nearest C and O p-orbitals of the Ff molecule, can be used to explain the stability of the Ff molecule on these surfaces. We find that the hybridization between atoms with higher electronegativity and the metal d-states plays a crucial role in determining the stability of these systems. Furthermore, we also find electron transfer from metal to the Ff molecule on the Ni and Pd surfaces, with a reverse process occurring on the Pt surface.

A computational investigation of the adsorption of small copper clusters on the CeO2(110) surface.

We report a detailed density functional theory (DFT) study of the geometrical and electronic properties, and the growth mechanism of a Cun (n = 1-4) cluster on a stoichiometric, and especially on a defective CeO2(110) surface with one surface oxygen vacancy, without using pre-assumed gas-phase Cun cluster shapes. This gives new and valuable theoretical insight into experimental work regarding debatable active sites of promising CuOx/CeO2-nanorod catalysts in many reactions. We demonstrate that CeO2(110) is highly reducible upon Cun adsorption, with electron transfer from Cun clusters, and that a Cun cluster grows along the long bridge sites until Cu3, so that each Cu atom can interact strongly with surface oxygen ions at these sites, forming stable structures on both stoichiometric and defective CeO2(110) surface. Cu-Cu interactions are, however, limited, since Cu atoms are distant from each other, inhibiting the formation of Cu-Cu bonds. This monolayer then begins to grow into a bilayer as seen in the Cu3 to Cu4 transition, with long-bridge site Cu as anchoring sites. Our calculations on Cu4 adsorption reveal a Cu bilayer rich in Cu+ species at the Cu-O interface.

A DFT and KMC based study on the mechanism of the water gas shift reaction on the Pd(100) surface.

We present a combined density functional theory (DFT) and Kinetic Monte Carlo (KMC) study of the water gas shift (WGS) reaction on the Pd(100) surface. We propose a mechanism comprising both the redox and the associative pathways for the WGS within a single framework, which consists of seven core elementary steps, which in turn involve splitting of a water molecule followed by the production of an H-atom and an OH-species on the Pd(100) surface. In the following steps, these intermediates then recombine with each other and with CO leading to the evolution of CO2, and H2. Seven other elementary steps, involving the diffusion and adsorption of the surface intermediate species are also considered for a complete description of the mechanism. The geometrical and electronic properties of each of the reactants, products, and the transition states of the core elementary steps are presented. We also discuss the analysis of Bader charges and spin densities for the reactants, transition states and the products of these elementary steps. Our study indicates that the WGS reaction progresses simultaneously via the direct oxidation and the carboxyl paths on the Pd(100) surface.

The electronic properties of Au clusters on CeO2 (110) surface with and without O-defects.

We use density functional theory with Hubbard corrections (DFT+U) to understand the local electronic properties of Au adatom and Au2 dimer adsorption on the CeO2 (110) surface. We show that, based on the initial geometries, we can observe Au species in a variety of charge states including Au+, Au-, Auδ- and Auδ+-Auδ-. We present a detailed discussion using Bader charge analysis and partial density of states to support our observations. We also discuss the influence of solvent on the adsorption of Au adatoms adsorbed on top of an O-vacancy, which shows interesting geometrical and electronic properties.

The adsorption of Cu on the CeO2(110) surface.

We report a detailed density functional theory (DFT) study in conjunction with extended X-ray absorption fine structure (EXAFS) experiments on the geometrical and local electronic properties of Cu adatoms and Cu(ii) ions in presence of water molecules and of CuO nanoclusters on the CeO2(110) surface. Our study of (CuO)n(=1,2&4) clusters on CeO2(110) shows that based on the Cu-O environment, the geometrical properties of these clusters may vary and their presence may lead to relatively high localization of charge on the exposed surfaces. We find that in the presence of an optimum concentration of water molecules, Cu has a square pyramidal geometry, which agrees well with our experimental findings; we also find that Cu(ii) facilitates water adsorption on the CeO2(110) surface. We further show that a critical concentration of water molecules is required for the hydrolysis of water on Cu(OH)2/CeO2(110) and on pristine CeO2(110) surfaces.

The reaction of formic acid with RaneyTM copper.

The interaction of formic acid with RaneyTM Cu proves to be complex. Rather than the expected generation of a monolayer of bidentate formate, we find the formation of a Cu(II) compound. This process occurs by direct reaction of copper and formic acid; in contrast, previous methods are by solution reaction. This is a rare example of formic acid acting as an oxidant rather than, as more commonly found, a reductant. The combination of diffraction, spectroscopic and computational methods has allowed this unexpected process to be characterized.

Room temperature methoxylation in zeolites: insight into a key step of the methanol-to-hydrocarbons process.

Neutron scattering methods observed complete room temperature conversion of methanol to framework methoxy in a commercial sample of methanol-to-hydrocarbons (MTH) catalyst H-ZSM-5, evidenced by methanol immobility and vibrational spectra matched by ab initio calculations. No methoxylation was observed in a commercial HY sample, attributed to the dealumination involved in high silica HY synthesis.

Optimised photocatalytic hydrogen production using core-shell AuPd promoters with controlled shell thickness.

The development of efficient photocatalytic routines for producing hydrogen is of great importance as society moves away from energy sources derived from fossil fuels. Recent studies have identified that the addition of metal nanoparticles to TiO2 greatly enhances the photocatalytic performance of these materials towards the reforming of alcohols for hydrogen production. The core-shell structured Au-Pd bimetallic nanoparticle supported on TiO2 has being of interest as it exhibited extremely high quantum efficiencies for hydrogen production. However, the effect of shell composition and thickness on photocatalytic performance remains unclear. Here we report the synthesis of core-shell structured AuPd NPs with the controlled deposition of one and two monolayers (ML) equivalent of Pd onto Au NPs by colloidal and photodeposition methods. We have determined the shell composition and thickness of the nanoparticles by a combination of X-ray absorption fine structure and X-ray photoelectron spectroscopy. Photocatalytic ethanol reforming showed that the core-shell structured Au-Pd promoters supported on TiO2 exhibit enhanced activity compared to that of monometallic Au and Pd as promoters, whilst the core-shell Au-Pd promoters containing one ML equivalent Pd provide the optimum reactivity.