Nano-crumples induced Sn-Bi bimetallic interface pattern with moderate electron bank for highly efficient CO2 electroreduction.

CO2 electroreduction reaction offers an attractive approach to global carbon neutrality. Industrial CO2 electrolysis towards formate requires stepped-up current densities, which is limited by the difficulty of precisely reconciling the competing intermediates (COOH* and HCOO*). Herein, nano-crumples induced Sn-Bi bimetallic interface-rich materials are in situ designed by tailored electrodeposition under CO2 electrolysis conditions, significantly expediting formate production. Compared with Sn-Bi bulk alloy and pure Sn, this Sn-Bi interface pattern delivers optimum upshift of Sn p-band center, accordingly the moderate valence electron depletion, which leads to weakened Sn-C hybridization of competing COOH* and suitable Sn-O hybridization of HCOO*. Superior partial current density up to 140 mA/cm2 for formate is achieved. High Faradaic efficiency (>90%) is maintained at a wide potential window with a durability of 160 h. In this work, we elevate the interface design of highly active and stable materials for efficient CO2 electroreduction.

A Moving Front Kinetic Monte Carlo Algorithm for Moving Interface Systems.

This work presents the development of a new kinetic Monte Carlo algorithm, referred to as Moving Front kinetic Monte Carlo (MFkMC), for simulating processes subject to moving interfaces. This framework is designed to capture the movement of transiently varying interfaces in a kinetic-like manner so that its movement can be described using Monte Carlo sampling. The MFkMC algorithm accomplishes this task by evaluating the behavior of the interfacial molecules and assigning kinetic Monte Carlo-style rate equations that describe the transition probability that a molecule would advance into the neighboring phase, displacing an interfacial molecule from the opposing phase and thus changing the interface. Due to its kinetic Monte Carlo structure, the MFkMC algorithm can additionally account for other important interfacial phenomena, such as interfacial surface reactions. The proposed algorithm was tested via applications to three different simple interfacial case studies. These studies validate the MFkMC algorithm and demonstrate its capabilities to accurately and efficiently simulate a variety of different moving interface systems.

Structural and Morphological Engineering of Benzothiadiazole-Based Covalent Organic Frameworks for Visible Light-Driven Oxidative Coupling of Amines.

Covalent organic frameworks (COFs) are appealing platforms for photocatalysts because of their structural diversity and adjustable optical band gaps. The construction of efficient COFs for heterogeneous photocatalysis of organic transformations is highly desirable. Herein, we constructed a photoactive COF containing benzothiadiazole and triazine (BTDA-TAPT), for which the morphology and crystallinity might be easily tuned by slight synthetic variation. To unveil the relationship of photocatalytic properties between the structure and morphology, analogous COFs were synthesized by precisely tailoring building blocks. Systematic investigations indicated that tuning the structure and morphology might greatly impact photoelectric properties. The BTDA-TAPT featuring ordered alignment and perfect crystalline nature was more beneficial for promoting charge transfer and separation, which exhibited superior photocatalytic activity for visible light-driven oxidative coupling of amines. Outcomes from this study reveal the intrinsic synergy effects between the structure and morphology of COFs for photocatalysis.

Defect-Enriched Nitrogen Doped-Graphene Quantum Dots Engineered NiCo2 S4 Nanoarray as High-Efficiency Bifunctional Catalyst for Flexible Zn-Air Battery.

Flexible Zn-air batteries have recently emerged as one of the key energy storage systems of wearable/portable electronic devices, drawing enormous attention due to the high theoretical energy density, flat working voltage, low cost, and excellent safety. However, the majority of the previously reported flexible Zn-air batteries encounter problems such as sluggish oxygen reaction kinetics, inferior long-term durability, and poor flexibility induced by the rigid nature of the air cathode, all of which severely hinder their practical applications. Herein, a defect-enriched nitrogen doped-graphene quantum dots (N-GQDs) engineered 3D NiCo2 S4 nanoarray is developed by a facile chemical sulfuration and subsequent electrophoretic deposition process. The as-fabricated N-GQDs/NiCo2 S4 nanoarray grown on carbon cloth as a flexible air cathode exhibits superior electrocatalytic activities toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), outstanding cycle stability (200 h at 20 mA cm-2 ), and excellent mechanical flexibility (without observable decay under various bending angles). These impressive enhancements in electrocatalytic performance are mainly attributed to bifunctional active sites within the N-GQDs/NiCo2 S4 catalyst and synergistic coupling effects between N-GQDs and NiCo2 S4 . Density functional theory analysis further reveals that stronger OOH* dissociation adsorption at the interface between N-GQDs and NiCo2 S4 lowers the overpotential of both ORR and OER.

Construction of Oxygen-Deficient La(OH)3 Nanorods Wrapped by Reduced Graphene Oxide for Polysulfide Trapping toward High-Performance Lithium/Sulfur Batteries.

Despite the high theoretical capacity (2600 Wh kg-1) of a sulfur cathode, lithium/sulfur (Li/S) batteries still face several serious challenges on the road to commercial success. Herein, a unique three-dimensional hierarchical microsphere architecture assembled by oxygen-deficient La(OH)3 and reduced graphene oxide (rGO), as the sulfur host material for Li/S batteries, has been rationally designed using a facile spray-drying method for the first time. The robust microsphere architecture can reduce ion diffusion pathways and provide adequate space to modulate volume variation during cycling. It is noted that the abundant inner void spaces in the microspheres formed by rGO and oxygen-deficient La(OH)3 nanorod stacking provide physical adsorption for polysulfides. Meanwhile, the hydroxyl groups and defective sites on the surface of polar La(OH)3 nanorods provide strong chemical adsorption to lithium polysulfides, which was confirmed by density functional theory calculations. Additionally, rich oxygen-deficient La(OH)3 nanorods as an effective electrocatalyst promote the reversibility and conversion kinetics of polysulfides. The fast polysulfide conversion reactions can prevent accumulation in the cathode and loss in the electrolyte. Consequently, a sulfur cathode with rGO-La(OH)3 exhibits a high initial specific capacity of 1160.4 mAh g-1 at 0.2C and retains long-term stability for a capacity of 541.7 mAh g-1 after 600 cycles at 1C.

Self-Assembly of Spinel Nanocrystals into Mesoporous Spheres as Bifunctionally Active Oxygen Reduction and Evolution Electrocatalysts.

The present work introduces spinel oxide nanocrystals self-assembled into mesoporous spheres that are bifunctionally active towards catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The electrochemical evaluation reveals that (Ni,Co)3 O4 demonstrates a significantly positive-shifted ORR onset and half-wave potentials [-0.127 and -0.292 V vs. saturated calomel electrode (SCE), respectively], whereas Co3 O4 results in a negative-shifted OER potential (0.65 V vs. SCE) measured at 10 mA cm-2 . Based on the DFT analysis, the potential at which all oxygen intermediate reactions proceed spontaneously is the highest for (Ni,Co)3 O4 (U=0.66 eV) during ORR, whereas it is the lowest for Co3 O4 (U=2.09 eV) during OER. The high ORR activity of (Ni,Co)3 O4 is attributed to the enhanced electrical conductivity of the spinel lattice, and the high OER activity of Co3 O4 is attributed to relatively weak adsorption energy promoting rapid release of evolved oxygen.

Numerical modeling of solid-phase microextraction: binding matrix effect on equilibrium time.

Solid-phase microextraction (SPME) is a well-known sampling and sample preparation technique used for a wide variety of analytical applications. As there are various complex processes taking place at the time of extraction that influence the parameters of optimum extraction, a mathematical model and computational simulation describing the SPME process is required for experimentalists to understand and implement the technique without performing multiple costly and time-consuming experiments in the laboratory. In this study, a mechanistic mathematical model for the processes occurring in SPME extraction of analyte(s) from an aqueous sample medium is presented. The proposed mechanistic model was validated with previously reported experimental data from three different sources. Several key factors that affect the extraction kinetics, such as sample agitation, fiber coating thickness, and presence of a binding matrix component, are discussed. More interestingly, for the first time, shorter or longer equilibrium times in the presence of a binding matrix component were explained with the help of an asymptotic analysis. Parameters that contribute to the variation of the equilibrium times are discussed, with the assumption that one binding matrix component is present in a static sample. Numerical simulation results show that the proposed model captures the phenomena occurring in SPME, leading to a clearer understanding of this process. Therefore, the currently presented model can be used to identify optimum experimental parameters without the need to perform a large number of experiments in the laboratory.

Carbon clusters on the Ni(111) surface: a density functional theory study.

To understand the nucleation of carbon atoms to form carbon clusters on transition metal substrates during chemical vapor deposition (CVD) synthesis, the structure, energetics, and mobility of carbon intermediates up to 6 atoms on the Ni(111) surface were investigated using Density Functional Theory (DFT). Carbon clusters were found to be more thermodynamically stable than adsorbed atomic carbon, with linear carbon structures being more stable than branched and ring structures. Carbon chains were also found to have higher mobility than branched configurations. The interaction energy between carbon clusters and the Ni surface shows that branched carbon clusters have stronger interaction with the Ni substrate when compared with the carbon chains, supporting that carbon chains generally have higher mobility than branched clusters. The transition states and energy barriers for the formation of different carbon clusters were also studied. The results show that the formation of the branched configurations is kinetically favored as it presents lower energy barriers than those obtained for carbon chains.