Search

Molybdenum disulfide (MoS 2 ) is considered as a promising candidate to Pt-based catalysts. Literatures report the active centers of MoS 2 locate at its edges, while the perfect in-plane domains are not active. In this study, a simple Co Mo S precursor decomposition approach is used to synthesize Co-doped MoS 2 in-situ grown graphite paper (GP) substrate. Electrochemical analyses reveal the Co-doped MoS 2 possesses excellent electrocatalytic activity comparable to Pt. Density functional theory (DFT) calculations indicate the inert in-plane S atoms neighboring the doped Co atoms become active towards triiodide reduction, as revealed by the adsorption energies ( E ad ) of iodine atom decreasing from 0.36 eV to −0.52 eV, identical with value obtained from Pt (−0.52 eV). Due to increased active sites, highly conductive of GP, and excellent electrical connection between Co-doped MoS 2 and GP substrate, the dye-sensitized solar cell fabricated using Co-doped MoS 2 /GP as counter electrode (CE) shows higher photoelectric conversion efficiency (7.26%) than those based on MoS 2 /GP CE (6.57%) and platinized F-doped tin oxide (Pt/FTO) electrode (6.87%). [ABSTRACT FROM AUTHOR]

Two-dimensional nanolayered Mo 2 CT x is an excellent electrode material due to its large surface area and high conductivity. In this paper, Mo 2 C powders and metal Ga with the molar ratio of 1:3 as raw materials were used to prepare phase-pure Mo 2 Ga 2 C ceramic materials by non-pressure sintering at 750 °C, and two-dimensional nano-layered Mo 2 CT x materials were etched successfully using a facile oil bath method by HF. Capacitive behaviors of flexible and freestanding Mo 2 CT x film electrode prepared by the facile vacuum filtration in 1 M H 2 SO 4 , 1 M Na 2 SO 4 and 1 M NaOH electrolytes were systematically investigated for the first time. Mo 2 CT x film electrode exhibits the pseudo-capacitive behavior in H 2 SO 4 electrolyte, while double layer capacitance is presented in Na 2 SO 4 and NaOH electrolytes. The maximum volumetric specific capacitance of 563.05 F/cm3 at 2 mV/s is in H 2 SO 4 electrolyte, corresponding to the mass specific capacitance of 154.26 F/g. This is due to the obvious redox reaction in sulfuric acid solution Notably, density functional theory (DFT) calculation was executed to investigate the capacitive behavior and mechanism of the Mo 2 CT x film electrode in the three different electrolytes. [ABSTRACT FROM AUTHOR]

• A heterostructure consisting of Co@NC and NiMo-LDH was achieved. • Electron coupling in heterogeneous structures accelerates the electron transport rate. • The DFT results confirm the synergetic effect between the Co@NC and NiMo-LDH. • The assembled Zn-air battery exhibit a high paek density of 210 mW cm-2. It remains an urgent task to design electrocatalysts with fast oxygen evolution reaction (OER) kinetics and enriched active sites for flexible Zn-air batteries. In this paper, a structure engineering strategy is proposed to design an electrocatalyst with a heterostructure comprising Co@NC and NiMo-LDH on carbon cloth, which serves as an air electrode for a quasi-solid-state Zn-air battery. This unique heterostructure significantly enhances electrocatalytic activity, producing low OER overpotentials of 198 mV at 10 mA cm-2. Moreover, the assembled rechargeable Zn-air battery exhibits a high peak density and long cycle stability. Density functional theory calculations indicate that the multimetallic heterostructure induced synergistic and electronic coupling effects among the metal active sites, facilitating rapid ion and electron transport during the OER process. In addition, the migration of oxygen species at the Ni and Mo sites reduces the reaction potential barrier, resulting in a low OER overpotential of 160 mV. The construction of multi-metallic heterostructures enables optimisation of the electronic environment around the active sites and synergistic enhancement of the OER activity, leading to high performance quasi-solid-state Zn-air batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

The organised layer of molecules on a solid surface is at the centre of numerous molecular devices. Although the adsorption of molecules from aqueous electrolytes has been thoroughly investigated, only a limited number of studies have focused on the adsorption from ionic liquid electrolytes. This paper characterises the 4,4′-bipyridine adsorption at the Bi(111) | ionic liquid interface. We combined electrochemical impedance spectroscopy and scanning tunnelling microscopy with density functional theory calculations to gain a comprehensive overview of the interfacial processes. The results show a notable influence of electrode potential and the electrolyte on the 4,4′-bipyridine adsorption behaviour. The formation of organic adlayer on the electrode's surface was demonstrated, while highly organised striated adlayer structure was visualised only in a narrow potential range. [Display omitted] [ABSTRACT FROM AUTHOR]

• The oxygen vacancy-regulated BiVO 4 (Ov-BiVO 4) photoelectrodes were synethesized via a simple method. • The Ov-BiVO 4 photoelectrode exhibits superior slectivity and sensitivity for tetracycline hydrochloride (TC) detection. • This PEC sensor could be applied in milk samples. Unveiling the mechanism of the oxygen vacancy modulated photoelectrochemical sensors with high selectivity of the molecules including electron donating groups has become an innovative research field. In this paper, a novel oxygen vacancy modulated BiVO 4 photoelectrode (Ov-BiVO 4) was fabricated for tetracycline hydrochloride (TC) detection. The Ov-BiVO 4 has positive electrostatic potential and can interact with the TC molecules that have a large number of electrons donating groups. A series of experiments confirmed that the formed oxygen vacancies facilitate the adsorption of TC. Based on the good activity of Ov-BiVO 4 , a wide linear relationship was obtained from 0.1 to 800 nM, with a lower detection limit of 0.17 nM. In addition, the Ov-BiVO 4 photoelectrode could detect TC in milk samples with good reliability. Furthermore, density functional theory (DFT) calculations reveal that the oxygen vacancies will widen the depletion layer of BiVO 4 and reduce the charge recombination. It is believed that the surface modulation through oxygen vacancies can be extended to other semiconductors for advanced performance in the fields of photoelectrochemical bioanalysis. [Display omitted] [ABSTRACT FROM AUTHOR]

Pt nanoparticles (NPs) on nitrogen-functionalized mesoporous carbon have proved to be interesting materials for oxygen reduction reaction. In this paper, we employed a new synthetic route to simultaneously deposit Pt NPs and introduce N-doping in the carbon support, by using dichloro(1,10-phenanthroline)platinum(II) or dichloro(2,2′-bipyridyl)platinum(II) as a precursor of both platinum and nitrogen. Pt NPs (average size 2.5 nm) were successfully synthesized by solid state reduction of Pt(II) under N 2 /H 2 flow at 650 °C on a commercial mesoporous carbon. The synthesis was also carried out by employing PtCl 2 or Pt(acac) 2 as platinum precursors and 1,10-phenanthroline or 2,2′-bipyridyl as nitrogen dopant agents and the resulting materials were taken for comparison. XPS analysis confirmed that during the thermal treatment the ligand degrades and the nitrogen is embedded in the mesoporous carbon structure, resulting in a surface modification of the carbon support with preservation of bulk conductivity and thermal stability. Electrochemical characterization at a rotating disk electrode in O 2 -saturated 0.1 M HClO 4 revealed a superior catalytic activity for ORR, in terms of E 1/2 and mass activity, in those catalysts showing higher Pt N interaction, expressed as binding energy shift of nitrogen components. Furthermore, cyclic voltammetry analysis in Ar purged 0.1 M HClO 4 electrolyte showed that nitrogen doping appears to inhibit PtO formation. The influence of nitrogen incorporation in the carbon matrix on Pt NPs/support interaction was also rationalized on the basis of density functional theory simulations. [ABSTRACT FROM AUTHOR]

• Systematic study of 3d transition metal-doped CNTs. • V(Cr, Mn, Co)-doped CNTs show spin-polarization effects. • The 3d transition metal doping makes a big difference to the energy band. • 3d transition metal doping increases the quantum capacitance. • Ni-CNT has the largest quantum capacitance near zero potential. Supercapacitors are valued as one of the new green energy storage devices, but the low energy density limits the wide application of supercapacitors. In this paper, the effects of 3d transition metal doped on electronic structure and quantum capacitance of carbon nanotubes are investigated using DFT. The calculations show that elemental doping has caused the break-up of two degenerate states near the Fermi level, quasi-local state changes in the energy band, and the creation of new energy bands. The doping of V(Cr, Mn, Co) causes spin polarization in the energy band. The change in energy band affects the density of states near the Fermi level, effectively increasing the quantum capacitance and surface charge density of the carbon nanotube electrode. The quantum capacitance of Ni-doped carbon nanotubes is the largest, at 59.74 µF/cm2. In the range of water stability, Ti(V, Gr, Mn, Co)-CNT are suitable for use as electrode materials in symmetrical double layer supercapacitors. Sc(Fe, Cu, Zn)-CNT is suitable for use as anode materials in asymmetric double layer supercapacitors. Ni-CNT is suitable for use as a cathode material for asymmetric double layer supercapacitors. This study verifies the feasibility of 3d transition metal doping to improve the quantum capacitance of carbon nanotube electrodes. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper aims to understand the differences in the oxidation of ferrocene in several scenarios. The first scenario focuses the direct oxidation of ferrocene in an aqueous conventional support electrolyte and the second one is when ferrocene is directly placed in mineral oil, forming an oil phase and causing an oil/water interface. Additional experiments were also conducted in an emulsion, which was constituted by ferrocene in oil and mixed with conventional electrolytes and tetrabutylammonium chloride (TBAC). A Boron-Doped Diamond Electrode (BDD) was used as the working electrode. We observed an approximately 0.07 V shift when the ferrocene oxidation was conducted at the oil/water interface compared with the direct oxidation in the conventional aqueous phase. This potential shift was also calculated using the Density Functional Theory (DFT) as a theoretical tool. An additional comparison was conducted related to the interface and emulsions, finding that the ionic strength is the most determining factor in these types of electrochemical studies. Finally, Tafel plots indicated that the reaction mechanisms and reaction geometry are different when the electrode is placed at the interface versus directly in the aqueous phase. [ABSTRACT FROM AUTHOR]

In this work, we synthesize a sandwich-structured graphite-metallic silicon@C (MS-G@C) composite, which shows good electrochemical performance compared to metallic silicon or graphite-metallic silicon. The improved electrochemical performance may be ascribed to the sandwich structure of the composite with the carbon coating on metallic Si and to the metallic Si particles with high electronic conductivity according to the results of four probe tester measurement and a density functional theory study. When evaluated as an anode material for LIBs, the low cost MS-G@C anodes Exhibit 830 mA h g −1 at 0.5 C, 650 mA h g −1 at 1 C, and 251.2 mA h g −1 at 5 C, respectively, and after 100 cycles with an average capacity loss of only 0.02% per cycle at 0.5 C. The synthetic method presented in this paper is provided a facile and low-cost strategy for the large-scale production of silicon-based material as an anode in LIBs. [ABSTRACT FROM AUTHOR]

The paper focuses on theoretical and experimental aspects of an oxide surface optimization for oxygen reduction reaction (ORR). Various doped α-MnO 2 based electrocatalysts were prepared by microwave-assisted hydrothermal synthesis and electrochemically characterized to validate density functional theory (DFT) based predictions of the oxidation state and local structure effects on the catalytic activity of α-MnO 2 catalysts in ORR. Both theory and experiments conclude that the highest activity in ORR is to be expected in the case of clustered Mn 3+ sites which yield activity comparable with that of the polycrystalline Pt. These active sites have to be formed under in-operando conditions and their formation is hindered in doped α-MnO 2 catalysts. The activity of the other conceivable active sites based on non-clustered Mn 3+ or Mn 4+ is inferior to that of clustered Mn 3+ . The activation of Mn 3+ or Mn 4+ based active sites leads to a shift in selectivity of the ORR process towards 2 electron formation of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Nitrogen shows a positive influence on the ORR activity of certain catalysts, such as N-doped carbon and N-doped ZrO 2 . In this paper, we report a method to dope nitrogen into La 2 Zr 2 O 7 nanoparticles by the sol-gel process combined with ammonolysis. XPS results indicate that the nitrogen content in La 2 Zr 2 O 7 is approximately 0.92 at.%. Compared to the ORR activity of La 2 Zr 2 O 7 , ORR activity of the N-doped La 2 Zr 2 O 7 is considerably enhanced. Density functional theory (DFT) calculations indicate that the band gap is reduced in N-doped La 2 Zr 2 O 7 , which may be one of the factors that contribute to the improvement. [ABSTRACT FROM AUTHOR]

The oxygen-evolution reaction (OER) is pivotal in many energy-conversion technologies as it is an important counter reaction to others that convert stable chemicals to higher-value products using electrochemistry. The local microenvironment and pH for the anode OER can vary from acidic to neutral to alkaline depending on the system being explored, making definitive mechanistic insights difficult. In this paper, we couple experiments, first-principles calculations based on density functional theory, microkinetics, and transport modeling to explore the entire pH range of the OER. At low current densities, neutral pH values unexpectedly perform better than the acidic and alkaline conditions, and this trend is reversed at higher current densities (> 20 mA cm−2). Using multiscale modeling, this switch is rationalized by a change from a dual-reaction mechanism to a single rate-determining step. The model also shows how the alkaline reaction rates dominate in the middle to high pH range. Furthermore, we explore that the local pH for near-neutral conditions is much different (e.g., 2.4 at the reaction surface vs. 9 in the bulk) than the pH extremes, demonstrating the criticality that transport phenomena plays in kinetic activity. [ABSTRACT FROM AUTHOR]

Commercial lithium-ion batteries with carbon-based anodes exhibit low specific capacities and pose potential safety risks of lithium plating. As possible alternatives, conjugated carboxylic acid-based electrode materials have attracted extensive attention owing to their suitable discharge potential, low solubility in electrolytes, and low-cost reproducibility. However, their theoretical capacities are limited by the number of active sites. In this paper, we introduce 2,2′-bipyridine-5,5′-dicarboxylic acid (H 2 bpy) as a new anode material demonstrating high specific capacity, good cycle stability, and remarkable rate performance in both lithium- and sodium-ion batteries. In particular, H 2 bpy possesses an ultrahigh initial capacity of lithium-ion battery of 1200 mAh g−1 at a current density of 200 mA•g−1, and the specific capacity can maintain 550 mAh•g−1 after 100 cycles. Whereas the sodium-ion battery retains a specific capacity of 258 mAh•g−1 under the same conditions. We find, through density functional theory analysis, that the superior performance is due to the molecular structure and stacking form of H 2 bpy. Furthermore, we perform an ex situ spectroscopic analysis and find that the H 2 bpy electrode has good electrochemical stability. These findings suggest that bipyridine carboxylic acids can effectively broaden the application of heterocyclic carboxylic acids as anode materials. [ABSTRACT FROM AUTHOR]

Abstract: This paper described characterization of hydrazine adsorption on Cu surface with high-selectivity of component at right angle down to single molecular level using a plasmonic antenna enhancing Raman scattering. The antenna deposited by Cu with concentric pattern was designed by Finite Difference Time Domain (FDTD) calculation to enhance the electric field by focusing surface plasmon. By using this antenna, Raman peaks of adsorbed hydrazine on Cu was provided at 385cm−1. Furthermore, these peaks were only observed at 1–2nm from the antenna surface which meant that this approach had a potential to define the structure of adsorbed hydrazine just only on the plasmon antenna. The structure of adsorbed hydrazine was gauche-conformation. This data corresponded to the Density Functional Theory (DFT) of adsorption model of hydrazine on fcc-Cu (111) surface. These results suggest that this method creates a wide range of spin-off effects to the characterization of solid–liquid interface. [Copyright &y& Elsevier]

Abstract: In this paper we report density-functional theory (DFT) calculations at various levels of accuracy to compare the electrochemical properties of several silicate compounds as possible cathode materials in Li-ion batteries. We have tested the already known olivine-like structure (LiMSiO4, M=Mn, Fe, Co, and Ni) and the more recently discovered tetrahedral Pmn21 Li2MSiO4 (M=Mn, Fe, Co, and Ni). Our calculations show the influence of exchange and correlation potentials used to compute the redox potentials, electronic band gaps and other properties of these materials. A detailed study of the multicomponent effect on those characteristics gives us useful insight about how to improve the electrochemical performance of the cathode and its efficiency in the Li-ion battery. [Copyright &y& Elsevier]

A sulfur composite active material for lithium-sulfur batteries with a highly active interface structure can display excellent electrochemical performances. For this reason, in this paper, we design a type of V 2 O 5-x /TiO 2 active interface structure with high polysulfide adsorption energy as a high-performance sulfur-wrapped matrix. Physical property characterization indicates this interface is constructed from circular anatase structure TiO 2 and anoxic vanadium oxide structure composed of V4+ and V5+. After sulfur wrapping, Ti-S and S-S bond structures are produced by chemical and physical adsorption. Density functional theory calculations show that the V 2 O 5-x /TiO 2 interface has very high adsorption energy (-5.93 eV) with lithium polysulfide (Li 2 S 6). After sulfur wrapping as a cathode active material, it displays low electrochemical charge transfer resistance (31.89 Ω) and high lithium-ion transfer efficiency (3.50 × 10−12). In addition, it has rather high discharge specific capacities of 1466.47, 963.84 and 801.16 mAh.g−1 at 0.1, 0.2 and 0.5 C, respectively. After 500 cycles, the discharge capacity retention at 0.5 C is up to 76.11% corresponding to 0.048% capacity decay rate per cycle. This is the reason that the V 2 O 5-x /TiO 2 active interface has very strong adsorption to polysulfide and can effectively suppress the shuttle effect (Q low /Q high =1.44 at 0.2 C). [ABSTRACT FROM AUTHOR]

• Full characterization of NiII( tpa ) complexes gives information about its electronic structure which corelates with electrochemical behavior. • NiII( tpa ) complexes presented tunable redox potential for the NiII/NiI reduction. • NiII complex with more negative redox potential presented the high catalytic activity for CO 2 reduction. • Theoretical approach was useful for the analysis and description of electrochemical mechanisms. In this paper, we report the synthesis, characterization, as well as electrochemical, spectroelectrochemical, and density functional theory (DFT) calculations of a series of novel NiII complexes with a flexible tetradentate ligand, tris(2-pyridylmethyl)amine) ( tpa ). The complexes [NiII( tpa )(H 2 O)(MeCN)](BF 4) 2 , [NiII( tpa )(NO 3) 2 ], and [NiII( tpa )Cl 2 ] were studied for their ability to electrochemically reduce CO 2. These complexes were compared with the tris-chelate complex [Ni(bpy) 3 ](BF 4) 2 to understand the role of flexible tetradentate ligands containing a pyridinic ring in the electrochemical reduction of CO 2. Spectroelectrochemical experiments and theoretical studies were performed to rationalize the electrochemical reductions occurring and to predict the redox potential and pathway of CO 2 reduction. The electrochemical behavior of Ni(II) complexes with the ligand tris(2-pyridylmethyl)amine) was studied, in order to explore its ability to reduce electrochemically CO 2. Theoretical studies allowed to rationalize where the electrochemical reductions occur and predict redox potential and the pathway of CO 2 reduction. [Display omitted] [ABSTRACT FROM AUTHOR]

• The DFT method is used to predict the complexing ability of GLY, PT and HEDP. • In the absence of H 2 O 2 , GLY has the strongest complexing capability. • In the presence of H 2 O 2 , HEDP has the strongest complexing capability. • PT is identified as the best candidate complexing agent for Co barrier CMP. Glycine (GLY), potassium tartrate (PT), and hydroxyethylidene diphosphonic acid (HEDP) have been used as effective complexing agents for chemical mechanical polishing (CMP) of a cobalt (Co) barrier layer, but the most suitable of these three complexing agents is still unclear. In this paper, the density functional theory (DFT) method is employed to predict the complexing capability of the three complexing agents to Co ions. The prediction results show that the complexing capability of the three complexing agents is in the order of: HEDP > GLY > PT. Then, electrochemical experiments, static corrosion tests, UV-Vis spectra, and XPS analysis successfully prove the effectiveness of the DFT method for molecular activity prediction. The experimental results show that regardless of the presence or absence of H 2 O 2 , PT has the weakest complexing capability, which results in sufficient Co removal rate without causing unnecessary Co dissolution. In addition, the complexation capability of HEDP is stronger than that of GLY when the oxidation of the Co surface is not a limiting factor. [Display omitted] [ABSTRACT FROM AUTHOR]

Conductive CoS 2 and cycling stable MoS 2 are integrated to form the interconnected CoS 2 /MoS 2 nanosheet composite with electroactive interface grown on Mo foil substrate to act as high-performance supercapacitor anode material with electrochemical and mechanical stability. The band gap and density of state of CoS 2 /MoS 2 determined by density functional theory simulation calculation indicates its improved electrical conductivity. The interface binding energy and differential charge density reveal that strong crystal interface interaction between MoS 2 (002) and CoS 2 (111) enables effective charge transfer in interconnected CoS 2 /MoS 2 nanosheet composite. CoS 2 /MoS 2 exhibits higher specific capacitance of 605.77 mF cm−2 than MoS 2 of 218.1 mF cm−2 at 1.0 mA cm−2 in 0.5 M Na 2 SO 4. The rate capacitance retention is improved from 57.8% of MoS 2 to 82.8% of CoS 2 /MoS 2 at 1–10 mA cm−2. The high cycling stability is achieved for MoS 2 (100.2%) and CoS 2 /MoS 2 (104.05%) after 5000 cycles at 10 mA cm−2 due to self-activation of multilayered MoS 2. An asymmetric solid-state supercapacitor using CoS 2 /MoS 2 anode and MnO 2 /carbon paper cathode achieves a capacitance of 4.32 F cm−3 at 1.0 mA cm−2 and an energy density of 1.944 mWh cm−3 at a power density of 18 mW cm−3, 97.8% after 5000 cycles at 5.0 mA cm−2, presenting effective energy storage. [ABSTRACT FROM AUTHOR]

In this paper, novel arrays of rutile SnO 2 nanorods (r-SnO 2 -NRs) are successfully grown vertically on the arrays of the rutile TiO 2 nanorods (r-TiO 2 -NRs) and directly supported on the carbon cloth (CC) to form a hierarchical nano-heterostructure material (r-TiO 2 -NRs@r-SnO 2 -NRs/CC) through a two-step hydrothermal process. Such a reverse core-shell nano-heterostructure design with r-SnO 2 -NRs as shell layer epitaxially grown on the r-TiO 2 -NRs backbone is directly used as a binder-free and flexible lithium-ion batteries (LIBs) anode. Both high initial Coulombic Efficiency and high reversible capacity are demonstrated, which are much better that those of the single components. The enhanced electrochemical performances are attributed to a heterostructure of r-TiO 2 -NRs and r-SnO 2 -NRs as well as the unique branched nanostructures. The density functional theory (DFT) analysis further manifest that such a r-TiO 2 -NRs@r-SnO 2 -NRs heterostructure can achieve the faster electron transport kinetics than their single components due to a change in the energy band gap after heterogenization. Due to the arrayed and crosslinked structure of such a anode material and its flexible CC supporter, the strong structure stability and flexibility can be realized for flexible LIBs. [ABSTRACT FROM AUTHOR]