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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]

• 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]

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]

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]