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The boron nitride nanomesh is a corrugated monolayer of hexagonal boron nitride (h-BN) on Rh(111), which so far has been studied mostly under ultrahigh vacuum conditions. Here, we investigate how copper underpotential deposition (upd) can be used to quantify defects in the boron nitride monolayer and to assess the potential window of the nanomesh, which is important to explore its functionality under ambient and electrochemical conditions. In dilute sulfuric acid, the potential window of h-BN/Rh(111) is close to 1 volt, i.e. larger than that of the Rh substrate, and is limited by molecular hydrogen evolution on the negative and by oxidative removal on the positive side. From copper upd on pristine h-BN/Rh(111) wafer samples, we estimate a collective defect fraction on the order of 0.08–0.7% of the geometric area, which may arise from line and point defects in the h-BN layer that are created during its chemical vapour deposition. Overpotential deposition (opd) is demonstrated to have significant consequences on the defect area. We hypothesise that this non-innocent Cu electrodeposition involves intercalation originating at initial defects, causing irreversible delamination of the h-BN layer; this effect may be used for 2D material nanoengineering. On the relevant timescale, upd itself does not alter the defect area on repeated cycling; therefore, metal upd may find use as a general tool to determine the collective defect area in hybrids between 2D materials and various substrate metals. [ABSTRACT FROM AUTHOR]

Abstract: We report, for the first time, symmetric (versus cluster potential of zero charge) charging of narrowly dispersed monolayer-protected Au145 cluster films in a room temperature ionic liquid. Near-reversible voltammetric features are found, indicating up to nine electrochemically accessible charge states with assigned values between −4 and +5. The zero charge state has a stability range of 276mV, very similar as found in solution-phase voltammetry. All other charge states are more narrowly spaced, indicating a sudden increase in cluster capacitance. We ascribe this effect to an abrupt change in local dielectric constant on insertion of one or more counter ions, following departure from zero charge, with a possible contribution of coupled electron–ion transfer. Our findings open perspectives of potential technological importance involving nanocrystal-based device-like behaviour. [Copyright &y& Elsevier]

The inhibition effects of sodium dodecylbenzenesulphonate (SDBS) and hexamethylenetetramine (HA) on the corrosion of mild steel in sulphuric acid solution have been studied using weight loss, electrochemical impedance and Tafel polarisation measurements. For HA, a monotonous increase in inhibition efficiency is observed as a function of concentration. For SDBS, however, an optimum in the inhibition efficiency is observed for a concentration close to 250 ppm, which is ascribed to the formation of hemi-micellar aggregates that provoke inhibitor desorption from the metal/solution interface at higher concentrations. Upon mixing HA and SDBS, concentration regions showing synergistic and antagonistic inhibition behaviour are identified, and it is concluded that electrostatic interactions between adsorbate ions are likely responsible for both phenomena. Langmuir and Frumkin isotherms were tested for relevance in describing the adsorption behaviour of both HA and SDBS. [Copyright &y& Elsevier]

Two newly synthesised Schiff bases [H2A3, N,N′-ortho-phenylene(salicylaldimine-acetylacetone imine) and H2A4, N,N′-ortho-phenylene(salicylaldimine-2-hydroxy-1-naphthaldimine)] were studied as inhibitors for the corrosion of mild steel in 0.5 mol dm−3 sulphuric acid. Results of weight loss, electrochemical impedance and Tafel polarisation measurements consistently identify both compounds as good inhibitors, with efficiencies of around 95% at a concentration of 400 ppm. The inhibition is in both cases of a mixed anodic–cathodic nature. Differences in inhibition efficiency between H2A3 and H2A4 are correlated with their chemical structures. Several adsorption isotherms are assessed, and the Temkin isotherm is found to provide an accurate description of the adsorption behaviour of the investigated Schiff bases. [Copyright &y& Elsevier]

Bismuth(III) sulfide (Bi 2 S 3) is a promising cathode material for aqueous zinc ion batteries (ZIBs), yet suffers from serious capacity issues due to its poor electrical conductivity and microstructural degradations. In this work, Bi 2 S 3 anchored on reduced graphene oxide (rGO) is prepared through hydrothermal reaction and is used as cathode material for aqueous ZIBs. Raman and XPS characterizations confirmed that the oxygen bridge in Bi–O–C heterostructures is successfully created during the hydrothermal synthesis. These oxygen bridges are energy favourable in the Bi 2 S 3 /rGO composite materials and serve as the electron transfer channels for rapid charge compensation during Zn2+ incorporation/extraction. Rotating ring–disc electrode (RRDE) measurements demonstrate improved electrochemical stability of the Bi 2 S 3 /rGO composite material compared to pristine Bi 2 S 3. As a result of these improved characteristics, Bi 2 S 3 /rGO composite shows notably better rate performance and cycling stability than unsupported Bi 2 S 3. Ex-situ X-ray diffraction and XPS characterizations indicate that Zn2+ undergoes a reversible conversion reaction with Bi 2 S 3 to form ZnS/Bi0, rather than being intercalated into Bi 2 S 3 crystal interlayers. The rGO substrate forms chemical bonds with bismuth in the composite material, and the strongly anchored bismuth on the rGO through a Bi–O–C bridge enables a highly reversible conversion reaction. As a result, the Bi 2 S 3 /rGO composite with 8 wt% rGO can deliver a reversible capacity of ∼186 mAh g−1 at the current density of 500 mA g−1 after 150 cycles, showing high promise as Zn-ion battery material. [ABSTRACT FROM AUTHOR]

Abstract: We present a simple yet absolute method for the assignment of the zero charge state of metal nanoparticle films during their electrochemical charging. The method is based on measuring the current transient that accompanies the potential controlled immersion of a pristine, ion-free cluster film in an electrolyte, and does not rely on relative quantities such as mass changes of an already immersed film. Therefore, the method is impervious to details of counter ion insertion — for instance whether the electrolyte can partition into the film or not — without which no charging can be observed. Examples of positive and negative ion-limited charging are presented, and an example of ambipolar cluster charging, covering the three possible cases. The immersion method can be readily applied to other cases of coupled electron–ion transfer, as in the three-phase electrochemistry of redox droplets and thin films. [Copyright &y& Elsevier]

[Display omitted] • Two strategies for covalent attachment of MOFs to graphene are proposed. • High density of COOH groups on graphene leads to 'desert rose' MOF growth. • The 'desert rose' NiCo MOF/graphene composite is superior as OER electrocatalyst. Highly efficient and stable earth-abundant metal electrocatalysts are of great significance for improving water splitting systems and rechargeable metal–air batteries, in which the oxygen evolution reaction (OER) plays a central part. Among other strategies, anchoring metal–organic frameworks (MOFs) onto conductive materials has proven fruitful towards enhancing their OER performance. Here we explore two strategies for covalent functionalization of graphene flakes as templates for in situ growth of a bimetallic MOF (NiCo-H 2 bpydc) that is formed using 2,2′-bipyridine-5,5′-dicarboxylic acid as the organic linker, and Ni2+/ Co2+ (1:1) as the metal nodes. The graphene template modified with low density functional groups preserves the original octahedral shape of 3D NiCo-H 2 bpydc, while functionalization with high density functional groups transforms the MOF octahedra into nanoflowers with 'desert rose' morphology, leading to increased accessible active sites, electric conductivity and enlarged active surface area, thus boosting the OER performance with a small overpotential (241 mV) at 10 mA cm−2 in alkaline solution. This synthetic strategy therefore presents an efficient pathway towards controlling morphology and properties of graphene supported electrocatalytic materials with excellent OER performance. [ABSTRACT FROM AUTHOR]

The adsorption and self-assembly of several thiacarbocyanine dyes on hexagonal boron nitride (hBN) was investigated by combining steady-state spectroscopy and atomic force microscopy. The adsorption isotherms indicate that at saturation the density of the cationic TDC (5,5-dichloro-3-3′-diethyl-9-ethyl-thiacarbocyanine) molecules on hBN is similar to that of TD2 (3-3′-diethyl-9-ethyl-thiacarbocyanine) molecules, while the densities of TD0 (3-3′-diethyl-thiacarbocyanine) molecules and the zwitterionic THIATS (5,5-dichloro-3-3′-disulfopropyl-9-ethyl-thiacarbocyanine) molecules are significantly higher. The intermolecular distances between neighboring adsorbed dyes, calculated from these saturation densities indicate a flat-on adsorption for TDC, TD2 and TD0 and a partial edge-on adsorption for THIATS. AFM micrographs of the adsorbed TDC, TD0 and THIATS molecules indicate that already at low dye concentrations in the solution, where only a small fraction of the hBN surface is covered, the dye molecules already form upon adsorption to hBN aggregates of at least 10 nm, separated by areas where no adsorbed dye molecules can be detected. The resolution of the micrographs was however insufficient to show details of the packing of the adsorbed molecules. For THIATS, the thickness of the adsorbed layer is compatible with an edge-on adsorption, while for TDC and TD0, the thickness of the adsorbed layer is twice the thickness expected for flat-on adsorption. The exciton interaction extracted from the steady-state spectroscopy of the adsorbed dyes is much smaller than observed for H- or J-aggregates of the same dyes in solution or adsorbed to other surfaces such as Langmuir films or silver halides. For TDC, TD2 and TD0, the values of the exciton interaction are compatible with a close packed flat-on adsorption. Hence, optimizing the interaction between the adsorbed dye and hBN rather than between the adsorbed dye molecules governs the packing of the adsorbed dye molecules. The observation of the spectral shifts attributed to the exciton interaction at low average coverage of the hBN surface indicates that the exciton interaction already occurs at low coverage of the hBN surface. This observation is in agreement with the AFM micrographs, which show clustering of the adsorbed dye molecules already at low coverages. • TDC, TD2 and TD0 on hBN have flat-on adsorption due to optimization of dye-hBN interactions. • Exciton interaction observed already at low hBN surface coverage agrees with clustering of adsorbed dyes shown by AFM. • The packing suggested by molecular mechanics simulations is compatible with the observed exciton interaction. [ABSTRACT FROM AUTHOR]

Abstract: In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system. For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1–50μg AuL−1 in the size range from 5 to 80nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle–membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup. Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles. [Copyright &y& Elsevier]

The longevity of lithium-ion batteries is determined by the rate of chemical and electrochemical side reactions that limit their charge storage capacity. In particular, dissolution of transition metals from the cathode accelerates the blockage of Li x C 6 anodes, but few direct dissolution studies have been made to date. Although LiMn 2 O 4 (LMO) has been frequently used as a model electrode for dissolution studies, the cause and nature of dissolution and dissolution-free states are still unclear. By online inductively coupled plasma analysis, we detect dissolution from LMO electrodes in real time to reveal the role of surface versus bulk structure effects, electrode potential and degree of lithiation on Mn dissolution. We find that fully lithiated LMO, with an average Mn redox state of 3.5, readily dissolves when brought in contact with 0.2 M Li 2 SO 4 , but that on initial charging a dissolution–passivation event preceding delithiation abruptly stops further detectable dissolution, until well past fully delithiated λ-MnO 2. Dissolution reactivates on returning to the initial potential of pristine LMO, and increases exponentially in the overlithiation region. Our results provide access to much more detailed dissolution information than post-mortem battery analysis allows, enabling targeted materials screening and informing best practices in charging/discharging profiles. In particular, our data suggests that suitable potential conditioning of electrodes may mitigate dissolution, as an alternative or additional measure to the use of protective surface films or incorporation of dopants. [ABSTRACT FROM AUTHOR]