Surface or bulk?:Real-time manganese dissolution detection in a lithium-ion cathode

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 LixC6 anodes, but few direct dissolution studies have been made to date. Although LiMn2O4 (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 Li2SO4, but that on initial charging a dissolution–passivation event preceding delithiation abruptly stops further detectable dissolution, until well past fully delithiated λ-MnO2. 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

Nitrogen-carbon-encapsulated Fe3C nanoparticles as highly efficient earth-abundant oxygen reduction electrocatalysts

The design and synthesis of the highly active metal-organic framework (MOF)-based catalysts open new avenues to facilitate the kinetically unfavorable oxygen reduction reaction (ORR). In this paper, we elucidate the design and fabrication of an efficient electrocatalyst with a novel structure for the enhancement of the ORR performance by decorating the surface of the ZIF-8 precursor with ferrocene formic acid, followed by a two-step carbonization process, which is critical for the encapsulation of pyrolytic Fe3C nanoparticles (NPs) into carbon nanotubes (CNTs) and the isolation of Fe single atoms onto an N-doped carbon (NC) matrix. Moreover, the relative Fe content is vital to optimize the ORR performance of the catalysts. The resulting Fe3C@CNT/NC-M catalyst has an optimized structure. It shows great long-term stability and excellent electrocatalytic ORR performance in alkaline solution, with the half-wave potential and limiting current reaching 0.941 V and 6.31 mA cm−2, respectively. Furthermore, the electrocatalyst has a strong tolerance to and good stability in a methanol solution. The Fe3C@CNT/NC-M zinc-air battery delivers a large open-circuit potential of 1.525 V, a peak power density of 348 mW cm−2 at 420 mA cm−2, and a maximum capacity of 843 mA h gZn−1 at 10 mA cm−2. Thus, this synthetic strategy provides a promising pathway toward constructing MOF-based electrocatalytic materials with effective and stable ORR performance

Graphite and Graphene Fairy Circles:A Bottom-Up Approach for the Formation of Nanocorrals

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm 2 ) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated. © 2019 American Chemical Society

Copper underpotential deposition on boron nitride nanomesh

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. © 201

Wetting, adhesion and stiction of 2D materials

The wetting properties of surfaces, including the adhesion and stiction (static friction) of liquid drops, are critical for processing materials and post-production problems such as fouling. For the novel but very active research field of 2D materials, the interaction of liquids with one- or few-atom-thick matter and its support poses new questions in our understanding of wetting. This paper presents a brief overview of recent research in this area, highlighting differences with materials of other dimensionalities, and remaining issues. © The Electrochemical Society

Synergism and antagonism in mild steel corrosion inhibition by sodium dodecylbenzenesulphonate and hexamethylenetetramine

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. © 2003 Published by Elsevier Science Ltd

Study of interfacial film growth with ac measurements

The relevance of ac measurements for the study of developing films at solid-liquid interfaces is discussed. An electrical model is introduced, and the correspondence of each circuit element with a chemical or physical process is explained. Further details are discussed mostly by considering the spontaneous development of a solid film at a Zn/CrO3(aq) interface. It is shown that less straightforward ac behavior may be understood after modification of the general electrical model, based on supplementary information on the studied system. For the experimental system considered, the most important film growth characteristics are derived. (C) 2000 Academic Press

Electrical models for shielded electrodes

Electrical models for metal electrodes that are shielded from the electrolyte by a partially insulating layer are discussed. It is shown that the structure of the electrical model depends on the degree of adhesion between the solid phases involved. The results are then extended to systems in which two layers showing different properties coexist on the electrode surface. Wherever relevant, reference is made to experimental results and to systems that have been described in the literature. © 2000 Akadémiai Kiadó

Study of zinc passivation in chromium(VI)-containing electrolytes with short-term impedance measurements

The development of a passivating layer on zinc in an acidic chromium(VI)-containing solution is studied by measuring electrical impedance. After examining the passivated electrode in its stationary state, a method is derived to study the pre-stationary state (having, by definition, time-dependent properties). Three hypotheses concerning the layer development are introduced, and their possible relevance is examined by comparison with experimental proof or known literature data. With one of these hypotheses, accordance with all available data is obtained, thus identifying this model as possibly valid. Based upon this model, some further growth characteristics of the passivating layer are derived

Dimensional changes during corrosion of polymer-coated metals

The importance of dimensional changes in a corroding system metal/polymer films/ electrolyte is demonstrated by studying the impedance behaviour of 55%Al-Zn with a very thin polymer film coating, upon degradation in an aqueous NaCl solution. The effective polymer film thickness proves to account for the associated effects, thus allowing the interpretation of the evolution of the corroding system in terms of changes in phasial and interfacial properties