Towards the development of safe and commercially viable nickel–iron batteries: improvements to Coulombic efficiency at high iron sulphide electrode formulations

NiFe batteries are emerging as an important energy storage technology but suffer from a hydrogen-producing side reaction which has safety implications and reduces coulombic efficiency. This manuscript describes a systematic improvement approach for the production of Fe/FeS-based anodes at high concentrations of iron sulphide. Electrodes were made by mixing varying amounts of iron sulphide in such a way that its concentration ranges from between 50 and 100 % (compositions expressed on a PTFE-free basis). Electrode performance was evaluated by cycling our in-house-produced anodes against commercially available nickel electrodes. The results show that anodes produced with larger concentrations outperform their lower concentration counterparts in terms of coulombic efficiency although a slight decrease in the overall cell performance was found when using pure FeS anodes. At high FeS concentrations a hydrogen-producing side reaction has been virtually eliminated resulting in coulombic efficiencies of over 95 %. This has important implications for the safety and commercial development of NiFe batteries

Helmholtz bright and boundary solitons

We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart

Helmholtz solitons in optical materials with a dual power-law refractive index

A nonlinear Helmholtz equation is proposed for modelling scalar optical beams in uniform planar waveguides whose refractive index exhibits a purely-focusing dual powerlaw dependence on the electric field amplitude. Two families of exact analytical solitons, describing forward- and backward-propagating beams, are derived. These solutions are physically and mathematically distinct from those recently discovered for related nonlinearities. The geometry of the new solitons is examined, conservation laws are reported, and classic paraxial predictions are recovered in a simultaneous multiple limit. Conventional semi-analytical techniques assist in studying the stability of these nonparaxial solitons, whose propagation properties are investigated through extensive simulations

Korteweg-de Vries description of Helmholtz-Kerr dark solitons

A wide variety of different physical systems can be described by a relatively small set of universal equations. For example, small-amplitude nonlinear Schrödinger dark solitons can be described by a Korteweg-de Vries (KdV) equation. Reductive perturbation theory, based on linear boosts and Gallilean transformations, is often employed to establish connections to and between such universal equations. Here, a novel analytical approach reveals that the evolution of small-amplitude Helmholtz–Kerr dark solitons is also governed by a KdV equation. This broadens the class of nonlinear systems that are known to possess KdV soliton solutions, and provides a framework for perturbative analyses when propagation angles are not negligibly small. The derivation of this KdV equation involves an element that appears new to weakly nonlinear analyses, since transformations are required to preserve the rotational symmetry inherent to Helmholtz-type equations

Bistable Helmholtz bright solitons in saturable materials

We present, to the best of our knowledge, the first exact analytical solitons of a nonlinear Helmholtz equation with a saturable refractive-index model. These new two-dimensional spatial solitons have a bistable characteristic in some parameter regimes, and they capture oblique (arbitrary-angle) beam propagation in both the forward and backward directions. New conservation laws are reported, and the classic paraxial solution is recovered in an appropriate multiple limit. Analysis and simulations examine the stability of both solution branches, and stationary Helmholtz solitons are found to emerge from a range of perturbed input beams

Intelligent copolymers based on poly (N-isopropylacrylamide) PNIPAm with potential use in biomedical applications. Part i: PNIPAm functionalization with 3-butenoic acid and piperazine

The synthesis and characterization of the thermosensitive copolymers based on Poly (N-Isopropylacrylamide) (PNIPAm) and 3-butenoic acid and functionalized with piperazine was carried out. The free radical polymerization of the PNIPA copolymer with 3-butenoic acid was performed under microwave radiation. After obtaining this copolymer, the carboxyl groups present in the copolymer chain were activated with 1-ethyl- (3-3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide, improving its reactivity to incorporate the piperazine through its amino group. The characterization consisted: differential scanning calorimetric and ultraviolet-visible spectrophotometry to determine the LCST phase transition temperature, ranging from (30-35)°C. Structurally it was analyzed by infrared spectroscopy. A morphological analysis was performed using scanning electron microscopy, after simulating an injectable process, with the objective to observe internally the porosity and interconnectivity. The biocompatibility was evaluated through hemocompatibility tests and it was observed that the copolymers obtained were not cytotoxic. In base of the results, the chemical structure of these new copolymers confers a functionality that allows them to serve as nuclei to graft other molecules, such as polysaccharides. Then, the results obtained on the LCST temperature, porosity, interconnected pore network morphology, the ability to be injectable and the biocompatible nature of these copolymers are indicative that these new synthetic biomaterials have the potential to be used in biomedical, pharmacological and for tissue engineering. Also, once their biocompatibility was demonstrate, they may serve to generate interesting compounds having chemical anchor points for the possible addition of polysaccharides using insertion reactions, thereby generating graft copolymers with potential use in biomedical applications

Wave envelopes with second-order spatiotemporal dispersion : I. Bright Kerr solitons and cnoidal waves

We propose a simple scalar model for describing pulse phenomena beyond the conventional slowly-varying envelope approximation. The generic governing equation has a cubic nonlinearity and we focus here mainly on contexts involving anomalous group-velocity dispersion. Pulse propagation turns out to be a problem firmly rooted in frames-of-reference considerations. The transformation properties of the new model and its space-time structure are explored in detail. Two distinct representations of exact analytical solitons and their associated conservation laws (in both integral and algebraic forms) are presented, and a range of new predictions is made. We also report cnoidal waves of the governing nonlinear equation. Crucially, conventional pulse theory is shown to emerge as a limit of the more general formulation. Extensive simulations examine the role of the new solitons as robust attractors

Wave envelopes with second-order spatiotemporal dispersion: II. Modulational instabilities and dark Kerr solitons

A simple scalar model for describing spatiotemporal dispersion of pulses, beyond the classic “slowly-varying envelopes + Galilean boost” approach, is studied. The governing equation has a cubic nonlinearity and we focus here mainly on contexts with normal group-velocity dispersion. A complete analysis of continuous waves is reported, including their dispersion relations and modulational instability characteristics. We also present a detailed derivation of exact analytical dark solitons, obtained by combining direct-integration methods with geometrical transformations. Classic results from conventional pulse theory are recovered as-ymptotically from the spatiotemporal formulation. Numerical simulations test new theoretical predictions for modulational instability, and examine the robustness of spatiotemporal dark solitons against perturbations to their local pulse shape

Effect of polycrystallinity on the optical properties of highly oriented ZnO grown by pulsed laser deposition

We report the results of photoluminescence and reflectance measurements on highly c-axis oriented polycrystalline ZnO grown by pulsed laser deposition. The samples measured were grown under identical conditions and were annealed in-situ at various temperatures for 10-15 min. The band-edge photoluminescence spectra of the material altered considerably with an increase in grain size, with increased free exciton emission and observable excitonic structure in the reflectance spectra. The green band emission also increased with increasing grain size. A deformation potential analysis of the effect of strain on the exciton energy positions of the A- and B-excitons demonstrated that the experimental exciton energies could not be explained solely in terms of sample strain. We propose that electric fields in the samples due to charge trapping at grain boundaries are responsible for the additional perturbation of the excitons. This interpretation is supported by theoretical estimates of the exciton energy perturbation due to electric fields. The behaviour of the green band in the samples provides additional evidence in favour of our model