Electrodeposited Na-Birnessite on Carbon Cloth as Positive Electrode for Capacitive Deionization

Capacitive Deionization (CDI) based on traditional activated carbon (AC) electrodes faces some important intrinsic hurdles, such as the co-ion expulsion phenomenon and unwanted faradaic reactions, harming efficiency, operational stability, and electrode lifetime. The incorporation of ion-exchange membranes (IEM) in CDI, as free-standing films applied onto the electrodes, was shown to be an effective solution to improve charge efficiency and has led in fact to the commercialization of MCDI (membrane-CDI). An alternative way to improve CDI performance is the use of ion insertion materials, such as metal oxides and layered double hydroxides. In this work, we examine the performance of sodium-birnessite electrodeposited on commercial carbon cloth (CC) as the positive electrode of a flowby CDI cell, coupled to an ordinary AC / AEM stack as the negative electrode

Evaluation of Co-Ion Desorption and Faradaic Losses in Capacitive Deionization

The efficiency of Capacitive Deionization (CDI) is largely determined by the charge loss associated with two distinct parasitic processes, namely, co-ion expulsion and faradaic reactions. There is wide agreement that the first factor dominates the inefficiency of CDI; however, the evaluation of the relative incidence of co-ion repulsion on CDI inefficiency remains somewhat elusive. In this work, in the assumption of relatively small ohmic losses, we propose a simple model to quantify charge losses due to either of these processes in CDI cells, disregarding ohmic losses

Boosting the Power of Na0.44MnO2: Unlocking Its Potential for Aqueous Sodium-Ion Storage through Nanostructuring and Hybridization

We report an effective processing route, combining nanostructure formation and hybridization, to improve the rate performance of the tunnel-structure sodium manganese oxide Na0.44MnO2 (NMO) as a cathode material for aqueous sodium ion storage. We use hydrothermal synthesis to prepare an NMO/CNF (Carbon NanoFiber) hybrid, consisting of uniform oxide nanowires with an average width of 70 nm and length in the range of several tenths of µm. The highly dispersed CNFs impart high conductivity to the NMO/CNF electrode, allowing high-rate performance at a C-rate of up to 20 C, with a delivered capacity of more than half the theoretical value in a 1 M Na2SO4 electrolyte. Moreover, the NMO/CNF hybrid shows good electrochemical stability under several hundred cycles at a high C-rate. However, the NMO nanowire electrodes reveal a lower-than-expected capacity, probably as a result of the tendency of nanowires to form bundles, which prevents direct contact with conductive fibers and induce the under-utilization of active material. With this study, we demonstrate a strong improvement of the otherwise inherently low-rate performance of NMO through oxide nanostructuring and hybridization with carbon fibers, paving the way for further research on NMO-based materials for aqueous sodium ion storage

Effect of a positive sea surface temperature anomaly on a Mediterranean tornadic supercell

Extreme events represent a topic of paramount importance and a challenge for modelling investigations. Due to the need of high-resolution models, the study of severe localized convective phenomena is even more critical, especially in relation to changes in forcing factors, such as sea surface temperatures (SSTs), in future climate scenarios. Here, we analyze the effect of changes in SSTs on the intensity of a tornadic supercell in the Mediterranean through modelling investigations. We show dramatic (nonlinear) changes for updraft helicity and vertical velocity, which measure the intensity of the supercell, even for variations of SST only of¿+¿/-1¿K.Peer ReviewedPostprint (published version

Structure and Mechanical Properties of Electrodeposited Nanocrystalline Ni-Fe Alloys

Nickel-iron alloy coatings were produced by electrodeposition from an additive free electrolyte, at room temperature and current density in the range of 1 to 5 A dm–2, with Fe content up to 75 wt.%. The structure and mechanical properties of the electrodeposited alloys are reported in the present work and analysed focusing on structure-property relationships. In particular, the influence of the hydrogen evolution reaction is highlighted as a process factor affecting alloy phase structure, notably the composition limit of the γ-phase field. The variations of the mechanical properties with alloy composition are analysed in the light of the concurrent modifications in phase structure and crystal size of the alloys. In particular, an assessment of the different factors influencing the hardness of γ phase alloys is proposed. Solid solution effects contribute significantly to the strength of γ phase alloys over a wide composition range, approximately from 5 to 25%, though a complex interplay between solid solution and Hall-Petch strengthening needs to be envisaged to account for the variations in hardness with composition over this range. Moreover, it is emphasized that with decreasing grain size, the increasing level of internal stresses and decreasing stiffness engender significant softening in nanocrystalline γ phase alloys with Fe content exceeding about 25%

Tin Whiskers

Pure tin is currently the most widely employed lead-free finish for plating of component terminals despite its propensity to spontaneous whisker formation. Whiskers are filamentary crystals, conductive and mechanically strong, measuring up to a few millimetres, though the common variety observed on matt tin finish on copper substrate was hardly ever reported to exceed 0.5 mm. A positive stress gradient within the Sn layer, that is either a lowering compressive or an increasing tensile stress towards the root of a whisker, is reputed as the driving force for whisker formation. The formation of whisker is a major reliability concern for the electronic industry. Whisker related failures in electric and electronic hardware have been reported since the 1940 and the failure risk cannot be overlooked especially in modern electronic systems. Understanding the tin whisker phenomenon and further developing mitigation strategies and test methods for evaluating whisker performance are all important tasks to be fulfilled in the future

Structure and Electrokinetic Study of Nickel Electrodeposition

Electrodeposited layers of nickel show different growth characteristics depending on the composition of the electrolyte, namely the type of the anion, the presence or the absence of boric acid and the pH. These process parameters are examined in the present work in order to elucidate their influence upon the growth texture and the related surface morphology of the electrodeposits. The relationship between process and structure is investigated by studying the transient electrochemical behavior during deposition, in order to discriminate between different interface conditions corresponding to different growth modes. The observed preferred orientations can be in this way linked to different reactive species, which are assumed to be present at the surface, and to their stability. The correlation between kinetics and structure in nickel electrodeposition reported in the present work and the similar correlation found in cobalt electrodeposition suggest a rationalization of the growth modes of ECD inert metals, based on the correspondence between the transient Tafel parameter and the growth texture observed in defined conditions

Growth of carbon nanotubes on aluminium foil for supercapacitors electrodes

A new approach for the preparation of carbon nanotubes (CNTs) electrode is proposed in the present work. Multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapour deposition on aluminium strips pre-plated with a nickel thin film as the catalyst. The CNTs were characterized by scanning and transmission electron microscopy, Brunauer–Emmett–Teller surface area measurement and thermogravimetric analysis. The nickel-plated aluminium foil with a layer of CNTs was further characterized for an assessment of its electrochemical behaviour as electrode for supercapacitors. The specific capacitances of the electrode, as derived from cyclic voltammetry measurement at 0.1 V s-1 scan rate, was found to be 54 and 79 F g-1 in aqueous and organic electrolytes, respectively, in line with the highest reported values for either activated carbon or MWCNTs electrodes. Further evidence in support of the viability of the present approach for the preparation of a CNTs electrode was obtained from electrochemical impedance spectroscop