Search

Abstract Water electrolysis is the cleanest method for hydrogen production, and can be 100% green when renewable energy is used as electricity source. When the hydrogen evolution reaction (HER) is carried out in alkaline media, nickel (Ni) is a low cost catalyst and an interesting alternative to platinum. Still, its performance has to be enhanced to meet the high efficiency of the nobler metals, an objective that requires further tailoring of the surface area and morphology of Ni-based electrode materials. Unlike commercially available porous Ni, these features can be easily controlled via electrodeposition, a one-step process, taking advantage of the dynamic hydrogen bubble template (DHBT). Generally, changes in surface porosity and morphology have been mainly achieved by altering the main parameters, such as the current density or the deposition time. However, very scarce work has been done on the role of supporting electrolyte (i.e., its concentration and composition) in tailoring the foam features and consequently their catalytic activity. Hence, this approach paves the way to optimum design of metallic foam structures that can be obtained only with modifications in the electrolytic bath. In this work, 3D Ni foams are obtained from different composition baths by galvanostatic electrodeposition in the hydrogen evolution regime on stainless steel current collectors. Their porosity and morphology are analysed by optical microscopy and SEM. The electrochemical performance is evaluated by cyclic voltammetry, while catalytic activity towards HER and materials' stability in 8 M KOH are tested using polarisation curves and chronoamperometry measurements, respectively. The recorded high currents and extended stability of the Ni foams with dendritic morphology demonstrate its outstanding performance, making it an attractive cathode material for HER in highly alkaline media. Graphical abstract Image 1 Highlights • Electrolyte composition and concentration can tailor 3D Ni foam morphology. • Dendritic and rough structures improve electrochemical utilisation of material. • Presence of highly porous structure (pores) influences Tafel slope. • High pore density with dendritic morphology are desirable electrocatalyst properties. [ABSTRACT FROM AUTHOR]

Nanostructured porous MnO 2 , especially its hydrated amorphous and low crystalline form (MnO 2 · n H 2 O), has been one of the most promising material considered for charge storage applications, due to electrochemical similarities with RuO 2 and its relative low cost. However, the intrinsic poor conductivity of MnO 2 combined with the presence of structural water, which provides high ionic but low electronic conductivity, is a great hindrance for wider application. An effective approach to overcome this drawback involves the deposition of thin MnO 2 layers on porous, high surface area metallic scaffolds. The present work addresses this route and provides novel insights thanks to the combination of MnO x · n H 2 O with custom-made Ni foams, fabricated via one-step electrodeposition using the dynamic hydrogen bubble template (DHBT). The porous Ni foams provide a scaffold with a 3D architecture with optimized pore size and surface. The composite electrode was fabricated by anodic deposition of MnO x · n H 2 O on the 3D Ni foams. The electrochemical behaviour was tested in 1 M KOH, since there are very few studies addressing the electrochemical behaviour of MnO x · n H 2 O in alkaline media for electrochemical supercapacitors applications. In addition, thermal treatment (150–250 °C) was performed to evaluate the effect of hydration on the material properties. The results revealed that the as-obtained composites are highly stable, displaying much higher specific capacitances with 73–90% (depending on the mass load) capacitance retention compared to their de-hydrated counterparts. The charge-discharge processes were found to be highly reversible throughout 5000 cycles, maintaining almost 100% columbic efficiency. In conclusion, the MnO x · n H 2 O@Ni composite electrodes showed a very stable pseudocapacitive behaviour and exceptional cycling performance in 1 M KOH, being therefore a promising alternative charge storage electrode for electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

Direct borohydride fuel cells, which use sodium borohydride as the fuel, are recently focussing on the use of hydrogen peroxide as oxidant instead of the traditional oxygen gas. Herein we study the electrocatalytic activity of nanostructured 3D Cu-M (M = Fe, Co, Ni) and single metal Ni and Co foams for hydrogen peroxide reduction reaction (HPRR) in alkaline media. The electrode materials are prepared by galvanostatic electrodeposition and their morphology, composition and crystallographic structure are characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The electrochemical characterisation is performed by voltammetry and chronoamperometry measurements, where it is concluded that Cu–Fe and Cu–Ni foams exhibit good catalytic activity for HPRR with a number of electrons transferred during the reaction close to 1. [ABSTRACT FROM AUTHOR]

In this work, α-Co(OH) 2 is electrodeposited onto carbon nanofoam forming a composite electrode operating in a potential window of 2 V in aqueous medium. Prior to electrodeposition, the carbon nanofoam substrate is subjected to a functionalization process, which leads to an increase of about 40% in its specific capacitance value. Formation of cobalt hydroxide clusters onto the functionalized carbon nanofoam by pulse electrodeposition further enhances the specific capacitance of the electrode. The combination of these factors with an enlarged working potential window, results in a material with specific capacitance close to 300 F g −1 at current density of 1 A g −1 , considering the total mass loading of the composite. This suggests the potential application of the prepared composites in high energy density electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

A 70Co–30Ni dendritic alloy was produced on stainless steel by pulse electrodeposition in the cathodic domain, and oxidized by potential cycling. X-ray diffraction (XRD) identified the presence of two phases and scanning electron microscopy (SEM) evidenced an open 3D highly branched dendritic morphology. After potential cycling in 1 M KOH, SEM and X-ray photoelectron spectroscopy (XPS) revealed, respectively, the presence of thin nanoplates, composed of Co and Ni oxi-hydroxides and hydroxides over the original dendritic film. Cyclic voltammetry tests showd the presence of redox peaks assigned to the oxidation and reduction of Ni and Co centres in the surface film. Charge/discharge measurements revealed capacity values of 121 mAh g −1 at 1 mA cm −2 . The capacity retention under 8000 cycles was above 70%, stating the good reversibility of these redox materials and its suitability to be used as charge storage electrodes. Electrochemical impedance spectroscopy (EIS) spectra, taken under different applied bias, showed that the capacitance increased when the electrode was fully oxidized and decreased when the electrode was reduced, reflecting different states-of-charge of the electrode. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical behaviour of trivalent chromium (Cr3+) in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4] ionic liquid solutions was studied by cyclic voltammetry and chronoamperometry. The reduction of Cr3+ occurs in two steps, Cr3+ to Cr2+ and Cr2+ to Cr0, respectively. The first step is quasi-reversible with a diffusion coefficient of Cr3+ in solution of 3.13×10−8 cm2 s−1 at 303K and 25.8×10−8 cm2 s−1 at 358K, estimated from cyclic voltammetry data. Black chromium films were electrodeposited on copper, stainless steel and carbon steel substrates at a constant potential of −1.5V vs Pt quasi-reference electrode. The films consist of aggregates of nanosized particles. The coatings in the as-deposited condition present an amorphous structure but after annealing for 4h, a nanocrystalline Cr2O3 phase is formed, with an average crystallite size of 17nm. [Copyright &y& Elsevier]

Abstract: The electrodeposition of gold from a HAuCl4.3H2O solution in 1-butyl-1-methyl-pyrrolidinium dicyanamide is reported in the present paper. A cyclic voltammetry study of the electrochemical behaviour of the plating solution showed that the reduction of gold occurs by a two-step process. Gold thin films were obtained by electrodeposition on nickel substrates under potentiostatic control at a constant potential of −1V, for temperatures from 293 to 353K and deposition times of 1500 and 4500s. The films prepared at 293 and 333K consist of 9–15nm diameter polyhedral particles aggregated in clusters 50–250nm in diameter. The films deposited at 353K consist of a quasi-continuous film of nanoparticles covered by nanosized dendrites. This morphology evolves towards a globular structure with increasing deposition time. [Copyright &y& Elsevier]