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Pd-based materials are attracting much interest as electrocatalysts in alkaline DAFC, due to intrinsic high activity and good stability of Pd in alcohol electro-oxidation. Many articles propose anodes consisting of finely dispersed Pd and Pd-alloy particles supported on nanostructured carbonaceous materials to obtain high Pd area and low noble metal content, thereby ensuring high mass activity and low cost. Few cases are reported of Pd-Ni alloy anodes obtained by electrodeposition. It is shown that alloying with Ni may warrant the catalyst stability in an alkaline environment, but the relation between composition and performances has received limited attention. In this contribution, we present the preparation of several compact and porous Pd-Ni anodes, either homogeneous or heterogeneus, and their application to ethanol oxidation in alkaline media. Different morphologies and structures (obtained by several routes) are compared. The dimensionless parameter fr,Pd is defined as the ratio between the estimated areas APd and Ageom, the former being measured by PdO reduction charge (for each sample) in CV experiments in alkali, and the latter by the PdO reduction charge for 1cm2 of mirror-flat Pd. This fr,Pd parameter expresses the equivalent Pd surface per unit area, reducing to a traditional roughness factor fr for pure Pd samples. Oxidation peak currents jp, recorded in anodic part of CV of ethanol oxidation, are plotted against the respective fr,Pd values. All the considered Pd-Ni samples show, despite different morphologies and compositions, an electrode activity proportional to fr,Pd, namely to the Pd surface exposed to the electrolyte. This finding indicates that only the exposed Pd surface sustains the catalytic activity, whereas Ni atoms present both in the substrate and admixtures are essentially inert.

Bimetallic alloys are attracting much interest for the production of efficient and cheap materials, applicable to many areas. In this context, Ag-Ni alloys are promising for applications in electric/magnetic devices and (electro)catalysis [1]. Ag and Ni have both face-centered cubic (fcc) structure, however due to large difference in atomic radii, they do not exhibit solubility at equilibrium in the solid state. Electrodeposition may generate materials of structure or composition far from thermodynamic equilibrium, made stable by their (very) slow rearrangement at room temperature [2]. However, the deposition of Ag-Ni films is complicated by a fairly large difference in standard reduction potentials, respectively 0.799 V for Ag and -0.25 V for Ni (vs NHE). Cyanide baths were used in the past to deposit Ag and Ag-based alloys, for their strong complexing action of Ag+ ions, leading to deposition of compact films, but nowadays less dangerous solutions are preferred, both for safety and environmental concerns. Ag-Ni thin films were already electrodeposited from baths containing thiourea as complexing agent, obtaining quite compact films but also undesired sulfur inclusions up to 20% [3]. We propose here the electrodeposition of Ag-Ni alloys from concentrated chloride baths, already used in the past for deposition of Ag-Pt and Ag-Pd alloys [4]. Concentrated chloride media may dissolve various metal ions and, in the specific case, the Ag-chloride complexes [Ag(Cl)n](1-n)- are more stable than the Ni ones, bringing closer the reduction potentials and promoting co-electrodeposition. Linear sweep voltammetries of Ag-Ni electrodeposition performed in 10 M chloride baths indicate that alloy formation occurs under transport-limited reduction of silver complexes, so that films of desired composition may be obtained by regulating the deposition current jdep. The obtained films have good compactness, with globular morphology (Fig.1, left); moreover, microanalysis indicates that they are free from foreign species. XRD spectra indicate the presence of two crystalline phases, one Ag- rich and the other Ni-rich (only for Ni >50 at%) with minimal inclusions (few atoms %) of the minority species. Tests of nitrate reduction, based on linear sweep voltammetries (Fig. 1, right) and constant potential electrolyses, were performed on an alloy of approximate composition Ag30Ni70, with a significant yet limited Ag content. The main observations from these tests are: a) lower overvoltages for nitrate reduction with respect to pure Ni; b) marked increase of reduction current with respect to both Ag and Ni, in a broad potential region; c) better selectivity to NH3 production and lower H2 evolution.

Ag-Ni alloys or bimetallic structures are arising much interest in the search for efficient and cheap materials in many applications, from electrical devices to (electro)catalysis [1]. Ag and Ni crystallize both in the fcc structure, but are immiscible in the solid state at equilibrium. Electrodeposition of Ag-Ni is complicated by the large difference in redox potentials (E0 = 0.799 V and E0 = -0.25 V for Ag and Ni, resp.), leading to formation of porous deposits in the absence of suitable additives [2]. Deposition baths should provide a complexation of Ag ions shifting closer the two reduction processes. Cyanide baths work well for the deposition of Ag alloys [3], but pose a severe safety hazard. Fairly good results are obtained using thiourea baths, but the obtained layers include up to 20 at% of sulfur [2]. The use of concentrated chloride baths as an alternative to cyanide for the deposition of Ag-Pt and Ag-Pd alloys is well established [3]. The basis of these approaches is that silver and several other metal ions form complexes in concentrated halide media and may be dissolved in suitable concentrations. To the best of our knowledge, deposition of Ag-Ni alloys from this medium has not been reported. The approach appears promising since chloride complexes with Ag ions are more stable than those with Ni ions, promoting co-deposition. Linear sweep voltammetries (LSVs) in the concentrated chloride medium (Fig. 1a) show a short diffusion plateau of Ag deposition, and a subsequent plateau of Ag-Ni deposition preceding H2 evolution. Galvanostatic depositions produce compact Ag-Ni layers with globular microscopic morphology (Fig. 1b). Formation of metastable solid solutions is investigated. The achievement of this approach is the deposition of compact, sulfur-free Ag-Ni layers [2], from a "green" aqueous bath devoid of toxic species like thiourea or cyanide.

Porous electroactive oxides are potentially interesting materials for electrochemical applications, e.g. as electrocatalysts, intercalation materials and supercapacitors. Our group has recently proposed the oxygen bubble templated anodic deposition as a route to achieve PbO2 layers with void fractions up to 0.7 .....

The Ag-Rh system is characterized by the presence of a large miscibility gap, especially by a total insolubility of Rh in Ag in the solid state. Nonetheless, the preparation of Ag-Rh nanoparticles by the polyol method has been recently reported [1]. We explore here the possibility to obtain a metastable Ag50Rh50 alloy by electrodeposition, in analogy to Cu-Rh alloys...

to investigate porous Cu-Zn alloys, in the range of Zn-rich compositions, made via electrodeposition using the Dynamic Hydrogen Bubble Template (DHBT) method....

Si descrivono vari metodi di preparazione di materiali elettrodici per la riduzione degli ioni nitrato, inquinanti delle acque di superficie. Mediante elettrodeposizione si ottengono leghe compatte o porose con proprietà superiori a quelle dei metalli componenti.Tramite deposizione spontanea di metalli nobili su schiume metalliche si producono elettrocatalizzatori compositi tridimensionali.

Les électrodes macroporeuses suscitent un intérêt croissant pour les traitements d'effluents industriels, grâce à leurs caractéristiques de grande surface active et de transport facile de matière dans les pores. Une méthode de préparation est le dépôt cathodique dans un régime de courant élevé avec évolution de bulles d'hydrogène qui agissent comme un template dynamique; la préparation de telles électrodes de Cu est bien établie dans la littérature (1). Nous avons montré récemment les avantages des alliages CuNi riches en Cu, par exemple Cu80Ni20, par rapport à Cu ou Ni purs, dans la réduction de nitrates en milieu alcalin (2). Dans cette communication nous présentons une méthode de dépôt cathodique d' alliages poreux CuNi à partir d' une solution citrique, qui nous a permis d'obtenir des matériaux avec un large spectre de compositions et une morphologie (image MEB dessus) caractérisée par des macropores de 15-30 ?m de taille et une porosité fine, à l'échelle des quelques centaines de nm. L'application des électrodes poreuses à la réduction de nitrate 0.1 M dans une solution de NaOH 1.0 M montre (voltampérometrie à gauche obtenue avec une EDT) une nette augmentation du courant de pic face aux électrodes lisses de même composition. Le produit de réaction principale est toujours NH3.

Cu and Ni have the same crystal structure (face-centred cubic), similar valence, close values of atomic radii and electronegativity, and may form homogeneous solutions over the entire composition range. Given the potential advantages of a CuNi alloy in electrocatalytic applications - the components are common, cheap, relatively low toxicity metals - it appears interesting to electrodeposit alloys of different composition and morphology and test them in the reduction of nitrate for which the single metals display interesting performances. We have deposited CuNi alloys from citrate baths of suitable compositions, using: potentiostatic control and low current densities to obtain compact deposits (right figure, top); galvanostatic control and large current densities, ca. 3 A cm-2, to obtain macroporous electrodes (right figure, bottom) under a regime of vigorous H2 evolution in which the bubbles acted like a dynamic template. In comparison with similar Cu (and Ni) electrodes, compact Cu-rich alloys show superior performances in the reduction of nitrate - larger efficiency, better stability and higher selectivity towards NH3 production - at moderately negative electrode potentials [1]. Experiments performed in solutions of 0.1 M NaNO3 in 1.0 M NaOH, recorded at smooth and porous Cu80Ni20 electrodes (left figure), show a remarkably higher reduction current in the latter case, due to the larger active surface area and easy transport in the macropores.

The cathodic reduction of nitrate is a process actively investigated for the fundamental interest in its reaction mechanism and the practical challenge of environmental remediation. Among the electrode materials, the Cu-Ni alloy has received limited attention despite the good catalytic performances of copper, nickel and several of their alloys with other metals [1]. We have performed deposition of Cu-Ni alloys of different composition from a citrate bath [2] and tested their performances in the electroreduction of nitrate and nitrite in alkaline solution. Voltammetric experiments performed at RDE (900 rpm) in a solution of 10 mM NaNO3 and 1.0 M NaOH (Figure) show that on Cu-Ni alloys (especially for Cu = 70-95 at%) the nitrate reduction starts at less negative potentials than on Cu. Chrono-amperometries show that upon polarisation the current decays in time comparatively less on copper-rich alloys than on copper. The alloy has been deposited on different substrates including a commercial Ni foam (Incofoam®), a chemically stable, large surface substrate (specific surface area > 200 cm2 for 1 cm3 volume of Ni foam) with a porosity in the range of hundreds of ?m. Results of electrolyses at Cu-Ni modified Incofoam® electrodes are discussed and compared with those obtained at copper electrodes, as a function of the applied potential and the other operating parameters.

Porous Ni electrodes were modified by electrodeposition of Ir nuclei fromH2IrCl6 solutions at 70°C, with the aim of activating them towards the hydrogen evolution reaction and comparing their performance with those of porous Ni electrodes activated by spontaneous deposition of noble metals (Ir and Ru). The current efficiency of Ir deposition was found to be very low (1% or lower, decreasing upon increasing deposition current density). Ir deposits characterised by SEM-EDX and XRD consisted of nanocrystals decorating the Ni dendrites forming the porous layers. Ir electrodeposition led to a strong activation of the hydrogen evolution reaction from aqueous 1 M NaOH. The electrocatalytic activity of the cathodes was independent of the Ir deposition charge above the minimum explored value of 1 Ccm-2. This charge is estimated to correspond to the deposition of ca. 2.5 10-8 Ir moles cm-2. The kinetic parameters for hydrogen evolution were similar for porous Ni electrodes modified by either spontaneous deposition (studied in a previous work) or electrodeposition of Ir.

The modern interest for phenomena at the semiconductor-electrolyte interface dates back to experiments performed in the 1950s with germanium, and has extended to most semiconducting materials for reasons of fundamental knowledge or potential application, going from semiconductor processing technology to heterogeneous photocatalysis to sensors. The subject is highly interdisciplinary and involves fields like electrochemistry, solid-state physics, and surface science. The aim of this article is to provide a concise survey of the basic concepts involved in the formation and operation of a semiconductor-electrolyte junction, both in the dark and under illumination. In most cases, terminologies and symbols recommended by IUPAC are used. Some important equations are reported but not derived.

Various strategies for the activation of porous Ni electrodes towards the hydrogen evolution reaction are compared. Porous Ni electrodes can be obtained by electrodeposition, at large cathodic current densities, from NiCl2 + NH4Cl solutions. Two main routes for the activation of these electrodes, respectively involving one or two preparation steps, were explored: (i) co-deposition of Ni and noble metal oxide particles and (ii) deposition of noble metal nuclei onto the pre-formed porous Ni layers. Porous Ni+RuO2 composites were obtained by electrolyzing suspensions of RuO2 in the NiCl2 + NH4Cl electrolyte. The co-deposition of RuO2 particles somewhat depressed the current efficiency of Ni deposition, but did not prevent the formation of deposits with a large surface roughness. The preparation of Ni+IrO2 composites was significantly more difficult at the high current densities required to promote the formation of porous Ni. Spontaneous deposition of either Ru or Ir onto porous Ni was achieved by immersion of the Ni deposits in deaerated solutions containing Ru(III) or Ir(IV) chloride complexes. Noble metal deposition and Ni dissolution occurred simultaneously, at open circuit, causing a further increase in the initial large area of the Ni deposits. The spontaneous deposition of Ru was faster than that of Ir. The preparation time of Ir-modified electrodes could be shortened by electrodepositing the noble metal nuclei. Both routes led to active cathodes for hydrogen evolution, mainly studied in basic solution. Typical kinetic parameters were: exchange current density around 10 mA cm-2 and Tafel slope in the range 40 to 50 mV. The best stability, both under hydrogen evolution conditions and upon polarity inversion, was shown by the porous Ni+RuO2 composites.