Electrocrystallization of Bi on Au(1 1 1) in an acidic chloroaluminate ionic liquid

The electrodeposition of Bi on Au(1 1 1) in an acidic chloroaluminate ionic liquid has been investigated by cyclic voltammetry and in situ STM. Two different UPD processes of Bi have been observed at 1.2 and 0.9 V versus Al/Al(III). Multiple domain structures are found for the first UPD, whereas a uniaxially commensurate monolayer is formed for the second one. More interestingly, high-resolution STM images reveal some meta-stable intermediate superstructure reported here for the first time. The co-adsorption of AlCl₄⁻ and Bi adatoms is clearly demonstrated. In the OPD region, different morphologies of Bi crystals have been obtained: a needle-like structure when the potential is swept continuously to 0.6 V, and ultrathin films of Bi when the potential is jumped from 1.3 to 0.4 V.     

Electrochemical aspects of black chromium electrodeposition from 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

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 303 K and 25.8 × 10⁻⁸ cm² s⁻¹ at 358 K, estimated from cyclic voltammetry data.Black chromium films were electrodeposited on copper, stainless steel and carbon steel substrates at a constant potential of −1.5 V 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 4 h, a nanocrystalline Cr₂O₃ phase is formed, with an average crystallite size of 17 nm.     

In situ STM study of underpotential deposition of bismuth on Au(1 1 0) in perchloric acid solution

The underpotential deposition (UPD) of Bi on Au(1 1 0) was investigated in HClO₄ solution using in situ scanning tunneling microscopy. The UPD of Bi occurred in three steps. A structure, in which Bi atoms formed dimers, was found for the first UPD adlayer. A (1 × 1) image was obtained by STM at the second UPD peak. For the third UPD peak, Bi atoms formed an incommensurate adlayer, and stripes of Bi were observed on terraces. After the third UPD, a structural reconstruction caused by adsorbed Bi was observed.     

In situ STM studies of Ga electrodeposition from GaCl3 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

In the present paper the electrodeposition of Ga on Au(1 1 1) from 0.5 mol L⁻¹ GaCl₃ in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, has been investigated by in situ scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The CV shows two redox processes: the one at −0.3 V vs. Pt is attributed to a Ga deposition on a Ga layer formed during an electroless deposition process at OCP and/or to the formation of a Au–Ga alloy; the other one at −0.9 V is due to the bulk deposition of Ga. The XPS measurement reveals that there is an oxide layer on the top of the gallium electrodeposit due to exposure to air. In situ STM measurements show that the first layer of the Ga deposit consists of islands of 10–30 nm in width and several nanometers in height surprisingly the result of an electroless deposition at the OCP. If the electrode potential is further reduced the bulk deposition of Ga sets in.     

In situ STM and EQCM studies of tantalum electrodeposition from TaF5 in the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide

The electroreduction of 0.5 M TaF₅ on Au(1 1 1) and on polycrystalline gold substrates was investigated at room temperature in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, by cyclic voltammetry, in situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM). The electrochemical reduction of TaF₅ in the employed ionic liquid occurs in several steps. The first redox process is attributed to the reduction of TaF₅ to TaF₃, which likely occurs in the solution, as EQCM indicates no mass change. The electrodeposition of tantalum occurs only in a very narrow potential window and is preceded by the formation of various non-stoichiometric tantalum subhalides. Attempts to deposit micrometer thick tantalum layers at room temperature fail, presumably because of kinetic reasons.     

Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Investigation of the peel behavior of polyethylene/polybutene-1 peel films using in situ peel tests with environmental scanning electron microscopy

The micro-deformation processes of sealed low-density polyethylene/isotactic polybutene-1 (PE-LD/iPB-1) films with different contents of iPB-1 up to 20 m.-% (mass-percentage) were investigated in this study.The peel process was analyzed in detail using in situ peel test measurements with environmental scanning electron microscopy (ESEM). This method enables the direct correlation of recorded force-elongation data with observed structural phenomena. Thus, important parameters, e.g., the peel initiation value, could be determined directly from in situ measurements. The dependence of the peel properties on the iPB-1 content was analyzed and the correlation between micro-structure and performance of the peel process was clarified.Furthermore, the structural reason behind the dependence of the peel properties on the peel angle was identified. The crack propagation types interlaminar and translaminar were analyzed in detail with the ESEM. The translaminar crack propagation was further characterized using a tilted microscope stage with a mounted tensile tester.The direct contact of the electron beam with the non-conductive sample surface can cause beam damage. The beam damage, indicated by the absorbancy band at 965 cm⁻¹ in the infrared spectrum, was investigated in dependence on the total irradiation time.     

Electrochemical growth and dissolution of Ni on bimetallic Pd/Au(1 1 1) substrates

In this work we study the electrochemical growth and dissolution of a Ni on Pd-Au(1 1 1) bimetallic surfaces using in situ scanning tunnelling microscopy. We also compare Ni deposition on monometallic electrodes, i.e. Au(1 1 1) and Pd(1ML)/Au(1 1 1), using electrochemical characterizations. Results evidence that the first Ni monolayer grows preferentially on Au(1 1 1) in a wide potential range, and that a full Ni monolayer covering the entire Pd-Au surface can be selectively dissolved from Pd islands. No such selectivity is observed upon growth of subsequent Ni atomic planes. We demonstrate that the Ni-substrate interactions play a key role in the above mentioned selectivity. The binding energy of Ni to Pd is found to be 80 meV smaller than of Ni to Au. The sign and the amplitude of this difference are discussed in light of the d band filling of the Pd-Au(1 1 1) bimetallic surface and the presence of adsorbed H on Pd before deposition.     

Alloy formation during the electrochemical growth of a Ag-Cd ultrathin film on Au(1 1 1)

The electrodeposition of a Ag/Cd ultrathin film on a Au(1 1 1) surface and the formation of a surface alloy during this process have been studied using classical electrochemical techniques and in situ Scanning Tunneling Microscopy (STM). The films were obtained from separate electrolytes containing Ag⁺ or Cd²⁺ ions and from a multicomponent solution containing both ions. First, the polarization conditions were adjusted in order to form a Ag film by overpotential deposition. Afterwards, a Cd monolayer was formed onto this Au(1 1 1)/Ag modified surface by underpotential deposition. The voltammetric behavior of the Cd UPD and the in situ STM images indicated that the ultrathin Ag films were uniformly deposited and epitaxially oriented with respect to the Au(1 1 1) surface. Long time polarization experiments showed that a significant Ag-Cd surface alloying accompanied the formation of the Cd monolayer on the Au(1 1 1)/Ag modified surface, independent of the Ag film thickness. In the case of an extremely thin Ag layer (1 Ag ML) the STM images and long time polarization experiments revealed a solid state diffusion process of Cd, Ag, and Au atoms which can be responsible for the formation of different Ag-Cd or Au-Ag-Cd alloy phases.     

A study of iodine adlayers on polycrystalline gold electrodes by in situ electrochemical Rutherford backscattering (ECRBS)

Iodine adsorption on a polycrystalline gold electrode was studied by in situ electrochemical Rutherford backscattering (ECRBS) using an ultrahigh vacuum (UHV)-electrochemical cell comprising of a thin-film silicon nitride window. The depth resolution of RBS allowed for measurement of nuclide concentration of the diffuse double-layer, electrode surface and near-surface regions. ECRBS measurements on the gold electrode, initially exposed to −500 mV vs. a platinum pseudo-reference electrode, in a potassium iodide solution, showed an increase in the 2.07 MeV iodine peak indicative of iodine adsorption. The surface concentration of the iodine adlayer was directly measured by ECRBS to be 1.3 ± 0.3 nmol/cm². ECRBS measurements on a gold electrode exposed to 1.5 V vs. a platinum pseudo-reference electrode, in a potassium iodide solution display a decrease in the 2.16 MeV gold peak and a shift to lower energies. Scanning electron microscopy images of electrodes studied by ECRBS displayed roughened surfaces consistent with gold dissolution. This work demonstrates the potential for in situ ECRBS using thin-film silicon nitride windows to become a powerful tool for the investigation of a wide range of electrochemical processes in areas such as corrosion, electrodeposition and electrocatalysis.     

An in situ Raman study of the intercalation of supercapacitor-type electrolyte into microcrystalline graphite

An initial Raman study on the effects of intercalation for aprotic electrolyte-based electrochemical double-layer capacitors (EDLCs) is reported. In situ Raman microscopy is employed in the study of the electrochemical intercalation of tetraethylammonium (Et₄N⁺) and tetrafluoroborate (BF₄⁻) into and out of microcrystalline graphite. During cyclic voltammetry experiments, the insertion of Et₄N⁺ into graphite for the negative electrode occurs at an onset potential of +1.0 V versus Li/Li⁺. For the positive electrode, BF₄⁻ was shown to intercalate above +4.3 V versus Li/Li⁺. The characteristic G-band doublet peak (E_2g2(i) (1578 cm⁻¹) and E_2g2(b) (1600 cm⁻¹)) showed that various staged compounds were formed in both cases and the return of the single G-band (1578 cm⁻¹) demonstrates that intercalation was fully reversible. The disappearance of the D-band (1329 cm⁻¹) in intercalated graphite is also noted and when the intercalant is removed a more intense D-band reappears, indicating possible lattice damage. For cation intercalation, such irreversible changes of the graphite structure are confirmed by scanning electron microscopy (SEM).     

Behaviour of highly crystalline graphitic materials in lithium-ion cells with propylene carbonate containing electrolytes: An in situ Raman and SEM study

The microcrystalline flaked graphites SFG6 and SFG44 were evaluated with regard to their compatibility with propylene carbonate (PC) by in situ Raman microscopy and postmortem scanning electron microscopy (SEM) study. PC is employed as electrolyte component in lithium-ion batteries. However, when used with certain types of graphitic materials, exfoliation occurs. To compare the effects of exfoliation, the first lithium insertion properties of these graphitic materials were measured with in situ Raman microscopy. Lithium half-cells containing either 1 M LiClO₄ 1:1 (w/w) ethylene carbonate (EC):dimethyl carbonate (DMC) or 1:1 (w/w) EC:PC were investigated. The commencement of the exfoliation process was detected in SFG44 EC:PC by the appearance of a shoulder band at 1597 cm⁻¹ on the G-band (1584 cm⁻¹) below 0.9 V versus Li/Li⁺. The band (assigned as the exfoliation or E-band) at higher wavenumbers (1597 cm⁻¹) corresponded to solvated lithium ions intercalated into graphite. The in situ Raman spectra of SFG6 in EC:DMC or EC:PC and SFG44 in EC:DMC did not show the E-band and instead displayed regular lithium intercalation spectra.In situ Raman microscopy and SEM were further employed to study the exfoliation process observed for SFG44 in 1:1 (w/w) EC:PC, when the potential was held under steady-state conditions at 0.8, 0.6 and 0.3 V, respectively. A blue-shift in the E-band from 1597 to 1607 cm⁻¹ was observed as the potential was lowered. SEM images showed dissimilar degrees of exfoliation at these three potentials.     

In situ FTIR study of the decomposition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ionic liquid during cathodic polarization of lithium and graphite electrodes

In this work we analyzed the cathodic reactions of an important ionic liquid (IL) based electrolyte solution, namely lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/N-methyl-N-methylpyrrolidinium (BMP) TFSI. In situ FTIR spectroscopy was used for the analysis of gaseous products of the electrochemical decomposition of this IL solution during cathodic polarization of lithium metal and graphite electrodes. The main volatile product of the reductive decomposition of the anion in these BMPTFSI solutions is trifluoromethane. BMP cations decompose to mixtures of tertiary amines and hydrocarbons. The composition of the products is influenced by the nature of the anode material. Graphite possesses a catalytic activity in the electroreduction process of BMP cations which occurs along with their intercalation into the graphite structure. The liquid phase after cathodic polarization of graphite electrodes was analyzed by multinuclear NMR spectroscopy coupled with FTIR spectroscopy. ¹⁵N NMR and FTIR spectra revealed an increase in the Li cations content in the electrolyte solution, as a result of BMP cations decomposition during repeated cycling of graphite electrodes.     

Adsorption of camphor and 2,2′-bipyridine on Bi(1 1 1) electrode surface

Impedance spectroscopy and in situ STM methods have been used for investigation of the camphor and 2,2′-bipyridine (2,2′-BP) adsorption at the electrochemically polished Bi(1 1 1) electrode from weakly acidified Na₂SO₄ supporting electrolyte solution. The influence of electrode potential on the adsorption kinetics of camphor and 2,2′-BP on Bi(1 1 1) has been demonstrated. In the region of maximal adsorption, i.e. capacitance pit in the differential capacitance versus electrode potential curve, the heterogeneous adsorption and diffusion steps are the rate determining stages for camphor and 2,2′-BP adsorption at the Bi(1 1 1) electrode. It was found that for camphor | Bi(1 1 1) interface the stable adsorbate adlayer detectable by using the in situ STM method has been observed only at the positively charged electrode surface, where the weak co-adsorption of SO₄²⁻ anions and camphor molecules is possible. At the weakly negatively charged Bi(1 1 1) electrode surface there are only physically adsorbed camphor molecules forming the compact adsorption layer. The in situ STM data in a good agreement with impedance data indicate that a very well detectable 2,2′-BP adsorption layer is formed at Bi(1 1 1) electrode in the wide region of charge densities around the zero charge potential.     

Halogen adsorption on crystallographic (1 1 1) planes of Pt, Pd, Cu and Au, and on Pd-monolayer catalyst surfaces: First-principles study

Halogen (Cl, Br and I) adsorption on crystallographic (1 1 1) planes of Pd, Pt, Cu, Au and on palladium monolayer catalysts surfaces was investigated by DFT calculations. Palladium monolayer catalyst here denotes either the Pd monolayer deposited over (1 1 1) crystallographic plane of Pt, Cu and Au monocrystals (Pd_ML/Me(1 1 1)), or the (1 1 1) crystallographic plane of Pd monocrystal with inserted one-atom thick surface underlayer of Pt, Cu and Au (Me_UND/Pd(1 1 1)). The adsorption on the 3-fold sites was found to be the strongest, and adsorption energies decreased if the size of the halogen atoms increased. For the case of Pd-monolayer catalysts it was demonstrated that energy of adsorption of halogen atoms could be correlated to the position of the d-band of surface atoms. Charge states of halogen adatoms and work function changes were evaluated. On the basis of calculated data and both experimental and theoretical data available in the literature, the changes in the catalytic activity toward oxygen reduction reaction of the Pd_ML/Pt(1 1 1) surface, caused by chloride adsorption, were discussed.     

Quasi in situ XPS study of electrochemical oxidation and reduction of highly oriented pyrolytic graphite in [1-ethyl-3-methylimidazolium][BF4] electrolytes

Highly oriented pyrolytic graphite (HOPG) electrodes were electrochemically oxidised and reduced in 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF₄] electrolytes and studied by X-ray photoelectron spectroscopy (XPS). Sample preparation and transfer have been performed under inert nitrogen atmosphere in a preparation chamber directly attached to an ultra high vacuum system. After electrochemical treatment, both, the electrolyte and the electrode surface were investigated. While on the oxidised HOPG surface the core levels of the detected elements shift towards lower energies, on the reduced samples a shift towards higher binding energies is observed. These shifts refer to a Fermi level shift proving that graphite intercalation compounds were formed. Intercalation occurs together with co-intercalation of the ionic liquid. XPS analysis of the ionic liquids before and after electrochemical treatment reveals changes in electrolyte composition. The influence of impurities on electrochemical behaviour and XPS data is discussed.