Anomalous electroless deposition of less noble metals on Cu in ionic liquids and its application towards battery electrodes.

Electroless deposition can be triggered by the difference in the redox potentials between two metals in an electrolyte. In aqueous electrochemistry, galvanic displacement takes place according to the electrochemical series wherein a more noble metal can displace a less noble metal. Herein we show anomalous behaviour in ionic liquids wherein less noble metals such as Fe and Sb were deposited on Cu at temperatures from 25 to 60 °C. Fe formed spherical structures whereas Cu2Sb/Sb formed nanoplates. A multistep process during the electroless deposition of Sb on Cu took place which was discerned from in situ XPS, and mass spectrometry. In situ AFM was also used to understand the nucleation and growth process of the galvanic displacement reaction. Subsequently, the Cu2Sb/Sb nanoplates were also tested as the anode for both Li-ion and Na-ion batteries. Thus, it is shown that the electrochemistry in ionic liquids significantly differs from aqueous electrolytes and opens up new routes for material synthesis.

The Au(111)/IL interfacial nanostructure in the presence of precursors and its influence on the electrodeposition process.

Ionic liquids have attracted significant interest as electrolytes for the electrodeposition of metals and semiconductors, but the details of the deposition processes are not yet well understood. In this paper, we give an overview of how the addition of various precursors (TaF5, SiCl4, and GaCl3) affects the solid/IL interfacial structure. In situ Atomic Force Microscopy (AFM) and vibrational spectroscopy have been employed to study the changes of the Au(111)/IL interface and in the electrolytes, respectively. Ionic liquids with the 1-butyl-1-methylpyrrolidinium ([Py1,4]+) cation and bis(trifluoromethylsulfonyl)amide ([TFSA]-), trifluoromethylsulfonate ([TfO]-) and tris(pentafluoroethyl)trifluorophosphate ([FAP]-) as anions were chosen for this purpose. In situ AFM force-distance measurements reveal that both the anion of the IL and the solutes (TaF5 or GaCl3) influence the Electrical Double Layer (EDL) structure of the Au(111)/IL interface, which can affect the deposition process of Ta and the morphology of the Ga electrodeposits, respectively. Furthermore, the concentration of the precursor can significantly alter the Au(111)/[Py1,4][FAP]-SiCl4 interfacial structure wherein the presence of 0.25 M SiCl4 a double layer structure forms that facilitates Si deposition. This study may provide some critical insights into the structure of the electrode/IL interface for specific applications.

Influence of a silver salt on the nanostructure of a Au(111)/ionic liquid interface: an atomic force microscopy study and theoretical concepts.

Ionic liquids (ILs) form a multilayered structure at the solid/electrolyte interface, and the addition of solutes can alter it. For this purpose, we have investigated the influence of the silver bis(trifluoromethylsulfonyl)amide (AgTFSA) concentration in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSA) on the layering using in situ atomic force microscopy. AFM investigations revealed that the Au(111)/electrolyte interface indeed depends on the concentration of the salt where a typical " IL" multilayered structure is retained only at quite low concentrations of the silver salt (e.g. ≤200 µM). However, at 200 µM AgTFSA/[Py1,4]TFSA and above this "IL" multilayered structure is disturbed/varied. A simple double layer structure was observed at 500 µM AgTFSA in [Py1,4]TFSA. Furthermore, the widths of the innermost layers have been found to be dependent on the concentration and on the applied electrode potentials. Our AFM results show that the concentration of solutes strongly influences the structure of the electrode/electrolyte interface and can provide new insights into the electrical double layer structure of the electrode/ionic liquid interface. We also introduce a semi-continuum theory to discuss the double layer structure.

Interfacial Nanostructure and Asymmetric Electrowetting of Ionic Liquids.

In this work, the interfacial nanostructure and electrowetting of ionic liquids having the same 1-ethyl-3-methylimidazolium cation ([EMIm]+) but different anions such as bis(trifluoromethylsulfonyl)imide (TFSI-), trifluoromethylsulfonate (TfO-), methylsulfonate (OMs-), acetate (OAc-), bis(fluorosulfonyl)imide (FSI-), dicyanamide (DCA-), and tris(pentafluorethyl)trifluorphosphat (FAP-) on bare metallic electrodes were investigated. In the investigated voltammetric potential regime, the contact angle versus voltage curve is asymmetric with respect to surface polarity. The electrowetting of the ILs occurs at negative potentials but does not occur at positive potentials. In situ atomic force microscopy (AFM) shows that the IL adopts a multilayered structure at the solid/IL interface, and a cation-rich layer is present in the innermost layer during cathodic polarization. The cations can change their orientation and propagate ahead of the three-phase contact line by diffusion, leading to further spreading on the negatively charged surface. The formation of such a surface layer is also evidenced by X-ray photoelectron spectroscopy. Such a surface diffusion mechanism does not occur during anodic polarization, where anions are enriched. In addition, the influence of substrate, water, and dissolved zinc salts on the electrowetting of ILs was studied. Our findings provide valuable insights for the interfacial nanostructure and the electrowetting of ILs.

Tuning the electronic environment of zinc ions with a ligand for dendrite-free zinc deposition in an ionic liquid.

In this work, we report on the influence of an organic ligand on the electrodeposition of Zn from an ionic liquid (IL) electrolyte. Zinc oxide was first dissolved in a protic IL. By introducing a 2-methylimidazole (2-MIm) ligand, the electronic environment of zinc ions, Zn(ii) complexes and the structure of the IL are considerably altered, as verified by both X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Due to the electron donation effect of the ligand, the zinc ions become less positively charged and exhibit a lower binding energy by -0.5 eV, compared to its absence. The atomic force microscopy (AFM) results show that a higher push-through force is required to rupture the interfacial layers in the presence of the ligand compared to its absence. The ligand can interact with both the cation and the anion of the IL via hydrogen bonds, forming compact layers on the surface, which also has a strong influence on the electrochemical performance. The cyclic voltammograms show reduction peaks at -1.4 V in all cases, but the current density decreases as the concentration of 2-MIm increases. Dendritic zinc deposits were obtained in 1.5 mol L-1 ZnO/[EIm]TfO, while dendrite-free zinc structures were obtained in the presence of 1.5 mol L-1 2-MIm.

Characterisation of the solid electrolyte interface during lithiation/delithiation of germanium in an ionic liquid.

In this paper, we present investigations of the interface of electrodeposited Ge during lithiation/delithiation in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide containing 0.5 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI/[Py1,4]TFSI). Cyclic voltammetry (CV) and infrared spectroscopy were used to study the electrochemistry and the changes in the electrolyte during the Li intercalation/deintercalation processes. From infrared spectroscopic analysis, it was found that the TFSI(-) anion decomposes during the lithiation process, resulting in the formation of a solid-liquid interface (SEI) layer. X-ray photoelectron spectroscopy was used to analyse the composition of the SEI layer and the changes in the electrodeposited germanium. Furthermore, atomic force microscopy (AFM) was used to evaluate the changes in the SEI layer which showed that the SEI layer was inhomogenous and changed during the lithiation/delithiation processes.

Surface modification of battery electrodes via electroless deposition with improved performance for Na-ion batteries.

Sodium-ion batteries (SIBs) are emerging as potential stationary energy storage devices due to the abundance and low cost of sodium. A simple and energy efficient strategy to develop electrodes for SIBs with a high charge/discharge rate is highly desirable. Here we demonstrate that by surface modification of Ge, using electroless deposition in SbCl3/ionic liquids, the stability and performance of the anode can be improved. This is due to the formation of GexSb1-x at the surface leading to better diffusion of Na, and the formation of a stable twin organic and inorganic SEI which protects the electrode. By judicious control of the surface modification, an improvement in the capacity to between 50% and 300% has been achieved at high current densities (0.83-8.4 A g(-1)) in an ionic liquid electrolyte NaFSI-[Py1,4]FSI. The results clearly demonstrate that an electroless deposition based surface modification strategy in ionic liquids offers exciting opportunities in developing superior energy storage devices.

Nanostructure of the H-terminated p-Si(111)/ionic liquid interface and the effect of added lithium salt.

Ionic liquids are potential electrolytes for safe lithium-ion batteries (LIB). Recent research has probed the use of silicon as an anode material for LIB with various electrolytes. However, the nanostructure of the ionic liquid/Si interface is unknown. The present communication probes the hydrogen terminated p-Si(111) interface using atomic force microscopy (AFM) in 1-ethyl-3-methylimidazolium bis(trifluoromethlysulfonyl)amide ([EMIm]TFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethlysulfonyl)amide ([Py1,4]TFSA). AFM measurements reveal that the imidazolium cation adsorbs at the H-Si(111)/[EMIm]TFSA interface leading to an ordered clustered facet structure of ∼3.8 nm in size. In comparison, the Si(111)/[Py1,4]TFSA interface appeared the same as the native surface in argon. For both pure ILs, repulsive forces were measured as the tip approached the surface. On addition of LiTFSA attractive forces were measured, revealing marked changes in the interfacial structure.

Electrodeposition of Three Dimensionally Ordered Macroporous Germanium from Two Different Ionic Liquids.

Three dimensionally ordered macroporous (3DOM) Ge films have been made via ordered polystyrene (PS) templates by electrodeposition from ionic liquids 1-Butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) amide and 1-Ethyl-3-methylimidazolium tris (pentafluoroethyl) trifluorophosphate at room temperature. We discuss the possibility of obtaining high quality 3DOM Ge films from two different ionic liquids by the simple and inexpensive template-assisted electrochemical pathway. Scanning electron microscopy confirms the quality of the samples, and the optical measurements demonstrate that 3DOM Ge made electrochemically shows photonic crystal behavior. Such a material has the potential to make 3DOM Ge feasible for electrical, optical applications and for photonic crystal solar cells.

Dendrite-Free Nanocrystalline Zinc Electrodeposition from an Ionic Liquid Containing Nickel Triflate for Rechargeable Zn-Based Batteries.

Metallic zinc is a promising anode material for rechargeable Zn-based batteries. However, the dendritic growth of zinc has prevented practical applications. Herein it is demonstrated that dendrite-free zinc deposits with a nanocrystalline structure can be obtained by using nickel triflate as an additive in a zinc triflate containing ionic liquid. The formation of a thin layer of Zn-Ni alloy (η- and γ-phases) on the surface and in the initial stages of deposition along with the formation of an interfacial layer on the electrode strongly affect the nucleation and growth of zinc. A well-defined and uniform nanocrystalline zinc deposit with particle sizes of about 25 nm was obtained in the presence of Ni(II) . Further, it is shown that the nanocrystalline Zn exhibits a high cycling stability even after 50 deposition/stripping cycles. This strategy of introducing an inorganic metal salt in ionic liquid electrolytes can be considered as an efficient way to obtain dendrite-free zinc.

Raman and FTIR spectroscopic studies of 1-ethyl-3-methylimidazolium trifluoromethylsulfonate, its mixtures with water and the solvation of zinc ions.

In this paper we report on the interactions of the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) with water and the solvation of zinc ions in neat [EMIm]TfO and [EMIm]TfO-water mixtures investigated by FTIR and Raman spectroscopy. The structures and physicochemical properties of the [EMIm]TfO-water mixtures are strongly dependent on the interaction between cations, anions, and water. The structure was changed from ionic-liquid-like to water-like solutions upon addition of water. In addition, zinc salts can precipitate in 0.2 M Zn(TfO)2/[EMIm]TfO upon addition of 10 % (v/v) water, presumably as a result of polarity change of the solution. The average coordination number of TfO(-) per zinc ion calculated from Raman spectra is 3.8 in neat [EMIm]TfO, indicating that [Zn(TfO)4](2-), and [Zn(TfO)3](-) complexes are present in the solution. However, in the presence of water, water interacts preferentially with the zinc ions, leading to aqueous zinc species. The solvation of zinc ions in 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ([Py(1,4)]TfO) was also investigated. In [Py(1,4)]TfO, there are, on average, 4.5 TfO(-) anions coordinating each zinc ion, corresponding to the weak interaction between [Py(1,4)](+) cations and TfO(-) anions. The species present in [Py(1,4)]TfO are likely a mixture of [Zn(TfO)4](2-) and [Zn(TfO)5](3-).

Electrochemical and spectroscopic study of Zn(ii) coordination and Zn electrodeposition in three ionic liquids with the trifluoromethylsulfonate anion, different imidazolium ions and their mixtures with water.

In this paper we report on the use of three ionic liquids, 1-methylimidazolium trifluoromethylsulfonate ([MIm]TfO), 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) and 1-ethyl-2,3-dimethylimidazolium trifluoromethylsulfonate ([EMMIm]TfO) containing zinc trifluoromethylsulfonate as electrolytes for zinc electrodeposition. By varying the cations from [MIm](+)via [EMIm](+) to [EMMIm](+), the vibrational band in the Far-IR spectra below 200 cm(-1), characterizing the cation-anion interaction, is shifted to lower wavenumbers, which suggests that the interaction between cations and anions is arranged in order of [MIm]TfO > [EMIm]TfO > [EMMIm]TfO. The coordination of Zn(2+) ions in these electrolytes was investigated by Raman spectroscopy. The Raman spectra show obvious differences in terms of the solvation of Zn(2+) ions in the dried electrolytes. The average number of TfO(-) anions bound to each Zn(2+) ion is lower in [MIm]TfO than in [EMIm]TfO and in [EMMIm]TfO, respectively. In ionic liquid-water mixtures, aqueous zinc species were formed in all cases. The differences in zinc species present in the electrolytes should have an influence on their electrochemical behavior and on the morphology of the deposits. In dried ionic liquids, the cyclic voltammograms reveal that the potentials for the deposition of zinc were shifted to more negative values by varying the cations, while in ionic liquid-water mixtures, the deposition of zinc occurs at almost the same potential. The SEM and XRD results show that the surface morphology, crystal shape and size as well as crystallographic orientation of the deposits are markedly affected by varying the cations of the ionic liquids.

LiTFSI in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide: a possible electrolyte for ionic liquid based lithium ion batteries.

In this communication, we show that the combination of 1 M lithium bis(trifluoromethylsulfonyl)amide and 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (LiTFSI/[Py1,4]FSI) can be regarded as a possible stable electrolyte for IL based lithium ion batteries. We compare the charge-discharge results with the electrolyte 1 M LiTFSI in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) on an electrodeposited Ge electrode and show using a charge-discharge analysis and Raman spectroscopy that 1 M LiTFSI/[Py1,4]FSI is advantageous in maintaining the charge capacity as well as electrolyte stability at high current densities.

Electroless Deposition of III-V Semiconductor Nanostructures from Ionic Liquids at Room Temperature.

Group III-V semiconductor nanostructures are important materials in optoelectronic devices and are being researched in energy-related fields. A simple approach for the synthesis of these semiconductors with well-defined nanostructures is desired. Electroless deposition (galvanic displacement) is a fast and versatile technique for deposition of one material on another and depends on the redox potentials of the two materials. Herein we show that GaSb can be directly synthesized at room temperature by galvanic displacement of SbCl3 /ionic liquid on electrodeposited Ga, on Ga nanowires, and also on commercial Ga. In situ AFM revealed the galvanic displacement process of Sb on Ga and showed that the displacement process continues even after the formation of GaSb. The bandgap of the deposited GaSb was 0.9±0.1 eV compared to its usual bandgap of 0.7 eV. By changing the cation in the ionic liquid, the redox process could be varied leading to GaSb with different optical properties.

Electrodeposition and magnetic characterization of iron and iron-silicon alloys from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate.

The electrodeposition of soft magnetic iron and iron-silicon alloys for magnetic measurements is presented. The preparation of these materials in 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, at 100 °C with FeCl2 and FeCl2 +SiCl4 was studied by using cyclic voltammetry. Constant-potential electrolysis was carried out to deposit either Fe or FeSi, and deposits of approximately 10 µm thicknesses were obtained. By using scanning electron microscopy and X-ray diffraction, the microstructure and crystallinity of the deposits were investigated. Grain sizes in the nanometer regime (50-80 nm) were found and the presence of iron-silicon alloys was verified. Frequency-dependent magnetic polarizations, coercive forces, and power losses of some deposits were determined by using a digital hysteresis recorder. Corresponding to the small grain sizes, the coercive forces are around 950-1150 A m(-1) and the power losses were at 6000 J m(-3), which is much higher than in commercial Fe(3.2 wt %)Si electrical steel. Below a polarization of 1.8 T, the power losses are mainly caused by domain wall movements and, above 1.8 T, by rotation of magnetic moments as well as domain wall annihilation and recreation.

Spectroscopic characterization of the interaction of lithium with thin films of the ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

In this experimental investigation the interaction of lithium with 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([OMIm]Tf2N) is shown. For this purpose thin films of lithium and [OMIm]Tf2N were successively vapor deposited on a copper substrate and analyzed by X-ray Photoelectron Spectroscopy (XPS) as well as by Ultraviolet Photoelectron Spectroscopy (UPS). When [OMIm]Tf2N is evaporated on top of a thin lithium film a chemical shift analysis of XPS spectra shows a variety of reaction products like LiF, Li2O and LixCHy which reveals the instability of the IL against lithium. Time resolved XPS spectra were discussed to distinguish cation reactions from beam damage effects. In a second step lithium is deposited on a [OMIm]Tf2N layer. The XPS spectra are in agreement with the results of the previous step, but show some differences concerning the [OMIm] cation. In a third step [OMIm]Tf2N has been deposited on a passivated lithium layer. XPS results show nearly unaffected [Tf2N](-) anions and partially decomposed [OMIm](+) cations. Interestingly the cation reactions show similarities when compared to the interaction of [C4C1Pyrr]Tf2N (1-butyl-1-methylpyrrolidinium bis[trifluoromethylsulfonyl]amide) and lithium.

Effect of alkyl chain length and anion species on the interfacial nanostructure of ionic liquids at the Au(111)-ionic liquid interface as a function of potential.

Colloid probe atomic force microscopy (AFM) force measurements are used to elucidate the effect of variation in the cation alkyl chain length and the anion species on IL nanostructure at Au(111) surfaces as a function of potential. Four ionic liquids (ILs) are examined: 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM] FAP), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP) and 1-butyl-3-methylimidazolium iodide ([BMIM] I). The step-wise force-distance profiles show the ILs adopt a multilayered morphology, with stronger near surface structure present at more biased potentials. The results suggest that the innermost (interfacial) layer is enriched in counter ions strongly bound to the Au(111) surface. For ILs with FAP(-) anions, the cations in the interfacial layer at negative potentials pack more neatly than the anions at positive potentials, and thus more effectively template structure in subsequent layers. [BMIM] FAP has the weakest interfacial structure. [EMIM] FAP has stronger interfacial structure because the imidazolium rings of [EMIM](+) cations in the interfacial layer are orientated towards the Au(111) surface, and this more parallel orientation is favourable for templating structure. [HMIM] FAP is more strongly structured than [BMIM] FAP because the longer cation alkyl chain increases solvophobic interactions which lead to better defined near surface structure. The response of [BMIM] I to changes in potential is opposite to that of the FAP(-) ILs. [BMIM] I interfacial nanostructure is stronger at positive potentials, because I(-) anions pack more neatly at the Au(111) surface than [BMIM](+) cations, which templates stronger structure in subsequent layers.

Two-dimensional Si(x)Ge(1-x) films with variable composition made via multilayer colloidal template-guided ionic liquid electrodeposition.

The binary alloy system Si(x)Ge(1-x) provides a continuous series of materials with gradually varying properties. In this paper, we report on a fundamental basis a method to make large-area macroporous Si(x)Ge(1-x) films with variable Ge content by electrodeposition in an ionic liquid, with SiCl(4) and GeCl(4) as precursors. The chemical composition of the products can be modified by changing the molar ratio of the precursors. Periodical macroporous Si(x)Ge(1-x) was made by a multilayer polystyrene (PS) template assembled as face-centered cubic lattice. Two-dimensional (2-D) Si(x)Ge(1-x) bowl-like and fishing-net structures can be obtained by applying different deposition temperatures. The results highlight the potential applications, including photonic bandgap and battery materials, as well as ultra-thin gratings, due to the effect of modification of light and improved tunability of composition, although Si(x)Ge(1-x) made by our method is sensitive to oxidation by air.

Enhanced photoluminescence of ordered macroporous germanium electrochemically prepared from ionic liquids.

Recently we reported our results on the successful synthesis of 3-D highly ordered macroporous (3DOM) structure of germanium via the template-assisted electrochemical deposition from air- and water stable ionic liquids. Herein we report our new results on the photoluminescence (PL) properties of the obtained ordered macroporous Ge and the Ge/polystyrene composite opal structure. The latter showed a strong green emission compared to a Ge film and a Ge inverse opal. The enhancement of PL intensity was ascribed to the disorder multiple scattering in polystyrene colloidal crystal structure which increased both the excitation light absorption efficiency and the light extraction efficiency. The X-ray photoelectron spectroscopy (XPS) results suggested that the ordered macroporous Ge was capped with an oxide layer including a considerable amount of GeO(2). The observed green emission (539 nm) was related to GeO(2), likely resulting from the Ge-O bond related intrinsic defects.

Control of nanoscale friction on gold in an ionic liquid by a potential-dependent ionic lubricant layer.

The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py(1,4)]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure.