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The influence of an ionic liquid on the band gap of H-terminated Si(111) was investigated using in situ XPS and scanning tunneling spectroscopy (STS). The changes in the electronic structure can be...

The mixtures of 1-butylpyrrolidine and ZnCl2 result in the formation of an ionic liquid, which can be used as an electrolyte for zinc electrodeposition. The feasibility of electrodepositing Zn from these electrolytes was investigated at RT and at 60 °C. The synthesized mixtures are rather viscous. Toluene was added to the mixtures to decrease the viscosity of the ILs. Vibrational spectroscopy was employed for the characterization of the liquids. The electrochemical behaviour of the liquids was evaluated by cyclic voltammetry. The electrode/electrolyte interface of this IL was probed by Atomic Force Microscopy (AFM). The suitable range for the electrodeposition of Zn was found to be ≥28.6 mol% of ZnCl2. Zn deposition occurs mainly from the cationic species of [ZnClxLy]+ (where x = 1, y = 1–2, and L = 1-butylpyrrolidine) in these electrolytes. This is in contrary to the well investigated chlorozincate ionic liquids where the deposition of Zn occurs mainly from anionic chlorozincates. Nanoplates of Zn were obtained from these mixtures of 1-butylpyrrolidine and ZnCl2.

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.

The NaFSI-[Py1,4]FSI/Au(111) interface was investigated using cyclic voltammetry (CV) and in situ atomic force microscopy (AFM). Raman spectroscopy was used to evaluate the Na+ solvation in [Py1,4]FSI. It was found that Na coordinates with three FSI– forming [Na(FSI)3]2–. In situ AFM revealed that the interaction of [Py1,4]FSI with Au(111) is much stronger compared with other ionic liquids measured using the same technique. On applying a potential, a force of ∼50 nN is required to penetrate through the innermost layer. On addition of low concentration of NaFSI (0.05 M), an insignificant change in the innermost solvation layer was observed, whereas on addition of 0.25 and 0.5 M NaFSI, a significant change in the interfacial structure was noted. The present study clearly shows that Na+ ions vary the ionic liquid/Au(111) interface and could provide insight into the interfacial processes in ionic-liquid-based sodium batteries.

Ionic liquids are potential designer electrolytes for energy storage devices such as batteries and capacitors wherein by changing the cation and anion of the ionic liquid (IL) the solid/liquid interface can be tuned, thereby influencing the charge and mass transfer processes. In this paper, we show the influence of water on the electrified ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([Emim]TfO)/Au(111) interface using in situ atomic force microscopy (AFM) and spectroscopy. A clear “water in IL” to “IL in water” transition could be observed in the range of 20–30 vol % of water using vibrational spectroscopy. Above 30 vol % of water the cation–anion interaction in the ionic liquid drastically reduced, which was ascertained by both spectroscopy and interfacial studies using in situ AFM. In situ AFM results further revealed that the structure of the innermost (Stern) layer depends both on the applied electrode potential and the amount of added water. A transition from a multilayered stru...

The electrochemical reduction of 0.1 M TaF 5 in two hydrophobic ionic liquids (1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py 1,4 ]FAP) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([Py 1,4 ]TFSA) is probed using three in situ techniques: scanning tunneling microscopy (STM), atomic force microscopy (AFM), and electrochemical quartz crystal microbalance (EQCM). These techniques reveal that under similar conditions TaF 5 is more easily reduced in the liquids with [TFSA] − than [FAP] − anions. Increasing the temperature reduced the viscosity and density of the ionic liquids which facilitates TaF 5 electroreduction, in particular, in [Py 1,4 ]TFSA. A herringbone reconstruction of the Au electrode was observed by STM for both ionic liquids with and without TaF 5 . Ta deposition was proved by STM and EQCM in [Py 1,4 ]TFSA. Cracked layers, with ionic liquid trapped inside, were obtained by direct plating from the [TFSA] − ionic liquid. No Ta containing deposits could be obtained in the liquid with the [FAP] − anion.

The electrochemical reduction of NbCl5 in alkylmethylpyrrolidinium TFSI based ILs is characterized by a multistep reduction process. Upon dissolution in the IL, NbCl5 does not dissociate, but remains in its bi-nuclear Nb2Cl10 structure. Its electrochemical reduction follows a mechanism typically observed in multi-nuclear complex electrochemistry, where the Nb-ions share electrons within an IL-cation coordinated NbxCly-complex, which grows in size at lower oxidation number. Due to the persistent Cl-coordination of the Nb-ions, the electron transfer follows an outer sphere reaction and does not involve any adsorption step on the electrode surface. The Cl-shell is found to be the main reason, why the electrochemical deposition of Nb fails at room temperature.

Halbleiternanostrukturen der Gruppe III–V sind wichtige Materialien fur optoelektronische Anwendungen und werden im Energiesektor erforscht. Ein einfacher Ansatz fur die Synthese dieser Halbleiter mit klar strukturierten Nanostrukturen wird angestrebt. Die stromlose Abscheidung ist eine schnelle und vielseitige Methode fur die Abscheidung eines Materials auf einem anderen und wird durch das Redox-Potential der zwei Materialien bestimmt. Hier zeigen wir, dass GaSb bei Raumtemperatur durch stromlose Abscheidung aus SbCl3/ionische Flussigkeit (IL) auf elektrochemisch abgeschiedenem Ga, auf Ga-Nanodrahten und auf kommerziell erhaltlichem Ga direkt hergestellt werden kann. In-situ-AFM-Messungen belegen die stromlose Abscheidung von Sb auf Ga und zeigen, dass der Prozess nach der Bildung von GaSb sogar weiter fortschreitet. Die Bandlucke des abgeschiedenen GaSb ist mit (0.9±0.1) eV vergleichbar mit der bekannten Bandlucke von 0.7 eV. Ferner beeinflusst der Wechsel des Kations der IL den Redoxprozess hinsichtlich verschiedener optischer Eigenschaften des GaSb.

In this paper, we present results on the nanoscale interactions of LiTFSI–[Py1, 4]TFSI with Au(111) using cyclic voltammetry and atomic force microscopy (AFM). Raman spectroscopy was used to understand the Li+ ion coordination with the TFSI– ion and showed that with increase in LiTFSI concentration in [Py1, 4]TFSI, the Li+ ion solvation structure significantly changes. Correspondingly, the force–distance profile in AFM revealed that at lower concentrations of LiTFSI (0.1 M) a multilayered structure is obtained. On increasing the concentration of LiTFSI (0.5 and 1 M), a significant decrease in the number of interfacial layers was observed. With change in the potential, the interfacial layers were found to vary with an increase in the force required to rupture the layers. The present study clearly shows that Li+ ions vary the ionic liquid/Au(111) interface and could provide insight into the interfacial processes in ionic liquid based lithium batteries.

The influence of an additive, 1,2-dimethyl-3-(trifluoromethyl)-1H-pyrazol-2-ium trifluoromethylsulfonate, on the electrodeposition of zinc from 0.2 M Zn(TfO)2 in the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) at room temperature was investigated by using cyclic voltammetry, scanning electron microscopy, and X-ray diffraction. Both in the presence and absence of the additive, the bulk electrodeposition of Zn is obtained at −0.7 V versus Zn. In the presence of the additive, two more reduction peaks, which correlate with the reduction of the additive, are observed at electrode potentials more negative than the bulk deposition of Zn. Both the concentration of the additive and the cathodic reverse potentials influence the zinc stripping process. Furthermore, it was found that the adsorption of the additive on the electrode surface obviously inhibits Zn nucleation and, thus, influences the morphology of the deposit as well as the preferred orientation.

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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.

Electrode materials as well as the electrolytes play a decisive role in batteries determining their performance, safety, and lifetime. In the last two decades, different types of batteries have evolved. A lot of work has been done on lithium ion batteries due to their technical importance in consumer electronics, however, the development of post-lithium systems has become a focus in recent years. This chapter gives an overview of various battery materials, primarily focusing on development of electrode materials in ionic liquids via electrochemical route and using ionic liquids as battery electrolyte components.

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.

Metal nanoparticles such as Au, Ag, Pt, and so forth have been deposited on silicon by electroless deposition in the presence of hydrofluoric acid (HF) for applications such as oxygen reduction reaction, surface-enhanced Raman spectroscopy, as well as for lithium ion batteries. Here, we show an HF-free process wherein metals such as Sb and Ag could be deposited onto electrodeposited silicon in ionic liquids. We further show that, compared to electrodeposited silicon, Sb-modified Si demonstrates a better performance for lithium storage. The present study opens a new paradigm for the electroless deposition technique in ionic liquids for developing and modifying functional materials.

The highly ordered pyrolytic graphite (HOPG)/1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm]Tf2N) interface is examined by ultrahigh vacuum scanning tunneling microscopy (UHV-STM), atomic force microscopy (UHV-AFM) (and as a function of potential by in situ scanning tunneling microscopy (STM)), in situ atomic force microscopy (AFM), and density functional theory (DFT) calculations. In situ STM and AFM results reveal that multiple ionic liquid (IL) layers are present at the HOPG/electrode interface at all potentials. At open-circuit potential (OCP), attractions between the cation alkyl chain and the HOPG surface result in the ion layer bound to the surface being cation rich. As the potential is varied, the relative concentrations of cations and anions in the surface layer change: as the potential is made more positive, anions are preferentially adsorbed at the surface, while at negative potentials the surface layer is cation rich. At −2 V an unusual overstructure forms. STM images and...

In this overview paper we present a combined in situ STM, AFM and EIS study on the structure and dynamics of the interfacial layers between Au(111) and two extremely pure ionic liquids, namely [Py1,4]FAP and [EMIM]FAP. The combination of these methods provides valuable information for both neutral and electrified interfaces. In situ STM and AFM results reveal that a multilayered ion morphology is present at the IL-Au(111) interface, with stronger near surface layering detected at higher electrode potentials. The in situ STM measurements show that the structure of the interfacial layers is dependent on the applied electrode potential, the number of subsequent STM scans and the scan rate. Furthermore, in the case of [Py1,4]FAP, the Au(111) surface undergoes herringbone reconstruction, Au(111)( 22 × 3 ), in the cathodic potential regime, and the ultra-slow formation of vacancies in the herringbone structure is probed with in situ STM. EIS measurements reveal the presence of two distinct capacitive processes at the interface taking place on different time scales. The time scale of the fast process is typically in the millisecond range and is governed by the bulk ion transport in the IL, which exhibits a Vogel–Fulcher–Tammann-type temperature dependence. The slow process takes place on a time scale of seconds and is Arrhenius activated. The contribution of this process to the overall interfacial capacitance is particularly large in the potential regime where the herringbone structure is probed. Furthermore, we analyze the temperature dependence of the interfacial capacitance.

The electrochemical reduction mechanism of niobium was studied in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([BMP][OTf]) containing niobium halides (NbCl5 and NbF5). The influence of the electrolyte composition, temperature, and nature of the substrate were systematically investigated. In situ electrochemical techniques, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical quartz crystal microbalance (EQCM) and rotating ring disc electrode (RRDE), were used, besides the ex situ characterization techniques scanning electron microscopy (SEM) and vibrational spectroscopy. The number of transferred electrons was estimated from the half width of the cathodic peaks in the DPV measurements. Furthermore, the product of the diffusion coefficient and the number of transferred electrons at the power of 3/2 were evaluated from RRDE measurements to be approx. 3 × 10−10 m2/s. Thicker and better adherent niobium-based deposits were obtained from NbCl5 in [BMP][OTf] than from NbF5 in [BMP][OTf]. EQCM measurements combined with DPV indicated the potential region where niobium-based deposits could be obtained as well as their stoichiometry. Vibrational spectroscopy reveals that NbF5 and NbCl5 interact differently with [BMP][OTf]. The spectra show that in the case of NbF5 – [BMP][OTf] only niobium(V) anionic species [NbF6A]2- and [NbF5A]- (where A = [OTf]-) are formed, while in NbCl5 – [BMP][OTf] both niobium(V) and niobium(IV) anionic species are present. At low NbCl5 concentrations, [NbCl4A2]2- and [NbCl4A2]- are obtained, while at high NbCl5 concentration, [NbCl5A]2- and [NbCl5A]- are found. The electrochemical niobium reduction mechanism depends on temperature and on the anionic species that are involved in the reduction process. In the case of NbCl5 – [BMP][OTf], at high cathodic potentials the formation of subvalent Nb-clusters (possibly Nb6Cl14) was observed.

Sustainable energy carriers such as sun light, wind or biomass will play a crucial role in our future. After converting the energy, one should be able to store it and transport it to places where it is needed most. Therefore, the research on materials for storage systems, such as batteries, supercapacitors and fuel cells is an important aspect. Electrodeposition is a powerful technique for the preparation of such materials. As industry strives to produce smaller portable devices, one needs also smaller and lighter batteries with a high storage capacity per gram of active material. The commercial graphite anodes are limited to ca. 370 mAh/g, but silicon and C-Si composites have a theoretical storage capacity beyond 1000 mAh/g. Thus, nanostructured Si, such as nanoporous Si layers, ordered arrays of Si (porous) nanopillars produced by using a combination of nanoimprint lithography and metal-assisted chemical etching or silicon thin films deposited from ionic liquids could be used as high-capacity anodes in Li-ions batteries. Another interesting semiconductor material besides Si is Cu2O. Photo-cathodes from Cu2O can be used to produce hydrogen as a chemical fuel by utilizing direct solar energy and its narrow bandgap of 2.0-2.2 eV that can lead to the theoretical value of solar-to-hydrogen efficiency of 18 %. One can fabricate Cu/Cu2O porous electrodes using the hydrogen bubbles as a dynamic and effective template by electrochemical deposition. These foam electrodes can then be used as photocathodes for water electrolysis under visible light irradiation. This contribution will discuss recent results from the authors’ labs on developing new anode materials for Li-ion batteries (Si based), new electrodes for electrochemical water splitting (Cu2O based) and for electrocatalysis. Further, approaches using light induced plating for electrical front side contacts of solar cells will be presented.

The electrodeposition of silicon was investigated from three different ionic liquids with the cation 1-butyl-1-methylpyrrolidinium ([Py1,4]+) and three different anions, namely, trifluoromethylsulfonate (TfO−), bis(trifluoromethylsulfonyl)amide (TFSA−) and tris(pentafluoroethyl)-trifluorophosphate (FAP−) at room temperature and at 100 °C, respectively. The electrodeposition was performed on gold and on copper substrates. Cyclic voltammetry was used to evaluate the possible influence of anions on the deposition process. In situ STM studies were also carried out to examine the interfacial behaviour of the SiCl4/[Py1,4]TFSA and SiCl4/[Py1,4]FAP on Au(111) at room temperature. In situ STM measurements revealed that an underpotential deposition of Si in [Py1,4]FAP occurred on Au (111) at ~ -0.5 V (vs. Fc/Fc+). In comparison, only adsorption of ionic liquid and gold surface reconstruction was found to occur in the potential regime between -0.3 and −1.8 V (vs. Fc/Fc+), respectively, in the case of [Py1,4]TFSA. In situ STM investigations reveal an effect of the anion on the interfacial processes. In situ I/U tunnelling spectroscopy shows that the band gap of the electrodeposits is ~1.1 eV, indicating that semiconducting silicon has been electrodeposited. Potentiostatic electrolysis was performed to deposit Si from the employed electrolytes at room temperature and at 100 °C. The deposits were characterised using scanning electron microscopy and X-ray diffraction. Thin films of Si could be obtained from the employed ionic liquids and the quality of the deposits was significantly improved at 100 °C.

The mixtures of 1-butylpyrrolidine and ZnCl

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.

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.

The Au(1 1 1)/1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIm]FAP) interface is examined using in situ scanning tunnelling microscopy (STM), atomic force microscopy (AFM) and distance tunnelling spectroscopy (DTS). Both in situ STM and AFM results reveal that multiple ionic liquid (IL) interfacial layers form at the Au(1 1 1) electrode interface. The applied potential determines whether cations (cathodic regime) or anions (anodic regime) are preferentially adsorbed to the substrate, with stronger near surface layering detected at higher surface potentials. DTS measurements suggest that the height of the tunnelling barrier between the STM tip and the gold substrate was 1.4 eV at open circuit potential (ocp). The IL double layer structure elucidated is not consistent with Stern–Gouy–Chapman model as per aqueous electrolyte systems due to the absence of a diffuse layer. Instead a capacitor-like structure is present with the potential decaying sinusoidally over the oscillatory ion arrangements.

The structure of the interfacial layer(s) between the extremely pure air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate and Au(111) has been investigated using in situ scanning tunneling microscopy (STM) at electrode potentials more positive than the open circuit potential. The in situ STM measurements show that layers/islands form with increasing electrode potential. According to recently published atomic force microscopy (AFM) data the anion is adsorbed even at low anodic overvoltages and adsorption becomes slightly stronger with increasing electrode potential. Furthermore, the number of interfacial layers increases with increasing electrode potential. The present discussion paper shows that these layers are not uniform and have a structure on the nanoscale, supporting earlier results that the interface electrode/ionic liquid is highly complex. It is also shown that the addition of solutes changes this structure considerably. AFM results reveal that in the pure liquid, interfacial layers lead to a repulsive force but the addition of 10 wt% of LiCl leads to an attractive force close to the surface. These preliminary results show that solutes strongly alter the interfacial structure of the ionic liquid/ electrode interface.

One challenge in the use of metallic lithium in secondary lithium ion or lithium air batteries is the dendritic growth of lithium upon repeated cycling which might either lead to a short circuit or at least to an uneven current distribution and bad cycling stability. In the present paper we present our first results on the electrodeposition of lithium from an ionic liquid within the voids of a polystyrene opal structure on copper. For this purpose polystyrene spheres with an average diameter of about 600 nm were applied onto a copper sheet by a simple dipping process resulting in a layer thickness of about 10 μm. Lithium can be deposited within this polymer structure without damaging it and the subsequent dissolution of the polystyrene spheres delivers a macroporous lithium film, proving that a mechanically stable composite electrode is feasible.

The double layer structure of two ionic liquids (ILs), 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([Py1,4]FAP) and 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIm]FAP) at the polarized Au(111) electrode interface is probed using Atomic Force Microscopy force measurements. The force-separation profiles suggest a multilayered morphology is present at the electrified Au(111)−IL interface, with more near surface layers detected at higher potentials. At the (slightly negative) open circuit potential, multiple ion layers are present, and the innermost layer, in contact with the Au(111) surface, is enriched in the cation due to electrostatic adsorption. Upon applying negative electrode potentials (−1.0 V, −2.0 V), stronger IL near surface structure is detected: both the number of ion layers and the force required to rupture these layers increases. Positive electrode potentials (+1.0 V, +2.0 V) also enhance IL near surface structure, but not as much as negat...

In the present study macroporous aluminium electrodes were made by template assisted electrodeposition from ionic liquids. Polystyrene (PS) spheres (diameter 600 nm) were applied onto polished copper electrodes by immersion into an alcoholic suspension containing PS spheres. Al was deposited from the chloroaluminate ionic liquid [EMIm]Cl/AlCl3 (40/60 mol.%) on this substrate. After chemical dissolution of the PS spheres a macroporous aluminium electrode was obtained which served as a host material for Li deposition from ionic liquids. Lithium deposition in this matrix is reversible showing certain activation with an increasing number of cycles. After 10 cycles of Li deposition/dissolution the macroporous structure is still visible.

Metal and semiconductor nanostructures are usually synthesized using vacuum techniques. Such processes are cost-intensive and need vacuum conditions for preparation thus making the semiconductors quite expensive. Electrodeposition is an alternative and relatively simple way to produce these materials. However for electrochemical synthesis, applying of a proper solvent is essential to produce metals and semiconductors. The electrodeposition from aqueous solutions is limited by a relatively low electrochemical stability of water. In the case of molten salts, high temperature is usually required for electrodeposition. Organic solvents are very volatile and many of them are quite toxic. The alternative to common electrolytes is to use ionic liquids (ILs), which exhibit wide electrochemical windows, good thermal stability, non-volatility, low toxicity and are liquid below 100 °C [1]. In this lecture we will show that ILs are well suited for the electrodeposition of metal and semiconductor nanostructures with various architectures. Consequently, metal (e.g. Ga, In, Zn, Al, Cu, etc.) and semiconductor (Si, Ge, SixGe1-x, etc.) nanowires, nanotubes and macroporous structures can be synthesized in ILs at room temperature by using template-assisted electrodeposition. Recently, these materials have received some attention as promising electrode materials in batteries [2]. Furthermore, III-V semiconductor (e.g. GaSb and InSb) nanowires can be directly synthesized at room temperature by electroless deposition [3]. Some nanowires (e.g. ZnS) can be obtained in ILs without any external template, which opens a new perspective for the synthesis of semiconductor nanostructures. The structure of the IL/electrode interface can significantly alter the deposition process that, in turn, may result in the deposits with various morphologies and properties. This offers the opportunity to influence the optical properties of obtained materials by changing the composition of the solvent. [1] F. Endres, A. Abbott, D. R. MacFarlane, Electrodeposition from Ionic Liquids. 2nd Edition. 2017, Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA. [2] M. Shapouri Ghazvini, G. Pulletikhurthi, Z. Liu, A. Prowald, S. Zein El Abedin, F. Endres, J. Solid State Electrochem., 19 (2015) 1453-1461. [3] A. Lahiri, N. Boriseko, M. Olschewski, R. Gustus, J. Zahlbach, F. Endres, Angew. Chem. Int. Ed., 54(40) (2015) 11870-11874.

In the present paper the electrodeposition of Ga on Au(1 1 1) from 0.5 mol L −1 GaCl 3 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.

The surface interaction of two air- and water-stable ionic liquids (ILs), 1-ethyl-3-methylimidazolium bis[(trifluoromethylsulfonyl]amide ([EMIm]TFSA) and 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]amide ([BMP]TFSA), with Au(111) has been investigated using atomic force microscopy (AFM), cyclic voltammetry, and scanning tunneling microscopy (STM) measurements. AFM experiments reveal that multiple solvation layers are present at the gold interface for both ILs and that the strength of the interaction between the innermost layer and the substrate is dependent on the cation type; the force required to rupture the innermost solvation layer is greater for [BMP]TFSA than for [EMIm]TFSA, attributed to stronger cation surface interactions. In situ STM elucidates the influence of IL species on restructuring of the Au(111) interface. In the presence of [BMP]TFSA, the Au(111) surface restructures to produce a wormlike pattern, but this unusual morphology is not observed for the [EMIm]TFSA−Au(111) sys...

The electroreduction of 0.5 M TaF 5 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 TaF 5 in the employed ionic liquid occurs in several steps. The first redox process is attributed to the reduction of TaF 5 to TaF 3 , 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.

The electrodeposition of silicon on Au(111) was investigated by cyclic voltammety (CV) and by in situ scanning tunneling microscopy (STM) in the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with a SiCl(4) concentration of 0.1 mol/L. A main reduction process begins in the cyclic voltammogram at about -1800 mV versus ferrocene/ferrocinium, which is correlated to the electrodeposition of elemental semiconducting silicon. It has been found that at an electrode potential more negative than the open circuit potential (OCP), the Au(111) surface is subject to a restructuring/reconstruction both in the case of the pure ionic liquid and in the presence of SiCl(4). The first STM-probed silicon islands with 150-450 pm in height appear at about -1700 mV versus ferrocene/ferrocinium. Their lateral and vertical growth leads to the formation of a rough layer with silicon islands of up to 1 nm in height. At about -1800 mV the islands merge and form silicon agglomerates. In situ I/U tunneling spectroscopy reveals a band gap of 1.1 +/- 0.2 eV for layers of about 5 nm in height, a value that has to be expected for semiconducting silicon.

Ionic liquids are superior media for production of semiconductors by a relatively simple electrochemical process. Nowadays ionic liquids are developing rapidly and their scientific and technological importance compasses a wide range of applications that attract the interest of the scientists. In this chapter the literature data on the feasibility of ionic liquids for electrochemical synthesis of semiconductors will be discussed.

Group III-V semiconductors are important in the production of a variety of optoelectronic devices. At present, these semiconductors are synthesized by high vacuum techniques. Here we report on the electrochemical deposition of GaN which seems to form in quite a thin layer from NH4Cl and GaCl3 in an ionic liquid.

The structure of the electrolyte/electrode interface plays a significant role in electrochemical processes. To date, most studies are focusing on understanding the interfacial structure in pure ionic liquids. In this paper in situ scanning tunnelling microscopy (STM) has been employed to elucidate the structure of the charged Au(111)-ionic liquid (1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate, [Py1,4]FAP) interface in the presence of 0.1 M LiCl. The addition of the Li salt to the ionic liquid has a strong influence on the interfacial structure. In the first STM scan in situ measurements reveal that Au(111) undergoes the (22 x √3) 'herringbone' reconstruction in a certain potential regime, and there is strong evidence that the gold surface dissolves at negative electrode potentials in [Py1,4]FAP containing LiCl. Bulk deposition of Li is obtained at -2.9 V in the second STM scan.

Ionic liquids are of high interest for the development of safe electrolytes in modern electrochemical cells, such as batteries, supercapacitors and dye-sensitised solar cells. However, electrochemical applications of ionic liquids are still hindered by the limited understanding of the interface between electrode materials and ionic liquids. In this article, we first review the state of the art in both experiment and theory. Then we illustrate some general trends by taking the interface between the extremely pure ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and an Au(111) electrode as an example. For the study of this interface, electrochemical impedance spectroscopy was combined with in situ STM and in situ AFM techniques. In addition, we present new results for the temperature dependence of the interfacial capacitance and dynamics. Since the interfacial dynamics are characterised by different processes taking place on different time scales, the temperature dependence of the dynamics can only be reliably studied by recording and carefully analysing broadband capacitance spectra. Single-frequency experiments may lead to artefacts in the temperature dependence of the interfacial capacitance. We demonstrate that the fast capacitive process exhibits a Vogel–Fulcher–Tamman temperature dependence, since its time scale is governed by the ionic conductivity of the ionic liquid. In contrast, the slower capacitive process appears to be Arrhenius activated. This suggests that the time scale of this process is determined by a temperature-independent barrier, which may be related to structural reorganisations of the Au surface and/or to charge redistributions in the strongly bound innermost ion layer.

In this discussion paper we discuss our recent results on the electrodeposition of materials and in situ STM/AFM measurements which demonstrate that ionic liquids should not be regarded as neutral solvents which all have similar properties. In particular, we focus on differences in interfacial structure (solvation layers) on metal electrodes as a function of ionic liquid species. Recent theoretical and experimental results show that conventional double layers do not form on metal electrodes in ionic liquid systems. Rather, a multilayer architecture is present, with the number of layers determined by the ionic liquid species and the properties of the surface; up to seven discrete interfacial solvent layers are present on electrode surfaces, consequently there is no simple electrochemical double layer. Both the electrodeposition of aluminium and of tantalum are strongly influenced by ionic liquids: in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]TFSA, aluminium is obtained as a nanomaterial, whereas in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]TFSA, a microcrystalline material is made. Tantalum can be deposited from [Py(1,4)]TFSA, whereas from [EMIm]TFSA only non-stoichiometric tantalum fluorides TaF(x) are obtained. It is likely that solvation layers influence these reactions.

In the present paper the underpotential deposition (UPD) of lithium on Au(111) from 0.5 mol L(-1) LiTFSA in the air- and water stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py(1,4)]TFSA, has been investigated by cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM). The pure [Py(1,4)]TFSA was found to be inert in the potential regime investigated. The results show that the lithium UPD on Au(111) in [Py(1,4)]TFSA begins at potentials considerably positive to the electrode potential of bulk deposition and follows a layer-by-layer mechanism with the formation of at least two monolayers. A large number of monoatomically deep pits appear when the potential reaches positive values, which is an indication that a Li-Au alloy was formed.

Group III-V semiconductors are important in the production of a variety of optoelectronic devices. At present, these semiconductors are synthesized by high vacuum techniques. Here we report on the electrochemical deposition of GaN which seems to form in quite a thin layer from NH4Cl and GaCl3 in an ionic liquid.

The electrical double layer at ionic liquid (IL)-Au(111) interfaces is composed of alternating ion layers. Interfacial layering is markedly weaker when small amounts of LiCl are dissolved in the IL for all potential between -2.0 V and +2.0 V (vs. Pt). This means that models developed for pure IL electrical double layers may not be valid when solutes are present.

We report about the use of different ionic liquids and catalyst materials in lithium-oxygen batteries. Different types of oxygen electrodes such as self-supporting oxygen electrodes and catalyst-coated separators were prepared by hot-pressing and spray-coating procedures, respectively. Porous carbon material such as Ketjen Black, binder material and different metal oxides were used to prepare the cathodes. Self-supporting oxygen electrodes and catalyst-coated separators consist of a carbon material loading of 10 and 1.5 mg/cm2, respectively. Electrolyte systems based on lithium bis-(trifluoromethylsulfonyl) imide (LiTFSI) in ionic liquids and lithium hexafluorophosphate (LiPF6) in carbonate solvents were investigated in lithium-oxygen batteries. 1-butyl-1-methyl-pyrrolidinium bis-(trifluoromethylsulfonyl) imide and 1-butyl-1-methyl-pyrrolidinium tetracyanoborate as well as 1-ethyl-3-methyl-imidazolium bis-(trifluoromethylsulfonyl) imide, thi oisocyanat and dicyanamide were tested. The cell potential recorded for ionic liquids ranged from 2 to 2.5 V during the discharge process. At a current density of 0.1 mA/cm2 geom discharge capacities were found to be higher for lithium-oxygen cells using imidazolium-based ionic liquids compared to pyrrolidinium-based ionic liquids. Discharge voltages between 2.7 and 2.8 V were observed for the carbonate-based solvents. The discharge potentials observed were independent of the metal oxide used, but the charge potentials were highly dependent on the catalyst materials employed. Good reversibility was obtained when the corresponding lithium-oxygen cells were cycled at 20–40% of their maximum capacity (mA h/g C).