Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PROCESS FOR PRODUCING ZINC NANOWIRES
Document Type and Number:
WIPO Patent Application WO/2016/110409
Kind Code:
A1
Abstract:
The present invention relates to a process for producing zinc nanowires comprising at least the process step of electrochemically depositing zinc directly onto at least one surface of an electrode from a solution comprising at least one zinc compound (A), at least one silicon compound (B) and at least one ionic liquid (C).

Inventors:
SOMMER HEINO (DE)
AL-SALMAN RIHAB (DE)
BREZESINSKI TORSTEN (DE)
Application Number:
PCT/EP2015/080914
Publication Date:
July 14, 2016
Filing Date:
December 22, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BASF SE (DE)
International Classes:
C25D3/66; C25D1/00; C25D1/04; C25D3/22; C25D3/56
Domestic Patent References:
WO2012170311A22012-12-13
WO2012170311A22012-12-13
WO2013052456A12013-04-11
Foreign References:
US20140248543A12014-09-04
US20100258443A12010-10-14
Other References:
CLAIRE FOURNIER ET AL: "Zn, Ti and Si nanowires by electrodeposition in ionic liquid", ELECTROCHEMISTRY COMMUNICATIONS, ELSEVIER, AMSTERDAM, NL, vol. 13, no. 11, 19 August 2011 (2011-08-19), pages 1252 - 1255, XP028320518, ISSN: 1388-2481, [retrieved on 20110831], DOI: 10.1016/J.ELECOM.2011.08.031
JIA-MING YANG ET AL: "Direct electrodeposition of FeCoZn wire arrays from a zinc chloride-based ionic liquid", ELECTROCHEMISTRY COMMUNICATIONS, ELSEVIER, AMSTERDAM, NL, vol. 13, no. 11, 2 September 2011 (2011-09-02), pages 1178 - 1181, XP028320499, ISSN: 1388-2481, [retrieved on 20110910], DOI: 10.1016/J.ELECOM.2011.09.002
J.P. HEREMANS; C.M. THRUSH; D. T. MORELLI; M.C. WU, PHYS. REV. LETT., vol. 91, 2003, pages 076804
J.G. WANG; M.L. TIAN; N. KUMAR; T.E. MALLOUK, NANO LETT., vol. 5, 2005, pages 1247
Y. CHEN; S.D. SNYDER; A.M. GOLDMAN, PHYS. REV. LETT., vol. 103, 2009, pages 127002
E. DEISS; F. HOLZER; O. HASS, ELECTRO-CHIM. ACTA, vol. 47, 2002, pages 3995
J.G. WANG; M.L. TIAN, MICROSC. MICROANAL., vol. 11, no. S02, 2005, pages 1888
P. SCHROEDER; M. KAST; E. HALWAX; C. EDTMAIER; O. BETHGE; H. BRIICKL, J. APPL. PHYS., vol. 105, 2009, pages 104307
D. YUVARAJ; K.N. RAO; K. BARAI, SOLID STATE COMMUN., vol. 149, 2009, pages 349
Y. TONG; M. SHAO; G. QIAN; Y. NI, NANOTECHNOLOGY, vol. 16, 2005, pages 2512
Y. WANG; L. ZHANG; G. MENG; C. LIANG; G. WANG; S. SUN, CHEM. COMMUN., 2001, pages 2632
Y.J. CHEN; B. CHI; H.Z. ZHANG; H. CHEN; Y. CHEN, MATER. LETT, vol. 61, 2007, pages 144
J. LI; X. CHEN, SOLID STATE COMMUN., vol. 131, 2004, pages 769
J. V.D.S. ARAUJO; R. V. FERREIRA; M. I. YOSHIDA; V. M.D. PASA, SOLID STATE SCI., vol. 11, 2009, pages 1673
R. CONG; Q. WANG; J. ZHANG; J. WANG; Y. XU; Y. JIN; Q. CUI, MATER. CHEM. PHYS., vol. 129, 2011, pages 611
J. G. WANG; M. L. TIAN; N. KUMAR; T. E. MALLOUK, NANO LETT., vol. 5, 2005, pages 1247
Z. LIU; S. ZEIN; EL ABEDIN; M. S. GHAZVINI; F. ENDRES, PHYS. CHEM. CHEM. PHYS., vol. 15, 2013, pages 11362
D. PRADHAN; S. SINDHWANI; K. T. LEUNG, PHYS. CHEM. C, vol. 113, 2009, pages 15788
C. FOURNIER; F. FAVIER, ELECTROCHEM. COMMUN., vol. 13, 2011, pages 1252
Download PDF:
Claims:
Claims

1. A process for producing zinc nanowires comprising at least the process step of

(a) electrochemically depositing zinc directly onto at least one surface of an electrode from a solution comprising (A) at least one zinc compound,

(B) at least one silicon compound and

(C) at least one ionic liquid, wherein the concentration of the silicon compound in the solution is in the range from 0.01 M to 1 M.

2. The process according to claim 1 , wherein the zinc compound (A) is a zinc dihalide.

3. The process according to claim 1 or 2, wherein the silicon compound (B) is a silicon tetra- halide.

4. The process according to any of claims 1 to 3, wherein the concentration of the silicon compound (B) in the solution is in the range from 0.4 M to 0.8 M.

5. The process according to any of claims 1 to 4, wherein the solution comprises at least one organic solvent (D). 6. The process according to any of claims 1 to 5, wherein the concentration of all ionic liquids (C) in the solution is at least 0.05 M.

7. The process according to any of claims 1 to 4, wherein the solution comprises at least one organic solvent (D) and wherein the concentration of all ionic liquids (C) in the solution is at least 0.05 M.

8. The process according to any of claims 1 to 7, wherein process step (a) takes place at a temperature in the range from 15 °C to 50 °C. 9. The process according to any of claims 1 to 8, wherein process step (a) takes place at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt quasi-reference electrode.

0. The process according to any of claims 1 to 9, wherein the surface of the electrode, where the zinc nanowires are deposited, is composed of a material selected from the group consisting of copper, zinc, and glassy carbon.

1. The process according to claim 1 , wherein the zinc compound (A) is zinc dichloride, wherein the concentration of zinc dichloride in the solution is in the range from 0.02 to 0.2 M, and the silicon compound (B) is silicon tetrachloride, wherein the concentration of silicon tetrachloride in the solution is in the range from 0.4 M to 0.8 M, and wherein process step (a) takes place at a temperature in the range from 15 °C to 50 °C and at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt quasi-reference electrode.

Description:
Process for producing zinc nanowires

Description The present invention relates to a process for producing zinc nanowires comprising at least the process step of electrochemically depositing zinc directly onto at least one surface of an electrode from a solution comprising at least one zinc compound (A), at least one silicon compound (B) and at least one ionic liquid (C). Zinc metal (Zn) has interesting catalytic, electrical and optical properties but in the form of Zn nanowires it possesses special thermoelectric and magneto-resistance [J. P. Heremans, CM. Thrush, D. T. Morelli, M.C. Wu, Phys. Rev. Lett., 91 (2003) 076804] as well as superconducting properties [J.G. Wang, M.L. Tian, N. Kumar, T.E. Mallouk, Nano Lett., 5 (2005) 1247, Y. Chen, S.D. Snyder, A.M. Goldman, Phys. Rev. Lett., 103 (2009) 127002]. Zn nanostructures have po- tential uses in rechargeable alkaline zinc-air batteries [E. Deiss, F. Holzer, O. Hass, Electro- chim. Acta, 47 (2002) 3995] and as a contact material to connect nanodevices [J.G. Wang, M.L. Tian, Microsc. Microanal., 1 1 (S02) (2005) 1888]. Furthermore, Zn nanowires have been utilized as a precursor to obtain other Zn-based semiconductors such as ZnO which have extensive applications in electronics, photoelectronics and phonics [P. Schroeder, M. Kast, E. Halwax, C. Edtmaier, O. Bethge, H. Bruckl, J. Appl. Phys., 105 (2009) 104307].

Zn nanostructures are mainly synthesized by high temperature techniques such as thermal evaporation of zinc metal at temperatures of 550 °C - 900 °C [D. Yuvaraj, K.N. Rao, K. Barai, Solid State Commun., 149 (2009) 349; Y. Tong, M. Shao, G. Qian, Y. Ni, Nanotechnology 16 (2005) 2512], thermal decomposition of ZnS powders at 1000 °C [Y. Wang, L. Zhang, G. Meng, C. Liang, G. Wang, S. Sun, Chem. Commun., (2001 ) 2632] and chemical reduction of ZnO by e.g. boron at 1050 °C [Y.J. Chen, B. Chi, H.Z. Zhang, H. Chen, Y. Chen, Mater. Lett. 61 (2007) 144], NHs at 1060 °C [J. Li, X. Chen, Solid State Commun. 131 (2004) 769] or by carbon (car- bothermal reduction) at 800°C-900°C [J. V.D.S. Araujo, R. V. Ferreira, M. I. Yoshida, V. M.D. Pasa, Solid State Sci., 1 1 (2009) 1673]. Plasma-assisted synthesis of Zn nanowires has also been reported [R. Cong, Q. Wang, J. Zhang, J. Wang, Y. Xu, Y. Jin, Q. Cui, Mater. Chem. Phys., 129 (201 1 ) 61 1]. However, these methods are considered to be disadvantageous for a technological process due to the relatively complicated procedures and due to the expensive heating steps as well as the high vacuum which is required in some cases. Template-assisted electrodeposition methods have been also reported, Wang et al. as an example reported on the fabrication of Zn nanowires in propylene carbonate (PC) and in anodic aluminium oxide (AAO) membranes from aqueous solutions. The authors metioned that Zn nanowires of diameters of 40 to 100 nm can be obtained by this method [J. G. Wang, M. L. Tian, N. Kumar, T. E. Mallouk, Nano Lett., 5 (2005) 1247]. Recently, Liu et al. reported on the electrodeposition of Zn nano- wires with an average diameter of 90 nm and a length of up to 18 μηη from ionic liquid solutions inside PC membranes [Z. Liu, S. Zein El Abedin, M. S. Ghazvini, F. Endres, Phys. Chem.

Chem. Phys., 15 (2013) 1 1362]. Although these electrochemical methods are considered to be more facile than the previous methods they are still disadvantageous for a technological pro- cess. This is because it is a multistep process where the template must be sputtered with a conductive material prior to the deposition process and it (the template) must be removed at the end of the process. Therefore, it is more effective to have a template-free electrochemical synthesis route. There are only few reports in literature on the template-free electrodeposition of Zn nanowires. Pradhan et al. as an example reported on the electrodeposition of Zn nanowires on ITO glass or on ln 2 Os/Au/Ag coated polyethylene terephthalate (PET) electrodes from aqueous solutions at 0 °C [D. Pradhan, S. Sindhwani, K. T. Leung, Phys. Chem. C, 1 13 (2009) 15788]. However, the diameter of the obtained nanowires was not uniform over the length (20 - 200 nm) and the nanowires exhibit numerous bends and turns at different angles and junctions with dou- ble and triple (and multiple) branches. Moreover, the nanowires are only obtainable at 0 °C which means a cooling step during the synthesis is needed. Fournier and Favier reported recently on the electrodeposition of Zn nanowires from ionic liquid-based solutions by kinetically- controlled electrochemical decoration of step-edges at highly oriented pyrolytic graphite (HOPG) surface [C. Fournier, F. Favier, Electrochem. Commun., 13 (201 1 ) 1252]. In this method the deposition of Zn nanowires occurs via two steps, first nucleation step of 10 ms at highly reductive potential which preferably occurs at the step-edges of HOPG. The second step includes the growth of the nuclei as particles by applying an overpotential for a few hundreds of seconds. If the density of the nuclei is high enough (along the step edges), growing particles will coalesce with neighbors to form continuous nanowires. According to the authors, the obtained nanowires can have a diameter of 10 to 100 nm and a length of few hundred micrometers. However, as can be realized, the method is limited to HOPG substrate and includes multi steps. In addition, it needs an accurate control of the deposition conditions to have the suitable density of nuclei and suitable size of the particles. Furthermore, it seems that the nanowires can be hardly harvested from the HOPG substrate without destroying them.

WO 2012/17031 1 discloses a method of making metal nanoneedles on the surface of a substrate material via electrodeposition. The SEM images of the nanoneedles show needles with an uneven surface and also needles being tapered along the axis. WO 2013/052456 describes a method for producing nanostructured materials such as silicon nanowires and their application as anode component for lithium ion batteries. The preparation of zinc nanowires is experimentally not disclosed.

Proceeding from this prior art, the object was to find a flexible and more efficient synthesis route to zinc nanowires which are useful in different applications as described above.

This object is achieved by a process for producing zinc nanowires comprising at least the process step of (a) electrochemically depositing zinc directly onto at least one surface of an electrode from a solution comprising (A) at least one zinc compound,

(B) at least one silicon compound and

(C) at least one ionic liquid, wherein the concentration of the silicon compound in the solution is in the range from 0.01 M to 1 M. The zinc nanowires obtainable or obtained by the inventive process are preferably crystalline. The thickness of zinc nanowires obtainable or obtained by the inventive process is usually in the range from 1 nm to 100 nm, preferably in the range from 5 nm to 50 nm, in particular in the range from 10 nm to 30 nm. The zinc nanowires obtainable or obtained by the inventive process can be covered by a surface layer comprising the elements silicon, oxygen and carbon. The thickness of the surface layer can vary in a wide range. Preferably the thickness of the surface layer is in range of a 1/50 to 1/3, more preferably 1/20 to 1/5 of the total thickness of the nan- owire.

In a preferred embodiment of the present invention the zinc nanowires, disregarding an existing surface layer, consist essentially of zinc, that means that the zinc-content of the zinc nanowires is preferably at least 80 %, more preferably in the range of from 90 % to 100 %, in particular from 97 % to 100 % by weight based on the total weight of the zinc nanowires disregarding the total weight of an existing surface layer. The length of the zinc nanowires can be varied in a wide range, depending on the reaction conditions. Zinc is electrochemically deposited onto at least one surface of an electrode.

In a preferred embodiment of the invention the zinc nanowires show an aspect ratio of at least 100, more preferably an aspect ratio in the range from 500 to 3000, in particular in the range from 1000 to 2000.

The definition of the aspect ratio as used herein is for example given in WO 2013/052456, page 8, paragraph [0050]. Depending on the concentration of silicon compound (B) the zinc nanowires obtainable or obtained by the inventive process can show different morphological arrangements, like porous structure of nanowires or closely-stacked zinc nanowires having a high-aspect-ratio.

The length, the thickness, the aspect ratio or the morphological arrangement of the zinc nan- owires obtained by the inventive process can be determined from the SEM images of the corresponding samples. In process step (a) of the inventive process zinc nanowires are directly electrochemically deposited onto at least one surface of an electrode from a solution comprising at least one zinc compound (A), at least one silicon compound (B) and at least one ionic liquid (C). The method of electrochemical deposition is well known as mentioned in WO 2013/052456, page 17, paragraph [0074] and referring the literature cited therein.

The solution from which zinc nanowires are electrochemically deposited comprises at least one zinc compound (A), also referred to hereinafter as component (A) for short. The zinc of compo- nent (A) is usually in the oxidation state +2. Component (A) is preferably at least partly, preferably completely soluble in the formed solution.

Examples of zinc compounds (A) in the oxidation state +2 are zinc(ll) halides like ZnC , Zn(ll) triflate, zinc(ll) oxalate, zinc(ll) acetate, zinc(ll) acetylacetonate or zinc(ll) stearate.

Instead of using a single zinc compound (A) it is also possible to use two or more different zinc compounds (A) in the solution.

Preferred zinc compounds (A) are zinc(ll) halides like zinc dichloride, zinc dibromide or zinc diiodide, in particular zinc dichloride.

In one embodiment of the present invention, the inventive process is characterized in that the zinc compound (A) is a zinc dihalide, in particular zinc dichloride. The concentration of component (A) in the solution can be varied in a wide range depending on the solubility of component (A) in the solution. Preferably the concentration of component (A) in the solution is in the range from 0.01 M to 0.5 M, more preferably in the range from 0.01 M to 0.3 M, in particular in the range from 0.02 M to 0.2 M. The solution from which zinc nanowires are electrochemically deposited comprises further at least one silicon compound (B), also referred to hereinafter as component (B) for short. The silicon of component (B) is usually in the oxidation state +4. Component (B) is preferably at least partly, more preferably completely soluble in the formed solution. Examples of silicon compounds (B) are silicon tetrahalides like SiCU or SiBr 4 , organo halo silanes like dimethyldichlorosilane, trichloro(phenyl)silane or trimethylchlorosilane.

Instead of using a single silicon compound (B) it is also possible to use two or more different silicon compounds (B) in the solution.

Preferred silicon compounds (B) are silicon tetrahalides like silicon tetrachloride or silicon tetra- bromide, in particular silicon tetrachloride. In one embodiment of the present invention, the inventive process is characterized in that the silicon compound (B) is a silicon tetrahalide, in particular silicon tetrachloride.

The electrochemical deposition of zinc from a solution comprising only one zinc compound (A) and an ionic liquid (C) and no silicon compound (B) results in the formation of large agglomerates of 100-200 nm hexagonal platelets of metallic zinc, while zinc nanowires are formed by the electrochemical deposition of zinc from a solution comprising component (A), component (B) and at least one ionic liquid (C), wherein the concentration of the silicon compound (B) in the solution is in the range from 0.01 M to 1 M, preferably in the range from 0.05 M to 1 M, more preferably the range from 0.1 M to 0.9 M, in particular in the range from 0.4 M to 0.8 M.

In one embodiment of the present invention, the inventive process is characterized in that the concentration of the silicon compound (B) in the solution is in the range from 0.4 M to 0.8 M. In addition to the at least one component (A) and to the at least one component (B) the solution, from which zinc nanowires are electrochemically deposited, comprises further at least one ionic liquid (C), also referred to hereinafter as component (C) for short. Ionic liquids (C) are known to the person skilled in the art. Several ionic liquids, which are liquid salts with a melting point below 100 °C, in particular below room temperature, are commercially available or can be pre- pared according to known protocols. The ionic liquid (C) can be varied in a wide range as long as component (C) is liquid at the temperature of the deposition and dissolves the components (A) and (B) sufficiently and does not chemically react with them. In addition the ions of the ionic liquid (C) preferably do not react under the conditions of the electrochemical deposition. Examples of suitable ionic liquids (C) are salts comprising a cation selected from the group of cations consisting of substituted imidazolium, substituted pyrrolidinium, substituted piperidinium, substituted pyridinium, substituted phosphonium and substituted ammonium, preferably consisting of substituted imidazolium and substituted pyrrolidinium, wherein substituted means the presence of at least on organic radical, and an anion selected from the group of anions consist- ing of (CF 3 S0 2 ) 2 N- (TFSI " ), CF 3 S0 3 - (TFO ~ ), ROSOs " , RSOs " (R= e.g. Me or Et), tosylate, acetate, dialkylphospates and hydrogensulfate, preferably consisting of of (CFsSC^N " , CF3SO3 " , ROSO3- and RSOs " with R = Me or Et.

Preferred example of ionic liquids (C) is 1 -ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide.

Instead of using only one ionic liquid (C) it is also possible to use two or more different ionic liquids (C) in the solution. In one embodiment of the present invention, the inventive process is characterized in that the ionic liquid (C) is selected from the group consisting of 1 -butyl-1 -methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP-TFSI) and 1 -ethyl-3-methylimidazolium

bis(trifluoromethylsulfonyl) imide (EMIm-TFSI), preferably EMIm-TFSI.

In addition to the at least one component (A), to the at least one component (B) and to the at least one ionic liquid the solution might comprise further components, which are inert under the conditions of the electrochemical deposition reaction like polar aprotic solvents which are usually used in electrolytes of electrochemical cell. Preferably the solution is essentially free of water, i.e. the water content in the solution is below 0.1 % by weight, preferably below 500 ppm, in particular in the range from 0.1 ppm to 10 ppm.

If component C, for example as technical grade, comprises more water than desired, the water can be removed by known methods, like stripping the water from component A by heating it under reduced pressure, or by adding drying reagents like molecular sieves or by adding scavengers like aluminum alkyls, magnesium alkyls or lithium alkyls. It is also possible to remove excess water by adding additional amount of silicon tetrachloride, which form insoluble compounds by reacting with water.

Preferably the sum of the weight of all components (A), (B) and (C) is at least 90% by weight, preferably in the range from 95% to 100% by weight, in particular in the range from 98% to 100% by weight based on the total weight of the solution.

The electrochemical deposition of zinc nanowires from a solution comprising at least one zinc compound (A), at least one silicon compound (B), wherein the concentration of the silicon compound (B) in the solution is in the range from 0.01 M to 1 M, preferably in the range from 0.1 M to 1 M, more preferably the range from 0.2 M to 0.9 M, in particular in the range from 0.4 M to 0.8 M and at least one ionic liquid (C) is also possible in the presence of at least one organic solvent (D). Preferably the organic solvent (D) is a polar aprotic solvent, more preferably a polar aprotic solvent selected from the group consisting of cyclic carbonates, in particular propylene carbonate, ethylene carbonate and fluoroethylene carbonate, acetonitrile, dimethylformamide, tetrahydrofurane, acetone and dimethyl sulfoxide.

In one embodiment of the present invention, the inventive process is characterized in that the solution comprises at least one organic solvent (D), preferably at least one polar aprotic solvent (D), more preferably a polar aprotic solvent selected from the group consisting of cyclic car- bonates, in particular propylene carbonate, ethylene carbonate and fluoroethylene carbonate, acetonitrile, dimethylformamide, tetrahydrofurane, acetone and dimethyl sulfoxide.

The concentration of component (C) in the solution, which comprises beside component (A) and component (B) also component (D), can be varied in a wide range. Preferably the concentration of all ionic liquids (C) in the solution is at least 0.05 M, more preferably at least 0.1 M, in particular at least 0.2 M up to the maximal concentration of the sum of all ionic liquids (C) in a solution comprising no organic solvent (D). In one embodiment of the present invention, the inventive process is characterized in that the concentration of all ionic liquids (C) in the solution is at least 0.05 M, more preferably at least 0.1 M, in particular at least 0.2 M up to the maximal concentration of the sum of all ionic liquids

(C) in a solution comprising no organic solvent (D).

For economic reasons the amount of ionic liquids, which are usually more expensive than suitable organic solvents, is reduced in the solution, which is the electrolyte, as far as possible.

In one embodiment of the present invention, the inventive process is characterized in that the solution comprises at least one organic solvent (D), preferably at least one polar aprotic solvent

(D) , more preferably a polar aprotic solvent selected from the group consisting of cyclic carbonates, in particular propylene carbonate, ethylene carbonate and fluoroethylene carbonate, acetonitrile, dimethylformamide, tetrahydrofurane, acetone and dimethyl sulfoxide, and wherein the concentration of all ionic liquids (C) in the solution is at least 0.05 M, more preferably at least 0.1 M, in particular at least 0.2 M up to the maximal concentration of the sum of all ionic liquids (C) in a solution comprising no organic solvent (D).

The solution used in process step a) is usually prepared by simply mixing the components (A), (B) and (C) preferably under inert and dry, i.e. water-free, conditions, using Schlenk technique or working in a glove-box.

The electrochemical deposition can be take place in a wide temperature range. Preferably process step (a) takes place at a temperature in the range from 0 °C to 100 °C, more preferably in the range from 15 °C to 50 °C, in particular in the range from 20 °C to 35 °C.

In one embodiment of the present invention, the inventive process is characterized in that process step (a) takes place at a temperature in the range from 15 °C to 50 °C, in particular in the range from 20 °C to 35 °C. The time of electrochemically depositing zinc can be varied in a broad range and is preferably adjusted to the desired length of the zinc nanowires deposited.

The electrochemical deposition can be take place in a wide range of deposition potentials which are given by reference to a Pt quasi-reference electrode. Preferably process step (a) takes place at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt quasi-reference electrode.

In one embodiment of the present invention, the inventive process is characterized in that process step (a) takes place at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt qua- si-reference electrode. During the electrochemical deposition the surface of the electrode and the solution can be static to each other or the solution is in motion relative to the surface of the electrode, e.g. by simply stirring the solution or by continuously supplying the surface of the electrode with new solution using a pump around system.

The surface of the electrode, where the zinc nanowires are deposited during the electrochemical deposition, can be selected from a large number of electrically conductive materials like metals and conductive carbons. Preferably the electrochemical deposition of the zinc nanowire takes place on the surface of an electrode, wherein the surface is composed of a material se- lected from the group consisting of copper, zinc and glassy carbon.

In one embodiment of the present invention, the inventive process is characterized in that the surface of the electrode, where the zinc nanowires are deposited, is composed of a material selected from the group consisting of copper, zinc, and glassy carbon.

Zinc nanowires with a high aspect ratio in the range from 500 to 2000 and a high number of nanowires per electrode area are preferably obtained in process step a) of the inventive process under conditions wherein the zinc compound (A) is zinc dichloride, wherein the concentration of zinc dichloride in the solution is in the range from 0.01 M to 0.3 M, in particular in the range from 0.05 to 0.2 M, and the silicon compound (B) is silicon tetrachloride, wherein the concentration of silicon tetrachloride in the solution is in the range from 0.4 M to 0.8 M, and wherein process step (a) takes place at a temperature in the range from 15 °C to 50 °C, preferably 20 °C to 35 °C, and at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt quasi-reference electrode. In one embodiment of the present invention, the inventive process is characterized in that the zinc compound (A) is zinc dichloride, wherein the concentration of zinc dichloride in the solution is in the range from 0.02 to 0.2 M, and the silicon compound (B) is silicon tetrachloride, wherein the concentration of silicon tetrachloride in the solution is in the range from 0.4 M to 0.8 M, and wherein process step (a) takes place at a temperature in the range from 15 °C to 50 °C and at a deposition potential in the range from -1.9 V to - 2.5 V vs. Pt quasi-reference electrode.

The zinc nanowires obtained in process step a) of the inventive process are usually isolated by separation them mechanically from the surface of the electrode, for example by cutting. The isolated zinc nanowires can be used in different applications e.g. in electronics, catalysis and for the preparation of nanowires comprising zinc oxide, which can be used in sensors and solar cells.

The present invention also provides zinc nanowires, preferably zinc nanowires having an aspect ratio in the range from 500 to3000, in particular in the range from 1000 to 2000 obtainable by a process for producing zinc nanowires as described above. This process comprises the above- described process step (a) especially also with regard to preferred embodiments thereof. The present invention likewise also provides zinc nanowires, preferably zinc nanowires having an aspect ratio in the range from 500 to3000, in particular in the range from 1000 to 2000, wherein the zinc nanowires are prepared by a process comprising at least the process steps of (a) electrochemically depositing zinc directly onto at least one surface of an electrode from a solution comprising

(A) at least one zinc compound, (B) at least one silicon compound and

(C) at least one ionic liquid, wherein the concentration of the silicon compound in the solution is in the range from 0.01 M to 1 M.

The process step a) has been described above. In particular, preferred embodiments of the process step have been described above. The zinc nanowires, preferably zinc nanowires having an aspect ratio in the range from 500 to 3000, in particular in the range from 1000 to 2000, which are obtainable or obtained by the inventive process, are preferably crystalline. The thickness of zinc nanowires obtainable or obtained by the inventive process is usually in the range from 1 nm to 100 nm, preferably in the range from 5 nm to 50 nm, in particular in the range from 10 nm to 30 nm. The zinc nanowires obtainable or obtained by the inventive process can be covered by a surface layer comprising the elements silicon, oxygen and carbon. The thickness of the surface layer can vary in a wide range. Preferably the thickness of the surface layer is in range of a 1/50 to 1/3, more preferably 1/20 to 1/5 of the total thickness of the nanowire. In a preferred embodiment of the present invention the zinc nanowires, disregarding an existing surface layer, consist essentially of zinc, that means that the zinc-content of the zinc nanowires is preferably at least 80 %, more preferably in the range of from 90 % to 100 %, in particular from 97 % to 100 % by weight based on the total weight of the zinc nanowires disregarding the total weight of an existing surface layer.

The present invention further provides a device comprising at least one electrochemical cell as described above.

The invention is illustrated by the examples which follow, but these do not restrict the invention.

Figures in percent are each based on % by weight, unless explicitly stated otherwise. Electrochemical deposition of

Used Chemicals:

The ionic liquid (IL) 1 -ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIm-TFSI, lo-Li-Tec) was purchased in the highest available quality and used after drying under vacuum at 100 °C for several hours to water content below 3 ppm. SiCU (99.998%, Alfa Aesar) was used as received.

General Electrochemical Setup:

Cu foil (> 99.9%, GOULD Electronics) was mainly used as a working electrode. Pt wires

(99.997%, Alfa Aesar) were used as quasi-reference and counter electrodes. The substrates were cleaned ultrasonically in acetone for 5 minutes before use. However, the use of Cu foil as- received seems not to affect the growth of Zn nanowires. The electrochemical cell was made of Teflon and clamped over a Teflon-covered O-ring yielding a geometric surface area of 0.5 cm 2 of the used substrate. A Pt wire was coiled into three rings with a diameter of ~ 1 .5 cm and was embedded into the Teflon cavity (0.6 cm deep and 0.5 cm thick) which surrounds the reaction area of the working electrode. In other words, the Teflon cell looks like a small cylinder (8 mm in diameter, where the working electrode is underneath) surrounded by a bigger cylinder (18 mm in diameter, where the coiled Pt wire is placed on its Teflon ground). This coiled wire was serv- ing as a counter electrode. A Pt wire was immersed into the reaction solution near from the working electrode (about 2 mm away from it) to serve as a quasi-reference electrode.

General Performance of Electrochemical Experiments:

Due to the hygroscopic nature of some of the utilized chemicals like SiCU, all of solutions were prepared inside an argon-filled glove-box (MBRAUN) with oxygen and water content below 1 ppm. All of the electrochemical measurements were performed inside the glove-box as well. These measurements were performed by using BioLogic potentiostat/galvanostat controlled by EC-Lab software. 1.1 Comparative and inventive examples for the electrochemical deposition of zinc Example 1 (comparative)

The above described Teflon cell was filled with about 2 ml solution of 0.05 M ZnC in EMIm- TFSI IL. The Zn deposition on Cu foil was then performed by applying a constant potential of - 2.0 V vs. Pt quasi-reference electrode for 1 .5 hour at 25 °C. A total charge of ~ 0.4 C/cm 2 was consumed during this period of time. Figure 1 shows SEM images of the obtained deposit. No nanowires were obtained in the absence of SiCU. Example 2 (inventive)

The Teflon cell was filled with about 2 ml of 0.05 M ZnCI 2 and 0.5 M SiCI 4 in EMIm-TFSI IL solution and the substrate was a Cu foil with a geometric surface area of 0.5 cm 2 . The deposition was performed by applying a constant potential of - 2.0 V vs. Pt quasi-reference electrode for 75 minutes which corresponds to a total charge flow of 0.42 C/cm 2 . Figure 2 shows SEM images of the obtained Zn nanowires.

Example 3 (inventive)

The Teflon cell was filled with about 2 ml solution of (0.5 M SiCI 4 + 0.1 M ZnCI 2 ) in EMIm-TFSI IL. The Zn deposition on Cu foil was then performed by a constant potential of - 2.0 V vs. Pt quasi-reference electrode for 1 hour which corresponds to a total charge flow of 0.94 C/cm 2 . Figure 3 shows SEM images of the obtained Zn nanowires.

Figure 1 .: SEM images of Zn deposit obtained from a solution of 0.05 M ZnC in EMIm-TFSI

IL. Deposition potential: -2.0 V, deposition time: 1.5 hour. Temperature: 25 °C. Figure 2.: SEM images of Zn nanowires obtained from a solution of (0.5 M SiCI 4 + 0.05 M

ZnCI 2 ) in EMIm-TFSI IL. Deposition potential: -2.0 V, deposition time: 75 minutes. Temperature: 25 °C.

Figure 3.: SEM images of Zn nanowires obtained from a solution of (0.5 M SiCI 4 + 0.1 M

ZnC ) in EMIm-TFSI IL. Deposition potential: -2.0 V, deposition time: 1 hour. Temperature: 25 °C.