RU2841640C1 - Method for electrochemical deposition of silicon-carbon film on electrically conductive substrate made from organic precursor containing lithium perchlorate - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to the field of thin-film coating technologies and can be used to produce materials of supercapacitors, fuel cells, electrodes of lithium-ion batteries and photocatalysts. Method comprises forming, on an electrically conductive substrate, a silicon-carbon film by electrochemical deposition from an organic silicon- and carbon-containing precursor containing hexamethyldisilazane in methyl or ethyl alcohol, to which lithium perchlorate (LiClO₄) powder is added in an amount at which its concentration in organic precursor reaches values of not more than 0.4 M. Electrochemical deposition of the silicon-carbon film is carried out in a potentiostatic mode in a three-electrode cell. As the working electrode, which is the cathode, an electroconductive substrate is used, as the counter electrode, which is the anode, a platinum plate is used. Comparison electrode used is silver wire. Distance between cathode and anode is set equal to 1 cm. Voltage not higher than 6 V is applied to electrodes with current density of up to 200 mA/cm².

EFFECT: forming a dense silicon-carbon film, having a silicon carbide SiC phase, on an electroconductive substrate.

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Description

The proposed invention relates to the field of technologies for creating thin-film coatings and can be used in industry for the production of materials for supercapacitors, fuel cells, lithium-ion battery electrodes and (photo)catalysts.

Materials based on silicon-carbon films, in particular, based on silicon carbide, are in high demand on the innovation market for use in various industries due to their mechanical strength, chemical inertness, high thermal and electrical conductivity and other sought-after functional characteristics. In this regard, new methods are being developed for both the synthesis of such materials and their application to substrates of various elemental compositions.

Known is patent US 2011/0290655 A1 "Method for electrochemically depositing carbon film on a substrate". The essence of the invention: obtaining a dense carbon film by electrochemical deposition from an electrolyte containing a melt of an alkali and/or alkaline earth metal halide and, predominantly, calcium carbide on a conductive substrate acting as an anode, in the presence of a cathode-counter electrode when applying a constant voltage in the range from 1 to 3 V to the electrodes and maintaining the operating temperature in the range of 250-800°C.

In the analogue the term “electrolyte” is used, in the proposed invention it is replaced by the term “precursor”.

The features of the analogue, common with the claimed method, are the following: obtaining a dense carbon-containing film by electrochemical deposition from a precursor containing an alkali metal salt onto a conductive substrate when applying a constant voltage to the electrodes.

However, when implementing this method, there is a need to maintain a high operating temperature of the process from 250 to 800°C to prevent the transition of electrolyte salts from the liquid aggregate state; there is a limitation in the choice of substrate material to those conductive structures that can immobilize alkali and/or alkaline earth metal ions; there is a procedure for additional cleaning of the carbon film from the alkali and/or alkaline earth metal salt that is part of the electrolyte that has adhered to it during the electrochemical deposition; there is no information on the possibility of electrochemical deposition of films containing other chemical elements in addition to carbon using this method.

A method for producing thin diamond-like films is also known, described in the article: Grishin, M.V. Electrochemical synthesis and study of thin diamond-like films on the surface of oxidized aluminum by STM-STS methods [Text] / M.V. Grishin, F.I. Dalidchik, A.I. Kulak, A.I. Kokorin, T.I. Kulak, B.R. Shub // CHEMICAL PHYSICS. - 2008. - Vol. 27, No. 5. - P. 31-39. The essence of the method is that carbon films containing predominantly carbon in ^sp3 hybridization are obtained on an aluminum or nickel substrate by electrochemical oxidation of acetylide ions in a dimethyl sulfoxide solution of lithium acetylide in a potentiostatic or galvanostatic mode (at a fixed current density of 0.005-10 mA/ ^cm2 , electrode voltage of 0.5-2 V), room temperature and normal atmospheric pressure in a sealed two-electrode glass cell with a platinum counter electrode.

The analogue uses the term “working solution”, in the proposed invention it is replaced by “precursor”.

The features of the analogue, common with the claimed method, are the following: carbon-containing films are obtained on an electrically conductive substrate electrochemically from a precursor containing a lithium compound in a potentiostatic mode, at room temperature and normal atmospheric pressure in a cell with a platinum counter electrode.

The disadvantages of the method described in the article include: the difficulty of obtaining a working solution of lithium acetylide in dimethyl sulfoxide, which consists of preparing a dimethyl sulfoxide solution of lithium salt by heating a mixture of dimethyl sulfoxide and lithium hydride for 5-6 hours at a temperature of 70±2°C, followed by passing gaseous acetylene through the resulting solution; the lack of data on the possibility of using other conductive substrates as a working electrode in addition to aluminum foil and nickel-containing steel, capable of effectively catalyzing the process of electrochemical dehydrogenation; this method allows the formation of exclusively carbon films.

The closest to the proposed invention is the "Method for the electrochemical deposition of silicon-carbon films on electrically conductive materials" (Patent of the Russian Federation No. 2676549 C1, published on 09.01.2019). When implementing this method, a silicon-carbon film is formed by electrodeposition from an organic silicon- and carbon-containing precursor consisting of hexamethyldisilazane in methyl or ethyl alcohol, on an electrically conductive substrate located on the cathode, to which a voltage of up to 600 V with a current density of up to 70 mA/cm ² is applied relative to the anode, and the distance between the cathode and the anode is set to 1 cm.

The prototype uses the term “electrodeposition”, in the proposed invention it is replaced by “electrochemical deposition method”.

The prototype features common to the claimed method: the silicon-carbon film is formed by electrochemical deposition from an organic silicon- and carbon-containing precursor consisting of hexamethyldisilazane in methyl or ethyl alcohol, onto an electrically conductive substrate located on the cathode, and the distance between the cathode and the anode is set to 1 cm.

The disadvantage of the prototype is the need to supply high voltage of up to 600 V to the electrodes to achieve the current density values required to start the electrochemical deposition process, which leads to an increased risk of equipment overload and short circuit.

The proposed method is aimed at forming a silicon-carbon film having a silicon carbide SiC phase by electrochemical deposition on an electrically conductive substrate made of an organic precursor when applying a voltage of no more than 6 V to the electrodes.

The technical result, which the proposed method is aimed at achieving, is the formation of a dense silicon-carbon film having a silicon carbide SiC phase on an electrically conductive substrate.

The technical result is achieved by adding lithium perchlorate powder LiClO ₄ to a precursor consisting of hexamethyldisilazane in methyl or ethyl alcohol in an amount such that its concentration in the organic precursor reaches values no higher than 0.4 M, after which electrochemical deposition of a silicon-carbon film is carried out in a potentiostatic mode in a three-electrode cell, where an electrically conductive substrate is used as the working electrode, which is the cathode, onto which the silicon-carbon film is electrochemically deposited, a platinum plate is used as the counter electrode, which is the anode, and a silver wire is used as the reference electrode, wherein a voltage of no more than 6 V with a current density of up to 200 mA/cm ² is applied to the electrodes.

The operation of the claimed method is as follows: an electrochemical cell is used, including three electrodes (cathode, anode and reference electrode), a platinum plate and silver wire are used as the anode (counter electrode) and reference electrode, respectively, an electrically conductive substrate is used as the cathode (working electrode). The substrate can be made of any electrically conductive material (for example: copper, nickel foam, carbon paper) or a dielectric material, but with an electrically conductive film (conductive glass, polycor with an electrically conductive film, etc.). The distance between the cathode and the anode should not exceed 1 cm. Then the electrodes are immersed in an organic silicon- and carbon-containing precursor (hexamethyldisilazane in methyl or ethyl alcohol) with the addition of lithium perchlorate powder LiClO ₄ in an amount at which its concentration in the organic precursor reaches values no higher than 0.4 M. After this, a constant voltage of no higher than 6 V with a current density of up to 200 mA/cm ² is applied to the electrodes, as a result of which a silicon-carbon film having a silicon carbide SiC phase is deposited on the cathode surface during the reduction reaction. The thickness of the resulting films depends on the duration of the deposition process.

One of the device variants on which the proposed method can be implemented includes: a chemically resistant container, a dielectric cover with electrodes and a thermocouple, a potentiostat-galvanostat with an output to a personal computer.

The essence of the invention is disclosed in the following examples.

Example 1

An organic silicon- and carbon-containing precursor was prepared from hexamethyldisalazane in methyl alcohol in a ratio of 1:9 and a volume of 30 ml, after which 0.585 g of lithium perchlorate salt powder LiClO ₄ was added to it until the salt concentration reached 0.3 M. A copper plate, previously cleaned of oxides and thoroughly washed with distilled water, was used as an electrically conductive substrate; the copper plate was placed at a distance of 1 cm from the platinum counter electrode. Then the dielectric cover with electrodes and a thermocouple previously connected to the potentiostat-galvanostat was immersed in the precursor and a constant voltage of 5 V was applied to the electrodes. Electrochemical deposition was performed for 3600 seconds. As a result, a dense silicon-carbon film with a thickness of about 1 μm was obtained. The dependence of the current on the deposition time of the silicon-carbon film is shown in Fig. 1, the morphology of the resulting film is shown in Fig. 2.

Example 2

The silicon-carbon film was obtained by the method of electrochemical deposition according to Example 1 with the only difference: nickel foam, previously cleaned of oxides and thoroughly washed with distilled water, was used as the conductive substrate. The dependence of the current on the deposition time of the silicon-carbon film is shown in Fig. 3, the morphology of the obtained film is shown in Fig. 4.

A typical view of the Raman spectrum of silicon-carbon film samples is shown in Fig. 5.

Thus, the proposed method allows forming silicon-carbon films by electrochemical deposition on any electrically conductive materials. This method is technically simple, and its implementation does not require complex technological equipment. In addition, the proposed method increases the safety of the processes of forming silicon-carbon films.

Claims (1)

A method for the electrochemical deposition of a silicon-carbon film on an electrically conductive substrate, comprising forming a silicon-carbon film by electrochemical deposition from an organic silicon- and carbon-containing precursor containing hexamethyldisilazane in methyl or ethyl alcohol, on an electrically conductive substrate, wherein the distance between the cathode and the anode is set equal to up to 1 cm, characterized in that lithium perchlorate powder (LiClO ₄ ) is added to the organic precursor containing hexamethyldisilazane in methyl or ethyl alcohol in an amount such that its concentration in the organic precursor reaches values no higher than 0.4 M, after which the electrochemical deposition of the silicon-carbon film is carried out in a potentiostatic mode in a three-electrode cell, in which an electrically conductive substrate is used as the working electrode, which is the cathode, onto which the silicon-carbon film is deposited, and as the counter electrode, which is anode, a platinum plate is used, and a silver wire is used as a reference electrode, while a voltage of no more than 6 V with a current density of up to 200 mA/cm ² is applied to the electrodes.