US 20160305035A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2016/0305035 A1 LUBLOW et al. (43) Pub. Date: Oct. 20, 2016
(54) METAL CHALCOGENIDE THIN FILM COIG 53/04 (2006.01) ELECTRODE, METHOD FOR THE COIG 51/00 (2006.01) PRODUCTION THEREOF AND USE COIG 49/02 (2006.01) COIG 3/02 (2006.01) (71) Applicant: Technische Universitaet Berlin, Berlin COB 33/20 (2006.01) (DE) C25B I/O (2006.01) COIG 5L/04 (2006.01) (72) Inventors: Michael LUBLOW, Berlin (DE); Anna (52) U.S. Cl. FISCHER, Berlin (DE); Matthias CPC ...... C25D 9/08 (2013.01); C25B I/003 DRIESS, Berlin (DE); Thomas (2013.01); C25B II/0452 (2013.01); COIG SCHEDEL-NIEDRIG, Kleinmachnow 53/04 (2013.01); COIG 51/04 (2013.01); (DE); Marcel-Philip LUECKE, COIG 49/02 (2013.01); COIG 3/02 (2013.01); Vaihingen an der Enz (DE) C01B33/20 (2013.01); COIG 51/40 (2013.01); (21) Appl. No.: 15/101,639 COIP 2006/40 (2013.01) (57) ABSTRACT (22) PCT Filed: Dec. 4, 2014 The invention relates to a method for producing a metal (86). PCT No.: PCT/EP2014/076591 chalcogenide thin film electrode, comprising the steps: (a) contacting a metal or metal oxide with an elementary S 371 (c)(1), halogen in a non-aqueous solvent, producing a metal (2) Date: Jun. 3, 2016 halide compound in the Solution, (b) applying a negative electric Voltage to an electrically (30) Foreign Application Priority Data conducting or semiconducting Substrate which is in contact with the solution from step (a), and Dec. 4, 2013 (DE) ...... 10 2013 224 900.4 (c) during and/or after step (b) contacting the Substrate with an elementary chalcogen forming a metal chalco Publication Classification genide layer on the Substrate. The invention also relates to a metal chalcogenide thin film (51) Int. Cl. electrode which can be produced by the method and its use C25D 9/08 (2006.01) as an anode for releasing oxygen during (photo)electro C25B II/04 (2006.01) chemical water splitting. Patent Application Publication Oct. 20, 2016 Sheet 1 of 7 US 2016/0305035 A1
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METAL CHAILCOGENDE THIN FILM hydride Ti(+III) is partially reduced to Ti(+II) which reacts ELECTRODE, METHOD FOR THE in turn with the ketone. Titanium dioxide is released as a PRODUCTION THEREOF AND USE by-product. 0006. The underlying objective of the invention is to 0001. The invention relates to a method for producing a propose a method for producing a metal-chalcogenide thin metal chalcogenide thin film electrode, a metal chalcogenide film electrode for electrocatalytic development of oxygen thin film electrode which can be produced by the method and during electrochemical water splitting, which is simple to its use for electrochemical water splitting. perform and is ideally based on inexpensive starting mate 0002 The inexpensive and environmentally friendly pro rials. The electrodes produced by means of the method duction of hydrogen by means of (photo)electrochemical should exhibit good activity with respect to electrocatalytic water splitting (HO->H+/2 O.) is a key challenge for the oxygen development, and ideally should be photoactive. In production of alternative fuels, for example for fuel cells. addition, the produced metal chalcogenide layer should have Two part reactions take place at the electrodes during high stability. electrolysis: at the cathode there is the reduction of protons 0007 Said objectives are achieved fully or partly by to hydrogen (2H"+2 e->H) and at the anode the oxidation means of a method for producing a metal chalcogenide thin of oxygen (O->/2O+2 e). For good overall efficiency film electrode, a corresponding electrode that can be pro both part reactions should take place at a high and compa duced by means of the method as well as its use having the rable speed. Currently, the development of oxygen at the features of the independent claims. anode (i.e.: OER for oxygen evolution reaction) represents 0008. The method according to the invention for produc the limiting reaction and is why improved electrode mate ing a metal chalcogenide thin film electrode comprises the rials are wanted for this purpose. Photoactive anode mate steps: rials are particularly desirable which enable solar-powered 0009 (a) contacting a metal or metal oxide with an photoelectrochemical water splitting. Improved catalytic elementary halogen in a non-aqueous solvent, producing electrode materials are needed to lower the overpotential at a metal halide compound in the solution, the anode. 0010 (b) applying a negative electric voltage to an elec 0003 Transition metal oxides are a particularly active trically conducting or semiconducting Substrate which is material class for the (photo)electrochemical development in contact with the Solution from step (a), and of oxygen in water-splitting electrode systems (Cook et al., 0011 (c) during and/or after step (b) contacting the Chem. Rev. 110 (2010), S. 6474-6502; Walter et al., Chem. substrate with an elementary chalcogen forming a metal Rev. 110, (2010), S. 6446-6473). The manufacture of suit chalcogenide layer on the Substrate. able electrodes is mostly based on the oxidation (in anodic 0012. Thus according to the invention from the metal or conditions) of metal precursors, i.e. on the deposition of metal oxide, from which the later metal chalcogenide layer metals during electrode positioning on an electrode (the is to be formed, an interim metal halide compound is substrate) and their oxidation in the presence of water. For generated in Solution (step a), wherein the metal or the metal example, the electrochemical deposition of RuO films onto oxide is partially dissolved. Afterwards electrochemical an FTO substrate from an aqueous RuC1 solution (Tsuji et complexing and deposition are performed (step b), in that the substrate, on which the thin film is to be deposited, is al., Electrochim. Acta 56, (2011), S. 2009-2016) is known. charged in the metal halide-containing Solution with a nega 0004. A further approach involves electrophoretically tive Voltage, i.e. is Switched cathodically with respect to an transporting previously chemically or electrochemically anode. In contrast to known electrophoretic deposition the formed metal oxide clusters onto an electrode surface. For negative charging of the Substrate does not result in the example, a method is described for the electrolytic deposi formation of an electric field, which directs particle migra tion of TiO2 films onto a platinum cathode in Kamada et al. tion, but results in the Substrate functioning as an electron (Kamada et al., Electrochimica Acta 47 (2002), 3309-3313). transmitter during the electrochemical reduction reaction. It In this case a titanium sacrificial anode is used as a counter is particularly advantageous that thus in step (b) the metal is electrode to the platinum cathode functioning as a substrate deposited onto the substrate by reduction and due to the for the TiO, deposition and the reaction is performed in negative Voltage the Substrate is an electron transmitter acetone containing H2O traces in the presence of iodine (I2). during the reduction. The contacting of the deposited film In this case titanium is oxidised by oxidation by means of with the elementary chalcogen in step (c) (during or after iodine with in the presence of water to TiO'", released from step b) finally leads to the formation of the metal chalco the sacrificial anode and because of the electric field trans genide compound. ported in the direction of the cathode. The deposition on the 0013 At the same time and/or afterwards the elementary Pt cathode takes place there as TiO(OH) and the release of chalcogen is reduced by receiving electrons from the nega H and subsequent transformation into TiO. To perform the tive cathode (substrate) and reacts with the metal cations of electrophoretic transport of the titanium-yl ions to the cath the metal halide to the corresponding metal chalcogenide, ode this procedure requires an electrically conductive cath which is deposited on the surface of the substrate. The ode. method results in the formation of a highly compact and very 0005. It is also known from the literature that the forma stable metal chalcogenide layer on the substrate. The thus tion of a metal oxide (in Solution) can take place under produced metal chalcogenide layer has high activity with reducing conditions in which the coupling reaction of regard to electrochemical anodic oxygen development dur organic molecules (ketones) to olefins can take place known ing electrochemical water splitting. as a McMurry-reaction (McMurry & Fleming, J. Am. Chem. 0014 Preferably a metal is used which is able to form a Soc. 96 (1974), S. 4708-4709). Here a combination of metal halide compound in which the metal is present in LiAlH4 and TiCl is used in which the lithium aluminium oxidation state +2 or above, i.e. can bond two or more halide US 2016/0305035 A1 Oct. 20, 2016
anions. Compared to metals which can only be present in associated formation of water. Silicon (etched) is therefore monovalent form (oxidation state +1) bivalent or higher a preferred choice both for the cathode, on which the film is state metals can result Surprisingly in greater chalcogenide to be deposited, and for the anode, which is used for deposits. The reason for this is presumably the better com completing the closed circuit as an electron acceptor. In plexing of the bivalent or higher state metal cations by the order to ensure as far as possible the absence of water in the Solvent used. Solvent, it is an advantage to seal the electrochemical cell, 0015. In a preferred embodiment of the invention the from which the metal oxide film is deposited, from the metal is a transition metal. Preferably, it is selected from the environment (i.e. from environmental air), in order to pre group consisting of iron (Fe), cobalt (Co) and nickel (Ni), as vent the penetration water from humidity. In this embodi well as mixtures and alloys which comprise the latter or ment of the invention the formation of carbonic acid from consist of the latter. In this case the alloy or mixture can also the carbon dioxide in the air can also be prevented. contain metals for which the formation of a halide at ambient 0020 For producing the metal halide in step (a) of the temperature is not documented. Such as chromium (Cr) or method an elementary halogen is used. Suitable elementary manganese (Mn). These metals are also co-deposited by halogens comprise in particular iodine I, which can be used means of the method according to the invention as metal as a solid material, or bromine Br, which can be sputtered chalcogenide. In this way mixed metal chalcogenide layers into the solvent as a gas. Preferably, crystalline iodine is can be deposited, for example mixed oxides of different used. metals, whereby the catalytic properties of the electrode can 0021. An organic solvent is preferably used as the non be modified. aqueous solvent. Particularly preferably, the organic solvent 0016 A particular advantage of the method is that solid comprises a carbonyl group (CO) or cyanide group (CN). It metal bodies can be used as the starting metal, in particular is assumed that such solvents coordinate the metal cation of industrial metals or scrap metals. In this way inexpensive the halide compound with the free electron pairs of the raw materials can be used as the starting material, if neces carbonyl or cyanide group and thus activate them for the sary after chemically or mechanically cleaning the metal. following reaction with the cathode-generated chalcogenide 0017. The term “chalcogen refers to the elements in the anion. In addition, it has been observed surprisingly that the 6th main group of the periodic table of elements. Preferably Solvent participates in the reaction with the co-deposition of within the scope of the present invention the chalcogens carbon or carbon-containing compounds. The proportion of include elementary oxygen, elementary Sulphur or elemen carbon and/or carbon-containing compounds in the pro tary selenium. In this way by means of the method metal duced metal chalcogenide layer is up to 30 atomic percent. oxide, metal Sulphide or metal selenide layers can be pro The proportion of carbon and/or carbon-containing com duced. The preferably produced metal oxides are in particu pounds in the thin film originating from the solvent results lar nickel oxides NiO, cobalt oxides Co,O, and iron oxides in an unexpected compaction of the metal chalcogenide thin Fe.O. Different metal sulphides have particularly good layer and thus to improved Stability and imperviousness. The electrocatalytic properties on Suitable photoactive Substrates imperviousness is particularly important when using a semi so that they can be used in photovoltaic water electrolysis. conductor material as the Substrate, which typically has to be This includes in particular iron Sulphides, such as iron protected from contact with an aqueous electrolyte in an disulphide FeS (pyrite), or various CuZnSnS-compounds, electrochemical cell. Furthermore, by embedding carbon such as kesterite Cu(Zn,Fe)SnS. Compared to methods of and/or carbon-containing compounds in the thin film the the prior art which use hydrogen sulphide for the production loading transport between the Substrate and metal chalco of corresponding Sulphides, the method according to the genide can be improved. invention provides a less toxic method of preparation. 0022. The method is performed as far as possible with the 0018. The substrate itself is not chemically involved in exclusion of water, as the latter inhibits the formation of the various different reactions of the method, in particular it metal chalcogenide. Preferably, the proportion of water in is not used in the manner of a sacrificial anode as in the prior the used non-aqueous solvent is at most 0.2 wt.%, particu art as the provider of the metal or other reaction components. larly preferably at most 0.1 wt.%. For the electrochemical deposition of the metal chalco 0023. In a preferred embodiment the remaining water is genide and for later use as an electrode it is only necessary driven out of the solvent prior to the deposition and/or before for the substrate to be electrically conductive or semicon the formation of the halide. This is preferably performed by ductive and to function as an electron donor. For example, pre-electrolysis, wherein for example two electrodes are fluorine-doped tin oxide (FTO fluorine doped tin oxide) is introduced into the solvent already containing halogen. By used as the Substrate. Alternatively, an n-semiconductor applying a Voltage to the two electrodes (in particular in a material is used as the substrate which produces defective range of 5 to 20 V, preferably of 7 to 12 V. particularly electrons (holes) under the effect of light, i.e. is photoactive. preferably 10 V) the remaining water is decomposed, and n-semiconductor materials are particularly suitable for use oxidation takes place at one of the electrodes (the anode), as photoanodes for the development of oxygen during water whereas at the other electrode (the cathode) molecular electrolysis. In this case the defective electrons produced hydrogen is formed which leaves the electrolyte as gas. under the effect of light are transported from the substrate 0024 Contacting the electrochemically modified sub into the metal chalcogenide layer in order to reach from strate with the elementary chalcogen to form metal chalco there the solid body/electrolyte boundary and to catalyse the genide can be performed in a different way. On the one hand oxidation of O' to O. In particular, n-doped silicon is a the chalcogen can already be present in the solvent or can be possible n-semiconductor material for the Substrate. actively added to the latter. For example, the solvent can 0019. On the deposition of the metal oxide film oxide contain traces of dissolved oxygen or oxygen can be intro free, conductive substrates are particularly preferred, in duced by stirring into the Solution. If using Sulphur or order to avoid a reductive dissolution of the substrate and the Selenium as the chalcogen, elementary Sulphur or elemen US 2016/0305035 A1 Oct. 20, 2016
tary selenium can be added to the solution. Alternatively, the semiconductor. Such as n-doped silicon, the electrode can be chalcogen can be present in the atmosphere, such as for used for photoelectrochemical water splitting, i.e. as a example oxygen, which is already present in the atmosphere, photoanode. The heterostructure of a photoactive semicon or can be actively added to the atmosphere. In this case the ductor Substrate and metal chalcogenide layer deposited Substrate can be brought into contact with the atmosphere thereon makes it possible with the provision of light to after removal from the solution after step (b) and thus into transport defective electrons (holes) out of the semiconduc contact with the chalcogen, so that then the metal chalco tor into the metal chalcogenide layer, in order to reach the genide is formed on the surface of the substrate. This solid bodies/electrolyte boundary from there. procedure is particularly Suitable when a metal oxide layer 0029. Further preferred embodiments of the invention are needs to be produced and thus the atmospheric oxygen can described in the remaining features defined in the subclaims. be used. 0030 The various different embodiments of the invention 0025. In a preferred embodiment of the invention after mentioned in this application can be combined with one forming the metal chalcogenide layer on the Substrate a another advantageously, provided they do not have a differ chemical or electrochemical aftertreatment of the deposited ent configuration in individual cases. layer is performed for stabilising, for example for increasing 0031. The invention is explained in the following by way the oxidation state of the metal cation. This can be per of example embodiments with reference to the associated formed by electrochemical processing in aqueous hydrox drawings. In the latter. ide-containing electrolytes. 0032 FIG. 1 shows the morphology and electrochemical 0026. In a particularly preferred embodiment of the properties of metal oxide FTO thin film electrodes according invention after forming the metal chalcogenide layer on the to the invention after the cathode deposition of Ni (a), Co substrate or after the aforementioned (electro)chemical (b), Fe (c) and Cu (d); aftertreatment a thermal aftertreatment is performed. In this 0033 FIG. 2 shows results of the chemical analysis of an way the structure consisting of the Substrate and metal NiO, layer deposited onto Si (111): a) XPS before and after chalcogenide layer deposited thereon is treated at tempera anode use, b) EDX; tures in a range of 150 to 800° C., in particular 150 to 500° 0034 FIG. 3 shows results of the chemical analysis of a C., preferably 200 to 400° C., for a duration of 1 min to 10 Co.O., layer deposited onto Si (111): a) XPS before and after h, in particular for a duration of 1 to 30 min. The thermal anode use, b) EDX; aftertreatment, also referred to as “annealing, results in an 0035 FIG. 4 shows results of the chemical analysis of a increase in the crystallinity and/or the photoactivity of the FeO-layer deposited onto Si (111): a) XPS before and after deposited layer. The specific conditions are mainly directed anode use, b) EDX; towards the chalcogen and the desired crystallinity. 0036 FIG. 5 shows results of the chemical analysis of a 0027. A further aspect of the invention relates to a metal Cu(O)-layer deposited onto Si (111): a) XPS before and after chalcogenide thin film electrode, which can be produced by anode use, b) EDX; the method according to the invention. The electrode com (0037 FIG. 6 shows studies on an NiO/Si(100) thin film prises an electrically conducting or semiconducting Sub electrode: a) current Voltage behaviour during photoelectro strate and a thin film of a metal chalcogenide compound chemical oxygen development with continual illumination deposited thereon. The electrode produced by the method (continuous curve) and periodic illumination (broken according to the invention is characterised in particular in curve); b) SEM image in oblique view; c) SEM image in that carbon and/or compounds of carbon can be found in the plan view; d) TEM image in plan view: produced metal chalcogenide thin film. The proportion of (0038 FIG. 7 SEM images of an NiO/Si(100) thin film carbon and/or carbon-containing compound(s) in the pro electrode; produced a) in a water-free solution according to duced metal chalcogenide layer is up to 30 atomic percent. the invention and b) in a solvent mixture with 25 vol. 96 The carbon contributes to the increased strength and imper HO: viousness of the thin film. In this way both the charging 0039 FIG. 8 shows an analysis of a Fe/Si/Ni/Cr/Co/Mn transport of the Substrate to the metal chalcogenide can be oxide layer deposited on FTO: a) SEM images before and optimised and the stability of the substrate can be increased. after a thermal aftertreatment; b) EDX analysis: The latter is particularly significant when using a semicon 0040 FIG. 9 shows an electrochemical investigation of a ductor material which typically needs to protected from tempered Fe/Si/Ni/Cr/Co/Mn oxide/FTO electrode with contact with an aqueous electrolyte. The metal chalcogenide regard to the electrochemical oxygen development; on the thin film electrode according to the invention is thus char left) dark reaction with an external voltage of 0-1.4 V, on the acterised by improved stability. The thin film electrode right) intermittent illumination at a constant applied poten according to the invention has a layer thickness of the metal tial of 0.65 V): chalcogenide layer in a range of 50 to 1000 nm, in particular 0041. The method according to the invention is explained in a range of 100 to 500 nm. In addition, the deposited layer in more detail in the following. In this case for a clearer has a nanostructured Surface morphology with average sizes overview iodine is used as the halogen, oxygen is used as the of electron-microscopically identifiable structural elements chalcogen and a solid metal body is used as the provider for in a range S 500 nm. the metal of the metal chalcogenide layer, but the invention 0028. A further aspect of the present invention relates to is not restricted to this. the use of the metal chalcogenide thin film electrode accord 0042. In an optional step 1 a metal is cleaned of any ing to the invention as an electrode for the development of possible surface dirt and/or oxide or hydroxide layers on the oxygen for electrochemical water splitting with an applied Surface. The cleaning step can be performed mechanically external potential or under illumination. In other words, the for example by using abrasive materials such as sandpaper electrode is preferably used as an anode during water or the like. Alternatively, the cleaning can be performed by electrolysis. In particular, if the substrate is a photoactive chemical treatment, Such as for example oxide-dissolving US 2016/0305035 A1 Oct. 20, 2016
reactions. Preferably, a solid metal body is used as the metal, oxide layer significant proportions of carbon and/or carbon which can come in particular from industrial metal or scrap containing compounds are also deposited. metal. Solid bodies of any geometric form can be used, for 0047. Afterwards the substrate electrode with the layer example in the form of metal sheets, powders or the like. In deposited thereon is removed from the solvent/iodine-bath. chemical terms preferably metals are used which comprise This is preferably performed under dry nitrogen, to enable iron, cobalt and/or nickel or are made of the latter. the evaporation of possibly formed hydrogen iodide with the 0043. In step 2 the metal halide is formed, here metal exclusion of humidity. iodide. For this purpose the metal possibly cleaned in step 1 is placed into a non-aqueous solvent with a water content of 0048. In an optional subsequent step 4 a chemical or at most 0.2 wt.%. Preferably, acetone or acetonitrile is used electrochemical aftertreatment of the deposited layers takes as the solvent. A halogen, here crystallised iodine, is added place with the aim of increasing the stability of the metal to the solvent in a mass ratio of solvent:iodine of at least 1:1 oxide layer. In particular, the aim of the aftertreatment is to or a greater amount of iodine. Preferably, ultrasound is increase the oxidation state of the metal, that is to oxidise the applied to the mixture to achieve a better mixing result. The latter further. For this purpose the electrode can be intro reaction is carried out for a period of at least 5 minutes, duced for example into an aqueous hydroxide-containing preferably at ambient temperature. It is assumed that in this electrolyte solution and processed electrochemically. way the iodine, with a partial detachment of metal from the 0049. In a further optional step 5 athermal aftertreatment solid body to the corresponding metal iodide in the solution of the electrode takes place for increasing the crystallinity of reacts according to the following equation for example: the deposited metal chalcogenide layer. For this the elec trode is tempered at temperatures in a range of 150 to 800° C. for a duration of 1 minute to 10 hours. 0044 Electrochemical processing takes place in the next step 3. For this two electrically conductive or semiconduc 0050. The metal chalcogenide thin film electrode tive electrodes are moved into contact with the metal iodide obtained by the method according to the invention are containing Solution from step 2, once the remaining Solid characterised by having a particularly impervious and stable metal body has been removed from the latter. One of said metal chalcogenide layers, which also contain carbon. electrodes is used as a substrate for the thin film electrode to be produced, whereas the other one represents the counter EXAMPLES electrode for electrochemical processing. The substrate elec trode is made for example from a metal or a metal alloy, Measurement Techniques FTO, n-doped silicon or carbon. The counter electrode can be made in principle from the same material or from a 0051 XPS. different material than the substrate electrode. Voltage is applied to the electrodes, wherein the substrate electrode is 0.052 X-ray photoelectron spectroscopy, (XPS), was per allocated a negative voltage, i.e. is connected as a cathode. formed for the chemical analysis of the samples. The allo The applied voltage is s-2 Volt, in particular it is within a cation of the core contour lines to specific oxidation states range of -5 to -10 Volt, wherein the (-) sign refers to the was performed using published data (Chastain & King (Ed.). substrate electrode on which the metal oxide film is to be Handbook of X-Ray Photoelectron Spectroscopy, Physical deposited. The electrochemical deposition is preferably per Electronics, Minnesota, USA, 1995). formed at ambient temperature. The length of the reaction 0053 EDX. corresponds to the thickness of the metal oxide layer to be 0054 Energy dispersive X-ray analysis (EDX) was per deposited and depends on the applied Voltage. formed for chemical element analysis both integrally, i.e. 0045. Without wishing to commit to a specific theory it is averaging over the whole sample Surface, and also locally, assumed that the metal iodide in the solution is coordinated i.e. with later resolution (smallest resolution limit about 100 by the organic solvent, in particular its carbonyl or cyanide nm) on the scanning electron microscope. The excitation groups with the formation of metal organic complexes. Said energies were selected so that the expected element-specific complexes exhibit high reactivity compared to free oxygen, K or L lines of the elements can be detected, i.e. between 3 which is already present in traces in the solvent or in the keV and 10 keV. The allocation of the measured X-ray lines environmental air. The oxygen is reduced at the cathode (i.e. negatively) polarised substrate electrode with the capture of was automated by means of database values by the control electrons to O' anions which react with the metal halide to software (NSS 2.2, Thermo Fisher Scientific, USA). form the corresponding metal oxide. This leads to a direct 0055 Electrochemical Characterisation deposition of the metal oxide on the substrate (see following 0056. The electrodes produced in the examples were reaction equations). Possibly a reaction with oxygen takes tested in an electrochemical standard cell with respect to place and the associated metal oxide deposition only upon their suitability for generating oxygen in 0.1 mol/l NaOH later contact with the air oxygen, after the still wet, nega (pH 13). For this the samples were measured either in a three tively polarised electrode has been removed from the solu electrode configuration with a Pt counter electrode and an tion. Ag/AgCl reference electrode or in a two electrode configu ration with the short-circuiting of the Pt counter and Ag/AgCl reference electrode. The potential was controlled respectively by a potentiostat (VSP BioLogic, France). 0046 Although the chemical processes have already 0057 For photochemical studies lighting was provided been described in detail the organic solvent appears to using a W-I source of white light (MI-150, Dolan-Jenner, the participate in the reactions such that in the produced metal Netherlands) by fibre optics. US 2016/0305035 A1 Oct. 20, 2016
Example 1 Examples 9-12 Production of an NiO/FTO Electrode Production of Different M.O./Si(111) Electrodes I0058 As the solid metal body 2 cm of an extremely pure 0065. The method was performed as in examples 1-4, Ni-metal film (Goodfellow Corp. USA, purity >99.95 wt.%) except that 2 cm of an n-type Si(111) wafer (ABC Com was placed in a mixture of acetone (15 ml, w (HO)<0.2%) pany, Germany; doping N, -6x10') was used as the Sub and iodine crystal powder (80 mg). This mixture was mixed strate electrode (cathode) with. For the pre-treatment the for 5 min in an ultrasound bath at 37 kHz. During this Si(111) wafer was precleaned with ethanol and water and treatment the temperature increased from ambient tempera then chemically etched firstly with NHF (100 s) and then ture to about 35° C. Afterwards the metal film was removed with hydrofluoric acid (50%, 10 min) and then dried with from the solution. N. FTO was used as a counter electrode as in examples 1-3. 0059 FTO films (Solaronix, Switzerland, sheet resis tance 7 S2cm, 3x1.5 cm) were precleaned with acetone. An Example 13 FTO sample was placed as a cathode (Substrate) and a second as a counter electrode (anode) at a distance of 5-10 mm from another in the acetone solution. A potential of 10 Production of a Mixed Oxide/FTO Electrode V was applied between the substrate and counter electrode 0066. The method was performed as in example 1, but for 5 min. instead as the solid metal body 2 cm of a steel alloy of the 0060. Afterwards the substrate electrode was removed metals Fe?Si/Ni/Cr/Cof Mn was used. Furthermore, unlike from the solution and dried. example 1 the sample was tempered after drying at 300° C. for 10 min. Example 2 Example 14 Production of a Co,O/FTO Electrode 0061 The method was performed as in example 1, except Production of a CoO/ZnO/CoZnO/Si Electrode that as the solid metal body 2 cm of an extremely pure Co metal film was used (Goodfellow Corp. USA, purity >99.95 0067. The method was performed as in example 1, but wt.%). instead chemically synthesized CoZnO nanoparticles were used and n-doped Si(100) was used as the substrate. Example 3 0068. The substrates and metals used in the examples 1 to 14 are listed in table 1.
Production of a Fe, O/FTO Electrode TABLE 1.
0062. The method was performed as in example 1, except Metal metal that as the solid metal body 2 cm of an extremely pure Fe Example Substrate oxide Chalcogen metal film was used (Goodfellow Corp. USA, purity >99.95 1 FTO N O wt.%). 2 FTO Co O 3 FTO Fe O Example 4 4 FTO Cu O 5 Si(100) N O 6 Si(100) Co O Production of a Cu/FTO Electrode 7 Si(100) Fe O 8 Si(100) Cu O 9 Si(111) N O 0063. The method was performed as in example 1, except 10 Si(111) Co O that as the solid metal body 2 cm of an extremely pure Cu 11 Si(111) Fe O metal film was used (Goodfellow Corp. USA, purity >99.95 12 Si(111) Cu O wt.%). 13 FTO Steel O (FeSiNiCrCoMn) 14 Si(100) CoZnO O Examples 5-8 nanoparticles Production of Different M.O./Si(100) Electrodes 0064. The method was performed as in examples 1-4, Comparison Example 1 except that 2 cm of an n-type Si(100) wafer (ABC Com pany, Germany; doping N-6x10') was used as the Sub Production of an NiO/Si(100) Electrode in the strate electrode (cathode) respectively. For the pre-treatment Presence of Water the Si(100) wafer was precleaned with ethanol and water and then chemically etched in a solvent mixture of hydro 0069. The method of production was as described in fluoric acid (50%) and ethanol (HF:CHOH=3:1) for 30s example 5 with the use of an Ni metal film and crystalline and 10s, then rinsed with water and dried with N. FTO was iodine, but instead of the acetone a solvent mixture of used as the counter electrode as in examples 1-3 FTO. acetone and 25 volume 96 HO was used. US 2016/0305035 A1 Oct. 20, 2016
Comparison Example 2 0077 Interestingly carbon could be found in all of the thin films produced (FIG. 2 b) to 5 b)), which presumably Production of a Fe, O/Si(100) Electrode in the originates from the used solvent (acetone). Presence of Water (0078 Based on the example of the NiO/Si(100) thin film electrode produced according to example 5 the photo 0070 The method was performed as described in electrocatalytic behaviour is shown in FIG. 6a). In this case example 7 except that instead of acetone a solvent mixture the continuous curve shows the current-Voltage behaviour of acetone and 25 volume '% HO was used. with continuous lighting and the interrupted curve shows the (0071 Characterisation of the Produced Metal Oxide Thin current-voltage behaviour with periodic lighting. The mea Film Electrodes surements were made respectively in a three electrode 0072 FIG. 1 a) to d) shows the current densities as a configuration. It can be seen that the NiO/Si(100) thin film function of the applied potential of the thin film electrodes electrode according to the invention has good photoactivity. obtained in examples 1 to 4 during the development of However in the dark it is inactive itself with an applied oxygen in a 0.1 M NaOH solution, which were measured in voltage of 2 Volt, which is caused by the drop in current the dark between 0 and 2 volt against Ag/AgCl in a three density after switching off the light. electrode configuration. By comparison the behaviour of (0079 FIGS. 6b), c) and d) show SEM or TEM images of pure FTO is shown as a dashed-line in the respective graphs. the NiO/Si(100) thin film electrodes from example 5. It The nickel, cobalt and iron oxides show clear activity with can be seen that the nickel oxide layer has a roughness in the respect to the oxygen development (FIGS. 1 a) to c)). The nanometre range and a layer thickness of about 100 to 150 overpotentials determined by the curves range between 340 and 420 mV, wherein the cobalt and nickel oxide electrodes 0080 FIG. 7 shows for comparison with the NiO/Si have the highest activity and the iron oxide electrodes the (100) thin film electrode produced by according to the lowest activity. The copper electrode is only active however water-free method according to the invention of example 5 at high external potentials (FIG. 1 d)). The oxygen devel (FIG. 7a) the product according to comparison example 1, in opment was confirmed respectively by means of differential which the solution contained 25 vol.% (FIG. 7b). It can be electrochemical mass spectroscopy (DEMS). seen that the presence of water largely prevents the forma 0073 SEM images of the respective surfaces are also tion of a layer. Only individual Ni, O and C-containing shown in FIGS. 1 a) to d). They confirm a surface morphol islands can be observed (confirmed by EDX-analysis). ogy with a roughness in the nanometre range. I0081. A similar result was obtained in the comparison 0074 FIGS. 2 to 5 shows the results of the chemical example 2 with iron. Here too the inhibiting effect of water analyses of the deposited metal oxide layers on Si(111) on the film formation was clearly evident. The resulting flat according to the examples 9 to 12. In this case a) shows islands made EDX analysis possible which could here also respectively the results of the XPS analysis of the metal show Fe, O and C in the deposited islands (results not oxide layer after its deposition (upper graph respectively) shown). and after the use of the electrode for electrochemical acid I0082 FIG. 8 shows the results of the analysis of the metal development (lower graph respectively). b) of FIGS. 2 to 5 oxide layer according to example 13 (before and after the shows the results of the EDX measurements of the metal thermal aftertreatment), in which a steel alloy was used as a oxide layers after their production (before electrochemical starting material for the metal, which in addition to the main use). components iron and chromium contained additives of 0075. The allocation of individual XPS signals to specific nickel, cobalt, manganese and silicon. In the EDX analysis oxidation states was made more difficult by electrostatically shown in FIG. 8 b) it should be noted that the power range charging the fresh oxide layers after their production (see is shown from 0 to 5 keV at the top and from 5 to 10 keV FIGS. 2 a) to 5a) above respectively). By comparison after at the bottom. The steel staring material (curve I) is shown, the use of the electrodes for electrochemical oxygen devel the metal oxide thin layer after its deposition (curve II) and opment an allocation to different oxidation states of the after its tempering at 300° C. for 10 minutes (curve III). The metals was possible (see respectively FIGS. 2 a) to 5 a) EDX analysis shows that all of the elements contained in the below). For example the results in FIG. 2 a) show the steel are deposited onto the FTO substrate as oxides. simultaneous presence of NiO, and NiO within the infor 0083 FIG. 9 shows the electrochemical characterisation mation depth of the method of about 2 to 3 nm. of the same sample as in FIG. 8 as an anode for oxygen 0076. The EDX results show for nickel, cobalt and iron development. In this case the left side shows the current the presence of bonded oxygen in the form of the corre Voltage behaviour with an applied external Voltage of sponding oxides (see FIGS. 2 to 4 b)). In the case of copper between 0 and 1.4 V without the action of light. The in the deposited layer only a comparatively small amount of electrode shows rode an excess Voltage relative to the oxygen could be found (FIG. 5 b)), which in accordance oxygen development of about 300 mV, whereby its electro with the XPS analysis indicates the predominant deposition catalytic activity is confirmed. The measurement with an of metallic copper Cu(O). In line expectations this is asso applied constant potential of 0.65 Volt with intermittent ciated with the low activity with regard to the oxygen illumination is shown on the right hand side of FIG. 9. This development (cf. FIG. 1 d)). It is assumed that the insuffi measurement confirms the photoactivity of the electrode. cient deposition of copper oxide is associated with the I0084. The thin film produced according to example 14 property of copper of forming only monovalent iodide CuI with the use of CoZnO nanoparticles as a starting material during production. During a single electron transfer from the for the thin film to be deposited was also analysed (results cathode the formation of metal copper appears to be pref not shown). The analysis shows two different layers depos erable to the complexing in the organic solvent and Subse ited on top of one another. A thin film of the oxides CoO and quent oxidation. Zno could be identified immediately on the n-Si(100)- US 2016/0305035 A1 Oct. 20, 2016
Substrate, which also contained amounts of carbon. On said 4. The method according to claim 1, wherein the metal amorphous CoO/ZnO/C layer a second layer could be iden comprises at least one transition metal. tified which consisted of deposited CoZnO particles accord 5. The method according to claim 1, wherein the metal is ing to the starting material. It is assumed that the two thin a solid metal body. films of this heterostructure were produced by different 6. The method according to claim 1, wherein the elemen reaction routes. In this case the metal oxide particles in tary chalcogen is elementary oxygen, elementary Sulphur or contact with the iodine-containing solution were partly elementary selenium. dissolved, and the metal components enter into solution as 7. The method according to claim 1, wherein the substrate metal iodides. The following electrochemical treatment pro comprises an n-semiconductor material. duces (in a fast reaction phase) the amorphous, carbon 8. The method according to claim 1, wherein the elemen containing boundary layer on the Substrate. However, the tary halogen is iodine (I) or bromine (Br). remaining undissolved oxide particles (in a slower reaction 9. The method according to claim 1, wherein the non phase) are deposited onto said boundary layer by electro aqueous solvent is an organic solvent. phoretic transport. 10. The method according to claim 1, wherein a propor 0085 Example 14 shows that chemically synthesised tion of water in the non-aqueous solvent is at most 0.2 wt. metal oxides produced as powder can be deposited by the %. method onto the Substrate so that an (amorphous) protective 11. The method according to claim 1, wherein contacting layer is formed on the substrate. This enables the corrosion the substrate with the chalcogen is performed by the pres free operation of the thus forming substrate/oxide hetero ence of the chalcogen in the Solution or by contacting the structure. This is an advantage particularly for light-based Substrate with a chalcogen-containing atmosphere. water splitting by using sensitive semiconductor Substrates. 12. The method according to claim 1, comprising the step: I0086. As a by-product of the iron oxide layer formation (d) thermal after treatment of the substrate comprising the in example 3 in the aforementioned cathodic conditions metal chalcogenide layer. there was still a dispersion of black particles in solution. 13. A metal chalcogenide thin film electrode, comprising Said particles exhibited paramagnetic properties, i.e. they an electrically conducting or semiconducting Substrate and a were attracted by the magnetic field of a permanent magnet, thin film of a metal chalcogenide compound deposited without being permanently magnetised—as with ferromag thereon, which is produced or producible according to the netism. For the particles in the solution this means that they method of claim 1. disperse again and the external magnetic field is removed. 14. The metal chalcogenide thin film electrode according The method can thus also be used to produce nanoparticles to claim 1, wherein the metal chalcogenide layer comprises of iron or other metal materials. carbon or a carbon-containing compound. 1. A method for producing a metal chalcogenide thin film 15. A method of using comprising the step of electro electrode, comprising the steps: chemical water splitting for generating oxygen using the (a) contacting a metal or metal oxide with an elementary metal chalcogenide thin film electrode according to claim 13 halogen in a non-aqueous solvent, producing a metal as an electrode. halide compound in the solution, 16. The method according to claim 4, wherein the tran (b) applying a negative electric Voltage to an electrically sition metal is selected from the group consisting of iron, conducting or semiconducting Substrate which is in cobalt and nickel, or a mixture or alloy which comprises the contact with the Solution from step (a), and latter or consists of the latter. (c) during and/or after step (b), contacting the Substrate 17. The method according to claim 5, wherein the solid with an elementary chalcogen, forming a metal chal metal body is an industrial metal or scrap metal. cogenide layer on the Substrate. 18. The method according to claim 7, wherein the n-semi 2. The method according to claim 1, wherein the metal is conductor material is selected from n-doped silicon and able to form a metal halide compound in which the metal is fluorine-doped tin oxide (FTO). present in the oxidation state +2 or higher. 19. The method according to claim 9, wherein the organic 3. The method according to claim 1, wherein in step (b) Solvent comprises a carbonyl group or cyanide group. the metal is deposited onto the substrate by reduction and 20. The method according to claim 1, wherein the non because of the negative Voltage the Substrate is an electron aqueous solvent is one of acetone and acetonitrile. transmitter during the reduction. k k k k k