KR20020037772A - Amorphous metal/metallic glass electrodes for electrochemical processes - Google Patents

Abstract

(Iii) contains a major alloy element such as Ni, (iv) a metal alloy of Co and IVB, VB, VIB, VIIB and / or VIII, Preferably at least one element of the group consisting of C, B, Si and / or VIII B, preferably Cr and V alloy additives, when combined with Ni, the atomic fraction of the alloy being from 0.75 to 0.85; iv) P, or one or a combination of the elements, such that the atomic fraction of the alloy is 0.15 to 0.25. This electrode has excellent thermal stability, improved stability in the accepting electrolyte, and improved current efficiency - providing overvoltage characteristics of the anode or cathode. They are useful for the electrolysis of aqueous solutions such as caustic mixtures and water in the production of oxygen and hydrogen.

Description

TECHNICAL FIELD [0001] The present invention relates to an amorphous metal / metal glass electrode for an electrochemical process,

In an electrolytic cell for hydrogen and oxygen production such as anode and monopolar forms, the aqueous corrosion solution is electrolyzed to generate oxygen at the anode and hydrogen at the cathode, The decomposition of water to produce water. The product of the electrolysis is separated and maintained using a membrane / separator. It is known to use amorphous metal / metal glasses and nanocrystalline materials as electrocatalysts for the discharge reaction of hydrogen and oxygen. The term " amorphous metal " or " metal glass " is well known in the art, and does not have a long-range conformational rule, but is defined as a material having short-range conformation and chemical conventions. Therefore, in the present specification and claims, the two terms are synonymous and are used interchangeably. The term " nanocrystal " refers to a material having a crystal grain size of several nanometers. That is, the crystal structure has a particle size of less than about 10 nanometers. Further, in the present specification and claims, the term " metallic glass " includes a nanocrystalline material.

In electrolysis, not all the voltage passing through the cell during electrolysis is used for the production of hydrogen and oxygen. This degradation of cell efficiency is sometimes referred to as overpotential required for the reaction to proceed at the desired rate and is in excess of the reversible thermodynamic decomposition voltage. This cell overvoltage can be attributed to the following. Ii) a potential drop due to solution resistance between the two electrodes; or iii) a potential drop due to the presence of a membrane / separator between the anode and cathode. While the above i) is directly attributable to the activity of the electrode material used in the cell comprising any activation or pretreatment process, the latter two efficiencies are fixed in the cell design characteristics. Therefore, the performance of the electrode is directly related to the overcharge observed at the anode and cathode by measuring the Tafel slope and the exchange current density (described below).

By adding a metal salt to the electrolyte with a " homogeneous " catalyst that acts only in the liquid phase, excellent electrode performance can be obtained during electrolysis of water. However, such homogeneous catalysts have difficulties in practically adding such additives to the operating cell, in addition to the toxicity of the powder metal salt and the treatment of electrolytes containing additives. Thus, a preferred alternative is a base alloy of Ni and at least one such metal salt component that is electrochemically stable in an alkaline aqueous solution, while providing the same operating characteristics of low voltage, high current cell behavior for the release of hydrogen or oxygen.

July 4, 1995, Though, S.J. And Kirk, D. W. U. S. Patent No. 5,429, 725 discloses that the electrocatalytic behavior of alloys made by combining a Mo and Co component in a Ni-base metal glass is improved.

However, in the (Cr, V) -containing alloy as compared with the Mo-containing alloy, there is a need to combine a lower Tappel slope and a higher exchange current density, and therefore, there is a need to improve the operating efficiency of the electrocatalytic material for alkaline water electrolysis .

Reference List

The present specification cites the following documents. Each of which is specifically incorporated herein by reference.

literature

1. Rihanna, K. Kirk, D. W. And Though, SJ, "Electrocatalytic Behavior of Nickel-Based Amorphous Alloys", Electro Kim. Acta, 36, pp. 537-545, (1991).

2. Creation, And Hakanson, " Electrolysis of hydrogen and oxygen emissions by amorphous metals in alkaline solutions ", Journal Electroanal. Chemistry, 201, pp. 61-83, (1986).

3. Podesta, JJ, Piatti, Al., V., Ariba, AJ. "Behavior of Ni-Co-P base amorphous alloys for electrolysis of water in strong alkaline solutions prepared by electrodeposition", International Journal of Hydrogen Energy 17, pp. 9-22, (1992).

4. Alemu, H. And J. Turner, K., "Analysis of the Electrocatalytic Properties of Amorphous Metals for Oxygen and Hydrogen Release by Impedance Measurements", Electro Kim. Acta., 33, pp. 1101-1109 (1998).

5. Hoht, J. Wai. True Dew, M., Brosaad, El. And Schultz, Al. "Electrochemical and Electrocatalytic Behavior of Iron-Based Amorphous Alloys in 70 ° C Alkaline Solutions", Journal Electrochemical Society, 136, pp. 2224-2230, (1989).

6. Braca, LJ, and Conway, B., "Temperature dependence of electrocatalytic behavior of several glass transition metal alloys for cathodic hydrogen evolution in the electrolysis of water", International Journal of Hydrogen Energy, 15, Pages 701-713, (1990).

7. Willede, Raine, Manoha, M., Chatorago, Ie, Diegle, Albe Rain. And Hayes, A. K., " Influence of amorphous nickel-phosphorus alloy layer on hydrogen adsorption to iron ", Process. Symposium. Corrosion, electrochemistry and catalysis of metallic glass, 88-1, editors. Al. Diegle and Kay. Hashimoto, Electrochemical Society, Pennington, pp. 289-307, (1988).

8. Divish, Jay, Schmidt, and H. And Valey, " Nickel and Molybdenum Coatings as Hydrogen Cathode, " Journal Applied Electrochemistry, 19, pp. 519-530, (1989).

9. Hoht, J.-Way. And Brosard, EL., "In-Situ Activation of Nickel Cathode by Sodium-Molybdate in Alkaline Water Electrolysis at Constant Current", Journal Applied Electrochemistry, 20, page 281, (1990).

10. Hoht, J.-Way. Et al., "In situ activation of nickel cathodes during alkaline water electrolysis by dissolved iron and molybdenum species", Journal Applied Electrochemistry, 21, p. 508, (1991).

11. Raja, Ai, Ai. Quot; Nickel-based binary alloy coating of hydrogen electrode on transition metal base in electrolysis of alkaline solution ", International Journal of Hydrogen Energy, 20, p. 32, (1990).

12. Jack, M, M., Johansen, Rain. And Lee, M., "Electrocatalytic-situ activation of precious metals for hydrogen release", Hydrogen Energy Prog. VIII, ed. Bezier roast and blood. Takahashi, Pergamon Publishing Co., New York, page 461, (1990).

TECHNICAL FIELD The present invention relates to an improved electrode material used in an electrochemical process, and in particular, to an electrolytic solution of an aqueous solution, more specifically to an active surface of an electrode used for electrochemical production to produce oxygen and hydrogen by the electrolysis To an amorphous metal / metal glass electrode material.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference will now be made, by way of example only, to the preferred embodiments, which are illustrated in the accompanying drawings.

1 is a schematic view of an apparatus for making a metallic glass according to the present invention.

2 is a detailed schematic view of the interior of the vacuum chamber of the apparatus shown in FIG.

3 is a perspective view of a boron nitride ceramic crucible used in the apparatus of FIG.

4 is a schematic view of a three component cell used to evaluate the electrochemical activity and the stability of the material according to the present invention.

Figure 5 is a graphical representation of the device used to obtain the electrochemical measurements. Where the same numbers indicate the same parts.

It is an object of the present invention to provide an improved electrode having an electrochemically active surface that can be used for electrolysis of water.

It is also an object of the present invention to provide chemically stable and improved electrodes in an alkaline environment for both dynamic and static circulation of cells.

It is also an object of the present invention to provide an electrode material that is sufficiently activated to reduce one or both of the cathode overvoltage for hydrogen release or the anode overvoltage for oxygen release.

It is also an object of the present invention to provide an electrode containing a relatively inexpensive element component as compared with platinum group metals.

It is also an object of the present invention to provide an electrode that minimizes total manufacturing operations required for manufacturing a final electrode as compared with conventional electrode materials.

It is also an object of the present invention to provide an electrode that can operate at elevated temperatures in an alkaline environment to improve performance as the over-potential required to produce hydrogen or oxygen decreases when the operating temperature of the cell rises .

Thus, in one aspect, the present invention provides a metallic glass for an electrochemical process, said metallic glass being essentially of the general nominal composition

(Ni, Co) _{100-xta x} Z _t

A is an element selected from the group consisting of IVb, Vb, VIb, VIIb and VIII in the periodic table,

Z is an element selected from the group consisting of a metalloid element and carbon selected from the group of IIIa, IVa, Va and VIa of the periodic table,

x, t, and (100-x-t) are at.%. .

A is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Tc, Hg, Ta and W wherein x is selected from about 1 to 20 at.% , And more preferably, x is selected to be about 1 to 5 at.%.

Z is at least one element selected from the group consisting of silicon, phosphorus, carbon, and boron, wherein t is preferably selected from about 15 to 25 at.%, More preferably t is about 20 at.%.

It is most preferred that the metallic glass is homogeneous in one element, but some heterogeneity in both types of cation and anion can be tolerated.

It is to be understood that since the general formula defined above represents a nominal composition, there may be some variation from the exact atomic ratio observed.

Preferred materials according to the present invention have a nominal composition selected from Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ , Ni ₅₀ Co ₂₅ V ₅ B ₂₀ and Ni ₄₅ Co ₂₅ Cr ₅ V ₅ B ₂₀ .

The alloy of the present invention is easily made into a self-supporting structure.

The present invention also provides an electrode for use in an electrochemical cell comprising a metallic glass made of a material as defined above. As an acting electrode, this electrode can be utilized as an anode, a cathode, or both. The material of the present invention may constitute the entire electrode, or may form a surface coating on a base such as a metal or other electrical conductor.

The present invention also provides an improved process for electrochemically producing oxygen and hydrogen from an aqueous solution in an electrochemical cell comprising electrolyzing the aqueous solution with an electrode, And at least one electrode comprising a metal glass of the same material as the first electrode.

In the electrolytic production of oxygen and hydrogen, the aqueous solution is alkaline.

Surprisingly, the metallic glass according to the present invention does not cause loss of element " A " during use, and maintains the activity of the electrolyte even under harsh operating conditions. In short, we have found that, while the presence of element "A" in the alloy of the present invention provides the unexpected advantage described herein, it surprisingly does not lead to the decomposition of element "A" under an alkaline electrolysis environment.

Accordingly, the present invention provides a metallic glass / amorphous metal electrode material for electrochemical processes produced by rapid solidification comprising: i) a structure of amorphous or nanocrystalline, ii) a main alloy element such as Ni and Co, , Iii) an alloy additive such as Cr, V, Ti, Mn and Fe in an amount of 1 to 20 at% such that the atomic fraction thereof is 0.75 to 0.85 when combined with Ni and Co, Iv) Preferably, one or a combination of elements such as C, B, Si and P is contained so as to exhibit an atomic fraction of 0.15 to 0.25. This electrode has excellent thermal stability, improved stability in the accepting electrolyte, and improved current efficiency - providing overvoltage characteristics of the anode or cathode. They are useful for the electrolysis of water-soluble electrolyte solutions such as caustic (KOH, NaOH) mixtures and water in the production of oxygen and hydrogen.

The electrode is made by combining a semimetal element and a low-cost transition metal at a specific ratio that allows the alloy composition to solidify into an amorphous state. This electrode provides improved current efficiency through the overvoltage characteristics of the anode or cathode and provides improved stability in both static and periodic exposures. This electrode can also be used at elevated temperatures to enhance the concentration of alkaline solution and electrode properties. Electrodes are useful for electrolysis of alkaline solutions that produce oxygen and hydrogen through the decomposition of water, and further useful for electrodes for fuel cells, electro-organic synthesis or environmental waste treatment.

The rapid cooling process provides significant cost advantages over preparing conventional Raney Ni electrodes. This process is a single process from the liquid metal to the final catalyst, and the final catalyst can be made in the form of ribbons or wires to be incorporated into a network grid. In addition, the process can be used to produce sheets, powders, flakes, and the like, so that they can be incorporated into more desired shapes or patterns. Compared with the prior art, the production of conventional electrodes includes production of billets or rods, wire drawing and annealing operations, sieving to form wire mesh grids, surface treatment, powder attachment, powder coalescence and activation processes.

Table 1 summarizes the results of prior art investigations involving transition metal-semimetal glasses. The performance of the electrocatalyst in Table 1 depends on two main parameters: i) the tapel slope, βc and ii) the logarithm of the exchange current density, log i_oRespectively. The exchange current density is equivalent to the reversible rate at the equilibrium in the potential of the standard half-cell or redox reaction. The < RTI ID = Represents the slope of the line indicating the relationship between the overvoltage and the response rate reflected as the current density at which the line is present for the half-logarithmic plot of the overvoltage and current density.

Polarization data of Ni-Co base amorphous metal for hydrogen release reaction (HER) in alkaline solution Amorphous electrode solution Temperature ^{_{-log i o (A / cm 2}} ) β _c (mV / decade) Remarks Ni ₅₀ Co ₂₅ Si ₁₅ B ₁₀ Surface treated 1M KOH1M KOH 303050709030 5.76.510.67.67.95.4 110,178909312711391,145 122221 Ni ₅₀ Co ₂₅ Si ₁₅ B ₁₀ Surface treated 1M KOH1M KOH 3030 5.85.4 101,144,111,166 11 Co ₅₀ Ni ₂₅ P ₁₅ B ₁₀ Surface treated 1M KOH1M KOH 3030 5.45.1 124,1741,103 11 Heat treated and dynamically oxidized Ni _5.5 Co ₉₀ P _4.5 1M KOH 30507090 4.03.22.82.2 100120120100 3333 Ni ₅₈ Co ₂₀ Si ₁₀ B ₁₂ 1M KOH 30507090 5.04.74.74.3 140146155145 2222 Co ₂₈ Ni ₁₀ Fe ₅ Si ₁₁ B ₁₆ 1M KOH 30507090 4.65.55.45.3 174119120128 2222 Ni ₇₀ Mo ₂₀ Si ₅ B ₅ 1M KOH 307090 4.13.83.6 165106276 222 Fe ₃₉ Ni ₃₉ Mo ₂ Si ₁₂ B ₈ 1M KOH 30507090 5.04.84.94.9 123150173167 2222 Ni ₇₈ Si ₈ B ₁₄ Dopantly oxidized 1M KOH 30% KOH 2530505070759070 6.06.14.34.44.93.84.42.9 140102150144130125148130 42422425 Fe ₄₀ Ni ₄₀ B ₂₀ 1M KOH 30507090 3.93.84.33.0 174184230188 2222 Ni _66.5 Mo _23.5 B ₁₀ 0.5M NaOH 25 5.6 120 6

Amorphous electrode solution Temperature ^{_{-log i o (A / cm 2}} ) β _c (mV / decade) Remarks Ni _56.5 Mo _23.5 Fe ₁₀ B ₁₀ 0.5M NaOH 25 5.3 100 6 Ni _56.5 Mo _23.5 Cr ₁₀ B ₁₀ 0.5M NaOH 25 5.0 135 6 Ni ₇₀ P ₂₀ C ₁₀ Coating 1N NaOH 25 6.2-8.4 65-95 7 Ni ₇₅ Cr ₅ P ₂₀ 1 M HCl ^* 30 3.5 - 8 Ni ₇₃ Cr ₇ P ₂₀ 1 M HCl ^* 30 3.8 - 8 Ni ₇₀ Cr ₁₀ P ₂₀ 1 M HCl ^* 30 4.0 - 8

* Not for electrolysis in alkaline media

Polarization data of Ni-Co-based amorphous metal for hydrogen release reaction (HER) in alkaline solution with homogeneous catalyst additive Addition of substrate and catalyst (ppm x 10 ^-3 ) solution Temperature ^{_{-log i o (A / cm 2}} ) β _c (mV / decade) Remarks Gaseous CoFeNiPtFe addition = 0.014 7.6M KOH 70 3.93.93.74.2 79809575 9 Gas CoFeNiPtMo addition = 0.024 Fe addition = 0.024 7.6M KOH 70 3.43.12.83.1 151154182163 10 Gas Mild steel NiSO ₄ addition = 80Na ₂ MoO ₄ addition = 20 6.0M KOH 80 - 112 11 Gas Mild steel NiSO ₄ addition = 80Na ₂ MoO ₄ addition = 20 6.0M KOH 80 - 112 11 Gas Mild steel NiSO ₄ addition = 80Na ₂ WO ₄ addition = 20 6.0M KOH 80 - 25 11 Gas Mild steel NiSO ₄ addition = 80 ZnSO ₄ addition = 40 6.0 KOH 80 - 50 11 Gas Mild steel NiSO ₄ addition = 80 FeSO ₄ addition = 20 6.0M KOH 80 - 25 11 Gas Mild steel NiSO ₄ addition = 80CoSO ₄ addition = 20 6.0M KOH 80 - 112 11 Gas Mild steel NiSO ₄ addition = 80CrO ₃ addition = 20 6.0M KOH 80 - 150 11 Gaseous Pt molybdate addition 5.0M KOH 25 - 80 12

The electrode described in Table 1 contains a combination of various transition metals that bind to (Ni, Co), but element "A" is not compounded in these additions. The electrode described in Table 2 derives its activity from the presence of the decomposed salts of the abovementioned element " A " when added onto the solution of the electrolytic bath, not when it is directly combined with the gaseous material.

A general method for preparing and testing the materials of the present invention was as described in the aforementioned U.S. Patent No. 5,429,725.

Experiment

The electrode metal glass material was prepared as follows.

This example demonstrates that the ready electrode

Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀

.

In order to produce an amorphous alloy ribbon by a melt-spinning technique, a series of preparations were attempted. This process is divided into two processes. The first step is referred to as "pre-melting" by charging a powder mixture of pure materials such as nickel, cobalt, chromium and boron into a water-cooled copper furnace and melting it by vacuum arc melting. The second step uses a boron nitride ceramic crucible, which allows dedicated, milled buttons to be redissolved in a vacuum chamber and heated to temperatures above 1100 ° C. A flow of molten metal is then introduced onto the outer circumferential surface of the massive copper wheel rotating at high speed through the elongated hole of the ceramic crucible. Rapid cooling takes place on the cold surface of the wheel, and solidified deposits are produced in the form of thin ribbons. The following sub-paragraphs briefly describe the production of amorphous metals.

Device

Melt-Spinner: D-7400 Tübingen, Edmund Muller, Germany

3.3 x 10 ^-2 Pascal high vacuum chamber

Induction Heaters: TOCCOTRON 2EG 103. Ohio Crankshaft Company, USA

Maximum output 10kW, 450kHz

Pyrometer: Model ROS-SU, KepinTech Research Institute Co., Ltd., USA

Fig. 1 illustrates an experimental apparatus comprising a melt-spinner 10 and an induction heating unit 12. Fig. The melt-spinner assembly 10 comprises a high vacuum chamber 14, a ribbon collection tube 16 and a controller 18. The melt- The vacuum chamber 14 is connected to an argon cylinder 20 which supplies the argon gas to clean the chamber 14 and the ceramic crucible 22 (Figure 2) to discharge the melt of the liquid material. (Not shown). The temperature of the liquid melt in the ceramic crucible 22 is measured by an optical pyrometer 24 attached to a quartz glass window 26 located above the vacuum chamber 14. [

The induction heating unit 12 includes an induction heating coil 28 (FIG. 2) of the vacuum chamber 14, a three-step increasing transformer and a closed-loop cooling water recirculator (not shown) for supplying cooling water through the induction coil ).

2 shows the arrangement of the copper wheel 30 (20 cm in diameter, 3.8 cm in width), the ceramic crucible 22, the induction coil 28 of the high vacuum chamber and the ribbon guide 32.

A: Only.

The exemplified chemical composition is collectively expressed as Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ . Since the composition range of the alloy is relatively narrow, it is necessary to prepare a careful sample so as to be an effective comparison in subsequent electrochemical measurements. To obtain the desired composition with high accuracy, a dedicated button is first prepared using vacuum arc melting, using pure powder of material, and then redissolved using mechanical grinding and vacuum induction melting. In the illustrated powder, each mixture contains 50 at.% Nickel, 25 at.% Cobalt and 20 at.% Boron. The remaining 5 at.% Consists of chromium element A in this example. In another embodiment of the present invention, boron acts as a melting point depressant and causes the entire powder mixture to begin dissolving at a relatively low temperature of about 1035 ° C , And nickel-boride in the form of an intermetallic compound.

20-50 g of the powder mixture was charged at once into a quartz crucible (inner diameter = 19.05 mm, outer diameter = 22.2 mm, height = 130 mm round bottom). The quartz crucible is mounted in the vacuum chamber of the melt-spinner and placed in the middle of the induction coil. Then, the vacuum chamber is cleaned three times with argon, and exhausted at about 5 x 10 ^-4 torr (7 x 10 ^-2 Pa) before heating. The powder mixture of materials is dissolved in a quartz crucible at a temperature above 1100 ° C. The weight loss rate of the material through the dedicated solution was less than 1 wt.% In all components.

B: Melt spinning

The melt spinner used in this work is an experimental scale model, manufactured in Edmundseller GmbH and can be used to prepare 5 - 100 g alloy mixture samples in batch mode. The melt-spinner assembly includes a high vacuum chamber, a ribbon collection tube, and a motor speed controller. The induction heating unit includes an induction heating coil of a vacuum chamber, a three-stage incremental transformer, and a closed-loop cooling water recirculator that supplies cooling water through the induction coil upon heating. The vacuum chamber is connected to an argon cylinder, which supplies gas to clean the chamber and presses the ceramic crucible to release the liquid melt. The temperature of the liquid melt of the ceramic crucible is measured with an optical pyrometer attached to a quartz glass window located above the vacuum chamber.

Load one or two dedicated buttons into the BN ceramic crucible. Boron nitride has an advantage that it has high hardness at high temperature and oxidation resistance is good enough to heat the dissolved liquid to 1400 DEG C or more without any chemical reaction occurring in the crucible.

The crucible is mounted on the copper wheel of the vacuum chamber. This chamber is cleaned and evacuated in the same manner as described in the dedicated solution. Dedicated buttons are heated in the crucible with induction coils until the liquid temperature reaches a maximum stable temperature, depending on the composition of the alloy. The liquid melt is ejected onto the wheel through a slit nozzle (0.5 x 15 mm) that goes to argon pressure. A planar amorphous ribbon is formed on the surface of the wheel that rotates counterclockwise and is sent to the collection tube through the ribbon guide. This particular form of melt spinning is referred to as a planar flow casting technique. From the wheel rotational speed, the cooling rate is estimated to be approximately 10 ⁶ ° C / sec. One side of the ribbon has no glossy contact with the wheel and has a glossy appearance (glossy side) when compared to the blurry appearance (wheel side) of the other side in contact with the wheel. To minimize surface flaws on the blurry side due to contact with the wheel, the outer circumferential surface of the wheel is thoroughly polished with diamond paste and oil is removed with acetone prior to each test. Standard experimental parameters of the melt-spinning operation are summarized in Table 3.

Table 3: Summary of Melt-Spinning Working Variables Tolerance between the top corner of the crucible bottom and the wheel surface 0.5mm Crash point 12 degrees counterclockwise from the top of the wheel Dedicated button weight 20 - 50g Vacuum chamber pressure 7 x 10 ^-2 Pa or less Melt release pressure 40 kPa Wheel speed 1800 - 2900 rpm Heating temperature Above 1100 ° C

The alloys of the present invention made with flat flow casting were evaluated as follows.

The first evaluation relates to the actual composition of the alloy produced, since an insufficient number of times of dissolution can cause a potential bias between the nominal composition and the actual composition of a given alloy.

A second evaluation relates to the structure of the resulting alloy, since the above manufacturing process can naturally produce amorphous or nanocrystalline quasicrystals.

The third assessment relates to electrode performance, which is related to the overvoltage required for hydrogen production with a melt-spun ribbon in an environment related to the electrolysis of alkaline solutions.

The fourth evaluation relates to surface testing of electrode materials used in both constant potential and cyclic potential environment described above.

The first test was carried out using an inductively coupled plasma spectrometer (ICP) to obtain reliable information on the components of the amorphous alloy element. Even if a very small mass loss of less than 1 wt.% Is found during dedicated operation, if only one component is lost, it will lead to the inaccuracy of the desired composition. In addition, there is also a concern that compositional variation may occur in the longitudinal direction of the amorphous ribbon. For this reason, two points designated as intermediate appendages (tail) were taken from each ribbon and analyzed. ICP is a technique that provides quantitative analysis with a high degree of detection of almost all components.

This technique requires that the sample to be analyzed be dissolved in an aqueous solution since the sample must be introduced into the inductively coupled plasma in the form of an aerosol. Each amorphous ribbon is dissolved in concentrated nitric acid and diluted with water and hydrochloric acid to complete a designated matrix solution containing 4 wt% HNO ₃ and 4 wt% HCl. For the experimental error analysis, several standards were prepared as pure metal powders. The major elements analyzed were Ni, Co, Cr, V and B. The expected concentrations of Ni, Co, Cr, V and B in the standard and sample solutions are summarized in Table 4.

Summary of expected concentrations of ICP samples (ppm) Serial Number solute Ni Co Cr or V B #One Blank (1) 0 0 0 0 #2 Standard (2) - Metal 10.00 10.00 10.00 0 # 3 Standard (3) - Metal 100.00 100.00 100.00 # 4 # 5 # 6 Ni ₅₄ Co ₂₅ Cr ₁ B ₂₀ Intermediate Ni ₅₄ Co ₂₅ Cr ₁ B ₂₀ Tie Standard 53.7 24.7 0.954.0 24.8 1.054.0 25.0 1.0 20.620.120.0 # 7 # 8 # 9 Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ Medium Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ Tail Standard 50.6 24.6 5.049.9 24.6 5.750.0 25.0 5.0 19.919.720.0 # 10 # 11 # 12 Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ Intermediate part Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ Tail standard 35.6 25.1 20.235.7 25.1 20.235.0 25.0 20.0 19.118.920.0 # 13 # 14 # 15 Ni ₅₀ Co ₂₅ V ₅ B ₂₀ Medium Ni ₅₀ Co ₂₅ V ₅ B ₂₀ Tail Standard 50.8 25.3 4.650.9 25.3 4.750.0 25.0 5.0 19.319.120.0 # 16 # 17 # 18 # 19 Standard B1 Standard B2 Standard B3 Standard B4 0 0 00 0 00 0 00 0 0 102550100

The second test uses an X-ray diffraction technique to confirm the crystallinity of the produced ribbon. For comparison, crystallized pieces of amorphous alloys as well as pure elemental nickel, cobalt, chromium, boron and intermetallic nickel-boride were measured. Amorphous samples were prepared by cutting the ribbon into 4 mm x 10 mm rectangular pieces. The sample was then degassed sequentially with acetone, methanol and neutral water. The crystallized pieces had the same volume composition as the corresponding amorphous alloy and were in the form of predominantly plate-like fragile powders. Due to the sliced surface in the form of a plate, the crystallized amorphous alloy was grinded in the form of fine powder in an agate mortar and dispersed on a slide glass before measurement to avoid selective diffraction. The diffraction pattern was measured with a Siemens D 5000 X-ray diffractometer using 50 kV Cu-K radiation with a Ni filter in the range of 20-70 degrees -2? With a scanning speed of 2-2? Per minute. Data were processed with Diffrac AT software.

The third test involves measuring the electrochemical overvoltage for hydrogen evolution by measuring the inclination of the Tappel and the exchange current density of the alloy produced. A working electrode was prepared from a Ni-Co-Cr-B amorphous alloy ribbon having a thickness of about 20 - 50 탆 and a width of 4 - 15 mm. The glossy side of the ribbon was polished and polished to remove oil. The polished ribbon was cut into approximately 10 mm x 10 mm pieces, and each piece was connected to insulated copper lead. The bonded area, the unpolished wheel side and the periphery of the polished side were completely coated with Amercoat 90 ^R epoxy resin three times at 24 hour intervals. This masking coating is resistant to alkaline or acidic environments. The exposed geometric surface area of the fabricated electrode is typically 0.03 0.01 cm ² .

The electrolytic bath 40 shown in Fig. 4 has three compartment structures of a 300 ml capacity main body formed of Teflon in general. The electrolytic bath 40 has a working electrode 42, an opposite electrode 46, Teflon PTFE tube 48 filled with a mercury-mercury oxide paste (Hg / HgO).

The compartment was separated into an electrolyte permeable membrane 50 in the form of a diaphragm or frit. The opposite electrode 46 was a 25 mm x 12.5 mm platinum gauze having a surface area of about 4.4 cm ² . Hg / HgO paste in 1 M KOH aqueous solution was used as a reference electrode. The tip 54 of the Luggin capillary in the reference electrode compartment is at a distance of about 2 mm from the working electrode surface of the present invention alloy. All potentials referred to herein are for Hg / HgO electrodes in 1 M KOH solution at 30 占 폚. The electrolytic solution was prepared by pre-electrolyzing KOH and pre-electrolysis for at least 24 hours to remove impurities present in KOH, and then an aqueous 8M potassium hydroxide solution was prepared. The electrolyte was replaced with fresh electrolyte before each experiment and air was removed with argon at a rate of 30 ml / min. Argon bubbling continued during the experiment. The solution temperature was controlled at 70 캜 using an immersion heater (Polystat Immersion Circulator, Cole-Palmer) in the 18 L water tank 56 (FIG. 5).

The apparatus used for the electrochemical measurement was a water tank 56 electrically connected to a Hokuto Denko HA-501G electrostatic discharge / constant current device having a 200 MHz Pentium II PC via a GPIB interface 62, an arbitrary function generator, (Hokuto Denko HA-105B).

The electrocatalytic activity of the amorphous alloy for the hydrogen release reaction was studied by the quasi-steady-state polarization technique. In practice, the polarization curves of amorphous electrodes were measured at a very low sweep speed of 2 mV / min in the quasi-constant potential state. This potential sweep speed was found to be the maximum sweep speed at which reproducible steady state can be measured. The polished working electrode was ultrasonically cleaned sequentially with acetone, methanol and type I water before the test. Then, the electrode was placed in a cell together with air-removed 1M KOH, and the electrode surface was electrochemically cleaned by maintaining a potential of -1.3 V for Hg / HgO for 3 hours. The potential was applied in a combined cycle range of -0.9 to -1.5 V to evaluate the Tappel's behavior of the electrode reaction. The polarization curve was repeated at least three times for each electrode, and its reproducibility was analyzed.

The fourth test compares the surface roughness of the amorphous alloy and the crystal surface with an optical and scanning electron microscope before and after use as an electrocatalyst in a cell to compare degeneration of the electrode. Optical irradiation was performed with a light stereoscope and a light metallograph. Electronic images were obtained using a Hitachi S-570 scanning electron microscope equipped with a Link Analytical 10 / 85s X-ray analyzer. A nominal picture condition; An acceleration voltage of 20 kV, a beam current of 100 mu A, and a sample tilt of 15 DEG.

In the first test, a quantitative component analysis was performed using an inductively coupled spectroscope. The average experimental composition of each amorphous ribbon measured by inductively coupled spectroscopy analysis is shown in Table 5. All compositions of the measured amorphous ribbon showed good agreement with the desired composition. The average size of the deviation from nominal composition to actual composition was <1 at.%. In addition, at two different length-positions of the mid and tail portions, the change in the major element concentration was measured. There were no significant changes in the components at these two positions. From this data, the amorphous ribbon can be regarded as homogeneous in the longitudinal direction.

Composition of amorphous ribbon (at.%) Purpose composition Measured composition Ni ₅₄ Co ₂₅ Cr ₁ B ₂₀ Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ Ni ₄₅ Co ₂₅ Cr ₁₀ B ₂₀ Ni ₄₀ Co ₂₅ Cr ₁₅ B ₂₀ Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ Ni ₅₀ Co ₂₅ V ₅ B ₂₀ Ni _53.7 Co _24.8 Cr _1.O B _20.1 Ni _49.9 Co _24.6 Cr _5.7 B _19.7 Ni _45.1 Co _24.9 Cr _10.0 B _20.0 Ni _40.3 Co ₂₅ Cr _15.0 B _19.7 Ni _35.7 Co _25.1 Cr _20.2 B _18.9 Ni _50.9 Co _25.3 V _4.7 B _19.1

In the second test, the structure of the ribbon was evaluated by X-ray diffraction because it is an essential part of the electrode characteristic apart from the exact composition of the electrode material. A typical X-ray diffraction pattern for an amorphous material is known as a broad spectrum with no noticeable sharp peaks for the crystal structure. Therefore, amorphous characteristics of the alloy can be confirmed qualitatively through the broad band peak on the X-ray diffraction profile.

As an additional information, an exponent, or effective crystal dimension, was calculated to estimate the maximum potential size of the crystal embryo in the melt-spun ribbon. The effective crystal dimensions are expressed by the following equations.

D = (0.91?) / (? Cos?)

Where D is the effective crystal size in nm and λ is the wavelength of the Cu-K radiation at 0.1542 nm. β is the radian, which represents the maximum width of the diffraction peak given in half the maximum intensity. is the Bragg angle at the maximum peak. The effective crystal dimensions were measured for all melt-spun ribbons. Table 6 summarizes the calculated results. The melt-spun Ni-Co-Cr-B alloy exhibited a very small effective crystal size measured from the broad band peak of the X-ray diffraction image for confirming the amorphous properties of the melt-spun ribbon.

Effective crystal dimension Amorphous alloy composition Peak peak position 2 [theta] ([deg.]) Apparent mean d-distance d (A) The maximum width β (rad) at half the maximum intensity Effective crystal dimension D (nm) Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ Ni _51.4 Co ₂₅ Cr _3.6 B ₂₀ 45.145.746.3 1.9932.0152.015 0.1380.1260.136 1.11.21.1

In the third test, the electrocatalytic properties of various amorphous electrodes were measured and compared with the behavior of the elemental components. (Polarization curve) of crystalline Ni, Co, Cr and amorphous Ni-Co- (Cr, V) -B alloys in the potential range of -0.9 to -1.5 V with respect to Hg / HgO is about 0.001 to 1000 mA / cm &lt; ^{2 &} gt ;. Statistical regression analyzes to produce a method to tapel parameter βc and i _o, it was found that there is a linear correlation between the potential for logarithmic current plot (plot tapel). Table 7 summarizes the Tappel slope and the exchange current density.

Taffel parameters of the electrode for hydrogen release reaction at 30 ° C, 1M KOH material Tappel parameter -E ^* -logi _o βc ^*** decision Ni 1.25-1.56 3.2 ± 0.3 239 ± 14 Co 1.25-1.44 4.0 ± 0.1 178 ± 4 Mo 1.20-1.40 6.6 ± 0.2 90 ± 4 Amorphous Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ 1.01-1.50 3.15 161 Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ 1.01-1.50 3.58 114 Ni ₅₀ Co ₂₅ V ₅ B ₂₀ 1.00-1.50 3.96 100 Ni ₇₂ Mo ₈ B ₂₀ 0.94-1.55 4.0 ± 0.04 180 ± 2 Ni ₇₂ Co ₂ Mo ₆ B ₂₀ 1.00-1.50 5.1 ± 0.07 142 ± 3 Ni ₅₀ Co ₄ Mo ₄ B ₂₀ 1.00-1.50 5.1 ± 0.03 148 ± 2

* Potential range (V vs. Hg / HgO)

** Exchange current density (A / cm ² )

*** Tappel slope (mV / decade), high field

As shown in Table 7, as a function of the composition of the amorphous alloy, a clear difference in the current density values was clearly observed and the order of the electrocatalytic activity was as follows.

Ni ₅₀ Co ₂₅ V ₅ B ₂₀ > Ni ₃₅ Co ₂₅ Cr ₂₀ B ₂₀ > Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀

This ranking does not depend simply on the order of the Cr / V content of the amorphous alloy, but in particular on the elemental form. The highest electrocatalytic activity of Ni ₅₀ Co ₂₅ V ₅ B _{20 in} the amorphous alloy may be due to the synergistic effect of Ni-Co-V which may affect the properties of the oxide film formed on the amorphous alloy .

It is also apparent from the comparison of the properties of the amorphous alloy of Table 7 with respect to U.S. Patent No. 5,429,725 that the present invention has an advancement. The present invention shows lower tendel slope and higher current density in (Cr, V) containing alloys compared to Mo containing alloys; Both of these properties contribute to improving the working efficiency of the material as an electrocatalyst for alkaline water electrolysis.

In the fourth test, the specimens were tested using an optical microscope and a scanning electron microscope to obtain additional information on the state of the electrode surface after the combined cycle operation. It was found that the crystalline Ni, Co, and Mo electrodes having a potential cycle had a thick erosion-generating layer. The crystalline Ni electrode after 200 to 600 cycles showed the growth of the corrosion layer with the dislocation cycle. The crystalline Co electrode showed the sign of crystal / decomposition reaction by the constant adherence in the form of a polygonal plate on the electrode surface. The crystalline Mo electrode shows a heavily corroded surface and the remaining skeletal structure indicates active Mo decomposition. All the crystal electrodes showed much higher illuminance than the polished state.

On the other hand, the amorphous electrode to which the potential cycle was applied exhibited a very smooth surface and a noncorrosive state. Only a few superficial layers (possibly Ni oxides) can be distinguished as hazy transparent films covering very smooth surfaces of amorphous alloys. For the amorphous electrode before and after cycling, no noticeable difference was found. Therefore, after exposure to very severe dislocation cycling conditions, amorphous alloy electrodes were more stable than crystalline electrodes of Ni, Co, or Mo elements.

While the preferred specific embodiments of the invention have been described and illustrated, it should be understood that the invention is not limited to these specific embodiments. The present invention also includes all embodiments that are functionally or mechanically equivalent to the specific features and features described above.

The present invention can be used for an electrochemical electrode material, and particularly for an electrode material that produces oxygen and hydrogen by electrolysis.

Claims (15)

A metallic glass for an electrochemical process, said metallic glass essentially consisting of a nominal nominal composition (Ni, Co) _100-xt A _x Z _t ; Where A is an element selected from the group consisting of IVb, VB, VIb, VIIb and VIII of the periodic table, Z is an element selected from the group consisting of carbon and a half-metallic element selected from the group consisting of IIIa, IVa, Va and VIa of the periodic table, x, t, and (100-x-t) are atomic percentages. The method of claim 1, wherein A is at least one metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Tc, Hg, Ta, %. &Lt; / RTI &gt; The metal glass according to claim 2, wherein x is selected from about 1 to 5 at.%. The composition of any one of claims 1 to 3, wherein Z is at least one element selected from the group consisting of silicon, phosphorus, carbon and boron, and t is selected from about 15 to 25 at. Metal glass. The metal glass according to claim 4, wherein t is about 20 at.%. The metal glass according to any one of claims 1 to 5, characterized in that it is substantially homogeneous. 7. The metallic glass according to any one of claims 1 to 6, wherein the Ni, Co, A and Z are essentially elemental states. The metallic glass according to claim 1, characterized in that it consists essentially of a material having a nominal composition of Ni ₅₀ Co ₂₅ Cr ₅ B ₂₀ . The metallic glass according to claim 1, characterized in that it consists essentially of a material having a nominal composition of Ni ₅₀ Co ₂₅ V ₅ B ₂₀ . The metallic glass according to claim 1, characterized in that an essentially preferred nominal composition is composed of a material of Ni ₄₅ Co ₂₅ V ₅ Cr ₅ B ₂₀ . An electrode for an electrochemical cell, comprising a metallic glass essentially consisting of the material according to any one of claims 1 to 10. 12. The electrode of claim 11, comprising a support and a coating comprising the metal glass coated on at least a portion of the support. 13. An electrode according to claim 11 or 12, characterized in that it is in the form of a self-supporting structure. The electrode according to any one of claims 11 to 13, wherein the electrochemical cell is for electrochemically producing oxygen and hydrogen from an aqueous solution. An improved process for the electrochemical production of oxygen and hydrogen from an aqueous solution in an electrochemical cell, the process comprising electrolysis of the aqueous solution with an electrode, wherein the improvement essentially consists of any of the steps 1 to 10 A process comprising at least one electrode comprising a metallic glass of a material according to any one of the preceding claims.