Self-derivative iron-containing nickel anode for water electrolysis

Abstract

The invention discloses a self-derivative iron-containing nickel anode for alkaline water electrolysis and its preparation method. The anode comprises a nickel substrate and catalytic material layer. The catalytic layer is disposed on and integrated with the surface of the nickel substrate. The catalytic layer contains nickel oxide with iron components. The nickel oxide results from the reaction of the surface layer of the nickel substrate with an oxidant-rich alkaline solution and forms a nanosheet array layer. A nickel-oxidation state containing the iron component is formed by electrochemically induced iron-ion corrosion of the nickel-oxidation state. The invention can effectively reduce the potential difference between the anode and cathode of an electrolysis cell, thereby significantly reduces energy consumption and improves the efficiency of water electrolysis.

Claims

1. A method for preparing a self-derivative iron-containing nickel anode, the method comprising sequentially: placing a nickel substrate in an acid solution and ultrasonically cleaning the nickel substrate in the acid solution; treating the cleaned nickel substrate in a sealed environment at a constant temperature of 40 to 200 C. in a mixed aqueous solution of sodium hydroxide at a concentration of 0.01 to 6 moles per liter and 100 to 600 microliter aqueous oxidant with a 30% mass fraction for 2-10 hours to obtain, at a surface of the substrate, a self-derived nickel-oxide nanosheet array layer; and pulse current electrochemically inducing iron ion to corrode the nickel-oxide nanosheet array layer to obtain an iron-containing nickel-oxide nanosheet array on the surface of the substrate, wherein the step of pulse current electrochemically inducing comprising performing pulsed current to intermittently treat for 2 to 12 hours by using the nickel substrate with the self-derived nickel-oxide nanosheet array layer as an anode and using a nickel plate as a cathode, to achieve electrochemical inducement of ferrous ions oxidation to ferric ions, thereby corroding the self-derived nickel-oxide nanosheet array layer with said ferric ions to obtain the iron-containing nickel-oxide nanosheet array; and wherein the pulsed current is a constant current for 10 seconds at a current density of 10 to 50 mA per square centimeter, and a pulse interval for another 10 seconds, repetitively.

2. The method of claim 1, wherein the oxidant comprises at least one or more of potassium permanganate, sodium permanganate, potassium hypochlorite, sodium hypochlorite, potassium chlorate, sodium chlorate, potassium perchlorate, or sodium perchlorate.

3. The method of claim 1, wherein the step of pulse current electrochemically inducing iron to corrode the nickel-oxide nanosheet array layer is performed in a mixed solution of 0.5 to 20 mmole per liter ferrous iron and 0.2 to 1 mole per liter sodium citrate.

4. The method of claim 3, wherein a ferrous iron in the mixed solution comprises at least one or more of ferrous sulfate, ammonium ferrous sulfate, potassium ferricyanide, ferrous acetate or ferrocene.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1A and FIG. 1B show an untreated nickel mesh and a self-derivative iron-containing nickel-oxide anode in accordance with various embodiments, respectively.

(2) FIG. 2 is a scanning electron microscope (SEM) image of the surface of the nickel mesh of FIG. 1A.

(3) FIG. 3A, FIG. 3B and FIG. 3C are scanning electron microscope (SEM) images of the surface of the anode of FIG. 1B at various magnifications, and FIG. 3D is elemental map of the surface of the anode of FIG. 1B by X-ray Energy-Dispersive Spectroscopy (EDS), correspondingly.

(4) FIG. 4 is a graph showing a linear voltammetry scanning curve of water electrolysis by linear voltammetry test method through three electrode system.

(5) FIG. 5 is a timing potential curve of water electrolysis under different current densities by chronometric potential method through two electrode system.

(6) FIG. 6 is a flow chart tracing the steps of preparing a self-derivative iron-containing nickel-oxide anode.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) Further details of various embodiments of the invention are given below by way of example. The scope of the invention is not limited to these examples. The examples provide preparation methods and performance tests of water electrolysis anodes based on nickel mesh substrate between disclosed invitation and comparative traditional pure nickel anode.

(8) Example for disclosed preparation method as FIG. 6:

(9) Firstly, clean the nickel mesh (601). Prepare an untreated nickel mesh substrate, optical image is shown in FIG. 1A, SEM image is shown in FIG. 2 and indicates a smooth surface. Place it into acetone solution to ultrasonically clean for 20 minutes, then wash it with ethanol, therefore remove the grease layer on the nickel surface. For removing an oxide layer from the substrate surface, placing the substrate in hydrochloric acid solution with the concentration of 4 moles per liter, ultrasonically clean for 10 minutes; then standing in the hydrochloric acid solution for 15 minutes. Thereafter, wash the substrate with distilled water repeatedly.

(10) Secondly, treat the cleaned nickel substrate to obtain, at a surface of the substrate, a self-derived nickel-oxide nanosheet array layer (602). Prepare the oxidant-rich alkaline solution which is comprised 500 microliter of oxidant aqueous solution with a mass fraction of 30% added to one liter of sodium hydroxide solution (6 moles per liter). Thereafter the cleaned metal nickel substrate performs the treatment in a sealed environment at a temperature of 100 C. for 6 hours. Then wash the treated substrate with distilled water repeatedly and dry.

(11) Finally, electrochemically inducing iron ion to corrode the nickel-oxide nanosheet array layer to obtain an iron-containing nickel-oxide nanosheet array layer (603). The substrate with a self-derived nickel-oxide nanosheet array layer is performed pulsed current in a mixed solution of 0.5 mmole per liter of potassium ferricyanide and 0.5 mole per liter of sodium citrate, using the nickel substrate with the self-derived nickel-oxide nanosheet array layer as an anode and using a pure nickel plate as a cathode for 6 hours. The pulsed current uses a single-pulse current, density of 20 mA per square centimeter, time of about 10 seconds and pulse interval time of 10 seconds between the pulses to achieve electrochemical inducement of ferrous ion oxidation to iron ions, thereby corroding the self-derived nickel-oxide nanosheet array layer. Afterwards, wash it with distilled water repeatedly and dry, then a disclosed anode is obtained with significant color change, as shown in FIG. 1B. FIGS. 3A-3C show the scanning electron microscope (SEM) images of the surface of disclosed anode at various magnifications, indicate the nanosheet structure of the surface catalytic layer, and FIG. 3D shows elemental maps of Oxygen (O), Iron (Fe), and Nickel (Ni) on the surface catalytic layer of the disclosed anode (FIG. 1B) by X-ray Energy-Dispersive Spectroscopy (EDS).

(12) The comparative example directly uses a pure nickel mesh, as shown in FIG. 1A, as an anode for water electrolysis after cleaning treatment. Place the nickel mesh into acetone solution to ultrasonically clean for 20 minutes, then washing it with ethanol, therefore remove the grease layer on the nickel surface. For removing an oxide layer from the nickel surface, placing it in hydrochloric acid solution with the concentration of 4 moles per liter, ultrasonically clean for 10 minutes; then standing in the hydrochloric acid solution for 15 minutes. Thereafter, washing the substrate with distilled water repeatedly to obtain the pure nickel mesh anode.

(13) The self-derivative iron-containing nickel-oxide anode (FIG. 1B) and the comparative pure nickel mesh anode (FIG. 1A) are used as sample and control sample for oxygen-evolution performance test by linear voltammetry test method and chronometric potential method through three electrode system and two electrode system, correspondingly.

(14) By using linear voltammetry test method through a 3 electrode system, sample and control sample is used as the working electrode, a Silver/Silver Chloride electrode is used as the reference electrode, a platinum mesh is used as the auxiliary electrode. The electrolyte uses a mass of 1 mole per liter of potassium hydroxide solution. The oxygen-evolution performance is tested on an electrochemical workstation with a scanning rate of 5 millivolt per second and a scanning range of 0 to 1 volt. The test results are shown below table 1, as well as in FIG. 4, where

(15) JCurrent density, mA/cm.sup.2

(16) EPotential difference, V

(17) Ag/AgClsilver/silver chloride reference electrode filled with 3 moles per liter of potassium chloride solution

(18) TABLE-US-00001 TABLE 1 Overpotentials of different test electrodes at different current densities Overpotential at different current densities (V) Test electrode 20 mA/cm.sup.2 50 mA/cm.sup.2 100 mA/cm.sup.2 200 mA/cm.sup.2 Control 0.543 0.738 sample Sample 0.360 0.426 0.518 0.689

(19) By using chronometric potential method through a two electrode system, sample and control sample are used as the anodes, an industrial porous nickel mesh electrode is used as the cathode, a platinum mesh is used as the auxiliary electrode. The electrolyte uses a mass of 1 mole per liter of potassium hydroxide solution. The oxygen-evolution performance is tested on an electrochemical workstation with different current density of 100 and 200 mA per square centimeter for 24 hours. The test results are shown in FIG. 5.

(20) From the data analysis of the two oxygen-evolution performance tests, the disclosed invented anode has significant electrocatalytic performance improvement than traditional industrial pure nickel mesh anode. Under the condition of simulation of water electrolysis in the 2 electrode system test, approximately 0.4V is reduced. Based on the traditional pure nickel anode used in industry, disclosed herein through the treatment process of oxidation reaction and electrochemically induced corrosion, form a nickel-oxide nanosheet array layer on the surface of the pure nickel anode, and thereafter successfully introduce the iron component into the layer and becoming a self-derivative iron-containing nickel anode. Various embodiments provide one or more of the following advantages:

(21) First, the nanosheet array layer is derived from a nickel substrate. It strengthens the mechanical adhesion between the surface catalytic layer and the nickel substrate. The in-situ conversion strategy eliminates the strict phase interface between the substrate and the surface catalytic layer and improves the electron transfer. And therefore increases the catalytic durability.

(22) Second, the nanosheet array structure increases the roughness of the surface. It can effectively increase the surface area of catalytic activity, as well as increase the site where the catalytic reaction occurs and improve the catalytic performance.

(23) Third, the self-derivative iron-containing nickel anode for water electrolysis is based and inherited on the nanosheet array layer from oxidation reaction and electrochemically induced corrosion. It obtains an active catalytic system which has high nickel-iron oxygen-evolution.

(24) The disclosed herein solves the technical problem of low electrocatalytic performance of traditional industrial pure nickel anode, and the issues of complex production process, high cost, difficulties of large scale production, easily falling off, etc. of high activity nickel-iron oxygen-evolution catalyst.

(25) The above description in this specification is merely illustrative of the invention. Persons of ordinary skill in the art to which the invention pertains may make various modifications to the specific examples described, and may add, remove, or replace various components, steps, or features of these examples. Accordingly, the details provided above are not intended to limit the scope of protection.