KR102529278B1 - Hydrogen generating electrode using nickel-iron alloy and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a low-cost nickel-iron alloy hydrogen generation electrode that can replace a platinum-based catalyst electrode in a water electrolytic hydrogen generation reaction and a manufacturing method thereof, and more particularly, to an optimal bonding between a carbon support electrode and nickel-iron alloy particles. And it can be prepared by directly growing a catalyst on a carbon support electrode using a hydrothermal synthesis method for adhesion stability.
The nickel-iron alloy hydrogen generating electrode according to the present invention has excellent overpotential values because it can reduce crystal defects by adjusting the ratio of nickel and iron, facilitate water adsorption to the catalyst, and thereby generate more hydrogen. As a result, it consumes little energy to proceed with the water decomposition reaction, and has the advantage of having a long lifespan and long-term stability.

Description

Nickel-iron alloy hydrogen generating electrode and manufacturing method thereof {Hydrogen generating electrode using nickel-iron alloy and manufacturing method thereof}

The present invention relates to a nickel-iron alloy electrode catalyst material having high efficiency and long-term stability for hydrogen generation reaction in an alkaline water electrolysis system and a manufacturing method thereof, and a method for growing nickel-iron alloy crystals on a support using a hydrothermal synthesis method. It is about.

The development of new and renewable energy sources that can simultaneously alleviate the energy crisis caused by fossil fuel depletion and global warming caused by various environmental pollutants is receiving great scientific and industrial attention. Various studies on eco-friendly and infinite renewable energy sources have been conducted to replace fossil fuels, and among them, hydrogen energy is a representative energy carrier.

Hydrogen reacts with oxygen in the air to produce only water without producing other pollutants. The energy density per mass of hydrogen is 142 kJ/g, four to three times higher than that of gasoline and natural gas. There are various methods of producing hydrogen, but the most popular method of producing hydrogen at present is a method of extracting hydrogen from fossil fuels. However, since this method causes environmental problems, one of the eco-friendly hydrogen production methods is the water electrolysis hydrogen production method.

The water electrolysis method requires simple equipment, can be mass-produced, and can produce high-purity hydrogen. However, since the water electrolysis technology has the disadvantage of using a fairly large amount of electrical energy, the key to the water electrolysis system is to use a catalyst to lower the energy required to decompose water. Platinum (Pt), which is considered the best catalyst in the hydrogen generation reaction of the water electrolysis system, has high efficiency due to its low overpotential value and low Tafel slope.

Therefore, it is essential to develop new electrochemical catalysts to replace platinum. In addition, recently developed metal sulfide and phosphide-based catalysts are unstable in polar solvents, so active components are eluted during the reaction, and their conductivity is lower than that of metals or alloys, so they lack stability. Therefore, catalyst electrodes with high efficiency and long-term stability in alkaline water electrolysis systems is in need of development.

Republic of Korea Patent No. 10-2000974 (2019.07.11)

The present invention was created to solve the above problems, and the present invention provides an inexpensive, efficient and stable hydrogen generation reaction alloy catalyst and a manufacturing method that can replace the platinum catalyst in a water electrolysis hydrogen production system. There is a purpose.

In order to achieve the above object, the present invention comprises mixing a nickel precursor and an iron precursor (first step); Adding deionized water and sodium citrate to the solution mixed in the first step and stirring (second step); When the reaction mixture stirred in the second step becomes uniform, adding a basic material so that the pH becomes 10 (third step); immersing the carbon support in the solution of the third step, adding a reducing agent and stirring (fourth step); Transferring the reaction mixture stirred in the fourth step to an autoclave, sealing it, and raising the temperature to perform hydrothermal synthesis (fifth step); and cooling the autoclave to room temperature after completion of the reaction in the fifth step and obtaining a nickel-iron electrode grown on a carbon support (sixth step). do.

In addition, the present invention provides a nickel-iron alloy hydrogen generating electrode comprising a nickel-iron electrode (Ni _100-x Fe _x /CP electrode; where x is an integer from 1 to 19) grown on a carbon support.

The Ni _100-x Fe _x /CP electrode material according to the present invention shows a low overpotential value despite not using a noble metal, which means that hydrogen can be produced at a low price and using little energy. In addition, the Ni _100-x Fe _x /CP electrode material has excellent stability and durability even after 3000 repeated hydrogen generation reactions and 10 days of reaction, and can be used for a long time with high efficiency, so it is applied as a commercial material in the future. It is expected that the hydrogen generation reaction can be carried out very economically.

Figure 1 explains the manufacturing process of the nickel-iron alloy hydrogen generating electrode (Ni _100-x Fe _x /CP electrode) grown on the carbon support of the present invention.
2 is an XRD analysis result of the Ni _100-x Fe _x /CP electrode according to the present invention.
Figure 3 is a transmission electron microscope image and element distribution image of the Ni _100-x Fe _x /CP electrode according to the present invention.
4 is a scanning electron microscope image, SAED pattern, and elemental mapping image of the Ni ₉₀ Fe ₁₀ /CP electrode according to the present invention.
5 is an EDS-elemental mapping image of a scanning electron microscope of a Ni _100-x Fe _x /CP electrode according to the present invention.
6 is an elemental analysis result of the Ni _100-x Fe _x /CP electrode according to the present invention.
7 is a numerical table of elemental analysis results of the Ni _100-x Fe _x /CP electrode according to the present invention.
8 is a LSV curve, a Tafel plot, and a Nyquist plot of the Ni _100-x Fe _x /CP electrode according to the present invention.
9 is a measurement result of ECSA and double layer capacitance of the Ni _100-x Fe _x /CP electrode according to the present invention.
10 is a result of measuring 10 hours of chronopotentiometry of the Ni _100-x Fe _x /CP electrode according to the present invention and the measurement and calculation results of LSV 3000 cycle and Faraday efficiency.
11 is a result of chronopotentiometry measurement for 10 days in the Ni ₉₀ Fe ₁₀ /CP electrode according to the present invention.
12 is a Raman spectrum measurement result before and after the hydrogen generation reaction of the Ni _100-x Fe _x /CP electrode according to the present invention.
13 is an XPS measurement result before and after the hydrogen generation reaction of the Ni _100-x Fe _x /CP electrode according to the present invention.
14 shows the mechanism of the hydrogen generation reaction of the Ni _100-x Fe _x /CP electrode according to the present invention.

Hereinafter, the present invention will be described in more detail.

As a result of the inventors' diligent efforts to develop a low-cost alloy hydrogen generating electrode with high efficiency and long-term stability in an alkaline water electrolysis system, nickel and iron precursors are dissolved in deionized water, and acid or base sodium citrate and sodium hydroxide are dissolved. It is possible to control the size and shape of catalyst particles by controlling hydrolysis between precursors by adding hydrazine as a metal reducing agent. The present invention was completed by developing a nickel-iron alloy hydrogen generating electrode having an optimal iron/nickel ratio having efficient and long-term stability by imparting adhesion stability.

Accordingly, the present invention comprises mixing a nickel precursor and an iron precursor (first step); Adding deionized water and sodium citrate to the solution mixed in the first step and stirring (second step); adding a basic material to a pH of 9-11 when the reaction mixture stirred in the second step becomes uniform (third step); immersing the carbon support in the solution of the third step, adding a reducing agent and stirring (fourth step); Transferring the reaction mixture stirred in the fourth step to an autoclave, sealing it, and raising the temperature to perform hydrothermal synthesis (fifth step); And after the completion of the reaction in the fifth step, cooling the autoclave to room temperature and obtaining a nickel-iron electrode grown on a carbon support (sixth step), a nickel-iron alloy hydrogen generating electrode (Ni _100-x Fe _x /CP electrode) provides a manufacturing method.

In the first step, 80-99% by weight of the nickel precursor and 1-20% by weight of the iron precursor can be mixed, but if the iron content is higher than this, the overpotential increases, resulting in a problem that the hydrogen generation performance may be lowered. can

The nickel precursor may be at least one selected from the group consisting of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate and nickel hydroxide, but is not limited thereto.

The iron precursor may be at least one selected from the group consisting of ferric sulfate, ferric chloride, ferric nitrate, ferric carbonate, iron hydroxide and iron phosphate, but is not limited thereto.

In the second step, sodium citrate may be added in an amount of 100 to 300% by weight based on 100% by weight of the nickel precursor and iron precursor, and if the content is less than the above, the size of the NiFe alloy particles becomes too large so that the particles are stable on the carbon electrode. It is difficult to grow, and if the content is greater than the above content, the Ni precursor and the Fe precursor are not agglomerated, so there is a high probability of obtaining a single metal of Ni or Fe rather than a NiFe alloy.

The basic material may be at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, aqueous ammonia, and amine-based compounds, but is not limited thereto.

The carbon support may be at least one selected from the group consisting of carbon paper, carbon felt, carbon black, activated carbon, carbon nanofiber, nickel foam, and copper foam, but is not limited thereto.

The reducing agent may be at least one selected from the group consisting of hydrazine, sodium borohydride, lithium aluminum hydride, ethylene glycol, and oleylamine, but is not limited thereto.

In the fifth step, the reaction mixture can be hydrothermally synthesized by raising the temperature to 80 to 180 ° C at a rate of 2 to 15 ° C / min and maintaining it for 8 to 30 hours, preferably 120 ° C at a rate of 10 ° C / min. It can be hydrothermally synthesized by raising it up to 20 hours and maintaining it.

The present invention may further include washing the electrode obtained after the sixth step with ethanol and deionized water alternately, followed by drying.

In addition, the present invention provides a nickel-iron alloy hydrogen generating electrode comprising a nickel-iron electrode (Ni _100-x Fe _x /CP electrode; where x is an integer from 1 to 19) grown on a carbon support.

In addition, the present invention provides a nickel-iron alloy hydrogen generating electrode obtained according to the above manufacturing method.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

Hereinafter, the present invention will be described in more detail based on the drawings.

1 is a schematic diagram of the manufacturing process of the Ni _100-x Fe _x /CP electrode according to the present invention.

More specifically, after adding (100-x)M nickel chloride (NiCl ₂ 6H ₂ O) and xM ferric sulfate (FeSO ₄ 7H ₂ O) as precursors of nickel and iron according to the component ratio, deionized water Then, 2.5 g of sodium citrate was added and stirred for 1 hour. When the reaction mixture became homogeneous, 1.0M sodium hydroxide was added so that the pH was 10. After dipping carbon paper (CP) into the solution, 5 mL of hydrazine as a metal reducing agent was added and further stirred for 1 hour. After transferring the solution and CP to an autoclave for hydrothermal synthesis, it was completely sealed and the temperature was raised to 120 °C at a rate of 10 °C/min, and this temperature was maintained for 20 hours. After completion of the reaction, the autoclave was cooled to room temperature, and the CP electrode on which the metal component grew was removed to obtain a Ni _100-x Fe _x /CP electrode. These electrodes were washed three times with ethanol and deionized water and dried to finally obtain Ni _100-x Fe _x /CP electrodes to be used for the reaction.

The Ni _100-x Fe _x /CP electrode according to the present invention needs to be controlled to a size and shape that can maximize surface active sites by adding a dispersant to the metal precursor solution, and these sizes and shapes correlate with the performance of the catalyst. There is a relationship. In addition, in order to minimize the non-attachment phenomenon due to the difference in phase transition between the CP electrode and the catalyst during hydrogen generation reaction cycling, nickel and iron metals are grown directly on the CP electrode by using a hydrothermal synthesis method. At this time, in order to find the optimal ratio of iron and nickel Four types of Ni ₁₀₀ - _{x Fe x /CP electrodes were fabricated by making Ni 100} /CP electrodes composed of only nickel and increasing the iron concentration from 5% to 20% in nickel _- iron alloys.

2 shows the results of XRD analysis of a nickel and iron alloy electrode synthesized through a hydrothermal process. All nickel-iron electrodes show typical graphite diffraction peaks for carbon paper (CP) at 2θ = 26° and 54°. The Ni ₁₀₀ /CP electrode exhibited diffraction peaks corresponding to the (111), (200) and (220) planes of cubic Ni metal at 2θ = 44.5°, 52° and 76.5°, respectively. In the case of the Ni _100-x Fe _x /CP electrode containing both nickel and iron, the peak corresponding to the nickel-iron alloy shifted to a lower angle than that of pure nickel. This is because the crystal lattice area of nickel is replaced by iron atoms having a radius slightly larger than that of nickel atoms, so that the area of the crystal lattice increases. The higher the iron content, the sharper the diffraction peak of the Ni _100-x Fe _x particle and the narrower the peak. This indicates that the crystallite size of the alloy increased with increasing iron content.

3 shows a transmission electron microscope image of the Ni ₉₀ Fe ₁₀ /CP electrode. Spherical crystals with a size of about 0.25 μm were observed. It was found that the lattice distances of (111) and (200) planes, which are the main crystal planes of the Ni ₉₀ Fe ₁₀ alloy, were 2.07 and 1.76 Å, respectively, slightly larger than those of the reported pure nickel metal. In addition, when looking at the SAED pattern of the alloy, (111), (200), and (220) planes that can be confirmed in XRD can be observed, and nickel and iron are evenly distributed in the mapping image. From these results, it can be seen that nickel and iron in the catalyst were evenly synthesized as an alloy.

4 shows a scanning electron microscope image of a Ni _100-x Fe _x /CP electrode. The size and shape of the Ni _100-x Fe _x alloy particles grown on the CP electrode are shown. The size of the electrode increased as the iron content increased. A denser accumulation of alloy particles can also be observed. In the Ni _100-x Fe _x alloy, the reduction potential difference between the iron and CP electrodes was greater than that between the nickel and CP electrodes, so it could grow more stably and densely.

5 is Ni _100-x Fe _x /CP A scanning electron microscope mapping image of the alloy particles is shown. The nickel and iron components of all alloy catalysts were evenly dispersed in proportion to the concentration ratio without agglomeration. Oxygen, which could not be observed in the XRD results, was detected in the image, but it can be seen that it is very small.

6 shows EDS peaks of alloy particles present on the surface of Ni _100-x Fe _x /CP electrodes having different nickel to iron ratios. Carbon present in CP and partially present oxygen are neglected here. In the case of the Ni ₁₀₀ /CP electrode, only the EDS peak corresponding to the nickel element was observed, and in the Ni _100-x Fe _x alloy electrode, the size of the peak was proportional to the Fe and Ni content.

7 is a result of weight and element ratio analysis of nickel and iron alloy electrodes. The elemental ratios of nickel and iron in the Ni ₁₀₀ /CP, Ni ₉₅ Fe ₅ /CP, Ni ₉₀ Fe ₁₀ /CP, Ni ₈₅ Fe ₁₅ /CP and Ni ₈₀ Fe ₂₀ /CP electrodes were 100:0, 95:5, 90:10, 86:14 and 81:19. This ratio is almost the same as the ratio of nickel and iron added during the synthesis, and this confirms the quantitative growth of Ni _100-x Fe _x alloy particles in the CP electrode.

8 is a result of evaluating the electrochemical properties in a 1.0 M KOH solution saturated with nitrogen to evaluate the HER performance of the Ni _100-x Fe _x /CP electrode. 8A shows the LSV curves of the electrodes in the potential range of 0.4-0.6V (vs. RHE). For a current density of 100 mA/cm ² , the overvoltage of the Ni ₁₀₀ /CP, Ni ₉₅ Fe ₅ /CP, Ni ₉₀ Fe ₁₀ /CP, Ni ₈₅ Fe ₁₅ /CP and Ni ₈₀ Fe ₂₀ /CP electrodes is -0.24 (η = 291 mV), -0.28 (η = 275 mV), -0.29 (η = 246 mV), 0.31 (η = 317 mV) and 0.325 V (η = 333 mV). This indicates that the Ni ₉₀ Fe ₁₀ catalyst showed the best HER performance among all the Ni _100-x Fe _x alloy catalysts synthesized in the present invention. 8B shows the Tafel slope of the electrode obtained from the LSV results. Generally, the lower the Tafel slope of an electrode, the lower the exchange current density. Therefore, the overvoltage (η) applied to the electrode in the hydrogen generation reaction is reduced, thereby improving the catalytic performance of the electrode. The Tafel slopes of the Ni ₁₀₀ /CP, Ni ₉₅ Fe ₅ /CP, Ni ₉₀ Fe ₁₀ /CP, Ni ₈₅ Fe ₁₅ /CP, and Ni ₈₀ Fe ₂₀ /CP electrodes were 117.7, 114.4, 95.4, 122.9, and 131.1 mV/dec, respectively. , and it can be seen that the Ni ₉₀ Fe ₁₀ /CP electrode exhibits the highest catalytic activity. Although the Tafel slope of the Ni ₉₀ Fe ₁₀ /CP electrode was slightly larger than that of the commercial Pt/C electrode (52.0 mV/dec), it is a significantly better performance compared to other nickel–iron alloy catalysts reported to date. 8C shows a Nyquist plot of the Ni _100-x Fe _x /CP electrode. This is a very useful measurement result for determining the mass transfer and charge transfer resistance at the surface of the electrolyte and electrode. In general, an increase in resistance impedes charge transfer. Therefore, the smaller the charge transfer resistance (Rct), which represents the size of the semicircle, the lower the recombination rate and the lower the resistance, the better the electrical conductivity of the electrode. The Rct values of the Ni ₁₀₀ /CP, Ni ₉₅ Fe ₅ /CP, Ni ₉₀ Fe ₁₀ /CP, Ni ₈₅ Fe ₁₅ /CP, and Ni ₈₀ Fe ₂₀ /CP electrodes were 14.64, 12.02, 5.71, 15.62, and 18.05 Ω, respectively; In particular, the Ni ₉₀ Fe ₁₀ /CP electrode showed the lowest resistance, which showed the highest charge transfer efficiency.

9 is a result of deriving the double layer capacitance (Cdl) through the CV measurement method for the electrochemically active surface area (ECSA) of the electrode. Since ECSA is proportional to Cdl, ECSA was estimated by the following experimental method. ECSA has a direct effect on the activity of electrocatalysis. The Cdl of the electrode was measured in the non-faradaic region where the oxidation-reduction reaction of the Ni _100-x Fe _x alloy catalyst does not occur, and the difference in current density of ECSA obtained at a scan rate of 20–100 mV showed a linear trend. The Ni ₉₀ Fe ₁₀ /CP electrode showed the widest CV curve area among all electrodes. The width of the CV curve of the electrode decreased rapidly as the iron content increased by more than 10%. Therefore, the Ni ₉₀ Fe ₁₀ /CP electrode is expected to exhibit excellent electrocatalytic activity due to its high capacitance.

10 is a result showing long-term durability evaluation, stability evaluation for 3000 cycles, and Faraday efficiency. Chronopotentiometry and LSV results obtained for all Ni _100-x Fe _x /CP electrodes at 100 mA/cm ² for 10 hours showed that the Ni ₉₀ Fe ₁₀ /CP electrode showed the best catalytic performance for 3000 cycles. Except for the Ni ₈₀ Fe ₂₀ /CP electrode, which showed the poorest performance in FIG. 10A, the Ni _100-x Fe _x /CP alloy electrode had a smaller difference in overvoltage at the beginning and after 10 hours than in the case of the pure Ni ₁₀₀ /CP electrode. . This result indicates that the stability of the Ni ₁₀₀ /CP electrode is improved by adding an optimal amount of iron. 10B shows the lifetime of the Ni ₉₀ Fe ₁₀ /CP electrode, which showed the best activity among all electrodes by repeating the LSV measurement. The overpotential value of the electrode gradually shifted to a negative value up to 100 cycles and then hardly changed up to 3000 cycles. This result was stabilized up to 100 cycles through sufficient interaction between the electrolyte and the Ni ₉₀ Fe ₁₀ alloy catalyst, and the voltage difference between the first and 3000 cycles of the Ni ₉₀ Fe ₁₀ /CP electrode was negligibly small. This indicates a high stability of the electrode up to 3000 cycles. FIG. 10C shows the Faraday efficiency obtained from actual and theoretical hydrogen production at 100 mA/cm ² for the Ni ₉₀ Fe ₁₀ /CP electrode. The Faradaic efficiency of the Ni ₉₀ Fe ₁₀ /CP electrode was 97.07%, and almost all 97% of the participating electrons were used for the hydrogen evolution reaction without any other side reactions.

11 is a chronopotentiometry result of the Ni ₉₀ Fe ₁₀ /CP electrode obtained at 100 mA/cm ² for 10 days. Compared to the initial stage of the reaction, the potential gradually increased to a negative charge over time, but the increase is negligible. Even after 10 days, the potential (-0.274V) did not change significantly compared to the initial value of -0.255V. This means that the Ni ₉₀ Fe ₁₀ /CP electrode showed excellent durability even when exposed to strong alkaline conditions for a long time.

12 shows Raman spectra of the Ni ₁₀₀ /CP and Ni ₉₀ Fe ₁₀ /CP electrodes before and after the hydrogen evolution reaction for 10 days. Both catalysts showed only peaks corresponding to a high nickel content before and after the reaction. In the spectra of the Ni ₁₀₀ and Ni ₉₀ Fe ₁₀ catalysts before the hydrogen evolution reaction, IP bands corresponding to lattice defects of Ni ⁰ were observed at 520 and 510 cm ^-1 , respectively. In particular, the intensity of the band increased after the hydrogen evolution reaction. This phenomenon was more prominent in Ni ₁₀₀ than Ni ₉₀ Fe ₁₀ . These results indicate that the compositional change of the Ni ₁₀₀ catalyst is greater than that of the Ni ₉₀ Fe ₁₀ although the oxygen composition is different in the two electrode catalysts after the hydrogen generation reaction. In addition, two new bands corresponding to 2P and 2M were observed at 1010 and 1550 cm ^-1 in the spectrum of the Ni ₁₀₀ and Ni ₉₀ Fe ₁₀ electrodes after the reaction. The 2P band corresponds to defects in the ^NiO crystal, and the width of this band increases as the number of defects increases. Since the band of the Ni ₁₀₀ catalyst is wider than that of the Ni ₉₀ Fe ₁₀ catalyst, it is assumed that more lattice defects are generated in Ni ₁₀₀ after the hydrogen evolution reaction. These results indicate that crystal defects occurred more rapidly in the Ni ₁₀₀ catalyst crystals without iron elements than in the Ni ₉₀ Fe ₁₀ catalyst crystals during the hydrogen evolution reaction.

13 shows XPS measurement results of Ni ₁₀₀ , Ni ₉₀ Fe ₁₀ , and Ni ₈₀ Fe ₂₀ alloy catalysts before and after hydrogen generation reaction. In all three catalysts before reaction, 2p _1/2 and 2p _3/2 peaks corresponding to Ni ²⁺ were observed at 872.8 and 854.8 eV, and 2p _1/2 and 2p _3/2 peaks corresponding to Ni ⁰ were observed at about 869.4 and 869.4 eV, respectively. observed at 852.3 eV. In catalysts with high Fe content, the peaks corresponding to Ni ²⁺ were shifted to higher binding energies. The peak of Ni 0 appeared low because the abundance ratio of Ni ⁰ and Ni ²⁺ was low because the nickel content of ^the catalyst with high iron content was low. After the hydrogen generation reaction, the peak corresponding to Ni ⁰ disappeared in all three catalysts. This indicates that Ni ⁰ was oxidized to Ni ²⁺ after the hydrogen evolution reaction. Based on these results, it can be seen that the catalyst in which Ni ⁰ and Ni ²⁺ were mixed before HER was completely oxidized to Ni ²⁺ by electrolyte and water after the hydrogen evolution reaction. In the Ni ₉₀ Fe ₁₀ /CP and Ni ₈₀ Fe ₂₀ /CP electrodes, a 2p _3/2 peak corresponding to Fe ²⁺ was observed at about 711.5 eV, and a 2p _3/2 peak corresponding to Fe ⁰ was observed at about 706.8 eV. It became. There was no change in the position of the peak, but the peak area and intensity increased in the catalyst containing a large amount of iron. On the other hand, after the hydrogen generation reaction, the peak corresponding to Fe ⁰ disappeared from both electrodes, similar to the analysis result of nickel. Also, like the Ni2p spectrum, Fe0 was expected to be completely oxidized to Fe2 ⁺ by the electrolyte and water during the hydrogen evolution reaction. The O1s spectrum before the hydrogen evolution reaction was observed at 528.6 eV for the peak corresponding to the MO of the lattice and at 530.3 eV for the M-OH peak arising from water adsorption or surface defects. In all catalysts, the area of the peak corresponding to MO decreased significantly after the hydrogen evolution reaction, while the area of the peak corresponding to M-OH increased significantly. It is believed that the amount of M-OH was relatively increased because the metal component of nickel or iron was oxidized by water or electrolyte during the hydrogen generation reaction and more OH- was attached to the oxidized metal ion. In addition, it was observed that the peak corresponding to M-OH was stronger in the Ni ₈₀ Fe ₂₀ catalyst with a high iron content. This indicates that more water or OH ions were adsorbed on the iron component than on the nickel component.

14 shows the mechanism for the hydrogen evolution reaction in the catalyst. Energy is consumed by the initial water dissociation process, which supplies H ^* after cleaving the HOH bond in the Volmer step of the hydrogen evolution reaction in an alkaline solution. Therefore, this step is designated as the rate-determining step of the reaction. In the hydrogen evolution reaction on Ni _100-x Fe _x alloy catalyst particles, water is more easily adsorbed on Fe ²⁺ than on Ni ²⁺ , and the adsorbed water is transferred to Ni ⁰ along the catalyst particle interface. Since Ni ⁰ is an active site for water decomposition and exhibits excellent electron transport ability, electron transfer proceeds rapidly due to Ni ⁰ in the Volmer step, which is a rate-determining step, so that water can be decomposed with little energy. However, since Ni ⁰ bonds strongly with hydrogen, a relatively high overpotential is required to desorb the generated hydrogen. At this time, the Ni ²⁺ and Fe ²⁺ ions oxidized at the interface of the catalyst particles reduce the activation energy for hydrogen adsorption or desorption, thereby promoting hydrogen desorption by Ni ⁰ . Therefore, this study demonstrated that the hydrogen evolution reaction performance of a Ni _100-x Fe _x alloy catalyst with an optimal iron content can be improved by the synergistic effect of nickel and iron. The addition of excess iron resulted in a relatively low amount of nickel and low activity of the overall hydrogen evolution reaction of the catalyst. The optimal nickel to iron ratio for the best synergy between nickel and iron is 90:10.

Claims (12)

mixing a nickel precursor and an iron precursor (first step);
Adding deionized water and sodium citrate to the solution mixed in the first step and stirring (second step);
adding sodium hydroxide to a pH of 9-11 when the reaction mixture stirred in the second step becomes uniform (third step);
immersing the carbon paper in the solution of the third step, adding hydrazine and stirring (fourth step);
Transferring the reaction mixture stirred in the fourth step to an autoclave, sealing it, and raising the temperature to perform hydrothermal synthesis (fifth step); and
After completion of the reaction in the fifth step, cooling the autoclave to room temperature and obtaining a nickel-iron electrode grown on carbon paper (sixth step). The method of claim 1,
The first step is a method for producing a nickel-iron alloy hydrogen generating electrode, characterized in that mixing 80-99% by weight of the nickel precursor and 1-20% by weight of the iron precursor. The method of claim 1,
The nickel precursor is a method for producing a nickel-iron alloy hydrogen generating electrode, characterized in that at least one selected from the group consisting of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate and nickel hydroxide. The method of claim 1,
The iron precursor is a method for producing a nickel-iron alloy hydrogen generating electrode, characterized in that at least one selected from the group consisting of ferric sulfate, ferric chloride, ferric nitrate, ferric carbonate, iron hydroxide and iron phosphate. The method of claim 1,
The sodium citrate is a method for producing a nickel-iron alloy hydrogen generating electrode, characterized in that added in 100-300 parts by weight based on the total of 100 parts by weight of the nickel precursor and the iron precursor. delete delete delete The method of claim 1,
In the fifth step, the reaction mixture is heated to 80-180 ° C at a rate of 2-15 ° C / min and maintained for 8-30 hours for hydrothermal synthesis. Method for producing a nickel-iron alloy hydrogen generating electrode. The method of claim 1,
Method for producing a nickel-iron alloy hydrogen generating electrode, characterized in that it further comprises the step of washing the electrode obtained after the sixth step with ethanol and deionized water and then drying. delete delete

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