The invention relates generally to electrolytic hydrogen production, and more specifically to a method for preparing an inorganic porous material for the alkaline water electrolysis electrode.
Hydrogen is a high-efficiency and clean secondary energy source with the advantages of high combustion value, abundant resources and renewability. Hence, the desirability of generating and utilizing hydrogen has been widely recognized by countries all over the world. There are many preparation methods for hydrogen, including hydrogen production using fossil energy (where natural gas or methane is passed through a special reformer which reacts steam at high temperature to obtain the hydrogen), as an industrial by-product and by water electrolysis. Water electrolysis is an easy-to-operate hydrogen production process, resulting in a purity of hydrogen high enough for electrolysis to be widely used in the industry. In recent years, the utilization of renewable energy sources has been promoted to address the serious environmental pollution problems associated with fossil energy sources. Hydrogen production by water electrolysis has become an important task as a large amount of wind and hydropower resources cannot be integrated into electricity generation.
Although hydrogen production technology for water electrolysis has been widely used in the industry, the electric energy consumption for hydrogen evolution is large and energy transformation efficiency is low due to the increase of cell voltage during the process of water electrolysis. Currently, in the alkaline water electrolysis industry, the material used in the cathode during the hydrogen evolution process is nickel. However, the overpotential of hydrogen evolution is high, reaching 480 mV. In order to render alkaline water electrolysis more suitable for widespread use in hydrogen production, it is desirable to reduce the electricity consumption during the process of water electrolysis.
Porous nickel catalytic material has been researched for a long time, and various nickel-based electrodes have been developed. For example, U.S. Pat. No. 4,447,302A describes a porous electrode, hot pressed from nickel powder for alkaline water electrolysis, which is alloyed with 1-15% by weight of titanium, a precious metal. Further, Ragunathan et al. describe a method for preparing porous nickel electrodes by repeated spray coating, drying and pressing the nickel mix, and then sintering in a hydrogen atmosphere under 900-1000° C. (“Porous nickel electrodes in water electrolysis 1. Electrode preparation and polarization studies in strong alkali,” International Journal of Hydrogen Energy, Volume 6, Issue 5, 1981, Pages 487-496). In this research, the nickel mix consists of fine carbonyl nickel powder, nickel oxalate and methyl cellulose suspended in water, forming a thin paste. These and many other prior-art approaches make use of expensive raw materials, and increase the complexity of the preparation process.
The invention provides, in various embodiments, a high-efficiency porous nickel cathode catalytic material for hydrogen evolution by water electrolysis, as well as methods of making such material. As such, this material can reduce the overpotential of hydrogen evolution and improve the electro-catalytic activity at the cathode during the process of water electrolysis, which can directly and effectively reduce electricity consumption and, thus, the cost of hydrogen production by water electrolysis.
The invention only uses nickel carbonate powder as the additive, which is added without any other elements. The method used in the invention is more economical and easier to prepare the electrode. The sintering decomposes into CO2 and NiO. Hence, no other impurity will remain after sintering. Additionally, the CO2 produced by sintering benefits the formation of sintered nickel porous structure.
A method for preparing a sintered nickel alkaline water electrolysis electrode includes, in accordance with one example embodiment, the following steps:
Step 1: Add 10˜20 wt. % nickel carbonate to a chosen nickel powder with an average particle size of 20 or 50 microns and mix it evenly. After 24˜72 hours of ball-milling at 10˜400 rounds per minute (rpm), obtain a second nickel powder having an average particle size of 5˜50 microns.
Step 2: Add 0.5˜5 wt. % polyvinyl alcohol to the second nickel powder. Form nickel dies under cold-pressing agglomeration at a pressure of 100˜300 MPa.
Step 3: Put the dies into a vacuum sintering furnace. After the vacuum reaches 1×10−3˜1×10−4 Pa, start to raise the temperature. The temperature increases to 200˜350° C. at a heating rate of 1˜2° C./min. Keep dies at the raised temperature for 10˜30 minutes. Then, the temperature increases further to 800˜1000° C. at a heating rate of 0.5˜1° C./min. Keep dies at that further raised temperature for about 60 minutes to obtain the porous sintered nickel dies.
Step 4: The porous sintered nickel dies are homogenized at 500˜600° C. Keep them within this temperature range for 2˜6 hours to obtain porous nickel material.
The disclosed method and electrode material can provide multiple benefits:
The electrode material for hydrogen production by water electrolysis can be made by a simple preparation process and at low sintering temperature, providing energy savings.
The porous nickel material resulting from the disclosed process utilizes the small pores between the powders in the die and nickel carbonate decomposition reaction during the process of sintering to make pores. The pores are uniform in size (observed by SEM), as confirmed by testing the material performance by electro-chemical analysis. The diameters of the pores are between 1 and 500 micrometers as observed by scanning electron microscopy (SEM). Through the process, it is possible to obtain a porous cathode material with a high specific surface area.
The use of nickel as a raw material for the preparation of porous material, which can prevent acid and alkali corrosion, is suitable for the electrolyte environment that is used for hydrogen production by water electrolysis. The porous sintered nickel electrode has broad application prospects in the field of hydrogen production by water electrolysis.
First, a nickel powder with an average particle size of 20 microns and a nickel carbonate at analytical purity are selected to form a mixture according to a ratio of the weight of nickel powder to the total weight of nickel powder and nickel carbonate of 80%. The raw material (nickel powder mixture) is obtained after 30 hours ball-milling (101). Next, 2.5% polyvinyl alcohol is added to the raw material (nickel powder mixture), and a die is obtained by cold pressing under 120 MPa pressure (102). Then, the die is placed into a vacuum sintering furnace. The temperature is raised after the vacuum reaches 6×10−4 Pa. The temperature is raised to 520° C. with a heating rate of 1.5° C./min. The die is kept at this temperature for 30 minutes. After that, the temperature is raised to 800° C. with a heating rate of 0.5° C./min. The die is kept at this temperature for 60 minutes to obtain the porous sintered nickel die (103). Lastly, the porous sintered nickel die is homogenized at 550° C. for 2˜6 hours to obtain porous nickel material (104).
To characterize the catalytic activity of the prepared porous nickel material, cyclic voltammograms are obtained by subjecting the material to a cyclic voltage between −0.15 V to −0.05 V at scanning speeds of 2, 4, 6, and 8 mV/s (
where
S—Calculated specific surface area
A—Surface area of 1 cm2 sample
M—Weight of 1 cm2 sample
m1—Unit weight of porous nickel electrode in example 1
C1—Capacitance of the porous nickel electrode in example 1
Cs—Capacitance of the nickel flat electrode
First, a nickel powder with an average particle size of 50 microns and a nickel carbonate at analytical purity are selected to form a mixture according to a ratio of the weight of nickel powder to the total weight of nickel powder and nickel carbonate of 80%. The raw material (nickel powder mixture) is obtained after 30 hours ball-milling (101). Next, 2.5% polyvinyl alcohol is added to the raw material (nickel powder mixture), and a die is obtained by cold pressing under 120 MPa pressure (102). Then, the die is placed into a vacuum sintering furnace. The temperature is raised after the vacuum reaches 6×10−4 Pa. The temperature is raised to 520° C. with a heating rate of 1.5° C./min. The die is kept at this temperature for 30 minutes. After that, the temperature is raised to 800° C. with a heating rate of 0.5° C./min. The die is kept at this temperature for 60 minutes to obtain the porous sintered nickel die (103). Lastly, the porous sintered nickel die is homogenized at 550° C. for 2˜6 hours to obtain porous nickel material (104).
To characterize the catalytic activity of the prepared porous nickel material, cyclic voltammograms are obtained by subjecting the material to a cyclic voltage between 0.15V to −0.05V at scanning speeds of 2, 4, 6, and 8 mV/s (
where
S—Calculated specific surface area
A—Surface area of 1 cm2 sample
M—Weight of 1 cm2 sample
m2—Unit weight of porous nickel electrode in example 2
C2—Capacitance of the porous nickel electrode in example 2
Cs—Capacitance of the nickel flat electrode
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Savaris et al., Porous Ni Electrodes for Hydrogen Production from Water Electrolysis, International Conference on Renewable Energies and Power Quality (ICREPQ'13), Bilbao (Spain), Mar. 20-22, 2013 Renewable Energy and Power Quality Journal (RE&PQJ) ISSN 2172-038 X, No. 11, Mar. 2013 (Year: 2013). |