Hydrogen, as a zero-carbon energy carrier with very high energy density (140MJ-kg-1), is gaining more and more attention. 20% of the world's CO2 emission reduction can be accomplished through hydrogen substitution in 2050, and hydrogen consumption will account for 18% of the world's energy market, with green hydrogen obtained by electrolysis of water using renewable energy sources accounting for more than 80% of the total hydrogen energy supply.
Currently, mainstream electrolysis technologies for hydrogen production include alkaline water electrolysis (ALK), proton exchange membrane water electrolysis (PEM ), solid oxide water electrolysis (SOEC) and anion exchange membrane water electrolysis (AEM). Among them, China's alkaline water electrolysis equipment has obvious advantages in terms of large-scale single-tank and low equipment costs, and is the preferred technology route for large-scale hydrogen production projects. Sany Hydrogen, as a leading electrolyzer manufacturer in China, relies on the leading technology of Sany's traditional construction machinery, and has a wide range of industry-recognized alkaline electrolyzer and PEM electrolyzer products with stable performance in just two years.
For alkaline electrolyzer, electrode and diaphragm, as key materials, affect the energy consumption of the electrolyzer. Therefore, high-performance electrode and diaphragm can effectively reduce the voltage of the small chamber, so as to achieve the improvement of the electrolysis efficiency, reduce the power consumption, increase the gas production of a single tank, and improve the life of the electrolyzer. Sany Hydrogen Energy has recognized the importance of core materials as early as the early stage of its establishment, and quickly set up a hydrogen energy laboratory and a 20MW complete machine test site to provide data support for the optimization of key materials for the electrolyzer.
Wide range of electrodes
The alkaline electrolyzer has several small chambers, each of which contains two electrodes, one cathode and one anode, the shape of which generally corresponds to that of the electrolyzer (generally circular), and whose geometric area is equal to the effective area of the electrolyzer.
(Figure: Schematic of alkaline electrolyzer and electrodes)
Currently, there is a wide range of electrodes for hydrogen production from alkaline electrolyzed water available on the market and in the field of research and development:
The best performers are electrodes made of precious metals (Pt, Pd, Ru, etc.), which, according to theoretical data (Gibbs free energy of hydrogen adsorption), are the closest to the optimal catalytic activity for hydrogen precipitation of all metallic materials. The Italian company Dinola uses mixed precious metal oxide coatings to make precious metal electrodes by combining the catalyst with the substrate material through pyrolytic deposition and other means, and its publicized data show that the current density is up to 900 mA-cm-2 at 80 ℃ alkaline solution and 2 V voltage, and that it can be kept in operation for a long time, with an electrode performance degradation rate of only 0.5% per year. These electrodes have been proved experimentally and in the market that they are now cutting-edge materials for water decomposition catalysts, however, their wide application has been seriously hampered by their high cost and low storage capacity.
For the latest laboratory research on electrodes, including carbon-based electrodes, nickel foam self-growth electrodes, electrodeposition, hydrothermal coating, and other electrodes with precise structure and catalytic site control, their performance is often far better than ordinary industrial electrodes, but few new materials can meet the standards in the stability test, and many of the electrode manufacturing process is limited by the complexity and difficult to scale up the process, the high research and development of new materials and the production costs and other factors. Many electrode manufacturing processes are limited by complex and difficult-to-scale processes, high R&D and production costs of new materials, and other factors, making large-scale production and application difficult.
Nowadays, non-precious metal (Ni, Fe, Mo, Co, etc.) electrodes are widely used in large electrolysis tanks. At present, most of the electrodes used in large-scale alkaline electrolysis tanks in China are Raney nickel electrodes prepared by thermal spraying process, which is generally based on nickel mesh and sprayed with non-precious metal high-activity catalyst electrodes, and electrodes treated with spraying treatment are able to show high current density under a certain small chamber voltage, realizing the value-for-money electrodes.
With the continuous optimization of electrode performance, the need to go further to accomplish value for money requires increasing the number and activity of catalytically active sites. Optimization needs to be carried out on a more microscopic scale, such as using Ni mesh as the substrate, improving the spraying process parameters or formulations, spraying and manufacturing Raney nickel electrodes with a larger specific surface area or catalyst electrodes with multiple activities, forming a porous structure of the catalyst, so as to further increase its specific surface area, so that there are more sites to participate in water electrolysis reactions at a given chamber voltage, and the electrode performance will be further improved. The electrode performance will be further improved.
(Figure: Schematic of the preparation of various alkaline electrodes)
With a wide range of electrode products on the market, how do you choose the best of the best?
Sany Hydrogen's Hydrogen Laboratory and Test Site provide sufficient data support for electrode selection. Sany Hydrogen Laboratory evaluates the performance of electrode products in multiple dimensions, such as potential, bonding and stability, and selects electrode products according to Sany's standards. In the laboratory screening stage, products with excellent initial performance but poor long-term operational stability or poor binding force are not preferred; products with medium initial performance but good long-term operational performance are not poorly selected, and the electrodes will be screened according to a comprehensive assessment of the product situation. After that, the screened electrodes will be tested on the tank, run on the electrolyzer of Sany Hydrogen Changsha test site, and then evaluated in multiple dimensions under various operating conditions to optimize the electrodes again, so as to achieve the superiority of the electrode products with the facts and the data.
Seeing the smallest of diaphragms
For an efficient and reliable alkaline water electrolysis system, in addition to a highly active catalyst, the diaphragm not only plays the role of separating the cathode and anode, avoiding the mixing of hydrogen and oxygen, but also affects the energy consumption of the electrolyzer, and is a key material to ensure safe operation. Ideal diaphragm materials should have good ionic conductivity, low resistivity, high gas barrier, thin thickness, high mechanical strength, and long-term durability in high temperature and high concentration alkaline electrolyte.
Alkaline water electrolysis has developed through 3 generations of asbestos diaphragm, PPS diaphragm and composite diaphragm.
Asbestos diaphragm is the traditional alkaline electrolyzer diaphragm, which has the advantages of high strength, corrosion resistance, high temperature resistance and good hydrophilicity, but has been eliminated due to carcinogenicity.
PPS diaphragm has excellent heat resistance, high mechanical strength, and excellent electrical properties, but due to poor hydrophilicity, large thickness (>500 μm) and large through-hole size, it usually exhibits high ionic resistance and permeability, resulting in high energy consumption and easy interconjugation of hydrogen and oxygen, which can be improved by surface modification and other methods to improve its hydrophilicity. However, even if the hydrophilicity is improved by coupling organic hydrophilic groups on the surface, it is still difficult to completely solve the problems such as poor gas barrier.
The third generation of diaphragm is coated with inorganic functional coating on the surface of PPS fabric, similar to the sandwich structure of organic-inorganic composite diaphragm, which has become the main direction of the current diaphragm research. The inorganic functional coating on the surface of the composite diaphragm has a uniform microporous structure, which not only greatly improves the hydrophilicity and air barrier, but also reduces the ionic resistance and the thickness of the diaphragm.
(Figure: Electrolytic water voltage (4 kA/m2) for a single electrolytic cell with different diaphragms)
At present, domestic and foreign composite diaphragm has been successfully commercialized in the electrolyzer case, the future of the diaphragm materials will be based on the composite diaphragm, towards the development of higher corrosion resistance, to prevent hydrogen and oxygen cross-penetration, as well as a higher ionic conductivity of the diaphragm direction, in order to effectively reduce the energy consumption, and at the same time, to improve the purity of the hydrogen gas as much as possible.
Sany Hydrogen Energy has strict standards and processes for the screening of diaphragms just like electrodes. For the PPS diaphragm used in the mainstream application of circular electrolyzer, Sany Hydrogen Energy lab has more than 10 kinds of performance testing capabilities, including air tightness, surface resistance, etc., to comprehensively evaluate the performance of PPS diaphragm. After optimization, the PPS products are then run on the electrolyzer, and the performance testing data and actual running data are used as evaluation criteria to optimize the PPS products. For composite diaphragms, Sany Hydrogen Energy has square electrolyzer products to match. In terms of composite diaphragm preference, combined with the actual use of working conditions, in the face of the unique situation of composite diaphragm such as non-abrasion resistance and moisture preservation, a variety of tests are established, and safe, reliable and easy to operate composite diaphragm products are preferred.
The existing alkaline water electrolysis hydrogen production technology is highly mature, simple and low-cost, and has already been applied on a large scale to large-scale electrolysis hydrogen production projects in the three northern parts of China as well as in other regions. In the future, both the construction of new power systems, the urgent need for large-scale wind power consumption capacity, and the demand for low-cost green hydrogen supply in the chemical industry, transportation and other fields will require electrolysis tanks capable of adapting to the fluctuating power supply of wind power.
However, the current industrial technology mainly pursues the hydrogen production capacity of a single tank as the goal and makes similar improvements, while the technological advances that can improve the problems of low current density and poor dynamic performance are relatively limited. The new demand for green electricity to produce green hydrogen has put forward higher requirements for the key materials of alkaline water electrolysis technology. Alkaline water electrolysis electrodes and diaphragms have become one of the main directions for research and influencing future industrial applications, and ultimately realizing low-cost and high-performance material production and application, and realizing true value for money.
Sany Hydrogen has a clear understanding of the direction of electrolyzer development, which, combined with the continuous optimization of electrodes and diaphragm products in the market, can bring leading electrolyzer products to the hydrogen energy industry.
In the future, Sany Hydrogen will continue to focus on the "3+1" technology route of round tank, square tank, PEM tank and BOP, and continuously improve and strengthen the seven core competencies of integrated design, material research and development, simulation and analysis, test and verification, electrical control, manufacturing process and hydrogen safety design. Meanwhile, Sany Hydrogen looks forward to deepening cooperation with industry customers, design institutes, suppliers, research institutes, industry organizations, etc., to seek for the high-quality development of hydrogen energy equipment, and contribute Sany's power and Sany's solutions to realize the goal of "Double Carbon".
Citing Literature:
1. Bridging Laboratory Electrocatalysts with Industrially Relevant Alkaline Water Electrolyzers
2. Study on the properties of diaphragm and anode materials for hydrogen production from alkaline electrolytic water
