January 29, 2024
AWE Hydrogen Production Theory and Electrolyzer Composition
Alkaline water electrolysis (AWE) hydrogen production is a process of using electricity to split water into hydrogen and oxygen and get pure hydrogen through filter and dealkalization. It is a mature water electrolysis technology that can produce green hydrogen economically. In this article, we’ll learn about AWE hydrogen production theory and electrolyzer composition.
AWE Hydrogen Production Theory
AWE hydrogen production refers to the process of electrolyzing water to generate hydrogen in an alkaline electrolyte environment. The electrolyte is generally a 30% mass concentration KOH solution or a 26% mass concentration NaOH solution.
The cathode and anode of alkaline electrolysis water are mainly composed of metal alloys, using nickel mesh as the electrode. Water will be electrolyzed into hydrogen and oxygen under the action of direct current. And the generated gas needs further dealkalization to get purer.
An AWE hydrogen production system mainly includes the alkaline electrolyzer and the BOP auxiliary system. The biggest advantage of alkaline electrolysis technology is that the anode and cathode electrode plates do not contain precious metals, so the cost of the electrolyzer is relatively low.
The core feature of the technology is that the power should be stable and reliable, thus not suitable for intermittent power such as wind and solar energy. Among the current water electrolysis hydrogen production technologies, alkaline water electrolysis technology is the most mature and has the lowest production cost.
However, there are still some limits in AWE hydrogen production.
(1) The energy efficiency of alkaline electrolyzers is low, usually around 60%.
(2) Alkaline electrolytes (such as KOH) will react with CO2 in the air to form carbonates that are insoluble in water under alkaline conditions. These insoluble carbonates will block the porous catalytic layer and hinder products and reactants. transmission, greatly reducing the performance of the electrolytic cell.
(3) It is difficult to shut down or start up the alkaline electrolyzer quickly, and it is difficult to quickly adjust the hydrogen production speed, because the pressure balance on both sides of the anode and cathode of the electrolytic cell must be maintained at all times to prevent the hydrogen and oxygen gases from passing through the porous asbestos membrane and mixing to cause an explosion.
(4) The operating range is narrow, and the lower operating boundary is between 20% and 40%. It cannot match the input power of the full range of 0-100% renewable energy, resulting in an increase in the number of starts and stops, affecting the comprehensive utilization of system energy and the life of the electrolyzer.
(5) High energy consumption and increased electricity costs.
The current density is low, resulting in a large electrolytic cell taking large floor area.
Alkaline Electrolyzer Composition
The main body of an alkaline electrolyzer is assembled from end pressure plates, sealing gaskets, electrode plates, electric plates, diaphragms and other components.
The electrolyzer includes dozens or even hundreds of electrolytic chambers. All chambers are pressed together by screws and end plates to form into a cylindrical or square shape. Each electrolysis chamber is divided by two adjacent electrode plates and includes 6 parts: positive and negative bipolar plates, anode electrodes, separators, sealing gaskets, and cathode electrodes.
(1) Plate and pole frame
Main function: supporting electrodes and diaphragms and conducting electricity.
Performance requirements: Not easily corroded in alkaline solution.
Material: cast iron metal plate, nickel plate or stainless steel metal plate.
(2) Diaphragm
Main function: Prevent hydrogen and oxygen from mixing.
Performance requirements: Ensure that hydrogen and oxygen molecules cannot pass through the diaphragm, but allow electrolyte ions to pass; resist corrosion by high-concentration alkali solutions; have good mechanical strength; the porosity of the diaphragm is as high as possible; it can be maintained under electrolysis temperature and alkali solution conditions chemically stable; raw materials are easily available, non-toxic, non-polluting, and waste is easy to dispose of.
Materials: asbestos diaphragm (earliest), polyphenylene sulfide PPS diaphragm (currently mainstream in China); future research and development focus: polytetrafluoroethylene resin modified asbestos diaphragm, polyether ether ketone fiber diaphragm, polysulfone fiber diaphragm, etc.
(3) Electrode
Main function: The place where electrochemical reactions occur, which is the key to determining the efficiency of hydrogen production.
Performance requirements: alkali resistance, high temperature resistance, large surface area.
Material: Most China domestic materials use nickel-based ones, such as pure nickel mesh, foam nickel, or pure nickel mesh or foam cylindrical as the base to spray high-activity catalysts (high-activity nickel-based catalysts, precious metal-containing catalysts).
The specifications and performance of nickel wire mesh will affect its application scenarios and effects. Therefore, it’s necessary and important to choose appropriate specifications before purchasing.
As a professional manufacturer of nickel mesh, NHGT can provide full support from technical inquiries to nickel mesh supply, only hoping to better serve your industry.
