By means of direct current, water molecules are split apart to produce oxygen and hydrogen, which are then separated from the anode and cathode of the electrolytic cell, respectively. This process is known as water electrolysis. Water electrolysis hydrogen generation is often separated into alkaline water electrolysis (AE), proton exchange membrane (PEM) water electrolysis, and high temperature solid oxide water electrolysis depending on the various materials of the electrolyzer diaphragm (SOEC).
Alkaline water electrolysis hydrogen production
Asbestos makes up the majority of the diaphragm of the alkaline water electrolysis hydrogen generation electrolyzer, which separates gases. Metal alloys, such as Ni-Mo alloy, etc., which break down water to produce hydrogen and oxygen, make up the majority of the cathode and anode. Industrial alkaline water electrolyzers typically use KOH solution as their electrolyte; their mass fraction ranges from 20% to 30%; their operating temperature is 70°C to 80°C; their working current density is around 0.25 A/cm2; and their gas pressure ranges from 0.1 MPa to 3.0 MPa. Efficiency ranges from 62% to 82%.The technology for producing hydrogen via alkaline water electrolysis is well developed and has low startup and operational costs, but it has drawbacks such lye loss, corrosion, and high energy usage. Alkaline water electrolysis hydrogen generation is a focus of both domestic and international research on the development of water electrolyzer equipment.
PEM water electrolysis hydrogen production
The main components of the PEM water electrolyzer are proton exchange membrane, cathode and anode catalytic layer, cathode and anode gas diffusion layer, cathode and anode end plates, etc. from inside to outside. Among them, the diffusion layer, the catalytic layer and the proton exchange membrane form the membrane electrode, which is the main place for the material transmission and electrochemical reaction of the entire water electrolyzer. The performance and lifespan of the PEM water electrolyzer are directly impacted by the properties and structure of the membrane electrode.
Differences
Compared with alkaline water electrolysis hydrogen production, PEM water electrolysis hydrogen production has higher working current density, higher overall efficiency, and higher hydrogen gas fraction, higher gas production pressure, faster dynamic response speed, and can adapt to the fluctuation of renewable energy power generation, it is considered to be a very promising water electrolysis hydrogen production technology. At present, PEM water electrolysis hydrogen production technology has been demonstrated and gradually promoted in fields such as on-site hydrogen production at hydrogen refueling stations, electrolysis of water for hydrogen production from renewable energy sources such as wind power, and energy storage.
