Electrodes For Alkaline Water Electrolysis Hydrogen Production Electrolyzers - Principles, Materials And Structures

Electrodes For Alkaline Water Electrolysis Hydrogen Production Electrolyzers - Principles, Materials And Structures

1. Electrode action principle

First of all, the role of electrocatalyst in hydrogen production electrolyzer is crucial. It is the place where electrochemical reaction occurs and the fundamental factor that determines the hydrogen production efficiency of hydrogen production electrolyzer.

Theoretically, the voltage of water electrolysis is 1.23 V and the thermal neutral voltage is 1.48 V. However, in actual large-scale equipment, the voltage of a single electrolysis chamber reaches about 2 V. Under the condition of high current density operation (the operating current of industrial electrolyzer is about 3000-4000A), the electrochemical polarization of cathode and anode accounts for a large part.

2. Electrode materials and structure
Currently, there are many types of catalysts for alkaline water electrolysis from a scientific research perspective, including precious metal-based catalysts (Pt, Pd, Au, Ag etc.), non-precious metal-based catalysts (Fe, Co, Ni etc.), and non-metal-based catalysts (carbon materials, etc.).

Currently, most catalysts used in large electrolytic cells are Ni-based, pure nickel mesh or nickel foam or highly active Ni based catalysts (Raney nickel, activated nickel sulfide, NiMo alloy or activated NiAl, etc.) sprayed on this basis.

There are two catalysts in an electrolytic chamber, one at the cathode and one at the anode, distributed on both sides of the diaphragm and in direct contact with the diaphragm. The shape is generally consistent with the shape of the electrolytic cell (generally circular), and its geometric area is equal to the effective area of the electrolytic cell.

The Ni mesh is generally made of 40-60 mesh Ni wire mesh cut into a circle, and the diameter of the Ni wire is about 200um. Although the structure of Ni wire mesh is simple, its surface area is much larger than that of Ni plate. When the same cell voltage is applied, there are more sites for electrochemical reaction, which can generate a larger current.

With the continuous development of renewable energy hydrogen production industry, the requirements for large-scale electrolyzer equipment are getting higher and higher. The simple superposition of cells will cause the length of the electrolyzer to be too long, which is not conducive to the assembly and installation of the electrolyzer. There are also many problems such as sinking in the middle of the electrolyzer.

Therefore, it is a feasible path to improve the current density by optimizing the catalyst. According to Faraday's law, the mass of the substance undergoing chemical changes on the electrode interface is proportional to the amount of electricity passed in. The key to increasing the current density is to increase the rate of electrochemical reaction on the catalyst surface under a given cell voltage, which depends on two aspects of the catalyst's characteristics, namely the number of catalytic sites and the intrinsic activity of the catalytic sites.