Four ways to produce hydrogen by electrolysis of water
Hydrogen production from water electrolysis refers to the dissociation of water molecules under the action of direct current to generate oxygen and hydrogen, which are precipitated from the anode and cathode of the electrolytic cell respectively. At the technical level, water electrolysis for hydrogen production is mainly divided into alkaline water electrolysis (AWE), solid polymer PEM water electrolysis, solid polymer anion exchange membrane (AEM) water electrolysis and solid oxide (SOE) water electrolysis. Among them, AWE is an earlier industrialized water electrolysis technology with decades of application experience and a relatively mature technology. In recent years, PEM water electrolysis technology has developed rapidly in terms of industrialization, SOE water electrolysis technology is in the initial demonstration stage, and AEM water electrolysis research has just started.
1. Alkaline electrolysis of water for hydrogen production
The diaphragm of the electrolyzed water hydrogen production tank is mainly composed of asbestos, which plays the role of gas separation. The cathode and anode are mainly composed of metal alloys, such as nickel-molybdenum alloys, which split water to produce hydrogen and oxygen. The electrolyte of industrial alkaline water electrolyzer is usually potassium hydroxide solution with a mass fraction of 20%~30%, the operating temperature of the electrolyzer is 70~80°C, the working current density is about 0.25 ampere/square centimeter, and the generated gas pressure is 0.1 ~ 3.0 MPa, the total efficiency is 62%~82%. Hydrogen production from alkaline water is a mature technology with low investment and operating costs, but there are problems such as lye loss, corrosion, and high energy consumption.
2. Hydrogen production by electrolysis of water
Different from electrolysis of water for hydrogen production, proton exchange membrane (PEM) electrolysis of water for hydrogen production uses perfluorosulfonic acid proton exchange membrane with good chemical stability, proton conductivity and gas separation instead of asbestos membrane as solid electrolyte, which can effectively prevent electron transfer. , improve the safety of electrolyzers. The main components of PEM electrolyzers are proton exchange membrane, positive and negative catalyst layers, positive and negative gas diffusion layers, positive and negative end plates, etc. From the inside out. Among them, the diffusion layer, catalyst layer and proton exchange membrane constitute the membrane electrode, which is the main place for material transfer and electrochemical reaction in the entire water electrolyzer. The characteristics and structure of membrane electrodes directly affect the performance and service life of proton exchange membrane water electrolyzers.
3. High-temperature solid oxide electrolysis of water for hydrogen production
High-temperature solid oxide electrolysis of water for hydrogen production is different from alkaline water electrolysis and PEM water electrolysis. High-temperature solid oxide electrolysis of water for hydrogen production uses solid oxide as the electrolyte material, and the working temperature is 800~1 000. The electrochemical performance of the hydrogen production process Significantly improved and more efficient.
The electrode of SOEC electrolytic cell adopts non-precious metal catalyst, the cathode material adopts porous metal ceramic Ni/YSZ, the anode material adopts perovskite oxide, and the electrolyte adopts YSZ oxygen ion conductor. The all-ceramic material structure avoids material corrosion. The working environment of high temperature and high humidity limits the selection of materials with high stability, good durability and anti-attenuation for electrolyzers, and also restricts the selection of application scenarios and large-scale promotion of SOEC hydrogen production technology.
4. Solid polymer anion exchange membrane water electrolysis
Research on AEM water electrolysis is just beginning. In the past few years, polymeric anion exchange membranes (AEMs) for electrochemical devices have been developed, and alkaline electrolysis using AEMs can provide the advantages of PEM and liquid electrolyte cyclic alkaline electrolysis.