What does PEM electrolysis for hydrogen production mean?

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An article for literacy purposes; please ignore if you’re not interested. For PEM electrolysis for hydrogen production, it’s necessary to first understand what PEM means. PEM stands for proton exchange membrane – a membrane used in the process of producing hydrogen, and this method emerged as a contrast to traditional alkaline water-based methods for hydrogen production. Comparison between PEM water electrolysis for hydrogen production and traditional alkaline water electrolysis for hydrogen production: Pure water PEM hydrogen production has the following advantages over traditional alkaline water electrolysis: ① The separators in the two types of systems are different; the separator in the PEM type is an ion membrane with molecular-level pores and a very small thickness, which makes it less likely to cause hydrogen back-permeation. In contrast, the separator in traditional alkaline systems does not have molecular-level pores, so hydrogen back-permeation is more likely to occur. ②The electrodes of the two types are different. The catalytic electrode in the PEM type features molecular-level micropores that are located right against both sides of the ion membrane as well as within its internal pores; it is a zero-gap catalytic electrode. Its advantages include a large reaction area and high conversion efficiency. In contrast, traditional alkaline electrodes have a limited distance between them, which results in high inter-electrode resistance, increased current flow, higher heat generation, and lower conversion efficiency. ③The electrolyzer structures of the two types are different. In PEM-type electrolyzers, the collectors in the two chambers are tightly structured and elastic, which results in a lightweight and compact electrolyzer – its weight is only 1/3 that of conventional electrolyzers producing the same amount of hydrogen. The advantage here is zero electrode distance and low internal resistance. In contrast, the collectors in the anode chamber of traditional alkaline electrolyzers lack elasticity, leading to high electrical energy losses and low conversion efficiency. ④The electrolytes of the two types are different. The PEM type requires only pure water, with no additives needed, and it contains no corrosive liquids, thus causing no environmental pollution; at the same time, the purity of the gases produced is high. In contrast, traditional alkaline electrolytes require the addition of 15% NaOH or 30% KOH, which makes these electrolytes highly corrosive and prone to causing contamination of the pipelines due to fluid leakage. ⑤The mechanisms of electrical conduction in the electrolyzers of the two types are different. In PEM type, hydrogen ions move through an active proton exchange membrane, thereby producing reduced hydrogen gas at the cathode; whereas in conventional alkaline types, positive and negative ions move separately in the aqueous solution, resulting in the production of hydrogen and oxygen gases at the two electrodes. Furthermore, PEM water electrolysis technology is regarded as one of the most promising water electrolysis methods for hydrogen production. Compared with traditional alkaline water electrolysis for hydrogen production, it offers the aforementioned advantages in addition to higher gas output pressure and better purity. Moreover, the current density is high, which enables miniaturization of electric thrusters, facilitates integration, results in a simple system that requires few auxiliary devices; as a result, it is easy to install, requires little maintenance, and is easy to operate. At the same time, PEM electrolysis systems for hydrogen production have a fast response time and are capable of handling dynamic operations, which makes them highly suitable for addressing the unevenness and intermittency in the supply of renewable energy sources such as wind and solar power. In contrast, the response speed of traditional alkaline water electrolysis is relatively slow, and it is not as good as the dynamic response of PEM electrolysis for hydrogen production.