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The Charm of Anion Exchange Membranes: How to Challenge Traditional Electrolysis Technology at Low Cost?
In the current era of energy transition, how to produce hydrogen effectively and economically has become an area that many researchers continue to explore. Among numerous electrolysis technologies, anion exchange membrane (AEM) electrolysis technology has received widespread attention due to its potential of low cost and high efficiency. The main feature of this technology is the use of a semi-permeable membrane to conduct hydroxide ions (OH−). This type of membrane can effectively perform ion exchange while isolating products and providing electrical insulation.
Water electrolysis technology using anion exchange membranes does not require expensive noble metal catalysts, but can use low-cost transition metal catalysts, which greatly improves the economy of large-scale applications.
Advantages and Challenges
Advantages
The biggest advantage of AEM electrolysis is that it combines the characteristics of alkaline water electrolysis (AWE) and proton exchange membrane electrolysis (PEM) technology. AEM technology can not only use non-noble metal catalysts (such as Ni, Fe, Co, etc.), but can also operate in pure water or mildly alkaline solutions, which helps reduce the risk of leakage.
AEM's operating costs are significantly lower than the precious metal catalysts required for PEM electrolysis, such as platinum and ruthenium, making it a more viable alternative.
In addition to cost advantages, AEM electrolysis technology can operate within a wide operating range and can effectively reduce the cross-loss problem of hydrogen, with the hydrogen loss even being controlled below 0.4%. This not only improves the efficiency of the system but also enhances security.
Challenge
Although AEM electrolysis technology has many advantages, it is still in the early research stage and faces many challenges. One of the biggest challenges is the durability of the membrane. Compared with the PEM electrolysis stack's life span of 20,000 to 80,000 hours, the life of the AEM electrolyzer is only about 2,000 hours, which limits the scope of its commercial application.
To overcome these challenges, improving the conductivity and durability of membranes has become the focus of current research.
In addition, AEMs have insufficient stability in high-temperature environments and are often unable to withstand temperatures exceeding 60°C, which represents a potential obstacle to the operation of large-scale electrolysis systems. Therefore, it is crucial to find stable membrane materials that can maintain high pH and high temperature environments.
Scientific Principles
Reaction
In the process of AEM electrolysis, oxygen generation reaction (OER) and hydrogen generation reaction (HER) are key reaction steps. These reactions need to overcome higher energy barriers, especially in oxygen generation reactions, which result in increased overpotential due to the multi-step reaction process.
Efficient catalysts can reduce OER overpotential, thereby improving the overall performance of AEM electrolyzers.
Anion exchange membrane
The design of anion exchange membranes is critical to their performance. Typically, researchers use quaternary ammonium (QA) as the main bonding group of membranes, but this type of group is easily degraded in an alkaline environment, so there is a need to find more stable alternatives such as imidazole groups.
Membrane electrode combination
The membrane electrode assembly (MEA) is the core component of the AEM electrolyzer, consisting of anode and cathode catalyst layers and an intermediate membrane layer. The design and preparation method of the catalyst layer will directly affect the efficiency and performance of the electrolyzer.
Generally speaking, the emergence of anion exchange membrane water electrolysis technology marks a revolution in electrolysis technology. Not only does it improve the economics of hydrogen production, it also reduces the environmental impact and heralds the future of renewable energy. So, how will the future hydrogen energy industry use this new technology as the cornerstone to achieve wider applications?
