PEM or AEM? That is a good question in this rapidly evolving age of fuel cells and alternative energies. The proton exchange membrane or PEM is essential, yet it needs to be reasonably impermeable to gases serving as solid electrolytes. However, they are also constantly evolving in order to make them suitable for longer use and higher temperature settings.
The AEMs, on the other hand, are often described as having lower thermal durability and low OH- conductivity, and one study even said they should “combine the positive qualities of the Alkaline Water Electrolysis and the proton exchange membrane (PEM) Electrolysis – compactness, environmentally friendly, effectively and being economically priced.”
That doesn’t say which is better for any specific purpose, but a 2017 article in the International Journal of Hydrogen Energy did take a look at this issue. It explained the use of different membranes in water electrolyzers and considered them in terms of their uses as storage for renewable energy in a variety of fuel cells, and as methods for converting fuels into chemicals. One of the membranes was the Sustainion X37 from Dioxide Materials, not a proton exchange membrane but instead an imidazolium functionalized membrane with a styrene polymer backbonemembranes used in an alkaline AEM water electrolyzer.
The end result was quite clear, and the study determined that the it is possible to double the current output of any alkaline water electrolyzer with the AEM and not the proton exchange membranes. Why? The Sustainion® membranes have both superior conductivity and high current densities at low voltage. They also extended the life span of a CO2 electrolyzer into the commercially useful range having displayed conductivities above 100 mS/cm under alkaline conditions at temperatures as high as 60 degrees Celsius. Remaining stable for thousands of hours inat 1M KOH, they havealso operated more than 4k hours at high current densities and low voltages.
Where the proton exchange membrane is concerned, studies have explored how to get higher performances from them. Though one report noted that they are “energy efficient and environmentally friendly alternatives to conventional energy conversion systems”, it went on to say that they are highly prone to degradation. As we already saw, the AEM model from Dioxide Materials has a much higher capability and can go for thousands of hours thanks to its resistance to corrosion and its capacity for stability. There is no arguing the numbers and accepting that in a comparison of PEMs to AEMs, it is the latter that is currently far ahead.
