Goldman research13 Feb 2022 19:30
Alkaline and PEM technologies dominating the electrolyzer market today, yet innovation is ongoing, with new technologies making an entry
n Alkaline electrolysis: The most widely adopted and mature technology is alkaline
electrolysis, characterized by relatively low electrolyzer capital cost (less expensive metals typically used compared to other electrolysis technologies) and relatively high efficiencies - typically varying from 55% to 70%. The reaction occurs in a solution comprised of liquid electrolyte (typically potassium hydroxide) between two electrodes. When sufficient voltage is applied between the electrodes, the oppositely charged ions (OH- and H+) are attracted to the oppositely charged electrodes. The anode accumulates water (through the combination of OH- ions) while the cathode gives hydrogen. While the technology is the most mature and has been around for over a century thanks to its use in the chlorine industry, the comparatively low current density, longer response time (lower flexibility) and lower operating pressure vs other technologies present key challenges for the adoption of this technology across the entire clean hydrogen application spectrum.
n PEM electrolysis: This technology is based on the principle of using pure water as the electrolyte solution and therefore overcomes some of the issues associated with hydroxide solutions (used for alkaline electrolysis). The process involves the use of a conductive solid polymer membrane. When voltage is applied between the two electrodes, oxygen in the water molecules creates protons, electrons and O2 at the anode while the positively charged hydrogen ions travel through the proton conducting polymer towards the cathode where they combine to form hydrogen (H2). The electrolyte and two electrodes are sandwiched between two bipolar plates whose role is to transport water to the plates, transport product gases away from the cell, conduct electricity and circulate a coolant fluid to cool down the process. PEM electrolyzers typically require the use of expensive electrode catalyst materials (such as platinum and iridium) and membrane materials, resulting in overall higher costs vs alkaline at present. Nonetheless, they tend to be more compact, have a better response time, and operate at higher pressures resulting in a competitive advantage compared to alkaline for several applications.
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