The Impact of Cation Contamination on Proton Exchange Membrane Water Electrolyzer (PEMWE)

Abstract

Hydrogen has emerged as a promising clean energy carrier and source alternative to fossil fuels(1). Mass production of cost-effective hydrogen without pollution is essential for the so-called hydrogen economy and the hydrogen produced in this process is called green hydrogen(2). It uses renewable energy such as wind energy and solar energy to generate electricity and produce hydrogen via water electrolysis, with net-zero carbon emissions. The proton exchange membrane water electrolyzer (PEMWE) is one of the most commercially available devices for water electrolysis. A membrane electrode assembly (MEA), which is laminated from an anode, cathode, and proton exchange membrane, is prone to poor performance and low lifetime if exposed to cation contamination due to the chemical properties of the materials, such as the negatively charged polymer side chain and low potential on the cathode. Therefore, it requires ultra-pure water in the operation condition.Different cations may bring different challenges to the PEMWE. For example, some transition metals, such as Fe2+, once introduced into the membrane, may catalyze the chain formation of radicals (×OH, ×OOH, etc.) due to the Fenton reaction(3), which will cause the decomposition of the membrane. In addition, some common cations that exist in drinking water, such as Ca2+, Na+, and Mg2+, will migrate onto the cathode through the membrane and block the active sites of the catalyst(4). Moreover, typical radical scavengers such as Ce, may migrate through the membrane during the operation process(5) and become a source of contamination due to their mobility in the MEA.In this study, we will investigate the impact of different concentrations of contamination, such as Ca2+ on the polarization curve of PEMWC and discuss the possible influence on its hydrogen crossover. To further clarify the contamination impact on the cathode, the performance of MEAs with different catalyst loadings on the cathode when subjected to cations, will be presented and discussed. In addition, several analytical instruments, such as ion chromatography (IC), inductive coupled plasma mass spectroscopy (ICP-MS), and thermo-gravimetric analysis (TGA) will be utilized to gain deeper insight into the degradation process of these contaminated MEAs. Figure 1