Proton conduction in such membranes usually depends on the proton transport system between protons, sulfonic acid groups, and water molecules.
Normally, the higher the density of the sulfonic acid groups in the membrane, the greater the density of protons that can be launched from the sulfonic acid groups; for that reason, the greater density of the sulfonic acid groups generally results in higher proton conductivities.
However, utilizing a standard synthesis procedure, it is challenging to manufacture PEMs with a high density of sulfonic acid groups. To increase the density of sulfonic acid groups in a poly( styrenesulfonic acid)- based PEM, the sulfonation response need to be carried out over long hours or under extreme conditions. It typically uses extremely oxidizing compounds, such as fuming sulfuric acid and chlorosulfonic acid.
Regrettably, this leads to unwanted side responses, such as cleavage of the foundation chains of the polymer. To avoid undesirable side responses throughout polymer synthesis, commercially offered PEMs are generally manufactured to have a low density of sulfonic acid groups.
For commercially readily available Nafion or poly( styrenesulfonic acid)- based PEMs such as Selemion by AGC, the ion exchange capability (IEC), an index of the density of acid groups, is normally less than 1.0 meq./ g.
In the paper, Atsushi Noro and colleagues at the Graduate School of Engineering, Nagoya University, and from the Institutes of Innovation for Future Society also Nagoya University, have established poly( styrenesulfonic acid)- based PEM with an ultrahigh density of sulfonic acid groups.
The IEC of the PEM was 5.0 mequiv./ g. This is five times higher than the IEC of typical commercially available PEMs such as Nafion or Selemion. Its proton conductivity at 80 ° C under 90% RH (a typical operating condition for polymer electrolyte fuel cells) was 0.93 S/cm. This is 6 times greater than the conductivity of Nafion (0.15 S/cm) or Selemion (0.091 S/cm) under the very same measurement conditions.
Future fuel cells should be operated under more severe operating conditions such as greater temperature levels and lower humidities.
This study will add to the synthesis and development of next-generation higher-performance PEMs showing a good conductivity of 0.1 S/cm or greater under such extreme conditions. The research study will likewise contribute to the goal of reaching a net-zero carbon society.
Recommendation: “Synthesis of a Cross-Linked Polymer Electrolyte Membrane with an Ultra-High Density of Sulfonic Acid Groups” by Katsumi Sato, Takato Kajita and Atsushi Noro, 19 April 2023, ACS Applied Polymer Materials.DOI: 10.1021/ acsapm.3 c00150.
Researchers develop a brand-new ultra-high-density sulfonic acid polymer electrolyte membrane for fuel cells, which can be used for cars and combined heat and power systems. Credit: Atsushi Noro
Scientists at Nagoya University in Japan, under a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO), have created poly( styrenesulfonic acid)- based PEMs with a high density of sulfonic acid groups.
A crucial component in environment-friendly polymer electrolyte fuel cells is a polymer electrolyte membrane (PEM), which produces electrical energy through the interaction of hydrogen and oxygen gases. Practical applications of fuel cells consist of fuel cell cars (FCVs) and fuel cell combined heat and power (CHP) systems.
The best-known PEM is a membrane based on a perfluorosulfonic acid polymer, such as Nafion, which was established by DuPont in the 1960s. It has a great proton conductivity of 0.1 S/cm at 70-90 ° C under humidified conditions. Under these conditions, protons can be launched from sulfonic acid groups.
The best-known PEM is a membrane based on a perfluorosulfonic acid polymer, such as Nafion, which was established by DuPont in the 1960s. Under these conditions, protons can be released from sulfonic acid groups.
Utilizing a standard synthesis process, it is hard to manufacture PEMs with a high density of sulfonic acid groups. To increase the density of sulfonic acid groups in a poly( styrenesulfonic acid)- based PEM, the sulfonation response should be carried out over long hours or under serious conditions. It usually uses highly oxidizing compounds, such as fuming sulfuric acid and chlorosulfonic acid.