[ materials ]
parameters of the PFSA behaviour . In principle , high IEC results in high proton conductivity , although too high IEC leads to excessive membrane swelling . With increasing EW , PFSA ’ s crystallinity increases , while water content and glass transition temperature decrease ( thus , lower proton conductivity and thermal stability with FC increasing temperature ). Comparing the length of side chains for high conductivity perfluorosulfonated ionomers ( from LSC to SSC ), it can be noticed that SSC are characterized by higher crystallinity and glass transition temperature than LSC at the same EW , thus offering higher thermal , mechanical and chemical stability at high fuel cell operation temperatures .
Knowing that , it can be seen that the advantage of tinner membranes with lower EW lies in the higher water uptake , due to a lower degree of crystallinity ( thus significantly higher ion conductivity at lower RH ). On the other hand , this leads to lower mechanical properties and increased H 2
/ O 2 crossover ( thus , lower cell voltage especially at low-current densities ), hence the need for membrane reinforcement .
Although it has been investigated for decades , due to PFSA ’ s complex nature and the high level of complexity of transport phenomena across various fuel cell design elements , fuel cell mass adoption presented challenges that many cross-disciplinary research efforts have been trying to solve . Understanding PFSA involves a knowledge-based approach that bridges polymer science , chemistry , physics , and electrochemistry , involving numerous exsitu and in-situ characterization techniques as well as multiphysics computational simulations . It requires a deep dive into the fundamental parameters behind the materialsstructure-processing relationship influencing membranes functionality ( performance and durability ). The bottleneck in progress towards optimization of effective transport properties lie also in technical difficulties of in-situ characterizations .
Lesson 3 : When developing the design space for fuel cell , embrace holistic approach for pattern recognition excellence .
Examining the influence of the individual components on MEA performance in a fuel cell configuration is crucial for technology development and industrialization . This analysis provides an input for the potential cost reduction of fuel cell components , enhances final product reliability , and guides specifications for new supply chain entrants .
Membrane water uptake
The dual nature of the covalently bonded polar side chains and non-polar backbone results in the amphiphilic character of PFSA , leading to phase-separated morphology upon solvation with water or solvent molecules . This also endows PFSA with unique solvent and transport properties that have been of relevance in industry from membrane separation technologies to fuel cell and electrolyzer applications . The resulting water channels are pathways for proton transport ( being strongly influenced by the membrane water uptake ). Understanding membrane water uptake is important when ( i ) developing new ionomers and optimizing existing ones , and ( ii ) translating membrane conductivity as measured ex-situ on a membrane in equilibrium with partly humidified gases ( during fuel cell operation ). Taking Nafion as an example , due to the Schröders paradox , its water uptake differs from fully saturated gas ( max λ = 14 at 25 ° C ) and from immersion in liquid water ( max λ = 22 at 25 ° C ). This has a significant influence on Nafion ’ s proton conductivity : in liquid water , it is 0.1 S / cm at 20 – 30 ° C , whereas in equilibrium with water vapour , it equals 0.06 – 0.08 S / cm at 30 ° C .
22 Hydrogen Tech World | Issue 15 | April 2024