In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Proton exchange membranes (PEMs) that operate at temperatures above 120 °C are needed to avoid catalyst poisoning, enhance electrochemical reactions, simplify the design and reduce the cost of fuel cells This review summarizes developments in PEMs over the last five years In order to design new membranes for elevated temperature operation, one must understand the chemistry, morphology and dynamics of protons and water molecules in existing membranes The integration of experiment with modelling and simulation can shed light on the hierarchical structure of the membrane and dynamical processes associated with molecular transport Based on such a fundamental understanding, membranes can be modified by controlling the polymer chemistry and architecture or adding inorganic fillers that can retain water under low relative humidity conditions The development of anhydrous membranes based on phosphoric acid doped polymers, ionic liquid-infused polymer gels and solid acids can enable fuel cell operation above 150 °C Considerable work remains to be done to identify proton transport mechanisms in novel membranes and evaluate membrane durability under real world operating conditions

Recent developments in proton exchange membranes for fuel cells

The excess proton in aqueous media plays a pivotal role in many fundamental chemical (e.g., acid-base chemistry) and biological (e.g., bioenergetics and enzyme catalysis) processes. Understanding the hydrated proton is, therefore, crucial for chemistry, biology, and materials sciences. Although well studied for over 200 years, excess proton solvation and transport remains to this day mysterious, surprising, and perhaps even misunderstood. In this feature article, various efforts to address this problem through computer modeling and simulation will be described. Applications of computer simulations to a number of important and interesting systems will be presented, highlighting the roles of charge delocalization and Grotthuss shuttling, a phenomenon unique in many ways to the excess proton in water.

Proton Solvation and Transport in Aqueous and Biomolecular Systems: Insights from Computer Simulations

Understanding the hydrated proton is a critically important problem that continues to engage the research efforts of chemists, physicists, and biologists because of its involvement in a wide array of phenomena. Only recently have several unique properties of the hydrated proton been unraveled through computer simulations. One such process is the detailed molecular mechanism by which protons hop between neighboring water molecules, thus giving rise to the anomalously high diffusion of protons relative to other simple cations. Termed Grotthuss shuttling, this process occurs over multiple time and length scales, presenting unique challenges for computer modeling and simulation. Because the hydrated proton is in reality a dynamical electronic charge defect that spans multiple water molecules, the simulation methodology must be able to dynamically readjust the chemical bonding topology. This reactive nature of the chemical process is automatically captured with ab initio molecular dynamics (AIMD) simulation me...

The curious case of the hydrated proton.

Progress in the use of ionic liquids as electrolyte membranes in fuel cells

The solvation and transport properties of the sulfonate−hydronium ion pair have been studied in hydrated Nafion through molecular dynamics simulation. Explicit proton and charge delocalization of the excess proton transport, via the Grotthuss hopping mechanism, were treated using the self-consistent multistate empirical valence bond (SCI-MS-EVB) method. The nature of the sulfonate−hydronium ion pair was characterized through analysis of free-energy profiles. It was found that, in general, the excess proton is solvated between two water molecules of a Zundel moiety while in the contact ion pair position, but then it transitions to an Eigen-like configuration in the solvent-separated pair position. Furthermore, the positive charge associated with the excess proton passes between the contact and solvent-separated ion pair positions through the Grotthuss mechanism rather than simple vehicular diffusion. The total proton diffusion was decomposed into vehicular and Grotthuss components and were found to be of t...

Matt K. Petersen and

Papers

Characterization of the solvation and transport of the hydrated proton in the perfluorosulfonic acid membrane nafion.