Nafion

About: Nafion is a research topic. Over the lifetime, 9110 publications have been published within this topic receiving 320865 citations.

Proton solvation and transport in hydrated nafion.

Abstract: Proton solvation properties and transport mechanisms have been studied in hydrated Nafion using the self-consistent multistate empirical valence bond (SCI-MS-EVB) method that includes the effects excess proton charge defect delocalization and Grotthuss proton hopping. It was found that sulfonate groups influence excess proton solvation, as well as the proton hydration structure, by stabilizing a more Zundel-like (H(5)O(2)(+)) structure in their first solvation shells. Hydrate proton-related hydrogen bond networks were observed to be more stable than networks with water alone. Diffusion rates, Arrhenius activation energies, and transport pathways were calculated and analyzed to characterize the nature of the proton transport. Diffusion rate analysis suggests that a proton-hopping mechanism dominates the proton transport for the studied water loading levels and that there is a clear degree of anticorrelation with the vehicular transport. The activation energy drops quickly with an increasing water content when the water loading level is smaller than ∼10 H(2)O/SO(3)(-), which is consistent with experimental observations. The sulfonate groups were also found to affect the proton hopping directions. The temperature and water content effects on the proton transport pathways were also investigated.

Metal–organic framework–graphene oxide composites: a facile method to highly improve the proton conductivity of PEMs operated under low humidity

Abstract: This work studies Nafion based proton exchange membranes (PEMs) modified by a metal–organic framework–graphene oxide composite (ZIF-8@GO). The ZIF-8@GO/Nafion hybrid membrane displays a proton conductivity as high as 0.28 S cm−1 at 120 °C and 40% RH, resulting from a synergetic effect of ZIF-8 and GO.

Sulfonated Aromatic Polymers for Fuel Cell Membranes

Abstract: Aromatic and heteroaromatic polymers are well known for their often excellent thermal and chemical stability as well as their good mechanical properties and high continuous service temperatures. Therefore, they have long been considered promising candidates for the development of proton-conducting membranes for fuel cells, especially for applications above 80 °C. Typically, sulfonic or phosphonic acid groups are introduced to provide acidic sites. While it is possible to introduce these groups by post-modification of the preformed polymers, the preferred method in many cases is modification of the monomers and subsequent polymer synthesis, because this allows better control of the number, distribution, and position of the acidic sites. Compared to perfluorosulfonic acid polymers, such as Nafion, proton-conducting membranes based on aromatic hydrocarbon polymers tend to exhibit excellent conductivities in the fully hydrated state and significantly reduced crossover, especially of methanol in DMFC applications. However, this often comes at the expense of a higher degree of swelling and a greater loss of conductivity with decreasing water content, which is considered a severe drawback e.g., for automotive applications. Recent approaches to improving the property profile of hydrocarbon membranes include block copolymers, rigid rod polymers, and the attachment of acidic groups via side chains.

Fuel Cell Geared in Reverse: Photocatalytic Hydrogen Production Using a TiO2/Nafion/Pt Membrane Assembly with No Applied Bias

Abstract: A polymer membrane electrode assembly (MEA) consisting of a TiO2 photoanode, a Pt cathode, and a proton exchange membrane (PEM) was constructed to generate hydrogen continuously under UV excitation with no applied bias. The acidified methanol is oxidized at the UV-irradiated TiO2 photocatalyst, and H+ ions are driven to the Pt cathode surface through the Nafion membrane. Photocurrent generation of 0.34 mA/cm2 under UV irradiation (λ > 300 nm) shows effective operation of the fuel cell in reverse for solar hydrogen production. A polarization curve of the photoelectrolysis cell exhibits an open circuit voltage of 0.5 V and a maximum power of 45 μW/cm2. The reduction of H+ at a Pt cathode under no applied bias was confirmed from the evolution of H2 gas with a rate of 69 μL h−1 cm−2.