Nafion

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

Electrochemical synthesis of ammonia directly from air and water using a Li+/H+/NH4+ mixed conducting electrolyte

Abstract: Ammonia has been successfully synthesised directly from air and water using an electrochemical cell based on an H+/Li+/NH4+ mixed conducting membrane and Pt/C electrodes. It is found that the Nafion 211 membrane exhibits mixed H+/Li+ conduction after exchanging in 0.1 M Li2SO4 solution. The ionic conductivity of the mixed conductor is slightly lower than that of H+-form Nafion 211. The introduction of Li+ ions to the cell did not improve the ammonia formation rates in our experiments. Reasonably higher temperature may favour ammonia formation and the highest ammonia formation rate (9.37 × 10−6 mol m−2 s−1) and Faraday efficiency (0.83%) was obtained at 80 °C when a voltage of 1.2 V was applied. The ammonia formation rate decreased when 0.1 M Li2SO4 solution instead of water was used in the cell. Under the applied potential, the presence of Li+ ions might have a blocking effect on the transfer of protons resulting in a lower current at higher applied voltage, particularly at lower temperatures.

Proton Dynamics of Nafion and Nafion/SiO2 Composites by Solid State NMR and Pulse Field Gradient NMR

Abstract: Proton mobilities in Nafion and Nafion/SiO2 composites have been studied using high-resolution solid-state MAS NMR. High-resolution solid-state 1H NMR show that low concentrations of TEOS or short permeation times are necessary to allow complete hydrolysis of TEOS in Nafion. Incomplete hydrolysis of TEOS leaves residual ethyl groups on the surface of silica, which not only reduces the amount of water adsorbed by silica but also blocks the pathway of proton transport in the Nafion/SiO2 composites. The diffusion coefficients established using PFG NMR show that the best Nafion/SiO2 composite can be obtained from synthesis with a low concentration of TEOS in a methanol solution. This composite gives a higher diffusion coefficient than pure Nafion under dry conditions, although no differentiation in performance is observed when the membranes are hydrated. 29Si NMR shows that this composite has a high ratio of Q3/Q4 sites, consistent with a small particle size and many surface hydroxyl groups. Together, these d...

Nature of proton dynamics in a polymer electrolyte membrane, nafion: a first-principles molecular dynamics study

Abstract: First-principles molecular dynamics simulations have been carried out to investigate the nature of proton dynamics in Nafion, a representative polymer electrolyte membrane (PEM) widely used in PEM fuel cells. From the trajectories of the simulations, diffusion coefficients for the protonic defects were calculated to be 0.3 × 10−5 cm2 s−1 and 7.1 × 10−5 cm2 s−1 for λ = 4.25 and 12.75, respectively, where λ denotes hydration levels inside Nafion defined as a number of water molecules per sulfonic group. Our simulations show that proton hopping probability does not depend much on the water content inside Nafion. This finding indicates that the classical vehicular (or en masse) diffusion model, which has been employed to account for the slow diffusion process of protons in low water-content Nafion, is an oversimplification and does not correctly describe proton dynamics. Furthermore, it is found that difference in the value of the proton diffusion coefficient with respect to water content inside Nafion is related to the different character of proton hopping occurring in the water hydrogen bond network. When the water content is low, the proton hopping occurs in a manner that does not contribute constructively to proton mobility, while when the water content is high, it occurs in a manner which is beneficial to overall proton mobility. Such a different nature of proton hoppings arises mainly from the difference in the connectivity of water hydrogen bond network. Our results broadly support earlier simulation studies and provide the molecular level origin of properties arising from the proton dynamics in Nafion.