Interfacial Water Drives Improved Proton Transport in Siliceous Nanocomposite Nafion Thin Films

Abstract

Nafion proton exchange membranes dehydrate when they are used in the gas phase and in high-temperature applications, such as fuel cells and (photo)electrolysis. Retaining a high level of membrane hydration under such conditions can be achieved by using inorganic fillers, but has never been demonstrated for thin films. Herein, several types of siliceous nanoparticles were incorporated for the first time into Nafion thin films. For composite Nafion materials, increased water uptake does not always induce increased proton conductivity. Here, increased water uptake did result in higher proton conductivity due to a synergistic effect within the composite film. The nanocomposites displayed a higher water uptake than could be expected based on the water uptake of the individual materials. Excess water present at the Nafion-filler interface was found to cause the proton conductivity of nanocomposite Nafion/Ludox AS-40 thin films to double compared with pristine Nafion at low relative humidity (from 2 to 4 mS cm ). Knowledge about the properties of such interfaces will allow for the better design of self-humidifying nanocomposite Nafion membranes, films, and catalyst layers.

Water as a tuneable solvent: a perspective

“…100,103 Changes in hydrogen bond length are sensitively probed by the chemical shift in 1 H Nuclear Magnetic Resonance spectroscopy (NMR), which spans a 20 ppm range depending on hydrogen bond length. 14,[104][105][106][107][108][109] Mono-and multidimensional NMR can be used to identify and quantify the chemical environments of water and solutes, [110][111][112] revealing dynamics (exploiting relaxation behaviour and chemical exchange), yield diffusion coefficients, speciation, kinetics of chemical reactions, and deliver molecular and material structures. The evolution of the 1 H (or 2 H) and 17 O chemical shift and associated relaxation parameters are key measurements, revealing the evolution of the water hydrogen bonding network and the formation of water pools with different properties or in different environments.…”

“…The evolution of the 1 H (and 2 H) chemical shift and associated relaxation constants will reveal the evolution of water hydrogen bonding network and the formation of water pools with different properties or in different environments. 105,106,111,113 For solutes with NMR observable nuclei ( 1 H, 13 C, 129 Xe, etc. ), also changes in their local chemical environment will be revealed.…”