# Impact of Titanium Dioxide on Water Uptake and Diffusion in Nafion

## TL;DR

This study examines how adding titanium dioxide to Nafion membranes affects water uptake and diffusion, finding optimal performance at 2 wt% TiO2.

## Contribution

The paper introduces a detailed analysis of water behavior in Nafion with TiO2 using advanced techniques like NMR and relaxometry.

## Key findings

- Water uptake and diffusion in Nafion are maximized at 2 wt% TiO2.
- Two distinct water diffusion components were identified, with different diffusion coefficients.
- Hydrated Nafion with 2 wt% TiO2 shows the highest water relaxation times.

## Abstract

Inorganic fillers are commonly integrated into ion-exchange
membranes
to alter water hydration, improve ion conductivity, and tune transport
properties. Here, we measure water uptake and diffusion in Nafion,
which contains various concentrations of TiO2 (0–5
wt %). With adsorption–desorption isotherms measured by dynamic
vapor sorption, we probe the moisture kinetics and find a maximum
change in hydrated Nafion mass by water vapor adsorption at 2 wt %
TiO2. Pulsed field gradient nuclear magnetic resonance
(NMR) reveals that with increasing TiO2 concentration,
the two measured components of water diffusion are also maximized
at 2 wt % TiO2. The first component had a diffusion coefficient,
on the order of 1 × 10–9 m2/s, which
approaches the diffusion of free water. Observing root-mean-square
displacement as a function of increasing observation time indicates
that this water population is affected by the ionomer-TiO2 morphology. The second component had a diffusion coefficient on
the order of 1× 10–11 m2/s, which
is attributed to water molecules that interact more strongly with
sulfonic acid groups. With solid-state proton NMR relaxometry under
low (near 0%) and high (near 100%) relative humidity, we measure T1 and T2 relaxation of water molecules on different
time scales. Hydrated Nafion+2 wt % titania offers the highest water
relaxation times with T1 = 413 ms and T2 = 4.77
ms. This high T1/T2 ratio further indicates
a two-component water environment and semirestricted water diffusion.