Water states measurement in proton-exchange membranes using humidity-controlled terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy (THz-TDS) has previously been demonstrated to resolve water states inside industrially relevant proton-exchange fuel-cell membranes under ambient conditions. As these membranes will operate under various humidities, in this work we quantify water states inside commercially available Nafion membranes in-situ at various humidities for direct comparisons against literature values from differential scanning calorimetry and Fourier transform infrared spectroscopy where correlations are observed.