Dynamic Distribution of Chemical States of Water inside a Nafion Membrane in a Running Fuel Cell Monitored by Operando Time-Resolved CARS Spectroscopy

Abstract

The distribution and the chemical states of water in the electrolyte membrane of proton-exchange membrane fuel cells (PEMFCs) directly affect the performance and stability during cell operation. Coherent anti-Stokes Raman scattering (CARS) spectroscopy was used to investigate the transient behavior of water inside a Nafion membrane with a high time resolution of 0.5 s. After a current-density jump from 0.1 to 1.0 A cm −2 , the cell voltage rapidly dropped, then increased, and reached equilibrium in 7 s, whereas the ohmic resistance immediately dropped due to the increase in the water species that contributed significantly to the proton conductivity. The number of water molecules per sulfonic acid group, λ, at the membrane surface of the cathode side initially overshot and reached equilibrium after 7 s. This synchronous change of the cell voltage and λ is suggested to be caused by the change in oxygen partial pressure near the catalyst layer. This CARS technique is expected to be useful for analyzing many transient phenomena in materials science.

Formation of Water-Free Cavity in the Process of Nafion Swelling in a Cell of Limited Volume; Effect of Polymer Fibers Unwinding

“…The polymer Nafion is intensively studied in various fields, such as physics, chemistry and hydrogen energetics (see, e.g., the lists in References [1][2][3][4][5][6] of the articles issued in 2020). In Reference [7], the histogram of publications retrieved from Web of Science from 2004 to 2014, using the keywords "Nafion" and "Nafion and fuel cell" is presented; this histogram includes several thousands of Figure 1.…”

Operando Monitoring of Oxygen Drop in Catalyst Layers Accompanied by a Water Increase in Running Proton Exchange Membrane Fuel Cells

“…The decrease in p (O 2 ) near the CL was clearly observed to follow the voltage drop. During this p (O 2 ) change, the oxygen concentration in the CL was lowered as discussed in the previous study …”

“…In the center of the cathode side of the GDL, a pinhole 90 μm in diameter was created down to the CL. 12,[14][15][16]22 An optical probe was inserted directly into a PEMFC through the hole.…”

Advanced Label-Free Laser Scanning Microscopy and Its Biological Imaging Application

“…The synchronous change of the cell voltage and distribution of chemical states of water inside a nafion membrane was monitored with CARSM. For example, the transient values of the number of water molecules per sulfonic acid group increased rapidly from 7.4 at 0 s to 11.7 at 4.5 s under current density jump from 0.1 to 1.0 A•cm −2 [37]. In addition, CARSM also found applications in gas phase analysis [38] and material characterization [39].…”