Pressure, Temperature, and Dew Point Broadband Electrical Spectroscopy (PTD-BES) for the Investigation of Membranes for PEMFCs

This work describes the construction, testing, and implementation of an instrument to measure the complex impedance (Z*(ω)) spectra, from which the complex conductivity (σ*(ω)) and complex permittivity (ϵ*(ω)) spectra are derived, of conducting polymer membranes for fuel cells. The instrument consists of several interconnected components including a humidifier, a broadband electrical measurement cell with pressure, temperature, and humidity sensors, a heat circulator and a broadband electrical spectrometer. It is possible to control the cell (Tgas) and dew point (Tdp) temperatures with a precision greater than ±0.2 °C to obtain values of relative humidity (RH) with an error lower than ±1.4%. The experiments demonstrate that the values of Tdp and Tgas inside the cell are stable over time at the set point temperatures of Tgas = 0–140 °C and Tdp = -20–99.9 °C (for any desired value of Tgas within ±0.2 °C). The powerful capability of the broadband electrical spectroscopy (BES) method is demonstrated by studying the electrical response of Nafion117® at various temperatures and dew points. This technique allows the investigation of the electrical response of ionomeri