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

摘要

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 (T_(gas)) and dew point (T_(dp)) temperatures with a precision greater than ±0.2℃ to obtain values of relative humidity (RH) with an error lower than ±1.4%. The experiments demonstrate that the values of T_(dp) and T_(gas) inside the cell are stable over time at the set point temperatures of T_(gas) = 0-140℃ and T_(dp) = -20-99.9℃ (for any desired value of T_(gas) within ±0.2℃). The powerful capability of the broadband electrical spectroscopy (BES) method is demonstrated by studying the electrical response of Nafion 117 at various temperatures and dew points. This technique allows the investigation of the electrical response of ionomeric materials, where the thermal effects are decoupled from the compositional modulation of the membranes in the presence of water vapor.