Investigating the Equilibration Time of Catalyst Coated Membranes Using AC and DC Methods

Methods to quantitatively measure the time for rolls of catalyst coated membrane to equilibrate to a controlled temperature and relative humidity were investigated. It is important to ensure that the water content of a catalyst coated membrane roll has equilibrated before it is used in the manufacturing of a proton exchange membrane fuel cell stack. Equilibration is achieved when the water content in the catalyst coated membrane reaches equilibrium with controlled relative humidity and temperature conditions. Alternating current and direct current methods were compared to measure the through-plane ionic resistance and in-plane electronic resistance as the catalyst coated membrane equilibrated. It was found that both alternating and direct current methods showed strong correlations as the CCM equilibrated in response to a relative humidity change. The average equilibration time estimated from the through-plane ionic measurements was 14.5 hours and the average equilibration time estimated from the in-plane electronic measurements was 13 hours.