Investigation of the effect of carbon-covering layer on catalyst layer in polymer electrolyte membrane fuel cell in low relative humidity condition

The application field of the fuel cell system has recently expanded to portable devices and unmanned aircraft systems, which require development of high performance fuel cell systems that function in versatile environments including near-dry operation conditions. In such low relative humidity condition, hydration of membrane electrode assembly in the fuel cell system is essential in prevention of performance degradation caused by decreased ion conductivity of the Nafion (R) membrane. Herein, we successfully improved the device performance of the membrane electrode assembly in low relative humidity condition by depositing a functional carbon-covering layer onto the catalyst layer on the cathode side. The carbon-covering layer plays an effective role of retaining generated water in the membrane electrode assembly without interfering with the electrochemical reaction of the catalyst as confirmed by the electrochemical impedance spectroscopy and cyclic voltammograms. Moreover, we have investigated the optimized Nafion (R) ionomer loading and the thickness of the carbon-covering layer.