Search

Abstract It is necessary to obtain internal heat and water distribution of proton exchange membrane fuel cells in order to perform water-heat management. Most of the existing works focus on the measurement in small experimental fuel cells, which cannot effectively guide the development of large-area fuel cells. In this study, an in-situ measurement method using micro-sensors is developed to observe the temperature and relative humidity in a commercial-size fuel cell with parallel flow fields and an active area of 250 cm2. A sensor array is incorporated into the cathode flow field, and well-designed waterproof and sealing structures protect sensors from liquid water. The sensors are verified with accuracy and response speed. The fuel cell performance and electrochemical impedance spectroscopy under co-flow and counter-flow configurations considering anode gas humidification are investigated. The results show that the temperature distribution is more uneven in the cases with lower output voltage, and the fuel cell performance is significantly affected by the humidity near the air inlet area. As current density increases, the relative humidity drops while dew point temperature keeps almost unchanged. The experimental method and analysis are beneficial to the understanding of the water-heat state and optimization of fuel cell stack design. Highlights • Measurement with micro-sensors for the commercial-size fuel cell is effective. • Uneven temperature and humidity distribution in the cathode flow field is obtained. • Performance and resistance are greatly related to temperature-humidity distribution. • Counter-flow without humidification gets good performance and water-heat balance. [ABSTRACT FROM AUTHOR]

• A type of gradient wettability cathode CL with three sub-layers is designed. • Gradient CL's performance (895 mW/cm2@0.6 V) is higher than normal (721 mW/cm2@0.6 V). • This CL can adapt high current density, cathode humidity and air stoichiometry. • Gradient CL with best performance is found through comparison of 18 structures. The design of cathode catalyst layer (CL) is essential to improve the mass transfer capacity of proton exchange membrane (PEM) fuel cell and increase power density. In this work, cathode CL is divided into three sub-layers, and each sub-layer is added nano-particles with different wettability. The gradient CL with hydrophilic SiO 2 particles at inner layer and hydrophobic polytetrafluoroethylene (PTFE) particles at outer layer significantly enhances the performance of membrane exchange assembly (MEA). Its performance is 895 mW/cm2@0.6 V, which is 24.1 %higher than CL without any particles (721 mW/cm2@ 0.6 V). Under operating conditions of high current density, high cathode humidity and high air stoichiometry, the gradient CL has only a little voltage loss. Through Electrochemical Impedance Spectroscopies (EIS) impedance analysis under high current density (1.8A/cm2), mass transfer resistance of gradient CL is 25.4 Ω, and is much smaller than the mass transfer resistance of the homogeneous CL of 35.1 Ω, which reflects the significant enhancement in mass transfer capacity of gradient CL. The gradient catalyst layer is suitable for a wider range of current density, humidity, and stoichiometry, but excessive cathode gas stoichiometry causes a decrease in performance, which is caused by excessive drainage capacity. In addition, 18 different gradient CLs are designed and manufactured, and the gradient CL with catalyst coated membrane (CCM) structure has the best performance. In gradient CL, increasing the capillary pressure difference between sublayers is the key to performance improvement. It is confirmed that the property of MEA with appropriate wettability gradient design can be significantly improved. [ABSTRACT FROM AUTHOR]