The poor durability of proton exchange membrane fuel cells still is their greatest barrier preventing commercialization. In this paper, we perform a 1465 h in situ durability test with a single fuel cell operating at a constant-current of 800mA cm −2 . Polarization curves, cyclic voltammetry, and electrochemical impedance spectroscopy are used for diagnostics and to understand changes in performance during the test. Limiting current method is used to analyze the oxygen transport resistance of the gas diffusion layer (GDL) before and after durability test. The results indicate that the oxygen transport resistance in single cell increases greatly, and GDL is the first component leading to fuel cell failure after1465h test. At 150 kPa and 20% dry oxygen mole fraction, the limiting current decreases to about 700mA cm −2 and total oxygen transport resistance increases by 0.1623s cm −1 , implying more serious flooding occurs in GDL after the 1465 h durability test. The increase of oxygen transport resistances of the substrate and micro porous layer of GDL confirm the loss of water management capability of GDL. SEM images show that these may be caused by oxidation of carbon and loss of polytetrafluoroethylene in GDL.
In this paper, we evaluated the oxygen reduction reaction (ORR) activities of Pt/C, PtCo/C, and PtCoMn/C catalysts using charge-transfer resistance (Rct) and ΔRct onset voltage from electrochemical impedance spectroscopy as indicators in proton exchange membrane fuel cells (PEMFC) over a wide voltage range of 0.66 V∼0.95 V. ORR activity of the PtCoMn/C ternary alloy catalyst is higher than that of Pt/C over a large voltage range. A decal transfer method was used to prepare a membrane electrode assembly (MEA) with PtCoMn/C as a cathode catalyst. The cross-sectional micrograph of MEA-PtCoMn/C was characterized using scanning electron microscopy. A continuous ultrathin cathode catalyst layer that was 3 μm thick was successfully prepared. The performance of MEA-PtCoMn/C with an ultralow Pt loading of 0.147 mg/cm2 was evaluated using the single cell test. The highest achieved power density of MEA-PtCoMn/C was 1.42 W/cm2. The corresponding amount of platinum was 0.1035 gPt/kW, which reaches the index of the Department of Energy (DOE).
Membrane electrode assembly (MEA) is a core component of fuel cells, and its durability constitutes the bottleneck of fuel cells commercialization. In this paper, the effects of relative humidification (RH) on durability of membrane electrode assembly (MEA) are studied by the limiting current method. In-situ durability tests are carried out for 2040 h under constant current density of 800 mA cm−2 and relative humidification (RH) of 70%. The results are then compared to those of our previously published 1465h-MEA obtained for 1465 h under 100% humidification. The degradation in the voltage during the process is analyzed, and degradation mechanisms are investigated by electrochemical impedance spectroscopy and limiting current methods to analyze the change in oxygen transport resistance of the gas diffusion layer. The data suggest that the decline in the humidification can greatly improve the durability of MEAs, especially from 0 to 1000 h. The voltage decay rate of 2040h-MEA is half that of 1465h-MEA. The main degradation occurs in the substrate layer after durability tests for 2040 h under 70%RH. By comparison, 1465h-MEA operating at 100% RH shows a serious decay not only in the substrate layer but also in the MPL, as confirmed by the changes in contact angles.
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