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).
With the advent of the knowledge economy, technological innovation has become more and more complex. Firms in innovation system need to cooperate with others to upgrade their knowledge level and market competitiveness. Proper partner selection can increase the efficiency of the entire innovation system. Different partner selection mechanism has a significant impact on the efficiency of knowledge transfer for the enterprises and innovation system. In this study, a multiagent simulation is conducted to explore the effects of four different partner selection modes on knowledge transfer of innovation network: random selection mode, mode of selection based on space, mode of selection based on knowledge capital and mode of selection based on complementary knowledge. The results indicate that: in a period time, (1)the spatial selection mode limits the scope of partner selection and reduces the knowledge transfer path;(2)mode of selection based on the knowledge capital enables the large firms to have more cooperation opportunities;(3)complementary knowledge based selection mode improves the knowledge transfer efficiency of the system.
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