PEM fuel cell performance improvement through numerical optimization of the parameters of the porous layers

A numerical model for a PEM fuel cell has been developed and used to investigate the effect of some of the key parameters of the porous layers of the fuel cell (GDL and MPL) on its performance. The model is comprehensive as it is three-dimensional, multiphase and non-isothermal and it has been well-validated with the experimental data of a 5 cm2 active area-fuel cell with/without MPLs. As a result of the reduced mass transport resistance of the gaseous and liquid flow, a better performance was achieved when he GDL thickness was decreased. For the same reason, the fuel cell was shown to be significantly improved with increasing the GDL porosity by a factor of 2 and the consumption of oxygen doubled when increasing the porosity from 0.40 to 0.78. Compared to the conventional constant-porosity GDL, the graded-porosity (gradually decreasing from the flow channel to the catalyst layer) GDL was found to enhance the fuel cell performance and this is due to the better liquid water rejection. The incorporation of a realistic value for the contact resistance between the GDL and the bipolar plate slightly decreases the performance of the fuel cell. Also the results show that the addition of the MPL to the GDL is crucially important as it assists in the humidifying of the electrolyte membrane, thus improving the overall performance of the fuel cell. Finally, realistically increasing the MPL contact angle has led to a positive influence on the fuel cell performance

Monthly values of delta 2H, delta18O, dexcess, temperature, relative humidity and precipitation in Râmnicu Vâlcea, Romania, between January 2012 and December 2018

The Database contains monthly values of delta 2H, delta18O, dexcess, temperature, relative humidity, and precipitation in Râmnicu Vâlcea, Romania, between January 2012 and December 2018. All measurements were performed at the National Institute of Cryogenics and Isotopic Technologies, 4, Uzinei str., 240050 Ramnicu Valcea, Romania. The analysis of these data suggests an Atlantic origin of moisture with episodic Mediterranean transport. Also, it was noticed a significant correlation between the North Atlantic Oscillation on the local temperature during the winter season. The monthly values of all parameters formed equal spaced Time Series whose detailed analysis confirmed that delta 2H, delta 18O, temperature, and relative humidity present well-evidenced one-year periodicity. Different from them, the precipitation and dexcess seasonality could not be evidenced

SSITKA Investigation of CO and H2 Competitive Adsorption at PEM Fuel Cell Anode Catalysts

Steady-state isotopic transient kinetic analysis (SSITKA) experiments have been performed using the isotopic exchange between 13CO and 12CO to investigate the competitive adsorption of hydrogen and CO on commercial Pt and PtRu catalysts. PtRu alloys are known to be more tolerant fuel cell anode catalysts than platinum, in the instance where the hydrogen fuel contains ppm levels of CO. It has been recently demonstrated that there is a dynamic equilibrium between CO adsorbed on platinum or platinum/ruthenium nano-particles and CO in the gas phase. In this paper, the effect of the competitive adsorption between hydrogen and CO on this equilibrium has been demonstrated. For 1400ppm CO in hydrogen little difference was observed in the measured exchange rates for Pt and PtRu at room temperature, 9.91×10-4 for Pt compared to 1.15×10-3 for PtRu, however there is a significant effect observed at 100ppm CO in hydrogen, where the rates on PtRu are considerably smaller than on Pt (3.61×10-4 desorption rate constant for PtRu and 5.49×10-4 for Pt). The presented methodology using the SSITKA technique has demonstrated a novel way to measure these rate constants, and the implications of these measurements on the mechanistic understanding of the anode reaction are presented.JRC.D.3-Knowledge Transfer and Standards for Securit

Direct Absorption Method and Liquid Scintillation Counting for Radiocarbon Measurements in Organic Carbon from Sediments

From the 20th International Radiocarbon Conference held in Kona, Hawaii, USA, May 31-June 3, 2009.In this paper, we investigate a procedure for radiocarbon determination in forest soil and slurry from lake sediments. The total carbon in these samples can be both inorganic and organic. Inorganic carbon can be analyzed in a straightforward manner using the direct absorption method by sample acidification and CO2 capture. For organic carbon, we investigate a hybrid method using the wet-oxidation of organic carbon followed by direct absorption. To evaluate the wet-oxidation processes with potassium dichromate (K2Cr2O7) and potassium permanganate (KMnO4), we performed several experiments using different quantities of soil and sediments in order to establish the quantity of CO2 for each type of sample. The 2 methods offer comparable results for 14C-specific activity (about 0.234 0.024 Bq/g C), values that are expected for these kinds of samples. We also investigated the possibility of isotopic fractionation occurring during CO2 production from raw material by measuring 13C levels from samples and obtained CO2.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202