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Activation Overpotential

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Xianguo Li – One of the best experts on this subject based on the ideXlab platform.

  • A three-dimensional agglomerate model for the cathode catalyst layer of PEM fuel cells
    Journal of Power Sources, 2008
    Co-Authors: Xianguo Li


    Abstract In this work, a three-dimensional, steady-state, multi-agglomerate model of cathode catalyst layer in polymer electrolyte membrane (PEM) fuel cells has been developed to assess the Activation polarization and the current densities in the cathode catalyst layer. A finite element technique is used for the numerical solution to the model developed. The cathode Activation Overpotentials, and the membrane and solid phase current densities are calculated for different operating conditions. Three different configurations of agglomerate arrangements are considered, an in-line and two staggered arrangements. All the three arrangements are simulated for typical operating conditions inside the PEM fuel cell in order to investigate the oxygen transport process through the cathode catalyst layer, and its impact on the Activation polarization. A comprehensive validation with the well-established two-dimensional “axi-symmetric model” has been performed to validate the three-dimensional numerical model results. Present results show a lowest Activation Overpotential when the agglomerate arrangement is in-line. For more realistic scenarios, staggered arrangements, the Activation Overpotentials are higher due to the slower oxygen transport and lesser passage or void region available around the individual agglomerate. The present study elucidates that the cathode Overpotential reduction is possible through the changing of agglomerate arrangements. Hence, the approaches to cathode Overpotential reduction through the optimization of agglomerate arrangement will be helpful for the next generation fuel cell design.

  • Numerical analysis of dynamic processes in fully humidified PEM fuel cells
    International Journal of Hydrogen Energy, 2007
    Co-Authors: Hao Wu, Xianguo Li, Peter Berg


    Abstract The dynamic performance of PEM fuel cells (PEMFCS) during startup or load change processes is an important factor in PEMFC design and operation, especially for automotive applications where dynamic response is crucial. In this study, a two-dimensional, isothermal, transient model has been developed. For comparison purposes, both steady-state and transient analysis have been conducted. The variation of reactants concentration, Activation Overpotential, reaction rate and corresponding current density distribution in the catalyst layer (CL) are analyzed in detail. The steady-state results indicate that the current density distribution is closely related to the Activation Overpotential in the CL. Meanwhile, this model is capable of predicting various transient phenomena as the cell experiences load changes in working conditions. The transient results demonstrate that the dynamic behavior of fully humidified PEMFC is mainly determined by the cathode flooding conditions and oxygen transport in the gas diffusion layer; the transient variations in the dry cathode case are well within 0.3 s, while this variation periods are prolonged to around 1 s if the cathode is severely flooded. Hence, it can be concluded that the dynamic responses of a cell with partially flooded cathode is in the range of 0.3–1 s time period.

  • Analytical approach to polymer electrolyte membrane fuel cell performance and optimization
    Journal of Electroanalytical Chemistry, 2007
    Co-Authors: Xianguo Li


    The performance of polymer electrolyte membrane (PEM) fuel cell is mainly influenced by ohmic, Activation, and concentration Overpotentials. Ohmic Overpotential is directly proportional to electric resistance in the fuel cell components that can be estimated from the experimental data or from the empirical relation for the cell polarization curve. However, such simple relation is not available for the Activation Overpotential; hence a need exists to develop simple analytical formulation for calculating Activation Overpotential. In this study, an analytical expression for the Activation Overpotential in the cathode catalyst layer has been developed to investigate the performance and optimization of a PEM fuel cell. It is found that the analytical expression of Activation Overpotential with the combination of proper estimates of ohmic Overpotential has accurate predictive capabilities. It also provides an excellent agreement with available experimental, numerical, and empirical results. Following this, a performance optimization of cathode catalyst layer in PEM fuel cells has been carried out. It is observed that in a typical PEM fuel cell, excess platinum is neither desirable nor favorable. The optimum platinum loading is found to be 0.19–0.20 mg/cm 2 when the cell output is set to 0.8 V. The higher the membrane content in the catalyst layer, the better the cell performance in terms of Activation Overpotential. Conversely, optimum catalyst layer thickness is found to be 9–11 lm for the platinum loading of 0.20 mg/cm 2 at the cell voltage of 0.8 V. It is found desirable for the catalyst layer slightly thicker than the optimum value as the cell performance is less sensitive then; whereas performance decreases rapidly if the thickness of the catalyst layer is below the optimum value. � 2007 Elsevier B.V. All rights reserved.

Andrei A. Kulikovsky – One of the best experts on this subject based on the ideXlab platform.

  • The effect of non-uniform aging of a polymer electrolyte fuel cell on the polarization curve: A modeling study
    Electrochimica Acta, 2014
    Co-Authors: Andrei A. Kulikovsky


    Using the variational technique we show that in PEM fuel cells, an exponential shape of the local current density along the oxygen channel provides the best cell performance. A simple method for checking the quality of the local current density distribution by comparison of two polarization curves measured at different oxygen stoichiometries is suggested. Aging processes running non-uniformly along the channel distort the optimal shape of the local current and affect the cell polarization curve. Non-uniform aging of the cathode catalyst (agglomeration) increases the Activation and transport Overpotentials, not changing the limiting current density. Local lowering of the GDL oxygen diffusivity decreases the cell limiting current, not affecting the Activation Overpotential. A combined effect of the two aforementioned processes increases the slope of the polarization curve, which may be misinterpreted as the growth of the cell ohmic resistivity. An equation for reconstruction of the local current, exchange current density and GDL oxygen diffusivity shapes from the cell polarization curve is discussed. © 2014 Elsevier Ltd.

Takeo Ohsaka – One of the best experts on this subject based on the ideXlab platform.

  • Electrocatalytic sensing of NADH at an in situ functionalized self-assembled monolayer on gold electrode
    Electrochemistry Communications, 2001
    Co-Authors: Takeo Ohsaka


    In situ functionalization of a self-assembled monolayer (SAM) of an aromatic thiol, 4-aminothiophenol (4-ATP), on gold electrode in neutral pH yields a redox active monolayer of 4′-mercapto-N-phenylquinone diimine (NPQD). The in situ functionalized electrode shows an excellent electrocatalytic activity towards the oxidation of NADH with an Activation Overpotential, which is ca. 600 mV lower than that at the bare electrode. The sensitivity of the functionalized electrode towards the oxidation of NADH was found to be . The electrode shows a linear response for a wide range of concentration (10–190 μM) and it can detect as low as 10 μM NADH at neutral pH. The mixed monolayer of cystamine (CYST) and NPQD is used to mitigate the interference of ascorbate (AA) in the measurement of NADH. The selective electrocatalytic sensing of NADH in the presence of AA at the mixed monolayer modified electrode is demonstrated for the first time.

  • Preparation of Poly(thionine)-Modified Electrode and Its Application to an Electrochemical Detector for the Flow-Injection Analysis of NADH
    Analytical Sciences, 1993
    Co-Authors: Koichiro Tanaka, Noboru Oyama, Koichi Tokuda, Shin Ikeda, Takeo Ohsaka


    Poly(thionine)-modified electrodes have been prepared using basal-plane pyrolytic graphite, glassy carbon and In-Sn oxide conducting glass as electrode substrates by an electrooxidative polymerization of thionine in both aqueous and acetonitrile media. It was found that the prepared films, the surface concentration of which can be controlled over the range of ca. 10-10-10-8mol cm-2 by appropriately choosing the electropolymerization conditions (e.g., solvent, concentration of thionine and electrolysis time), are electroactive (the formal potential is ca. 0.0V vs. Ag/AgCl at pH 7.0) and chemically stable. The modified electrodes exhibited excellent electrocatalysis for NADH oxidation in neutral aqueous solutions, with an Activation Overpotential which is ca. 400mV lower than that of a bare electrode. Further, the modified glassy carbon electrode was found to be promising as an amperometric detector for the flow-injection analysis of NADH, typically with a dynamic range of 5μM-1mM.

  • Electrocatalysis of poly(thionine)-modified electrodes for oxidation of reduced nicotinamide adenine dinucleotide
    Journal of The Chemical Society Chemical Communications, 1993
    Co-Authors: Takeo Ohsaka, Koichiro Tanaka, Koichi Tokuda


    A poly(thionine)-modified basal-plane pyrolytic graphite electrode, which can be prepared by a potential-sweep electrolysis of the corresponding monomer in acetonitrile media, shows an excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 6.9), with an Activation Overpotential which is ca. 400 mV lower than that of the bare electrode.