The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
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, 2008Co-Authors: Xianguo LiAbstract: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, 2007Co-Authors: Hao Wu, Xianguo Li, Peter BergAbstract: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, 2007Co-Authors: Xianguo LiAbstract: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.
-
Two-dimensional analysis of PEM fuel cells
Journal of Applied Electrochemistry, 2004Co-Authors: Xianguo LiAbstract:This study reports a two-dimensional numerical simulation of a steady, isothermal, fully humidified polymer electrolyte membrane (PEM) fuel cell, with particular attention to phenomena occurring in the catalyst layers. Conservation equations are developed for reactant species, electrons and protons, and the rate of electrochemical reactions is determined from the Butler–Volmer equation. Finite volume method is used along with the alternating direction implicit algorithm and tridiagonal solver. The results show that the cathode catalyst layer exhibits more pronounced changes in potential, reaction rate and current density generation than the anode catalyst layer counterparts, due to the large cathode Activation Overpotential and the relatively low diffusion coefficient of oxygen. It is shown that the catalyst layers are two-dimensional in nature, particularly in areas of low reactant concentrations. The two-dimensional distribution of the reactant concentration, current density distribution, and Overpotential is determined, which suggests that multi-dimensional simulation is necessary to understand the transport and reaction processes occurring in a PEM fuel cell.
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, 2014Co-Authors: Andrei A. KulikovskyAbstract: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, 2001Co-Authors: Takeo OhsakaAbstract: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, 1993Co-Authors: Koichiro Tanaka, Koichi Tokuda, Noboru Oyama, Shin Ikeda, Takeo OhsakaAbstract: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, 1993Co-Authors: Takeo Ohsaka, Koichiro Tanaka, Koichi TokudaAbstract: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.
-
An excellent electrocatalysis of poly(phenosafranine)-modified electrode for oxidation of reduced β-nicotinamide adenine dinucleotide
Journal of The Chemical Society Chemical Communications, 1993Co-Authors: Koichiro Tanaka, Koichi Tokuda, Takeo OhsakaAbstract:A poly(phenosafranine)-modified electrode, which can be prepared by a potential-sweep oxidative electrolysis of the corresponding monomer in both aqueous and acetonitrile media, shows excellent electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 7), with an Activation Overpotential which is more than 1 V lower than that of the bare electrode.
-
Electrocatalysis of poly(2,3-diaminonaphthalene)-filmed electrodes for reduction of oxygen
Journal of The Chemical Society Chemical Communications, 1991Co-Authors: Takeo Ohsaka, Takashi Watanabe, Fusao Kitamura, Noboru Oyama, Koichi TokudaAbstract:Poly(2,3-diaminonaphthalene)(PDAN)-filmed glassy carbon electrode, which can be prepared in situ by electropolymerization of the corresponding monomer, shows excellent electrocatalytic activity for O2 reduction to H2O2 in an acidic aqueous solution (pH 1.0), with an Activation Overpotential which is ca. 300 mV lower than that of the bare electrode.
Erik Kjeang - One of the best experts on this subject based on the ideXlab platform.
-
Nanofluidic fuel cell
Journal of Power Sources, 2013Co-Authors: Erik KjeangAbstract:Abstract Fuel cells are gaining momentum as a critical component in the renewable energy mix for stationary, transportation, and portable power applications. State-of-the-art fuel cell technology benefits greatly from nanotechnology applied to nanostructured membranes, catalysts, and electrodes. However, the potential of utilizing nanofluidics for fuel cells has not yet been explored, despite the significant opportunity of harnessing rapid nanoscale reactant transport in close proximity to the reactive sites. In the present article, a nanofluidic fuel cell that utilizes fluid flow through nanoporous media is conceptualized and demonstrated for the first time. This transformative concept captures the advantages of recently developed membraneless and catalyst-free fuel cell architectures paired with the enhanced interfacial contact area enabled by nanofluidics. When compared to previously reported microfluidic fuel cells, the prototype nanofluidic fuel cell demonstrates increased surface area, reduced Activation Overpotential, superior kinetic characteristics, and moderately enhanced fuel cell performance in the high cell voltage regime with up to 14% higher power density. However, the expected mass transport benefits in the high current density regime were constrained by high ohmic cell resistance, which could likely be resolved through future optimization studies.
-
Nanofluidic fuel cell
Journal of Power Sources, 2013Co-Authors: Jin Wook Lee, Erik KjeangAbstract:Fuel cells are gaining momentum as a critical component in the renewable energy mix for stationary, transportation, and portable power applications. State-of-the-art fuel cell technology benefits greatly from nanotechnology applied to nanostructured membranes, catalysts, and electrodes. However, the potential of utilizing nanofluidics for fuel cells has not yet been explored, despite the significant opportunity of harnessing rapid nanoscale reactant transport in close proximity to the reactive sites. In the present article, a nanofluidic fuel cell that utilizes fluid flow through nanoporous media is conceptualized and demonstrated for the first time. This transformative concept captures the advantages of recently developed membraneless and catalyst-free fuel cell architectures paired with the enhanced interfacial contact area enabled by nanofluidics. When compared to previously reported microfluidic fuel cells, the prototype nanofluidic fuel cell demonstrates increased surface area, reduced Activation Overpotential, superior kinetic characteristics, and moderately enhanced fuel cell performance in the high cell voltage regime with up to 14% higher power density. However, the expected mass transport benefits in the high current density regime were constrained by high ohmic cell resistance, which could likely be resolved through future optimization studies. © 2013 Elsevier B.V. All rights reserved.
Jesse S Wainright - One of the best experts on this subject based on the ideXlab platform.
-
Characterizing Slurry Electrodes Using Electrochemical Impedance Spectroscopy
Journal of The Electrochemical Society, 2015Co-Authors: Tyler J. Petek, Nathaniel C. Hoyt, Robert F. Savinell, Jesse S WainrightAbstract:Techniques for interpreting electrochemical impedance spectroscopy of different flowing slurry electrodes configurations are presented based upon models developed for macrohomogeneous porous electrodes. These models are discussed with regards to three different slurry systems; particles in deionized water, in supporting electrolyte without redox active species (akin to electrochemical flow capacitors), and in electrolytes supporting aqueous redox couples (akin to redox flow batteries). Through investigating each of these systems, the individual properties of a slurry can be determined. It was found that traditional Overpotential descriptions, (ohmic, Activation, and mass transfer) were insufficient to fully describe the impedance and polarization of the slurry electrodes. An Overpotential due to the distributed current distribution in the slurry electrode was considered in the frequency range of Activation Overpotentials that depends on the exchange current density and the ratio of the electronic and ionic conductivities. In slurry electrodes made with multi-wall carbon nanotube particles supporting the ferric/ferrous redox couple, the distributed Overpotential was found to be about the same order of magnitude as the Activation Overpotential and the total voltaic efficiency was over 80% at 200 mA/cm2.
