The effect of Nafion film on the cathode catalyst layer performance in a low-Pt PEM fuel cell

A single--pore model for performance of the cathode catalyst layer (CCL) in a PEM fuel cell is developed. The model takes into account oxygen transport though the CCL depth and through the thin Nafion film, separating the pore from Pt/C species. Analytical solution to model equations reveals the limiting current density $j_N^{\rm lim}$ due to oxygen transport through the Nafion film. Further, $j_N^{\rm lim}$ linearly depends of the CCL thickness, i.e., the thinner the CCL, the lower $j_N^{\rm lim}$. This result may explain unexpected lowering of low--Pt loaded catalyst layers performance, which has been widely discussing in literature.Comment: 11 page

Potentials near the curved anode edge in a PEM fuel cell: Analytical solution for placing a reference electrode

We consider a PEM fuel cell with concentric circular electrodes: the small anode and the large cathode. A model for in-plane distributions of the cathode overpotential ηc and the membrane potential Φ in the anode-free region of the cell is developed. Mathematically, the problem reduces to the axially symmetric Poisson–Boltzmann equation for ηc. An approximate analytical solution shows that |ηc| exhibits rapid decay to zero with the radius, while |Φ| grows to the value of |η0c|, the cathode overpotential in the working domain of the cell. For typical η0c, the radial shape of ηc far from the anode edge only weakly depends on η0c; this effect is analogous to Debye screening in plasmas. The smaller the anode radius, the faster Φ approaches η0c with the distance from the anode. It follows, that a reference electrode for measuring the cathode overpotential in the working area can be placed at a small distance from the curved anode edge

Performance of a PEM fuel cell cathode catalyst layer under oscillating potential and oxygen supply

A model for impedance of a PEM fuel cell cathode catalyst layer under simultaneous application of potential and oxygen concentration perturbations is developed and solved. The resulting expression demonstrates dramatic lowering of the layer impedance under increase in the amplitude of the oxygen concentration perturbation. In--phase oscillations of the overpotential and oxygen concentration lead to formation of a fully transparent to oxygen sub--layer. This sub--layer works as an ideal non polarizable electrode, which strongly reduces the system impedance.Comment: 4 pages, 3 figure

Performance of a PEM fuel cell with oscillating air flow velocity: A modeling study based on cell impedance

A model of PEM fuel cell impedance is developed taking into account imposed harmonic perturbation of the air flow velocity in the cathode channel. The flow velocity modulation with the amplitude proportional to AC amplitude of the cell potential lowers the resistivity $R_h$ due to oxygen transport in channel. When relative amplitudes of velocity and potential oscillations are equal, a complete compensation of $R_h$ occurs. This effect explains experimental findings of Kim et al. (doi:10.1016/j.jpowsour.2008.06.069) and Hwang et al.(doi:10.1016/j.ijhydene.2010.01.064), who demonstrated significant improvement of PEM fuel cell performance under oscillating air flow velocity.Comment: 6 pages, 4 figure

Comparison of two physical models for fitting PEM fuel cell impedance spectra measured at a low air flow stoichiometry

Local impedance spectra of a segmented PEM fuel cell operated at an air flow stoichiometry of λ = 2 are measured. The local spectra are fitted with the recent 1D and quasi–2D (q2D) physical models for PEMFC impedance. The q2D model takes into account oxygen transport in the gas channel, while the 1D model ignores this transport assuming infinite stoichiometry of the air flow. Analysis of the q2D expression for the GDL impedance Z∞gdl at λ → ∞ shows that the contribution of Z∞gdl to the total cell impedance rapidly decays with the frequency growth. We derive an equation for the boundary frequency flim, above which this contribution is small. We show that the 1D model can be fitted to the high–frequency part (f > flim) of a spectrum acquired at λ ≃ 2, ignoring the low–frequency arc due to the oxygen transport in the channel. Comparison of fitting parameters resulted from the 1D and q2D models confirms this idea

Endoscopic surgical interventions in the treatment of periampullary cancer

In this paper retrospective treatment result analysis of 386 patients with periampullary cancer, complications are carried out by obstructive jaundice. Patients were organized into two groups: the first group patients to whom traditional surgical interventions were applied, and entered the second – treated with endoscopic transpapillary surgeries. We have shown that at the nonresectable cancer of bodies of a pancreatoduodenal zone complicated by obstructive jaundice, endoscopic transpapillary interventions are the main method of decompression of a biliary tree, thus allowing complete avoidance of traditional surgical intervention

Polarization curve of a non - uniformly aged PEM fuel cell

We develop a semi-analytical model for polarization curve of a polymer electrolyte membrane (PEM) fuel cell with distributed (aged) along the oxygen channel MEA transport and kinetic parameters of the membrane–electrode assembly (MEA). We show that the curve corresponding to varying along the channel parameter, in general, does not reduce to the curve for a certain constant value of this parameter. A possibility to determine the shape of the deteriorated MEA parameter along the oxygen channel by fitting the model equation to the cell polarization data is demonstrated

PEM Fuel Cell Characterisation by Means of the Physical Model for Impedance Spectra

A recent analytical solution of the physical model for the PEM fuel cell impedance [A. A. Kulikovsky, J. Electrochem. Soc., 162, F217 (2015)] is used for least–squares fitting of experimental impedance spectra. Ten spectra are collected in one experimental run of a cell with ten segments operated at a current density of 100 mA cm− 2 under high stoichiometry of the oxygen flow. The model impedance is fitted to the spectra and the resulting physical parameters of the cathode side are discussed. Of particular interest is a low value of the oxygen diffusion coefficient in the cathode catalyst layer ( ≃ 0.45 · 10− 4 cm2 s− 1), a parameter, which has not been measured in situ so far. This low value, as well as a high value of the cathode catalyst layer (CCL) proton conductivity σp ≃ 0.054 Ω− 1 cm− 1 is attributed to a large amount of liquid water in the CCL

Positioning of a Reference Electrode in a PEM Fuel Cell

We report an analytical solution for the membrane potential in a PEM fuel cell which consist of a half-plane (semi-infinite) anode and a large-area (infinite) cathode. Mathematically, the problem is analogous to the Gouy–Chapman problem for the potential distribution inside the diffuse double layer at a flat metal/electrolyte interface. An expression for the characteristic length l* of the membrane potential variation in the anode-free domain is derived. This expression suggests a minimum distance 3l* between the anode edge and a reference electrode at which the potential of the reference electrode yields the cathode overpotential in the working domain of the cell