Göran Lindbergh

Influence of the composition on the structure and electrochemical characteristics of the PEFC cathode

The influence the composition of the cathode has on its structure and electrochemical performance was investigated for a Nafion content spanning from 10 to 70 wt.%. The cathodes were formed on a Na ...

A novel polymer electrolyte fuel cell for laboratory investigations and in-situ contact resistance measurements

A novel polymer electrolyte membrane fuel cell and assembly was developed for laboratory investigations. In this cell a simultaneous measurement of clamping pressure and contact resistances is possible. In the study presented this paper, the cell was utilised in in-situ contact resistance measurements of unplated and plated stainless steel (type 316). These contact resistances were studied in situ as a function of time, clamping pressure, gas pressure and current density. Ex-situ measurements were used to validate the in-situ contact resistance measurements. The validity and error sources of the applied in-situ measurement method were studied using both computer simulations and experiments.

Mathematical model of the PEMFC

A two-dimensional along-the-channel mass and heat transfer model for a proton exchange membrane fuel cell (PEMFC) is described. The model is used for calculation of cell performance (i.e., cell voltage against current density), ohmic resistance and water profile in the membrane, current distribution and variation of temperature along the gas channels. The following fuel cell regions are considered: gas channels, electrode backings and active layers at the anode and cathode side, and a proton exchange membrane. The model includes mass transfer in the gas channels and electrode gas backings, water transport in the membrane, electrode kinetics and heat transfer. Temperature in the cell is assumed to vary only along the gas channels, which means that it is the same at the anode and cathode and in the solid phase at a specified value of the channel coordinate. Electrode kinetics are considered only at the cathode, where major losses occur, whereas the anode potential is assumed to be equal to its equilibrium value. An agglomerate approach is used for the description of the active layer of the cathode. Simulations are carried out for different humidities of inlet gases, several different stoichiometric amounts of reactants and cooling media (air, water) with different heat transfer coefficients. Analysis of the results showed that the best performance of the PEMFC was obtained for well-humidified gases at conditions close to isothermal and at a stoichiometry of gases only somewhat higher than that corresponding to complete reactant consumption.

Investigation of Mass-Transport Limitations in the Solid Polymer Fuel Cell Cathode II. Experimental

In this work, we investigated the kinetics and mass-transport limitations of the oxygen reduction reaction in the solid polymer fuel cell. The information obtained from electrochemical experiments ...

Experimental and theoretical analysis of LiMn2O4 cathodes for use in rechargeable lithium batteries by electrochemical impedance spectroscopy (EIS)

Abstract A comparative study of the impedance response measured with composite electrodes and thin film electrodes of LiMn 2 O 4 was conducted. The electrodes were prepared on different current collectors (i.e. aluminium, carbonised aluminium and gold) and the experiments were run at various state-of-discharge (SOD) and liquid electrolyte compositions. The impedance response was shown to be strongly dependent on the current collector used. It was demonstrated that the high-to-medium frequency semicircle can be attributed to the contact resistance between the current collector and the active electrode material and that the medium-to-low frequency semicircle can be ascribed to the active electrode material. For the analysis, a mathematical model based on a resistance between the current collector and the active electrode material, interfacial-charge transfer coupled to the double-layer charging and solid-phase diffusion was developed. Potential distribution due to porous electrode effects was also considered. Fitting the model to experimental data enabled reasonable values of the exchange-current density, the double-layer capacitance and the solid-phase diffusion coefficient. However, the very low fitted value of the effective conductivity in the liquid phase indicates that this model does not give a satisfying description of the intercalation process of LiMn 2 O 4 .

Single-paper flexible Li-ion battery cells through a paper-making process based on nano-fibrillated cellulose

Recently, a need for mechanically flexible and strong batteries has arisen to power technical solutions such as active RFID tags and bendable reading devices. In this work, a method for making flexible and strong battery cells, integrated into a single flexible paper structure, is presented. Nano-fibrillated cellulose (NFC) is used both as electrode binder material and as separator material. The battery papers are made through a paper-making type process by sequential filtration of water dispersions containing the battery components. The resulting paper structure is thin, 250 μm, and strong with a strength at break of up to 5.6 MPa when soaked in battery electrolyte. The cycling performances are good with reversible capacities of 146 mA h g−1 LiFePO4 at C/10 and 101 mA h g−1 LiFePO4 at 1 C. This corresponds to an energy density of 188 mW h g−1 of full paper battery at C/10.

Quantifying Mass Transport during Polarization in a Li Ion Battery Electrolyte by in Situ 7Li NMR Imaging

Poor mass transport in the electrolyte of Li ion batteries causes large performance losses in high-power applications such as vehicles, and the determination of transport properties under or near operating conditions is therefore important. We demonstrate that in situ (7)Li NMR imaging in a battery electrolyte can directly capture the concentration gradients that arise when current is applied. From these, the salt diffusivity and Li(+) transport number are obtained within an electrochemical transport model. Because of the temporal, spatial, and chemical resolution it can provide, NMR imaging will be a versatile tool for evaluating electrochemical systems and methods.

Kinetic study of a porous metal hydride electrode

A physio-chemical approach has been used to describe the behaviour of a porous metal hydride electrode. The metal hydride alloy MmNi3.6Co0.8Mn0.4Al0.3, was studied. Electrochemical impedance spectr ...

In-situ measurements of gas permeability in fuel cell membranes using a cylindrical microelectrode

A new method to study permeation of gases in proton conducting membranes using a cylindrical microelectrode is presented. The focus of this work was to develop an in-situ method to study transport ...

An electrochemical impedance spectroscopy method for prediction of the state of charge of a nickel-metal hydride battery at open circuit and during discharge

A multivariate method for predicting state of charge, from electrochemical data, of a nickel-metal hydride (NiMH)-battery is presented. Partial least square (PLS) regression is used to evaluate ele ...