Fe-Based Catalysts for Oxygen Reduction in PEM Fuel Cells

Abstract

The dependence of the open-circuit potential on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. For the modeling of lithium–silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/deinsertion in a single silicon electrode particle under potentiodynamic control are modeled and compared with experiments to provide justification for the same. Only if asymmetric transfer coefficients and sluggish kinetics are experimentally observed can kinetic hysteresis be reasoned for the potential gap in Li–Si system. The particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. This work stresses the need for accurate experimental determination of kinetic parameters (and thus the exchange current density) in silicon nanoparticles. This model and knowledge thereof can be used in the cell-sandwich model for the design of lithium-ion cells with composite silicon negative electrodes.