Mathematical modeling and analysis of solid oxide fuel cells and a dye sensitized solar cell

Abstract

As the fuel cell and solar cell technologies have advanced significantly in the past decade, the need for a better understanding of the steady-state and dynamic behaviors of the cells has increased. Since many processes occurring in the cells are highly nonlinear, systematic analyses are required to unveil the nonlinear effects of operating conditions on the cell performance. The focus of this work is on Solid Oxide Fuel Cells (SOFCs) and dye sensitized solar cells (DSSCs), both of which are of high importance in the renewable energy technology arena. DSSCs currently have achieved energy conversion efficiencies of 12%. The design and operation of the cells can greatly benefit from a better fundamental quantitative understanding of the physical and electrochemical processes involved in the cells.In this work, the presence of multiple steady states for three different types of SOFCs, oxygen-ion (conventional)-, proton-, and co-ionic (oxygen ion and proton)-conducting SOFCs, are investigated. An objective of this study is to investigate the effect of process parameter values on the steady-state multiplicity and the location of steady state(s). The existence of multiple steady states in the system is investigated in terms of the air and fuel inlet temperatures, the convection heat transfer coefficient, and the external load resistance. The range of operating conditions for which steadystate multiplicity exists is determined.A macroscopic first-principles mathematical model of a DSSC is developed by accounting for four different recombination kinetic laws. The equations of continuity and transport for all the species in the cell including electrons and redox couple are considered. The model is used to estimate the key parameters in the DSSC operation including recombination rate constant, effective electron diffusion coefficient, the conduction band energy, and the exchange current density. The presence of electric field and the effect of migration on transport are theoretically investigated. In the case of quasi solid state electrolyte DSSC incorporating polymer electrolyte, it can be hypothesized that the conduction band edge movement arouses due to the possible surface changes which consequently increases the photovoltage of the cell.%%%%Ph.D., Chemical Engineering – Drexel University, 2012