Wednesday, October 19, 2011: 2:00 PM
101 H (Minneapolis Convention Center)
The mathematical analysis of mass transport in chemical systems usually involves the method of averaging to obtain system level information from the microscopic domain. Reactions in such systems are usually assumed to be occurring in the bulk (homogeneous reactions). However, in electrochemical systems (Batteries or Fuel Cells), the reactions are heterogeneous and they usually occur on catalytic surfaces. A diffusion-reaction model is developed to study concentration distributions and the behavior of the system within the porous anode catalyst layer of Direct Formic Acid Fuel Cells (DFAFCs). And at the same time an area-average approach is then implemented to obtain macroscopic concentration distributions within the domain, i.e., porous cavity. To analyze the role of averaging, this work is organized based on different cases of electrochemical kinetics. Firstly, the linearized form of the Butler-Volmer (concentration independent) kinetics is analyzed followed by classic Butler-Volmer (concentration dependent) type of kinetics. The system parameters varied are geometric (aspect ratio) and kinetic parameters. From this paper it is inferred that the averaging technique is valid for linearized form of Butler-Volmer kinetics at all conditions. But for the case of general Butler-Volmer kinetics, the area-averaging technique has certain limitations and it valid only for long pores. Also, the percentage of errors which is calculated from two methods is reported for different cases of Butler-Volmer kinetics to know the limitations of the system.