|
Abstract:
|
Oxygen gain is the difference in fuel cell performance operating on oxygen -depleted and oxygen -rich cathode fuel streams . Oxygen gain experiments provide insight into the degree of oxygen mass -transport resistance within a fuel cell . By taking these measurements under different operating conditions , or over time , one can determine how oxygen mass transport varies with operating modes and /or aging . This paper provides techniques to differentiate between mass -transport resistance within the catalyst layer and within the gas -diffusion medium for a polymer -electrolyte membrane fuel cell . Two extreme cases are treated in which all mass transfer limitations are located only (i ) within the catalyst layer or (ii ) outside the catalyst layer in the gas diffusion medium . These two limiting cases are treated using a relatively simple model of the cathode potential and common oxygen gain experimental techniques . This analysis demonstrates decisively different oxygen gain behavior for the two limiting cases . For catalyst layer mass transfer resistance alone , oxygen gain values are limited to a finite range of values . However , for gas diffusion layer mass transfer resistance alone , the oxygen gain is not confined to a finite range of values . This analysis is then extended to evaluate ionic effects within the catalyst layer . |