Analytical Description of a Dead Spot in a PEM Fuel Cell Anode

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are close to commercialization, with automotive companies expected to begin mass production of PEMFC–powered cars in the next few years. Nonetheless, the lifetime of fuel cells still needs to be substantially improved to make this technology less expensive and more reliable. Over the past decade, large efforts have been directed toward understanding the microscopic mechanisms of PEMFC degradation. 1 Some of these mechanisms include parasitic electrochemical reactions, which run many orders of magnitude faster in the domains where the reaction overpotential is larger. This raises the problem of local non–uniformities in fuel cells, which can produce large local overpotentials. In this work, we continue the study of a problem of potentials and current distributions in the domain near a dead spot in the anode catalyst layer of a PEMFC. The spot of no or low electrochemical activity may arise due to local poisoning of the catalyst surface, or due to delamination of the anode catalyst from the membrane. Last but not least, this problem arises in the transmission X–ray absorption spectroscopy of the PEMFC cathode. 2,3 Transmission XAS requires removal of Pt atoms from a small circular anode “window” to make it transparent to X–rays probing the state of Pt atoms in the cathode catalyst layer (CCL). In a previous analysis, the problem has been formulated and solved numerically. 4 The numerical solution reveals the formation of a current double layer (CDL) at the spot boundary. The main feature of this layer is a high HOR current density generated in a narrow ring just outside the spot (“hot ring”). Here, we report an analytical solution of the problem. This solution allows us to derive a simple relation for the characteristic width of the hot ring. The solution confirms the conjecture of 4 that the CDL is an autonomous structure, which is independent of the spot radius.