Manish Khandelwal

Characteristic Behavior of Polymer Electrolyte Fuel Cell Resistance during Cold Start

bHyundai Motor Corporation, Yongin, Korea In this study, experimental constant-current cold starts were performed on a polymer electrolyte fuel cell from �10°C to characterize high-frequency resistance behavior, water motion, and ice accumulation before, during, and after cold start. A diagnostic method for rapid and repeatable cold starts was developed and verified. Cold-start performance is found to be optimized when cell resistance is increasing prior to startup, which is indicative of polymer electrolyte membrane PEM dehydration. During cold start, cell resistance initially decreases due to PEM hydration by the product water. Interestingly, after a certain water-uptake capacity of the PEM is reached, resistance increases due to ice formation in and around the cathode catalyst layer CL, with some evidence of supercooled water flow at low currents. Utilizing lower startup currents apparently does not increase the PEM water-storage capability but does increase the total volume of ice formation in and around the CL. Lower startup currents were found to produce more total heat but at a reduced rate compared to high currents. Therefore, an acceptable current range exists for a given stack design which balances the total heat generation and time required to achieve a successful cold start.

Model to Predict Temperature and Capillary Pressure Driven Water Transport in PEFCs After Shutdown

To enhance durability and cold-start performance of polymer electrolyte fuel cells (PEFCs), residual water in the fuel cell components must be minimized during operation and after shutdown. A transient two-phase mathematical and computational model is developed to describe water redistribution in the PEFC components after shutdown, which for the first time includes thermo-osmotic flow in the membrane. The model accounts for capillary and phase-change induced flow in the porous media and thermo-osmotic and diffusive flow in the polymer membrane. In the porous media, liquid-water flow is dominated by capillary transport until irreducible saturation is achieved, after which water removal is dominated by phase-change induced flow. In the membrane, thermo-osmotic flow can significantly help or hinder water drainage from the catalyst layer, depending on the situation. During shutdown to the frozen state, residual water at the cathode can be controlled, and freeze damage can be avoided, through balancing the phase-change induced flux in the diffusion media with the net balance of thermo-osmosis and diffusion flux in the membrane.

Model to Investigate Interfacial Morphology Effects on Polymer Electrolyte Fuel Cell Performance

The purpose of this work is to investigate the impact of the interfacial contact morphology between the catalyst layer (CL) and micro porous layer (MPL) on the polymer electrolyte fuel cell (PEFC) performance. A single-phase anisotropic mathematical model has been developed to evaluate the role of interfacial morphology on ohmic, thermal and gas-phase transport. The novel feature of the model is inclusion of directly measured surface morphological information of the cathode catalyst and the micro porous layers. The preliminary results indicate that thermal disruption due interface morphology has low absolute impact in comparison to ohmic disruption. Ultimately, this model will be used as a tool to understand and minimize the PEFC performance loss, and to develop guidelines for optimal CL and MPL surfaces.