Roger Lujan

Ice Formation in PEM Fuel Cells Operated Isothermally at Sub-Freezing Temperatures

The durability of polymer electrolyte membrane (PEM) fuel cells operated at sub-freezing temperatures has received increasing attention in recent years. 1 The Department of Energy’s PEM fuel cell stack technical targets for the year 2010 include un-assisted startup from –40 o C and startup from -20 o C ambient in as low as 30 seconds with < 5MJ energy consumption. Moreover, the sub-freezing operations should not have any impact on achieving the other technical targets including 5000 hours durability. We have previously characterized the performance of both cloth (E-tek) and paper (SGL) GDLs and reported that the paper GDLs show lower tolerance to sub-freezing temperatures. 2 We have also reported the performance of MEAs at -10 o C where ice formation results in mass transport limitations. 3 Finally we reported on the effect of MEA preparation on durability and also provided low resolution neutron imaging data to identify ice formation in the land/channel areas. 4 In this paper we report the effect of MEA/GDL structure and cell assembly on sub-freezing performance. We also present highresolution neutron radiographs of single cells operated at sub-freezing temperatures to identify the exact location of ice formation and its effect on durability.

Durability Improvements Through Degradation Mechanism Studies

The durability of polymer electrolyte membrane (PEM) fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. By investigating cell component degradation modes and defining the fundamental degradation mechanisms of components and component interactions, new materials can be designed to improve durability. To achieve a deeper understanding of PEM fuel cell durability and component degradation mechanisms, we utilize a multi-institutional and multi-disciplinary team with significant experience investigating these phenomena.

Development of a Zirconia-Based Electrochemical Sensor for the Detection of Hydrogen in Air

Mixed potential sensors utilizing a machined, dense indium-tin oxide working electrode (In{sub 2}O{sub 3}:SnO{sub 2}; 90%:10%), a Pt wire counter electrode, and porous YSZ electrolyte were prepared using ceramic tape casting methods. The response of these devices to hydrogen concentrations up to 2% in air were studied from 600 to 740 C. The sensor response exhibited a reversible behavior and a fast response time with sensitivity increasing with decreasing temperature. GC analysis confirmed significant heterogeneous oxidation of the H{sub 2} on heated furnace tube wall surfaces thus driving sensor response at H{sub 2} concentrations greater than a few hundred ppm. The transition to a cold wall, miniature platform heater significantly reduced hydrogen oxidation although some flow rate dependence remains.

Solid State Electrochemical Sensor R&D

This document presents designs of electrochemical sensors for materials synthesis and integrated devices.