●  GOALS

The goal of this program is to develop efficient, cost-effective, and stable methods to convert hydrogen and other fuels into electricity using a fuel cell. Both high temperature solid oxide fuel cells (SOFC) and low temperature polymer electrolyte membrane (PEM) fuel cells are examined. For the former, efforts are directed at developing lower temperature conductors, higher durability materials, and more effective catalysts. In the latter, efforts are directed at developing more durable and effective catalyst supports, carbons which facilitate water management, and more effective and cheaper catalysts, especially for the oxygen reduction reaction. A parallel effort seeks to use CO₂ as a feedstock to produce value added chemicals. While a practical focus on new systems remains at the forefront of this effort, more fundamental studies provide insight to inform future directions.

●  RESEARCH HIGHLIGHTS AND ACCOMPLISHMENTS

Over the past year there have been a number of accomplishments. In the SOFC area, developments include new cathode materials exhibiting improved oxygen reduction kinetics, synthesis and characterization of thin ('nanoscopic') platinum films and dealloyed Pt-Al films exhibiting strain dependent changes in activation energies for oxygen reduction. Important chemical degradation mechanisms for SOFCs were characterized, including such causes as impurity poisoning, interdiffusion, and thermal cycling. Measurement of the surface temperature distribution in a microtubular SOFC is part of this characterization effort. Fundamental efforts directed at understanding the important rate limiting steps for the oxygen exchange reactions operative at electrode interfaces were developed.

In the proton exchange membrane (PEM) area, I²CNER Principal Investigators have continued characterization of a SnO₂ support for Pt electrocatalyts. These electrocatalyst supports exhibit substantially increased durability relative to the more commonly used carbon materials. Nano-channel mesoporous carbons have been developed as catalyst supports for PEM fuel cells. The nano channels can isolate and promote electrochemical reactions. Hybrid PEM membranes incorporating sulfonated polyimides exhibit enhanced durability and improved oxygen reduction kinetics. A new microporous layer-coated gas diffusion layer enhances PEM fuel cell performance under conditions of zero humidification. New methods to support catalyst structures were investigated, involving the interplay of mesoporous materials and ionic liquids.

Finally, new molecular-based catalysts for CO₂ conversion were developed which exhibit higher selectivity for CO production relative to hydrogen; this new catalyst may allow more practical conversion of CO₂ to fuels.

●  FUTURE DIRECTIONS

Research into both high- and low temperature fuel cells will continue. Promising directions in hybrid materials, both as electrolytes in the high temperature process and as membranes and catalyst supports in the low temperature area. Characterization of fundamental processess, particularly in the SOFC area, has the promise of leading to development of new electrolyte materials having both conductivity and activity at reduced temperatures. Micro SOFCs continue to provide convenient testbeds for concepts in catalysis and fuel cell durability. Studies of alternative combinations of materials to form more effective, durable, and active fuel cell structures will be a further emphasis.

Durability, supports, and catalysis also form the focus of future directions for PEM fuel cells. The SnO₂ materials are highly durable, but less active relative to carbon. Increasing activity is clearly a necessity. The polyimide materials provide considerable new opportunities both as membranes and as supports. New catalysts for CO₂ conversion will require investigation into the interplay between ligand structure, metals, and supports.