EAGER: New approach to rational design of efficient electrocatalysts for the oxygen reduction reaction in hydrogen fuel cells

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

Fuel cells are devices for direct conversion of the chemical energy of a fuel into electricity through electrochemical reactions. If successful, practical fuel cells would be a key enabling technology for movement to a green economy. However successful application of fuel cells has been hindered by factors relating to the kinetics of the oxygen reduction reaction. Expensive platinum-based catalysts seem to be required to catalyze these oxygen reduction reactions. Platinum is of course rare and expensive and is susceptible to poisoning by molecules such as carbon monoxide, leading to reduced catalyst lifetimes. Despite many decades of research, very few non-precious metal catalysts have been found with promising oxygen reduction catalytic activity and none have exhibited sufficient performance stability. One difficulty in developing new cost-effective materials which are better catalysts for ORR is that there are a limited set of elements that can endure the reaction environment of the PEM FC, which is highly acidic and at high operating potential. These elements are platinum, iridium, gold and palladium, all precious and rare. To reduce the costliness of these electrode materials, studies have taken place on the use of platinum-based alloys or platinum monolayers on platinum-free substrates. Success has been limited due to the necessity of high platinum percentage in these alloys. Nonetheless, these studies offer information useful in understanding the relationship between composition, geometry, surface electronic structure, and the ORR activity. Given this data, many combinatorial computational screening experiments for new materials have been made. These experiments lack a rational basis in general, and do not add much to the understanding of the factors controlling performance. Prof. Sergey Stolbov at the University of Central Florida proposes to use rational material design approaches to direct his computational catalyst studies. Several selected materials and composites have been chosen for this initial study. The work is based on earlier published computational results pointing to multiple metal approaches. Instead of platinum, silver is selected as the main electrode material. Although somewhat less stable to the reaction medium, the Stolbov's calculations have indicated that supporting the metal on a suitable substrate will increase the stability of the top layer to the fuel-cell chemical conditions. Furthermore, Stolbov has computational results which suggest that this substrate material may help tune the performance in the ORR reaction. A third metal may be added to further optimize the stability and behavior of this electrode sandwich. The PI, a female research associate, and a graduate student will conduct appropriate computation for the following sandwich systems: silver/ruthenium/niobium, silver/niobium, silver/tungsten, silver/molybdenum, and silver/chromium nitride. What will result from this EAGER award is a set of computations and data which will be used in the subsequent fabrication of these sandwich electrodes. BROADER IMPACTS The PI and associates are providing these computational directions to a group at Brookhaven National Laboratory, which is attempting to fabricate and evaluate these electrode systems predicted by the rational computational approach. A working relationship is already present, and these new materials will be subject to evaluation by these experts in the course of their program on fuel cells. The problems with PEM FCs are well-known and correctly characterized by the PI. Several agencies have invested many dollars in research to circumvent these problems. No solution is yet in hand. Stolbov proposes an interesting approach and has dialed the initial experimentation to accommodate the question of electrode expense. He believes the computational results will also read on the stability of the materials to the fuel-cell reaction medium, and will also allow for performance optimization based on composition. The PI realizes the evaluation will require expertise that is not available in his group, and has arranged for a recognized research group to actualize the results of the computations. Thus, if successful, the results may truly be transformative, and further rational design through computation may offer even better solutions to the PEM FC electrode problem. This approach may be viewed as high-risk in that the computational studies may lead only to performance or material stability that is no better than the current precious metal electrode approach. However if successful, the rewards will truly be worth the investment in this EAGER proposal.