Suljo Linic, University of Michigan
The largest culprit toward efficiency loss in low temperature polymer electrolyte membrane (PEM) fuels cells is the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode. Overcoming the ORR barrier has historically required the use of platinum electro-catalysts. High cost of platinum has made this technology unfeasible. We proposed to evaluate a number of silver-based electro-catalysts for the ORR. Our preliminary results obtained using quantum chemical studies of the molecular mechanisms of ORR suggest that these materials should offer a performance similar to Pt at a small fraction of the overall cost. In particular, we proposed to focus on two classes of materials: (i) shaped Ag particles (Ag nanocubes and nanowires) terminated by the Ag(100) surface facet. We note that conventional spherical Ag particles (synthesized using conventional impregnation synthesis) are mainly terminated by the (111) facet which exhibits low electro-chemical activity, and (ii) a number of Ag alloys combining 3d metals (mainly Ni and Co) with Ag. The common feature of these materials is that they can electro-activate molecular O2 (in its reaction with H+) with significantly lower activation barriers than conventional spherical Ag particles. Since this elementary step is the main source of over-potential losses on Ag, we anticipated that these nanostructured electro-catalysts should operate with efficiencies approaching those of Pt electro-catalysts. We proposed to synthesize, characterize and evaluate these Ag electro-catalysts. Ultimately, the electro-catalytic ORR performance of the Ag electro-catalysts will be compared to the state-of-the-art Pt materials.
This grant has been instrumental in training PhD students in the field of electrochemistry and electrocatalysis. Student working on the project are well equipped to model various electrochemical processes from molecular up to macroscopic level. They are also trained in performing detailed experimentation on electrochemical systems.
Finally, I also want to comment on the fact that large amount of allocated fund has not been spent to date. The main reason for this is that we had intended to hire a postdoctoral fellow; however, he had to cancel his move to the University of Michigan. We are in the process of hiring a new postdoc. The initial studies discussed above have been performed by a graduate student in my group. This should not affect our ability to execute the project as outlined in our original proposal.