Start
Jun 15, 2011 - 11:30
End
Jun 15, 2011 - 13:00
Venue
Dept Library (Skype)
Event Type
Speaker
Dr. Arindam Sarkar Lawrence Berkeley National Laboratory CA
Title
Electrochemical Oxygen Reduction on non platinum low platinum and non noble metal electrocatalyst.
Low temperature fuel cells like proton exchange membrane fuel cells (PEMFC) are expected to play a crucial role in the future hydrogen economy especially for transportation applications. However use of exotic and expensive platinum as the electrocatalyst poses serious problems for commercial viability. In this regard there is an urgent need to develop low-platinum or non-platinum electrocatalysts with electrocatalytic activity for the oxygen reduction reaction (ORR) superior or comparable to that of platinum. Among non platinum electrocatalysts palladium-based electrocatalysts particularly Pd-M (M = Mo and W) alloys were synthesized and investigated for their activities towards ORR. Rotating disk electrode (RDE) measurements reveal that the alloying of Pd with Mo or W significantly enhances the catalytic activity for ORR as well as the stability (durability) of the electrocatalysts. Additionally both the alloy systems exhibit high tolerance to methanol which is particularly advantageous for direct methanol fuel cells (DMFC). One of the key strategies for low platinum electrocatalyst is to selectively deposit platinum on the surface of other base metals. Regarding that novel carbon-supported binary Pt@Cu “core-shell” nanoparticles have been synthesized by galvanic displacement of Cu by Pt4+ ions at ambient conditions. Structural characterizations suggest that the Pt@Cu nanoparticles have a Pt-Cu alloy layer sandwiched between a Cu core and a Pt shell. The electrochemical data clearly point to an enhancement in the activity for ORR for the Pt@Cu “core-shell” nanoparticle electrocatalysts compared to the commercial Pt electrocatalyst both on per unit mass of Pt and per unit active surface area basis. The trend in activity also indicates that the electrocatalytic activity of platinum can be increased by changing the core composition. A large class of non noble metal transition metal oxide electrocatalysts show good activity for ORR in alkaline conditions. Lanthanum based perovskites and lithiated nickel oxide have been investigated for ORR and the electrochemical activity have been found to be comparable to that of platinum. These oxide electrocatalysts are promising for recently developed alkaline exchange membrane fuel cells. However the alkaline exchange membranes suffer from low ionic conductivity and stability at high temperatures. The main reason of degradation is the attack by poorly solvated OH- to the tetraalkylammonium headgroups especially at high temperature. Model room temperature ionic liquids such as tetraethyl ammonium hydroxide (TEOH) and TEOH-imidazole/triazole blends have been investigated and the results ndicate that solvation of OH- by imidazole/triazole prevents the deteioriation of tetraethyl ammonium hydroxide.