Dissertation Defense: Yanyan Wang
Candidate Name: Yanyan Wang
Advisor: YuYe Tong, Ph.D.
Title: Mechanistic Studies of Enhancing Performance of Pt-Based Electrocatalysts for Oxygen Reduction Reaction and Formic Acid Oxidation Reaction by Surface Modification
Dissertation Abstract: Proton exchange membrane fuel cell (PEMFC) has been a topic of great interest due to its importance in energy conversion. Currently, the insufficient activity and high cost of electrocatalysts are the main reasons that limit its application. To address these challenges, this dissertation focused on mechanistic understanding how the performance (activity and stability) of Pt-based electrocatalysts can be enhanced substantially by surface modifications for oxygen reduction reaction (ORR) on the cathode and formic acid oxidation reaction (FAOR) on the anode.
Previous studies showed that surface modification of Pt/C with moderate coverage of sulfide could effectively enhance the ORR activity, but left the questions of what the reason is for the enhancement and how sulfide modification affects the stability of the electrocatalysts unanswered. In this dissertation, not only have we confirmed that sulfide adsorption can generally enhance ORR on a Pt surface but also have we discovered that it can improve its stability. In situ EC SERS studies provided direct spectroscopic evidence that the sulfide adsorption made the Pt surface more resistant to oxidation.
In addition, the mechanism of this enhancement has been investigated by in situ EC ATR-SEIRAS,
which clearly showed that the ORR pathway changed as the sulfide coverage changed. O-OH pathway was dominant with the optimal sulfide coverage at θS=0.1~0.41. Both in-situ IR and micro-kinetics simulations on pure Pt and S2─*-Pt showed that adsorbed sulfide enhances the coverage of HO2* while suppressed ORR poisoning O* and OH*. A one-pot thermal synthesis method to prepare PtCo/C(I) was developed in the presence of iodine adsorption. The adsorbed iodine through preventing Co leaching effectively enhanced the durability of PtCo catalysts, for both home-made PtCo/C and commercial Ptek PtCo/C.
FAOR activity and stability were dramatically enhanced by the presence of trace cation (Pb2+, Bi3+) in the electrolyte. Electrochemical results indicated both the formation of cation from UPD metals and the relative distance to the active sites are critical to the activity enhancement. Combined isotope kinetic and in situ infrared experiments suggested that a new reaction pathway, HCOOad + OHad CO2 + H2O, is present in both PtPbTC and PtBiTC systems.
Friday, January 5 at 12:00pm to 5:00pm
Reiss Science Building, 238
37th and O St., N.W., Washington