Investigation on Sulfide-Enhanced Oxygen Reduction Reaction Activity By in-Situ Electrochemical Infrared Spectroscopy

Tuesday, 3 October 2017: 16:20
National Harbor 5 (Gaylord National Resort and Convention Center)
D. Chen (Georgetown University), Y. Wang (Georgetown Univeristy), T. C. Allison (National Institute of Standards and Technology), and Y. J. Tong (Department of Chemistry, Georgetown University)
Oxygen reduction reaction (ORR) has been intensively investigated due to its relevance to fuel cell applications. It was discovered recently that sulfide (S2-), a potent poison of Pt, could be a promotor for both ORR activity and stability of Pt. However, the underlying chemistry of working mechanism is still unclear. Understanding the mechanistic effect of non-metallic promotor(s) should help broaden the prospect of developing better ORR catalysts. In this presentation we will discuss the insights we have gained in this respect by in-situ electrochemical infrared spectroscopy and theoretical simulations. Figure 1a and b show the δ(HOO) infrared vibration bands of ORR intermediates HOOad and HOOHad and v(O-O) vibration of O2−ad under the kinetic potential control regime (at ~0.9 V vs. RHE) on PtSad with different sulfur coverage. The IR bands of intermediates HOOad and HOOHad are larger at lower Sad coverages at which the enhanced ORR activity was observed. The observation of the O2−ad band at higher Sad coverage is consistent with the increase in H2O2 production during ORR. Interestingly, even a small fraction of Sad, say a coverage of 0.1, can play a significant role in modifying the ORR reaction pathway by preventing the cleavage of O-O bonding of O2 molecule. The theoretical simulations in Figure 1c~d confirmed that the turnover frequency (TOF) of H2O produced at 0.9 V by ORR on PtSlow is much bigger than that on PtShigh. As a conclusion, our finding suggests that the catalyst design by shifting the pathway of ORR from cleavage of O-O bonding on pure Pt to HOOad or HOOHad pathway would accelerate water production on the fuel cell cathode.