| AVS 64th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Wednesday Sessions |
| Session HC+SA+SS-WeA |
| Session: | Bridging Gaps in Heterogeneously-Catalyzed Reactions |
| Presenter: | Toshimasa Wadayama, Graduate School of Environmental Studies, Tohoku University, Japan |
| Authors: | S. Kaneko, Graduate School of Environmental Studies, Tohoku University, Japan R. Myochi, Graduate School of Environmental Studies, Tohoku University, Japan S. Takahashi, Graduate School of Environmental Studies, Tohoku University, Japan N. Todoroki, Graduate School of Environmental Studies, Tohoku University, Japan T. Wadayama, Graduate School of Environmental Studies, Tohoku University, Japan T. Tanabe, Graduate School of Engineering, Tohoku University, Japan |
| Correspondent: | Click to Email |
Comprehensive understanding of oxygen reduction reaction (ORR) activity enhancement mechanisms for Pt-based alloy (Pt-M) catalysts is a key for developing highly-efficient, low-Pt-loading cathode catalysts for polymer electrolyte fuel cell. To clarify the effects of the alloy surface structures (e.g., Pt shell atomic arrangements, Pt/M ratio etc.,) on activity and durability, a number of studies have been performed. We have, thus, investigated ORR properties for the well-defined Pt-based bimetallic single crystal surface alloys prepared by vacuum depositions of metals on single crystal substrates in ultra-high vacuum (UHV) [1]. In this study, ORR activities are investigated for Pt/Co and Pt/Co-N model catalysts prepared on Pt(111) substrate by alternative arc-plasma depositions (APDs) of Pt and Co (Co-N).
The UHV-APD-EC apparatus is described elsewhere [2]. Pt and Co (Co-N) layers were alternately deposited onto a clean Pt(111) substrate by the APDs at 573K in UHV. As for the preparations of Co-N layers, Co was deposited by APD under 0.1 Pa of N2. Total thickness of the Pt/Co(Co-N) and thickness of the topmost-surface Pt and bottom Co layers are fixed to be 6 nm, 1.6nm, and 0.4nm, respectively; the Pt1.6nm/Co0.4nm/Pt3.6nm/Co0.4nm/Pt(111) (denoted as U_Co_4A), U_Co_8A, U_Co_16A, and U_Co_32A samples are prepared. Structural analysis is performed by in-plane XRD, cross-sectional TEM. Then, the Pt/Co/Pt(111) and Pt/Co-N/Pt(111) samples were transferred to an N2-purged glove box without air exposure. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted in N2-purged and O2-saturated 0.1M HClO4 in the glove-box. To discuss EC stability, square-wave potential cycling between 0.6(3s) ~ 1.0(3s) V vs. RHE was applied.
ORR properties (initial activity & durability) of the samples closely correlate with the Co (Co-N) thickness underlying the topmost Pt layer. For example, the activity enhancement factor for the U_Co_16A is highest (13-fold vs. Pt(111)) for the Pt/Co/Pt(111). ORR activity enhancement well corresponds to in-plane lattice distance estimated by the XRD. The results suggest that the ORR enhancements are determined by compressive surface strains that work on the topmost Pt(111) layers induced by underlying Co (Co-N) layers.
We wish to acknowledge the NEDO and JSPS.
[1] T.Wadayama et al., Electrochem.Commun. 12, 1112 (2010). N.Todoroki et al., PCCP, 15, 17771 (2013). M.Asano et al., ACS catal. 6, 5285 (2016).
[2] S. Takahashi et al., PCCP, 17, 18638 (2015). S. Takahashi et al., ACS Omega 1, 1247 (2016).