Abstract
A successful strategy for reducing the content of Pt without compromising the activity of a Pt-based catalyst is to deposit Pt as an ultrathin overlayer on the surface of another metal. Here, we report a facile one-pot synthesis of Pd@Pt 1L (1L: one atomic layer) core-shell octahedra using a solution-phase method. The success of this method relies on the use of metal precursors with markedly different reduction kinetics. In a typical synthesis, the ratio between the initial reduction rates of the Pd(II) and Pt(II) precursors differed by almost 100 times, favoring the formation of Pd-Pt bimetallic octahedra with a core-shell structure. The reduction of the Pt(II) precursor at a very slow rate and the use of a high temperature allowed the deposited Pt atoms to spread and cover the entire surface of Pd octahedral seeds formed in the initial stage. More importantly, we were able to scale up this synthesis using continuous-flow reactors without compromising product quality. Compared to a commercial Pt/C catalyst, the Pd@Pt 1L core-shell octahedra showed major augmentation in terms of catalytic activity and durability for the oxygen reduction reaction (ORR). After 10000 cycles of accelerated durability test, the core-shell octahedra still exhibited a mass activity of 0.45 A mg -1 Pt . We rationalized the experimental results using DFT calculations, including the mechanism of synthesis, ORR activities, and possible Pd-Pt atom swapping to enrich the outermost layer with Pd. Specifically, the as-synthesized Pd@Pt 1L octahedra tended to take a slightly mixed surface composition because the deposited Pt atoms were able to substitute into Pd upon deposition on the edges; ORR energetics were more favorable on pure Pt shells as compared to significantly mixed Pd-Pt shells, and the activation energy barriers calculated for the Pd-Pt atom swapping were too prohibitive to significantly alter the surface composition of the as-synthesized Pd@Pt 1L octahedra, helping sustain their activity for prolonged operation.
| Original language | English |
|---|---|
| Pages (from-to) | 1370-1380 |
| Number of pages | 11 |
| Journal | Chemistry of Materials |
| Volume | 31 |
| Issue number | 4 |
| DOIs | |
| State | Published - Feb 26 2019 |
Funding
This work was supported in part by an NSF joint grant (CHE-1505441) to Georgia Tech and UW-Madison, an NSF grant (CMMI-1634687) to Georgia Tech, and startup funds from Georgia Tech. As visiting Ph.D. students from Chongqing University and Donghua University, respectively M.Z. and H.W. were also partially supported by the China Scholarship Council (CSC). Z.D.H. gratefully acknowledges support from the National Science Foundation Graduate Research Fellowship under grant no. DGE-1148903 and the Georgia Tech-ORNL Fellowship. A portion of this research was completed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Calculations were performed at supercomputing centers located at the Environmental Molecular Sciences Laboratory, which is sponsored by the DOE Office of Biological and Environmental Research at Pacific Northwest National Laboratory; the Center for Nanoscale Materials at Argonne National Laboratory, supported by DOE contract DE-AC02-06CH11357; the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by DOE contract DE-AC02-05CH11231; and the UW-Madison Center for High Throughput Computing (CHTC), supported by UW-Madison, the Advanced Computing Initiative, the Wisconsin Alumni Research Foundation, the Wisconsin Institutes for Discovery, and the National Science Foundation. This work was supported in part by an NSF joint grant (CHE-1505441) to Georgia Tech and UW-Madison, an NSF grant (CMMI-1634687) to Georgia Tech, and startup funds from Georgia Tech. As visiting Ph.D. students from Chongqing University and Donghua University, respectively, M.Z. and H.W. were also partially supported by the China Scholarship Council (CSC). Z.D.H. gratefully acknowledges support from the National Science Foundation Graduate Research Fellowship under grant no. DGE-1148903 and the Georgia Tech-ORNL Fellowship. A portion of this research was completed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Calculations were performed at supercomputing centers located at the Environmental Molecular Sciences Laboratory, which is sponsored by the DOE Office of Biological and Environmental Research at Pacific Northwest National Laboratory; the Center for Nanoscale Materials at Argonne National Laboratory, supported by DOE contract DE-AC02-06CH11357; the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by DOE contract DE-AC02-05CH11231; and the UW-Madison Center for High Throughput Computing (CHTC), supported by UW-Madison, the Advanced Computing Initiative, the Wisconsin Alumni Research Foundation, the Wisconsin Institutes for Discovery, and the National Science Foundation.
| Funders | Funder number |
|---|---|
| Advanced Computing Initiative | |
| Center for Nanophase Materials Sciences | |
| Center for Nanoscale Materials | |
| DOE Office of Biological and Environmental Research at Pacific Northwest National Laboratory | |
| DOE Office of Science | |
| Georgia Tech-ORNL | |
| National Energy Research Scientific Computing Center | |
| UW-Madison | |
| Wisconsin Institutes for Discovery | |
| National Science Foundation | 1634687, CHE-1505441, DGE-1148903, CMMI-1634687 |
| U.S. Department of Energy | DE-AC02-06CH11357 |
| Wisconsin Alumni Research Foundation | |
| Office of Science | DE-AC02-05CH11231 |
| Argonne National Laboratory | |
| College of Engineering, University of Wisconsin-Madison | |
| National Energy Research Scientific Computing Center | |
| Chongqing University | |
| China Scholarship Council | |
| Donghua University |