Enhancement of oxygen reduction reaction activity by grain boundaries in platinum nanostructures
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tment of Materials Science and Engineering, University of California, Los Angeles, CA 90095, USA School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China 3 Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA 4 Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO 80309, USA 5 Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, USA 6 California NanoSystems Institute, University of California, Los Angeles, CA 90095, USA § Enbo Zhu, Wang Xue, and Shiyi Wang contributed equally to this work. 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 11 July 2020 / Revised: 23 July 2020 / Accepted: 23 July 2020
ABSTRACT Systematic control of grain boundary densities in various platinum (Pt) nanostructures was achieved by specific peptide-assisted assembly and coagulation of nanocrystals. A positive quadratic correlation was observed between the oxygen reduction reaction (ORR) specific activities of the Pt nanostructures and the grain boundary densities on their surfaces. Compared to commercial Pt/C, the grain-boundary-rich strain-free Pt ultrathin nanoplates demonstrated a 15.5 times higher specific activity and a 13.7 times higher mass activity. Simulation studies suggested that the specific activity of ORR was proportional to the resident number and the resident time of oxygen on the catalyst surface, both of which correlate positively with grain boundary density, leading to improved ORR activities.
KEYWORDS oxygen reduction reaction, nanowire, peptide, grain boundaries
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Introduction
Platinum (Pt)-based nanocatalysts have attracted intensive interest due to their promising applications in clean energy industries [1–7]. Particularly Pt-based nanomaterials have been considered as the most effective catalyst for oxygen reduction reaction (ORR) and are employed widely in proton exchange membrane fuel cell applications [8–13]. However, widespread commercial applications are constrained by the sluggish reduction kinetics of the cathodic ORR and the high cost of the Pt catalysts [14]. It has been demonstrated that the performance of catalysts strongly depends on the surface structures [15–20]. In particular, previous studies demonstrated that the catalytic structures rich in grain boundaries usually exhibit high catalytic activities, such as ORR, CO2 reduction reaction (CO2RR), and methanol oxidation reaction (MOR) [13, 21–24]. The grain boundaries can be developed inside polycrystalline crystals, but the density is usually scarce because of the consequent lattice distortion induced instability [25, 26]. On the other hand, abundant grain boundaries can be generated through the assembly of nanocrystals [27, 28]. To this end, biomimetic methods have been shown effective in guiding various assemblies taking examples from nature. With the help of biomolecules such as peptides, nanostructures rich in grain boundaries can
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