Facile Synthesis of Pt Icosahedral Nanocrystals with Controllable Sizes for the Evaluation of Size-Dependent Activity toward Oxygen Reduction

Platinum icosahedral nanocrystals are intriguing catalytic materials owing to the presence of a large number of twin boundaries and well-defined {111} facets on the surface. However, there are only two protocols available for their synthesis and the protocols required either the involvement of a metal carbonyl as the reductant or a very long reaction time up to one week. Here we report a facile route to the quick synthesis of Pt icosahedral nanocrystals with tunable sizes. The synthesis only involved Pt(acac) ₂ , tetraethylene glycol, poly(vinyl pyrrolidone), and as the metal precursor, solvent/reductant, and colloidal stabilizer, respectively. Noticeably, the synthesis could be completed within 20 min. By simply varying the amount of the precursor, we were able to tune the size of the Pt icosahedral nanocrystals in the range of 10–25 nm. Additionally, when ascorbic acid was introduced as a co-reductant to facilitate the reduction of the precursor, the size of the Pt icosahedral nanocrystals could be further reduced down to 7–12 nm. When used as a catalyst towards the oxygen reduction reaction, the Pt icosahedral nanocrystals with different sizes all exhibited a specific activity more than 2.4 times greater than that of commercial Pt/C. Moreover, their specific activity increased with the particle size. After 5,000 cycles of the accelerated durability test, the specific activities of the Pt icosahedral nanocrystals with three different sizes were still more than 2 times as high as that of the commercial Pt/C catalyst.