Search for: All records

There is an urgent need to develop cost‐effective electrocatalysts based on Pt for a broad spectrum of applications, including those vital to the operation of fuel cells. Hollowing out the interior of Pt nanocrystals offers a simple and viable strategy for maximizing the utilization efficiency of this precious metal while enhancing the electrocatalytic performance. Herein, we report the synthesis and electrocatalytic evaluation of Pt−Ag icosahedral nanocages with an average wall thickness of 1.6 nm. The Pt atoms are coated on the surface of Ag icosahedral seeds, leading to the formation of Ag@Pt_nLcore‐shell icosahedral nanocrystals with tunable shell thicknesses. The core‐shell nanocrystals are then converted to icosahedral nanocages by selectively etching away the Ag in the core. The as‐obtained nanocages with a composition of Pt_4.5Ag exhibit an almost 3‐fold enhancement in specific activity toward oxygen reduction relative to the commercial Pt/C in acid media.

We report a robust method for effectively removing the chemisorbed Br⁻ions, a capping agent, from the surface of Pd nanocubes to maximize their catalytic activity. The Br⁻ions can be removed by simply heating the sample in water, but the desorption of Br⁻ions will expose the underneath Pd atoms to the O₂from air for the formation of a relatively thick oxide layer. During potential cycling, the oxide layer evolves into detrimental features such as steps and terraces. By introducing a trace amount of hydrazine into the system, the Br⁻ions can be removed by heating without forming a thick oxide layer. The as‐cleaned nanocubes show greatly enhanced activity toward formic acid oxidation. This cleaning method can also remove Br⁻ions from Rh nanocubes and it is expected to work for other combinations of nanocrystals and capping agents.

We report a robust method for effectively removing the chemisorbed Br⁻ions, a capping agent, from the surface of Pd nanocubes to maximize their catalytic activity. The Br⁻ions can be removed by simply heating the sample in water, but the desorption of Br⁻ions will expose the underneath Pd atoms to the O₂from air for the formation of a relatively thick oxide layer. During potential cycling, the oxide layer evolves into detrimental features such as steps and terraces. By introducing a trace amount of hydrazine into the system, the Br⁻ions can be removed by heating without forming a thick oxide layer. The as‐cleaned nanocubes show greatly enhanced activity toward formic acid oxidation. This cleaning method can also remove Br⁻ions from Rh nanocubes and it is expected to work for other combinations of nanocrystals and capping agents.

We report a new catalytic system by partially covering the uniform Pt nanocrystals on a carbon support with an ultrathin film derived from polyacrylonitrile (PAN). The use of Pt nanocrystals uniform in both size and shape effectively suppresses Ostwald repining, while partially covering them with a PAN‐derived film prevents migration, aggregation, and detachment from the support. In addition, the pyridinic N atoms on the edges of the thermally‐treated PAN film can also weaken the O=O bond, accelerating the reduction of oxygen. Upon optimization, the new catalyst exhibits a mass activity of 0.51 mA ⋅ μg⁻¹_Pttoward oxygen reduction, substantially enhanced relative to the same catalyst without PAN (0.22 mA ⋅ μg⁻¹_Pt) and a commercial Pt/C (0.41 mA ⋅ μg⁻¹_Pt). The mass activity is essentially retained after 10,000 cycles of accelerated durability test between 0.6 V and 1.1 V in oxygen‐saturated HClO₄. Even after aging in H₃PO₄at 220 °C for one week, the electrochemical surface area of the catalyst is still maintained. This catalytic system holds great promise for use in various types of fuel cells with a long lifetime.

This article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I‐ions. The as‐synthesized nanocages feature a hollow interior, ultrathin wall of ≈2.5 nm in thickness, and a cubic shape. Our quantitative study suggests that the reduction rate of the Ru(III) precursor can be substantially accelerated upon the introduction of I‐ions and then retarded as the ratio of I‐/Ru³⁺is increased. The Pd‐Ru nanocages take an alloy structure, with the Ru atoms in the nanocages crystallized in a face‐centered cubic structure instead of the hexagonal close‐packed phase taken by bulk Ru. Using Pd nanocubes with different edge lengths, the dimensions of the nanocages in the range of 6−18 nm can readily be tuned. When tested as catalysts toward the electro‐oxidation of ethylene glycol and glycerol, respectively, the Pd‐Ru cubic nanocages prepared from 18 nm Pd cubes exhibit 5.1‐ and 6.2‐fold enhancements in terms of mass activity relative to the commercial Pd/C. After 1000 cycles of accelerated durability test, the mass activities of the nanocages are still 3.3 and 3.7 times as high as that of the pristine commercial Pd/C catalyst, respectively.

Platinum multipods are attractive for catalytic and electrocatalytic applications owing to their highly open, branched structure and thus high specific surface area. A number of methods have been reported for the synthesis of Pt multipods, but they are all limited in terms of throughput due to the use of batch reactors. Here we report the use of a fluidic device for the continuous and scalable synthesis of Pt multipods with sizes controlled in the ranges of 3–5 nm and 2–3 nm for the length and width, respectively, of the branched arms. The facile protocol involves the use ofas a precursor to Pt and oleylamine as a solvent, surfactant, and temperature‐dependent reductant. When a solution of these two components is pumped into the polytetrafluoroethylene tube immersed in an oil bath and held at 180 °C, Pt multipods are formed through fast autocatalytic surface growth and small particles attachment. Compared with the batch‐based synthesis, the throughput of the production in the flow system can readily be increased to 17 mg of Pt per hour while retaining a tight control over the quality of the products. When supported on carbon, the Pt multipods exhibit enhanced activity toward oxygen reduction relative to the commercial Pt/C catalyst.