Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

Abstract

An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PtnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

Porous AgPd–Pd Composite Nanotubes as Highly Efficient Electrocatalysts for Lithium–Oxygen Batteries

“…[25][26][27] As compared to pure monometallic systems, bimetallic catalysts have further garnered considerable interest because they exhibit distinctly different and often superior activity toward many chemical transformations, as determined via density functional theory calculations and experimental studies. [28][29][30][31][32][33][34][35] Because of a combination of ligand, geometric, and/or ensemble effects, bimetallic catalysts strongly enhance the kinetics of the ORR and OER. [ 8,21,28,32,[36][37][38][39] Therefore, some bimetallic composites with NT structure have been further designed by controlling the reaction process.…”

Platinum-based nanocages with subnanometer-thick walls and well-defined, controllable facets

“…An alternative to this strategy is to deposit the PGM conformally as subnanometer-thick shells of only a few atomic layers on the surfaces of NC templates made of another metal. In addition to the electrochemical approach explored by a number of groups (9-11), we recently developed a solution-phase method for the deposition of Pt on facet-controlled palladium (Pd) NCs to generate Pd@Pt nL core-shell structures (where n is the number of Pt atomic layers), in which the Pt shells could be controlled at 1 to 6 atomic layers in thickness (12)(13)(14). The Pd@Pt nL NCs showed great improvement in terms of both mass activity and durability toward ORR relative to a commercial Pt/carbon (C) catalyst.…”

“…Four atomic layers of Pt were then deposited on the surface of each Pd cube as a conformal shell ( fig. S1C) by introducing a Pt(IV) precursor at 200°C (12). The use of a slow injection rate and a relatively high temperature resulted in the formation of core-shell cubes with atomically flat surfaces (18).…”

Facile Synthesis of Three‐Dimensional Pt‐TiO2 Nano‐networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

“…[9] It provides unmatched capabilities for highly uniform coating of surfaces, powders,and porous structures with av ariety of materials at ambient temperatures.Furthermore,cyclic deposition nature of the ALD allows synthesis of nanoparticles with precise size and composition. Va rious types of well-dispersed catalysts, such as monometallic, [10] bimetallic, [11] and core-shell nanoparticles, [12] were successfully produced by ALD. Herein, we combined advantages of two bottom-up nanofabrication techniques to engineer an ovel metal/metal oxide 3D nano-network in ah ighly controlled manner.S elfassembling peptides were used to produce a3Dnano-network of high-aspect-ratio nanofibers as asoft organic template.The 3D peptide nanofiber aerogel was conformally coated with TiO 2 via ALD.T he 3D peptide-TiO 2 nano-network was further decorated with highly monodisperse Pt nanoparticles by using ALD (Pt@TiO 2 ,Scheme 1).…”