Improving Oxygen Reduction Performance of Surface-Layer-Controlled Pt-Ni Nano-Octahedra via Gaseous Etching.

This study demonstrates an atomic composition manipulation on Pt-Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt-Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt-Ni nano-octahedral sample shows a mass activity of 1.50 A/mgPt, exceeding the initial mass activity of the unetched counterpart (1.40 A/mgPt) and outperforming the benchmark Pt/C (0.18 A/mgPt) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features.

Colloidal synthesis of monodisperse trimetallic Pt-Fe-Ni nanocrystals and their enhanced electrochemical performances.

Among the multi-metallic nanocatalysts, Pt-based alloy nanocrystals (NCs) have demonstrated promising performance in fuel cells and water electrolyzers. Herein, we demonstrate a facile colloidal synthesis of monodisperse trimetallic Pt-Fe-Ni alloy NCs through a co-reduction of metal precursors. The as-synthesized ternary NCs exhibit superior mass and specific activities toward oxygen reduction reaction (ORR), which are ∼2.8 and 5.6 times as high as those of the benchmark Pt/C catalyst, respectively. The ORR activity of the carbon-supported Pt-Fe-Ni nanocatalyst is persistently retained after the durability test. Owing to the incorporation of Fe and Ni atoms into the Pt lattice, the as-prepared trimetallic Pt-alloy electrocatalyst also manifestly enhances the electrochemical activity and durability toward the oxygen evolution reaction with a reduced overpotential when compared with that of the benchmark Pt/C (△η= 0.20 V, at 10 mA cm-2). This synthetic strategy paves the way for improving the reactivity for a broad range of electrocatalytic applications.

High-Indexed Pt3Ni Alloy Tetrahexahedral Nanoframes Evolved through Preferential CO Etching.

Chemically controlling crystal structures in nanoscale is challenging, yet provides an effective way to improve catalytic performances. Pt-based nanoframes are a new class of nanomaterials that have great potential as high-performance catalysts. To date, these nanoframes are formed through acid etching in aqueous solutions, which demands long reaction time and often yields ill-defined surface structures. Herein we demonstrate a robust and unprecedented protocol for facile development of high-performance nanoframe catalysts using size and crystallographic facet-controlled PtNi4 tetrahexahedral nanocrystals prepared through a colloidal synthesis approach as precursors. This new protocol employs the Mond process to preferentially dealloy nickel component in the ⟨100⟩ direction through carbon monoxide etching of carbon-supported PtNi4 tetrahexahedral nanocrystals at an elevated temperature. The resultant Pt3Ni alloy tetrahexahedral nanoframes possess an open, stable, and high-indexed microstructure, containing a segregated Pt thin layer strained to the Pt-Ni alloy surfaces and featuring a down-shift d-band center as revealed by the density functional theory calculations. These nanoframes exhibit much improved catalytic performance, such as high stability under prolonged electrochemical potential cycles, promoting direct electro-oxidation of formic acid to carbon dioxide and enhancing oxygen reduction reaction activities. Because carbon monoxide can be generated from the carbon support through thermal annealing in air, a common process for pretreating supported catalysts, the developed approach can be easily adopted for preparing industrial scale catalysts that are made of Pt-Ni and other alloy nanoframes.

Facet-controlled facilitation of PbS nanoarchitectures by understanding nanocrystal growth.

Nanostructured lead sulphide is a significant component in a number of energy-related sustainable applications such as photovoltaic cells and thermoelectric components. In many micro-packaging processes, dimensionality-controlled nano-architectures as building blocks with unique properties are required. This study investigates different facet-merging growth behaviors through a wet-chemical synthetic strategy to produce high-quality controlled nanostructures of lead sulphide in various dimensionalities. It was found that 1D nanowires or 2D nanosheets can be obtained by the merging of reactive {111}- or {110}-facets, respectively, while promoting {100} facets in the early stages after nucleation leads to the growth of 0D nanocubes. The influence of temperature, capping ligands and co-solvent in facilitating the crystal facet growth of each intermediate seed is also demonstrated. The novelty of this work is characterized by the delicate manipulation of various PbS nanoarchitectures based on the comprehension of the facet-merging evolution. The synthesis of facet-controlled PbS nanostructures could provide novel building blocks with desired properties for use in many applications.