Recent advances in nonmetallic atom-doped metal nanocrystals: Synthesis and catalytic applications

Selenium-Doped Seeded Growth of Truncated Octahedral Gold Nanocrystals with Surface Concavities for Surface-Enhanced Raman Spectroscopy

Concave nanocrystals stand out as a testament to the importance of the nanoscale morphology in dictating the functional properties of materials. In this report, we introduce a facile synthesis method for producing gold (Au) nanocrystals with a truncated octahedral morphology that features surface concavities (Au CNTOs). The incorporation of selenium (Se) doping into the truncated octahedral Au seeds was essential for their enlargement and the formation of concave structures. By simply adjusting the quantity of seeds, we could control the size of the nanocrystals while maintaining their distinctive morphology and surface concavity. The formation mechanism suggests that Se doping likely passivates the side faces, thereby slowing growth and promoting atomic deposition at the edges and corners. The resulting Se-doped Au CNTOs exhibited strong localized surface plasmon resonance (LSPR) absorptions in the visible spectrum and the SERS performance of their assemblies was demonstrated through crystal violet detection, reaching enhancement factors around 105. This study presents an innovative approach to synthesizing concave Au nanocrystals through the incorporation of selenium during a seeded growth process, offering insights into the strategic design of plasmonic nanostructures.

What Elements Really Intercalate into Pd Lattice When Heated in Dimethylformamide?

Palladium hydrides (PdHx) are pivotal in both fundamental research and practical applications across a wide spectrum. PdHx nanocrystals, synthesized by heating in dimethylformamide (DMF), exhibit remarkable stability, granting them widespread applications in the field of electrocatalysis. However, this stability appears inconsistent with their metastable nature. The substantial challenges in characterizing nanoscale structures contribute to the limited understanding of this anomalous phenomenon. Here, through a series of well-conceived experimental designs and advanced characterization techniques, including aberration-corrected scanning transmission electron microscopy (AC-STEM), in situ X-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometry (TOF-SIMS), we have uncovered evidence that indicates the presence of C and N within the lattice of Pd (PdCxNy), rather than H (PdHx). By combining theoretical calculations, we have thoroughly studied the potential configurations and thermodynamic stability of PdCxNy, demonstrating a 2.5:1 ratio of C to N infiltration into the Pd lattice. Furthermore, we successfully modulated the electronic structure of Pd nanocrystals through C and N doping, enhancing their catalytic activity in methanol oxidation reactions. This breakthrough provides a new perspective on the structure and composition of Pd-based nanocrystals infused with light elements, paving the way for the development of advanced catalytic materials in the future.

Lattice engineering of noble metal-based nanomaterials via metal-nonmetal interactions for catalytic applications

Noble metal-based nanomaterials possess outstanding catalytic properties in various chemical reactions. However, the increasing cost of noble metals severely hinders their large-scale applications. A cost-effective strategy is incorporating noble metals with light nonmetal elements (e.g., H, B, C, N, P and S) to form noble metal-based nanocompounds, which can not only reduce the noble metal content, but also promote their catalytic performances by tuning their crystal lattices and introducing additional active sites. In this review, we present a concise overview of the recent advancements in the preparation and application of various kinds of noble metal-light nonmetal binary nanocompounds. Besides introducing synthetic strategies, we focus on the effects of introducing light nonmetal elements on the lattice structures of noble metals and highlight notable progress in the lattice strain engineering of representative core-shell nanostructures derived from these nanocompounds. In the meantime, the catalytic applications of the light element-incorporated noble metal-based nanomaterials are discussed. Finally, we discuss current challenges and future perspectives in the development of noble metal-nonmetal based nanomaterials.

Phosphorus-Doped PdSn Nanocatalyst with Abundant Defective Atoms for Enhanced Methanol Oxidation

The design of the nanostructure of palladium-based nanocatalysts is considered to be a very effective way to improve the performance of nanocatalysts. Recent studies have shown that multiphase nanostructures can increase the active sites of palladium catalysts, thus effectively improving the catalytic efficiency of palladium atoms. However, it is difficult to regulate the phase structure of Pd nanocatalysts to form a compound phase structure. In this work, PdSnP nanocatalysts with different compositions were synthesized by fine-regulating the doping amount of phosphorus atoms. The results show that the doping of phosphorus atoms not only changes the composition of PdSn nanocatalysts but also changes the microstructure, forming amorphous and crystalline multiphase structures. This multiphase nanostructure contains abundant interfacial defects, which effectively promotes the electrocatalytic oxidation efficiency of Pd atoms in small-molecule alcohols. Compared with the undoped PdSn nanocatalyst (480 mA mg_Pd^-1 and 2.28 mA cm^-2) and the commercial Pd/C catalyst (397 mA mg_Pd^-1 and 1.15 mA cm^-2), the mass (1746 mA mg_Pd^-1) and specific activities (8.56 mA cm^-2) of PdSn_0.38P_0.05 nanocatalysts in the methanol oxidation reaction were increased by 3.6 and 3.8 times and 4.4 and 7.4 times, respectively. This study provides a new synthesis strategy for the design and synthesis of efficient palladium-based nanocatalysts for the oxidation of small-molecule alcohols.

Small amounts of main group metal atoms matter: ultrathin Pd-based alloy nanowires enabling high activity and stability towards efficient oxygen reduction reaction and ethanol oxidation

Proton-exchange membrane fuel cells are considered as promising energy-conversion devices. Alloying 3d transition metals with noble metals not only highly improves the performance of noble metal-based catalysts towards electrocatalytic reactions in fuel cells due to d-d hybridization interaction but also decreases the total cost. However, the rapid leaching of transition metal atoms leads to a fast decay of the activity, which seriously affects the performance of the fuel cell. Herein, alloyed Pd-main group metal (e.g. Pb, Bi, Sn) ultrathin nanowires were realized by a facile one-step wet-chemical strategy. The content of the main group metal could be tuned in a certain range while maintaining the same one-dimensional ultrathin nanowire morphology, which provided a large surface area and many more active sites. These Pd-based alloys showed a significant improvement in electrocatalytic activity and durability towards the oxygen reaction reaction as well as ethanol oxidation reaction. Optimal activity occurred when a small amount of main group metal existed, which could be explained through calculations by a strong p-d hybridization interaction between the main group metal and Pd to optimize the surface electronic structure collaboratively. Besides, high stability was achieved, which could be ascribed to the increased antioxidant activity of Pd by the main group metal. Furthermore, the low amount of the main group metal atoms also prevented them from leaching out of the crystal lattice.

Ethanol-Induced Hydrogen Insertion in Ultrafine IrPdH Boosts pH-Universal Hydrogen Evolution

Engineering Pt-free catalysts for hydrogen evolution reaction (HER) with high activity and stability is of great significance in electrochemical hydrogen production. Herein, in situ chemical H intercalation into ultrafine Pd to activate this otherwise HER-inferior material to form the ultrafine IrPdH hydride as an efficient and stable HER electrocatalyst is proposed. The formation of PdIrH depends on a new hydrogenation strategy via using ethanol as the hydrogen resource. It is demonstrated that H atoms in IrPdH originate from the OH and CH₂  of ethanol, which fills the gap of ethanol as the hydrogen source for the preparation of Pd hydride. Thanks to the incorporation of H/Ir atoms and ultrafine structure, the IrPdH exhibits superior HER activity and stability in the whole pH range. The IrPdH delivers very low overpotentials of 14, 25 and 60 mV at a current density of 10 mA cm^-2 respectively in 0.5 m H₂ SO₄ , 1 m KOH, and 1 m PBS electrolytes, which are much better than those of commercial Pt/C and most reported noble metal electrocatalysts. Theoretical calculations confirm that interstitial hydrogen availably refines the electronic density of Pd and Ir sites, which optimizes the adsorption of *H and leads to the significant enhancement of HER performance.

Emerging interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic elements for electrocatalytic applications

Palladium (Pd)-based nanomaterials have been identified as potential candidates for various types of electrocatalytic reaction, but most of them typically exhibit unsatisfactory performances. Recently, extensive theoretical and experimental studies have demonstrated that the interstitial/substitutional modification of Pd-based nanomaterials with nonmetallic atoms (H, B, C, N, P, S) has a significant impact on their electronic structure and thus leads to the rapid development of one kind of promising catalyst for various electrochemical reactions. Considering the remarkable progress in this area, we highlight the most recent progress regarding the innovative synthesis and advanced characterization methods of nonmetallic atom-doped Pd-based nanomaterials and provide insights into their electrochemical applications. What's more, the unique structure- and component-dependent electrochemical performance and the underlying mechanisms are also discussed. Furthermore, a brief conclusion about the recent progress achieved in this field as well as future perspectives and challenges are provided.