Influence of Metal–Ligand Coordination on the Elemental Growth and Alloying Composition of Pt–Ni Octahedral Nanoparticles for Oxygen Reduction Electrocatalysis

Understanding the role of surfactants or ligands on the growth mechanism of metal/alloy nanoparticles (NPs) is important for controlled synthesis of functional metallic NPs with tailored structures and properties. There have been a number of works showing the significant impact of surfactants/ligands on the shape-controlled synthesis of nanocrystals with well-defined surfaces. Beyond the morphological shape control, impact of the surfactants/ligands on the alloying structure of bimetallic nanocrystals, however, still remains largely unaddressed. We reveal here a significant effect of benzoic acid ligand on the elemental growth and alloying phase structure of octahedral Pt–Ni NPs, a class of highly active electrocatalyst for oxygen reduction reaction in fuel cells. Contrary to previous reports showing the critical role of benzoic acid in directing the growth of octahedral Pt–Ni NPs, we found that benzoic acid played a minor role in forming the octahedral shape; instead, it can strongly coordinate with Ni cation and significantly slows down its reduction rate, leading to a phase separation in the Pt–Ni NP products (a mixture of Pt-rich octahedral NPs and nearly pure Ni NPs). Such phase separation further resulted in a lower catalytic activity and stability. These results help us comprehensively understand the effect of metal–ligand coordination chemistry on the elemental growth mechanism and alloying phase structure of bimetallic NPs, complementing previous emphasis on the role of surfactants in purely morphological shape control

Actively Tunable “Single Peak/Broadband” Absorbent, Highly Sensitive Terahertz Smart Device Based on VO₂

In recent years, the development of terahertz (THz) technology has attracted significant attention. Various tunable devices for THz waves (0.1 THz–10 THz) have been proposed, including devices that modulate the amplitude, polarization, phase, and absorption. Traditional metal materials are often faced with the problem of non-adjustment, so the designed terahertz devices play a single role and do not have multiple uses, which greatly limits their development. As an excellent phase change material, VO2’s properties can be transformed by external temperature stimulation, which provides new inspiration for the development of terahertz devices. To address these issues, this study innovatively combines metamaterials with phase change materials, leveraging their design flexibility and temperature-induced phase transition characteristics. We have designed a THz intelligent absorber that not only enables flexible switching between multiple functionalities but also achieves precise performance tuning through temperature stimulation. Furthermore, we have taken into consideration factors such as the polarization mode, environmental temperature, structural parameters, and incident angle, ensuring the device’s process tolerance and environmental adaptability. Additionally, by exploiting the principle of localized surface plasmon resonance (LSPR) accompanied by local field enhancement, we have monitored and analyzed the resonant process through electric field characterization. In summary, the innovative approach and superior performance of this structure provide broader insights and methods for THz device design, contributing to its theoretical research value. Moreover, the proposed absorber holds potential for practical applications in electromagnetic invisibility, shielding, modulation, and detection scenarios

Modulating Surface Composition and Oxygen Reduction Reaction Activities of Pt–Ni Octahedral Nanoparticles by Microwave-Enhanced Surface Diffusion during Solvothermal Synthesis

Compositional segregations in shaped alloy nanoparticles can significantly affect their catalytic activity and are largely dependent on their elemental anisotropic growth and diffusion during nanoparticle synthesis. An efficient approach to control the surface segregations while keeping the nanoparticle shape are highly desired for fine-tuning their catalytic properties. Using octahedral Pt–Ni nanoparticles as a typical example, we report a new strategy to modulate the surface composition of shaped bimetallic nanoparticles by microwave-enhanced surface diffusion during solvothermal synthesis. Compared to traditional solvothermal synthesis, the application of microwave significantly promotes atomic diffusion, particularly surface diffusion, within the Pt–Ni octahedrons, leading to Pt segregation on the {111} facets while largely keeping the octahedral shape. The obtained segregated Pt–Ni octahedral nanoparticles performed excellent activity toward oxygen reduction reaction. The revealed microwave-enhanced surface diffusion in a liquid phase provides a new way to modulate surface compositions of bimetallic alloy nanoparticles at relatively lower temperatures compared to the widely adopted high-temperature gas-phase thermal annealing

Remarkable Thermochromism in the Double Perovskite Cs2NaFeCl6

Lead-free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light-yellow to black over a temperature range of 10 to 423 K is investigated. First-principles, density functional theory (DFT)-based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron–phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK−1 based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group-IV, III–V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials.Funding agencies: This work was financially supported by the Knut and Alice Wallenberg Foundation (Dnr. KAW 2019.0082), the Swedish Energy Agency (2018-004357), Carl Tryggers Stiftelse, Olle Engkvist Byggmästare Stiftelse, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009-00971). I.A.A. is a Wallenberg Scholar. B.B. gratefully acknowledges financial support from the Swedish Research Council (VR) grant no. 2021-00357. F.J. was supported by the China Scholarship Council (CSC). W.N. acknowledges the Suzhou Key Laboratory of Functional Nano &amp; Soft Materials, the Collaborative Innovation Center of Suzhou Nano Science &amp; Technology (NANO−CIC), and the 111 Project for the financial support. S.I.S. acknowledges the support from the Swedish Research Council (VR) (Project No. 2019–05551) and the ERC (synergy grant FASTCORR project 854843). The computations were enabled by resources provided by the National Academic Infrastructure for Supercomputing in Sweden (NAISS), the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Center (NSC), and the Center for High Performance Computing (PDC), partially funded by the Swedish Research Council through Grant Agreements No. 2022–06725 and No. 2018–05973. F.W. gratefully acknowledges financial support from the Open Project Funding of Jiangsu Key Laboratory for Carbon-based Functional Materials &amp; Devices, Soochow University (KJS2152), and the Formas (2020-03001). M.M. acknowledges financial support from Swedish Energy Research (Grant no. 43606-1) and the Carl Tryggers Foundation (CTS20:272, CTS16:303, CTS14:310).</p