Building Durable Multimetallic Electrocatalysts from Intermetallic Seeds

Bimetallic Cu@Ru Core-Shell Structures with Ligand Effects for Endo-Exogenous Stimulation-Mediated Dynamic Oncotherapy

Dynamic therapies, which induce reactive oxygen species (ROS) production in situ through endogenous and exogenous stimulation, are emerging as attractive options for tumor treatment. However, the complexity of the tumor substantially limits the efficacy of individual stimulus-triggered dynamic therapy. Herein, bimetallic copper and ruthenium (Cu@Ru) core-shell nanoparticles are applied for endo-exogenous stimulation-triggered dynamic therapy. The electronic structure of Cu@Ru is regulated through the ligand effects to improve the adsorption level for small molecules, such as water and oxygen. The core-shell heterojunction interface can rapidly separate electron-hole pairs generated by ultrasound and light stimulation, which initiate reactions with adsorbed small molecules, thus enhancing ROS generation. This synergistically complements tumor treatment together with ROS from endogenous stimulation. In vitro and in vivo experiments demonstrate that Cu@Ru nanoparticles can induce tumor cell apoptosis and ferroptosis through generated ROS. This study provides a new paradigm for endo-exogenous stimulation-based synergistic tumor treatment.

Unveiling the Growth Mechanism of Ordered-Phase within Multimetallic Nanoplates

Tuning the crystal phase of alloy nanocrystals (NCs) offers an alternative way to improve their electrocatalytic performance, but, how heterometals diffuse and form ordered-phase remains unclear. Herein, for the first time, the mechanism for forming tetrametallic ordered-phase nanoplates (NPLs) is unraveled. The observations reveal that the intermetallic ordered-phase nucleates through crystallinity alteration of the seeds and then propagates by reentrant grooves. Notably, the reentrant grooves act as intermediate NCs for ordered-phase, eventually forming intermetallic PdCuIrCo NPLs. These NPLs substantially outperform for oxygen evolution reaction (221 mV at 10 mA cm-2) and hydrogen evolution reaction (19 mV at 10 mA cm-2) compared to commercial Ir/C and Pd/C catalysts in acidic media. For OER at 1.53 V versus RHE, the PdCuIrCo/C exhibits an enhanced mass activity of 9.8 A mg-1 Pd+Ir (about ten times higher) than Ir/C. For HER at -0. 2 V versus RHE, PdCuIrCo/C shows a remarkable mass activity of 1.06 A mg-1 Pd+Ir, which is three-fold relative to Pd/C. These improvements can be ascribed to the intermetallic ordered-structure with high-valence Ir sites and tensile-strain. This approach enabled the realization of a previously unobserved mechanism for ordered-phase NCs. Therefore, this strategy of making ordered-phase NPLs can be used in diverse heterogeneous catalysis.

Enabling Pd Catalytic Selectivity via Engineering Intermetallic Core@Shell Structure

Core@shell nanoparticles (NPs) have been widely explored to enhance catalysis due to the synergistic effects introduced by their nanoscale interface and surface structures. However, creating a catalytically functional core@shell structure is often a synthetic challenge due to the need to control the shell thickness. Here, we report a one-step synthetic approach to core-shell CuPd@Pd NPs with an intermetallic B2-CuPd core and a thin (∼0.6 nm) Pd shell. This core@shell structure shows enhanced activity toward selective hydrogenation of Ar-NO2 and allows one-pot tandem hydrogenation of Ar-NO2 to Ar-NH2 and its condensation with Ar-CHO to form Ar-N═CH-Ar. DFT calculations indicate that the B2-CuPd core promotes the Pd shell binding to Ar-NO2 more strongly than to Ar-CHO, thereby selectively activating Ar-NO2. The chemoselective catalysis demonstrated by B2-CuPd@Pd can be extended to a broader scope of substrates, allowing green chemistry synthesis of a wide range of functional chemicals and materials.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

A general protocol for precise syntheses of ordered mesoporous intermetallic nanoparticles

Intermetallic nanomaterials consist of two or more metals in a highly ordered atomic arrangement. There are many possible combinations and morphologies, and exploring their properties is an important research area. Their strict stoichiometry requirement and well-defined atom binding environment make intermetallic compounds an ideal research platform to rationally optimize catalytic performance. Making mesoporous intermetallic materials is a further advance; crystalline mesoporosity can expose more active sites, facilitate the mass and electron transfer, and provide the distinguished mesoporous nanoconfinement environment. In this Protocol, we describe how to prepare ordered mesoporous intermetallic nanomaterials with controlled compositions, morphologies/structures and phases by a general concurrent template strategy. In this approach, the concurrent template used is a hybrid of mesoporous platinum or palladium and Korea Advanced Institute of Science and Technology-6 (KIT-6) (meso-Pt/KIT-6 or meso-Pd/KIT-6) that can be transformed by the second precursors under reducing conditions. The second precursor can either be a second metal or a metalloid/non-metal, e.g., boron/phosphorus. KIT-6 is a silica scaffold that is removed using NaOH or HF to form the mesoporous product. Procedures for example catalytic applications include the 3-nitrophenylacetylene semi-hydrogenation reaction, p-nitrophenol reduction reaction and electrochemical hydrogen evolution reaction. The synthetic strategy for preparation of ordered mesoporous intermetallic nanoparticles would take almost 5 d; the physical characterization by electron microscope, X-ray diffraction and inductively coupled plasma-mass spectrometry takes ~2 days and the function characterization depends on the research question, but for catalysis it takes 1-5 h.

Tailored Lattice Compressive Strain of Pt-Skins by the L12 -Pt3 M Intermetallic Core for Highly Efficient Oxygen Reduction

The sluggish kinetics of oxygen reduction reaction (ORR) and unsatisfactory durability of Pt-based catalysts are severely hindering the commercialization of proton-exchange-membrane fuel cells (PEMFCs). In this work, the lattice compressive strain of Pt-skins imposed by Pt-based intermetallic cores is tailored for highly effective ORR through the confinement effect of the activated nitrogen-doped porous carbon (a-NPC). The modulated pores of a-NPC not only promote Pt-based intermetallics with ultrasmall size (average size of <4 nm), but also efficiently stabilizes intermetallic nanoparticles and sufficient exposure of active sites during the ORR process. The optimized catalyst (L12 -Pt3 Co@ML-Pt/NPC10 ) achieves excellent mass activity (1.72 A mgPt -1 ) and specific activity (3.49 mA cmPt -2 ), which are 11- and 15-fold that of commercial Pt/C, respectively. Besides, owing to the confinement effect of a-NPC and protection of Pt-skins, L12 -Pt3 Co@ML-Pt/NPC10 retains 98.1% mass activity after 30 000 cycles, and even 95% for 100 000 cycles, while Pt/C retains only 51.2% for 30 000 cycles. Rationalized by density functional theory, compared with other metals (Cr, Mn, Fe, and Zn), L12 -Pt3 Co closer to the top of "volcano" induces a more suitable compressive strain and electronic structure on Pt-skin, leading to an optimal oxygen adsorption energy and a remarkable ORR performance.

Quinary, Senary, and Septenary High Entropy Alloy Nanoparticle Catalysts from Core@Shell Nanoparticles and the Significance of Intraparticle Heterogeneity

Colloidally prepared core@shell nanoparticles (NPs) were converted to monodisperse high entropy alloy (HEA) NPs by annealing, including quinary, senary, and septenary phases comprised of PdCuPtNi with Co, Ir, Rh, Fe, and/or Ru. Intraparticle heterogeneity, i.e., subdomains within individual NPs with different metal distributions, was observed for NPs containing Ir and Ru, with the phase stabilities of the HEAs studied by atomistic simulations. The quinary HEA NPs were found to be durable catalysts for the oxygen reduction reaction, with all but the PdCuPtNiIr NPs presenting better activities than commercial Pt. Density functional theory (DFT) calculations for PdCuPtNiCo and PdCuPtNiIr surfaces (the two extremes in performance) found agreement with experiment by weighting the adsorption energy contributions by the probabilities of each active site based on their DFT energies. This finding highlights how intraparticle heterogeneity, which we show is likely overlooked in many systems due to analytical limitations, can be leveraged toward efficient catalysis.

Phase-Controlled Synthesis of Ru Nanocrystals via Template-Directed Growth: Surface Energy versus Bulk Energy

Despite the successful control of crystal phase using template-directed growth, much remains unknown about the underlying mechanisms. Here, we demonstrate that the crystal phase taken by the deposited metal depends on the lateral size of face-centered cubic (fcc)-Pd nanoplate templates with 12 nm plates giving fcc-Ru while 18-26 nm plates result in hexagonal closed-packed (hcp)-Ru. Although Ru overlayers with a metastable fcc- (high in bulk energy) or stable hcp-phase (low in bulk energy) can be epitaxially deposited on the basal planes, the lattice mismatch will lead to jagged hcp- (high in surface energy) and smooth fcc-facets (low in surface energy), respectively, on the side faces. As the proportion of basal and side faces on the nanoplates varies with lateral size, the crystal phase will change depending on the relative contributions from the surface and bulk energies. The Pd@fcc-Ru outperforms the Pd@hcp-Ru nanoplates toward ethylene glycol and glycerol oxidation reactions.

A General Concurrent Template Strategy for Ordered Mesoporous Intermetallic Nanoparticles with Controllable Catalytic Performance

We report a general concurrent template strategy for precise synthesis of mesoporous Pt-/Pd-based intermetallic nanoparticles with desired morphology and ordered mesostructure. The concurrent template not only supplies a mesoporous metal seed for re-crystallization growth of atomically ordered intermetallic phases with unique atomic stoichiometry but also provides a nanoconfinement environment for nanocasting synthesis of mesoporous nanoparticles with ordered mesostructure and rhombic dodecahedral morphology under elevated temperature. Using the selective hydrogenation of 3-nitrophenylacetylene as a proof-of-concept catalytic reaction, mesoporous intermetallic PtSn nanoparticles exhibited remarkably controllable intermetallic phase-dependent catalytic selectivity and excellent catalytic stability. This work provides a very powerful strategy for precise preparation of ordered mesoporous intermetallic nanocrystals for application in selective catalysis and fuel cell electrocatalysis.

High-Entropy Alloys for Electrocatalysis: Design, Characterization, and Applications

High-entropy alloys (HEAs) are expected to function well as electrocatalytic materials, owing to their widely adjustable composition and unique physical and chemical properties. Recently, HEA catalysts are extensively studied in the field of electrocatalysis; this motivated the authors to investigate the relationship between the structure and composition of HEAs and their electrocatalytic performance. In this review, the latest advances in HEA electrocatalysts are systematically summarized, with special focus on nitrogen fixation, the carbon cycle, water splitting, and fuel cells; in addition, by combining this with the characterization and analysis of HEA microstructures, rational design strategies for optimizing HEA electrocatalysts, including controllable preparation, component regulation, strain engineering, defect engineering, and theoretical prediction are proposed. Moreover, the existing issues and future trends of HEAs are predicted, which will help further develop these high-entropy materials.