Precise synthesis of hollow IrCu alloy nanoparticles for hydrogenation of substituted nitroaromatics

Hollow structured nanoparticles exhibit unique capabilities for catalytic applications; however, the accurate synthesis of these particles and a comprehensive understanding of the relationships between their structure and performance remain considerable challenges. In this work, hollow IrCu alloy nanoparticles were synthesized through chemical reduction and electrochemical post-leaching processes. The carbon-supported IrCu bimetallic nanoparticles were then evaluated for hydrogenation of various nitroaromatics. The IrCu/C bimetallic catalysts demonstrated significant enhancement in catalytic activity and product selectivity compared to single-metal Ir catalysts. Theoretical calculations alongside experimental findings suggest that the notable improvement originates from both the hollow structure and the composition of the binary IrCu alloy, which synergistically optimize their electronic configurations as well as modify the hydrogenation reaction pathways. This research introduces an innovative approach for constructing hollow alloy structures as efficient and selective hydrogenation catalysts, which might also be applicable to various metal-based catalysts.

Carbon-Extraction-Triggered Phase Engineering of Rhodium Nanomaterials for Efficient Electrocatalytic Nitrate Reduction Reaction

Phase engineering plays a crucial role in tuning the physicochemical properties of noble metal nanomaterials. However, synthesis of high-purity unconventional-phase noble metal nanomaterials remains highly challenging via current wet-chemical methods. Herein, we develop a unique synthetic methodology to prepare freestanding unconventional hexagonal close-packed (2H) Rh nanoplates (NPLs) via a rationally designed two-step strategy. By extracting C from pre-synthesized rhodium carbide of different sizes and morphology, phase-controlled synthesis of Rh nanomaterials can be achieved. Impressively, the obtained parallelogram 2H Rh NPLs have high phase purity, well-defined 2H (0001)h and (101 ¯ ${\mathrm{\bar{1}}}$ 0)h facets, and good thermostability (stable up to 300 °C). In the proof-of-concept electrocatalytic nitrate reduction reaction (NO3RR), the 2H Rh NPLs achieve higher ammonia (NH3) Faradaic efficiency (91.9%) and NH3 yield rate (156.97 mg h-1 mgcat -1) with lower overpotentials compared to the conventional face-centered cubic (3C) Rh nanocubes with (100)f facets. Density functional theory calculations reveal that the unconventional (0001)h surface has energetically favored NO3RR pathway and stronger H* absorption ability compared to the (100)f surface, which may lead to the higher activity and selectivity of NH3 production on 2H Rh NPLs. This work opens new avenues to the rational synthesis of unconventional-phase metal nanomaterials and provides important guidelines to design high-performance electrocatalysts.

Nanoarchitectured N-Heterocyclic Carbene-Pt Nanoparticles on Carbon Nanotubes: Toward Advanced Electrocatalysis in the Hydrogen Evolution Reaction

In response to the need for sustainable energy, this study focuses on advancing the electrocatalytic Hydrogen Evolution Reaction (HER). Considering platinum-based catalysts' efficacy, but acknowledging their cost and scarcity implications, our work pursues Pt content minimization, simultaneously upholding catalytic efficiency. Our approach introduces a precisely engineered nanoarchitecture, leveraging multiwalled carbon nanotubes (MWCNTs) bearing anchored N-heterocyclic carbenes (NHCs). These carbenes form robust covalent bonds with ultrastable, highly crystalline, platinum nanoparticles (PtNPs), establishing MWCNTs-NHC-PtNPs as a highly efficient electrocatalyst. The synergistic effect of NHCs and triazole moieties facilitates controlled nanoparticle growth and stabilization, yielding 2.0 ± 0.3 nm, uniformly distributed {1 1 1}-faceted PtNPs. The as-obtained MWCNTs-NHC-PtNPs nanomaterial exhibits exceptional HER efficiency in 0.5 M H2SO4 with an overpotential of 77 mV at -10 mA cm-2 and a 50 mV dec-1 Tafel slope, despite containing a merely 0.4% Pt/C atomic ratio content, as determined by XPS. Notably, at 200 mV overpotential, the mass activity reaches 8.6 A/mgPt and the specific activity is 53 mA/cm2Pt, highlighting the efficiency of each Pt site within this nanostructure. Cyclic voltammetry reveals a distinctive, reversible PtO/Pt redox process, demonstrating surface-controlled and diffusion-assisted kinetics with charge storage properties that stabilize the electrocatalyst's electron-surface and facilitate proton reduction. Equally important, the nanoarchitecture prevents aggregation and mitigates Pt irreversible oxidation, showcasing enhanced stability after extensive cycling and exposure to air. Comparative analyses with a control electrocatalyst lacking NHC-PtNPs ligation emphasize the unique role of NHC-Pt (0) bonding in enhancing electrocatalytic efficiency. Comprehensive surface and electronic property analyses validate the potential of the MWCNTs-NHC-PtNPs platform.

Electrocatalyst of PdNi Particles on Carbon Black for Hydrogen Oxidation Reaction in Alkaline Membrane Fuel Cell

This work reports the synthesis of PdNi bimetallic particles and Pd on Carbon black (Vulcan XC-72) by reverse microemulsion and the chemical reduction of metallic complexes. The physicochemical characterization techniques used for the bimetallic and metallic materials were TGA, STEM, ICP-OES, and XRD. Also, the electrocatalysts were studied by electrochemical techniques such as anodic CO stripping and β-NiOOH reduction to elucidate the Pd and Ni surface sites participation in the reactions. The electrocatalysts were evaluated in the anodic reaction in anion-exchange membrane fuel cells (AEMFC) and the hydrogen oxidation reaction (HOR) in alkaline media. The results indicate that PdNi/C electrocatalysts exhibited higher electrocatalytic activity than Pd/C electrocatalysts in both the half-cell test and in the AEMFC, even with the same Pd loading, which is attributed to the bifunctional mechanism that provides OH- groups in oxophilic sites associated to Ni, that can facilitate the desorption of Hads in the Pd sites for the bimetallic material.

Synthesis of Ag@Pd Nanocubes and Pd-based Nanoframes via One-Shot Injection of a Halide-Free Precursor for Continuous Production in a Flow Reactor

Noble-metal open nanostructures have remarkable catalytic capabilities toward a wide range of reactions. In particular, Pd-based open nanostructures have been synthesized and validated for superior catalytic performance toward formic acid oxidation. However, most of the syntheses are based on dropwise addition, making it challenging to increase the production volume. In this work, we present a facile approach to the synthesis of Ag@Pd core-frame nanocubes and then Pd-based nanoframes through one-shot injection. In a typical synthesis, Ag nanocubes are dispersed in an aqueous solution of ascorbic acid and polyvinylpyrrolidone at room temperature, followed by the injection of Pd(NH3)4(NO3)2 precursor in one shot. The Pd(NH3)4(NO3)2 precursor has a much slower reduction kinetics relative to Na2PdCl4, preventing self-nucleation and enabling controlled deposition of Pd atoms on the Ag nanocubes. The lower reduction potential of Pd(NH3)4(NO3)2 also helps minimize the galvanic replacement reaction, facilitating uniform deposition of Pd atoms. After selectively etching away the Ag template, Pd-based nanoframes with a rigid cubic structure are obtained. Finally, the synthesis is successfully adapted to a continuous flow system, generating Ag@Pd nanocubes with comparable quality to those obtained via one-shot synthesis, demonstrating a practical route to large-scale production of Pd-based nanoframes with H2O2 etching.

A Powerful Regulator to Enhance Electrocatalytic Reaction Kinetics and Thermodynamics: The Ordered Hetero-Nanowire

Optimizing the thermodynamics of electrode reactions is a valid strategy for achieving superior electrocatalysts for direct methanol fuel cells (DMFCs). However, as the catalyst downsizes to the nanoscale, the influence of mass transfer kinetics is pronounced in improving electrocatalytic activity. Herein, an ordered hetero-nanowire (NW) regulator that couples the virtues of kinetics and thermodynamics is reported. Finite element analysis demonstrates that the periodic arrangement of hetero-NWs could construct a uniform electric field, promoting the precise mass transfer of reactant molecules and accelerating the electrode reaction kinetics for the methanol oxidation reaction (MOR). In addition, the microscopic electronic structure effect of the well-defined catalyst weakens the bonding interaction toward toxic carbonaceous intermediates, which meanwhile strengthens the adsorption of hydroxyl species, critically contributing to enhanced MOR durability. The wide generality of this regulator has been confirmed by a series of as-prepared ordered hetero-NW catalysts, which show prominent electrocatalytic performance, including relatively high mass activity, superior CO resistance, and long-term stability. Therefore, this work reveals the importance of the tandem effect of kinetics and thermodynamics in electrocatalysis, which provides valuable insights for developing customized and highly efficient catalysts for extensive applications.

Pt catalyst protected by graphene nanopockets enables lifetimes of over 200,000 h for heavy-duty fuel cell applications

Proton exchange membrane fuel cells feature considerable scalability advantages over lithium-ion batteries for heavy-duty-vehicle applications. The different driving behaviours and operating conditions of heavy-duty vehicles pose challenging requirements, particularly on fuel cell lifetime and efficiency. Here we report the design of a graphene-nanopocket-protected, pore-confined and electrochemically accessible Pt nanocatalyst supported on Ketjenblack carbon for heavy-duty-vehicle applications. The membrane electrode assembly made from these nanocatalysts delivers an initial mass activity of 0.74 A mgPt-1 and a high rated power density of 1.08 W cm-2, as well as extraordinary long-term durability with an ultrasmall rated power loss of 1.1% after 90,000 aggressive square-wave cycles. The remarkable activity and durability throughout the operation conditions promise an unprecedentedly long fuel cell lifetime of over 200,000 h and high peak efficiency of 71.9%, making it highly attractive for emerging heavy-duty fuel cell applications.

Chemical Synthesis of ~1 nm Multilevel Capacitor-like Particles with Atomic Precision

Can the chemically synthesized nanoparticles act as nanodevices or nanomachines? Herein, we demonstrated this feasibility. A novel nanocluster (ultrasmall nanoparticle) [Au44Cd20(m-MBT)40][N(C8H17)4]2 (Au44Cd20 in short, m-MBTH: m-methylbenzenethiol) obtained via developing a synthesis method has a cannula-like structure of the outer shell and an internal sleeve, revealed by single-crystal X-ray diffraction. Natural population analysis (NPA) charge calculations, charge carrier transport of Au44Cd20 (during which an intra-nanocluster anti-galvanic reaction was observed) after unneutral charging using NaBH4 as well as voltammetry proved the capacitor-like character of Au44Cd20. The subsidiary capacitor-like character of the outer shell of Au44Cd20 was further probed via NPA charge calculations and electrocatalytic reduction of CO2 to CO. Thus, this study predicts a new era of engineering metal nanoparticles for realizing atomically precise ultrasmall nanodevices and nanomachines.

Recent Advances in Selective Chemical Etching of Nanomaterials for High-Performance Electrodes in Electrocatalysis and Energy Storage

To move beyond an energy economy dominated by fossil fuel utilization, high-performance electrochemical cells must be designed for energy storage and conversion. Selective etching is a promising, cost-effective solution-processing method for the large-scale top-down production of nanomaterials for high-performance electrodes. This review outlines general methodologies and mechanisms by which selective etching can be applied to create nanomaterials, including various template-assisted, facet-selective, and electrochemical methods, as well as in-depth case studies of state-of-the-art research involving selectively etched nanomaterials for electrocatalytic and energy storage applications. In addition, the standard design strategies by which the electrochemical performance of selectively etched nanomaterials is enhanced, including increased surface area, morphology, diffusion channels, heterojunction interfaces, and facet reactivity, are discussed. This review provides a foundation of knowledge for researchers seeking the rational design of nanomaterials for electrode application through selective etching.

Advanced electrocatalysts for fuel cells: Evolution of active sites and synergistic properties of catalysts and carrier materials

Proton exchange-membrane fuel cell (PEMFC) is a clean and efficient type of energy storage device. However, the sluggish reaction rate of the cathode oxygen reduction reaction (ORR) has been a significant problem in its development. This review reports the recent progress of advanced electrocatalysts focusing on the interface/surface electronic structure and exploring the synergistic relationship of precious-based and non-precious metal-based catalysts and support materials. The support materials contain non-metal (C/N/Si, etc.) and metal-based structures, which have demonstrated a crucial role in the synergistic enhancement of electrocatalytic properties, especially for high-temperature fuel cell systems. To improve the strong interaction, some exciting synergistic strategies by doping and coating heterogeneous elements or connecting polymeric ligands containing carbon and nitrogen were also shown herein. Besides the typical role of the crystal surface, phase structure, lattice strain, etc., the evolution of structure-performance relations was also highlighted in real-time tests. The advanced in situ characterization techniques were also reviewed to emphasize the accurate structure-performance relations. Finally, the challenge and prospect for developing the ORR electrocatalysts were concluded for commercial applications in low- and high-temperature fuel cell systems.

A Library of Seed@High-Entropy-Alloy Core-shell Nanocrystals With Controlled Facets for Catalysis

High-entropy-alloy (HEA) nanocrystals hold immense potential for catalysis, offering virtually unlimited alloy combinations through the inclusion of at least five constituent elements in varying ratios. However, general and effective strategies for synthesizing libraries of HEA nanocrystals with controlled surface atomic structures remain scarce. In this study, a transferable strategy for developing a library of facet-controlled seed@HEA nanocrystals through seed-mediated growth is presented. The synthesis of seed@HEA core-shell nanocrystals incorporating up to ten different metallic elements, with control over the number of solid-solution HEA atomic layers is demonstrated. Epitaxial HEA growth on nanocrystal seeds with low-index and high-index facets leads to the formation of seed@HEA catalyst library with composition- and facet-dependent catalytic activities in both electrocatalysis and photocatalysis. In situ synchrotron X-ray absorption spectroscopy and density-functional theory calculations are employed to identify surface active sites of the HEA, rationalizing the high level of catalytic activities achieved. This work enables facet engineering in the multi-elemental chemical space and unveils the critical needs for their future development toward catalysis.

Support-Free, Connected Core-Shell Nanoparticle Catalysts Synthesized via a Low-Temperature Process for Advanced Oxygen Reduction Performance

Nanostructured Pt-based catalysts have attracted considerable attention for fuel-cell applications. This study introduces a novel one-pot and low-temperature polyol approach for synthesizing support-free, connected nanoparticles with non-Pt metal cores and Pt shells. Unlike conventional heat treatment methods, the developed support-free and Fe-free connected Pdcore@Ptshell (Pd@Pt) nanoparticle catalyst possesses a stable nanonetwork structure with a high surface area. This approach can precisely control the atomic-level structure of the Pt shell on the Pd core at a low deposition temperature. The optimized Pd@Pt catalyst with a Pt/Pd atomic ratio of 0.8 and a Pt shell thickness of 1.1 nm exhibits a threefold improvement in oxygen reduction reaction (ORR) mass activity compared to that of commercial carbon-supported Pt nanoparticle catalyst (Pt/C). Durability evaluation demonstrated 100% retention of specific activity after 10,000 load cycles, owing to the stable nanonetwork and uniform coverage of the Pt shell. In addition, the support-free, connected core-shell nanoparticle catalyst overcomes the carbon corrosion issues commonly associated with conventional carbon-supported catalysts while simultaneously improving both ORR activity and load cycle durability. These findings highlight the potential of this innovative approach to develop support-free catalysts for polymer electrolyte fuel cells and other energy devices.

Transient Kinetic QXAFS Approach for Understanding the RDE-MEA Gap in Fuel Cell (Oxygen Reduction Reaction) Performances of Pt-Based Electrocatalysts

There is a large gap between the performances indicated by rotating disk electrode (RDE) results in acidic media and the actual performances obtained in membrane-electrode assemblies (MEAs) composed of the same electrocatalysts. It is unclear whether the intrinsic kinetic reactivity of the available surface Pt sites of Pt-based cathode electrocatalysts is similar or different at RDE and in MEA. To address this, we used an operando element-selective time-resolved Pt LIII-edge quick X-ray absorption fine structure (QXAFS) technique to determine transient response profiles and rate constants, k d(WL), k d(CNPt-O), and k d(CNPt-Pt), corresponding to changes in the oxidation states [white line (WL) intensity] and local structures (coordination numbers of Pt-O and Pt-Pt bonds) at Pt sites for nine representative Pt-based cathode electrocatalysts under transient voltage operations, aiming to understand the oxygen reduction reaction (ORR) performance gap between RDE and MEA. For the first time, the transient kinetics and reactivity of electrocatalyst themselves in MEA, characterized by the operando QXAFS analysis technique, were systematically compared with the electrochemical activity [mass activity (I mass) and surface specific activity (I specific)] of the electrocatalysts in MEA and at RDE. The operando time-resolved QXAFS analysis revealed that the ORR activities of available surface Pt sites at RDEs of the electrocatalysts, including notably structured electrocatalysts (concave octahedral PtNi x /C and Pt nanowire/C), were kinetically reflected at good levels of k d(WL) and k d(CNPt-O) in MEA performances, despite large RDE-MEA gaps observed in the electrochemically determined I mass and I specific. As the I mass and I specific of MEA increased, the relaxation time k d(CNPt-Pt) -1, which indicates long-term durability, decreased, reflecting a dilemma in the development of remarkable Pt-based electrocatalysts, while the k d(CNPt-Pt) -1 was almost independent of ECSA. The differences and similarities in the kinetic reactivity and durability of the Pt surface between RDE and MEA were examined using operando QXAFS transient kinetics and electrochemical performance measurements to elucidate the underlying factors contributing to the performance gap between RDE and MEA. The insights gained aim to support the development of next-generation polymer electrolyte fuel cells with enhanced performance and durability by leveraging the operando time-resolved QXAFS technique under the transient kinetic-response operation.

Boosting the oxygen reduction activity on metal surfaces by fine-tuning interfacial water with midinfrared stimulation

Heterogeneous catalysis at the metal surface generally involves the transport of molecules through the interfacial water layer to access the surface, which is a rate-determining step at the nanoscale. In this study, taking the oxygen reduction reaction on a metal electrode in aqueous solution as an example, using accurate molecular dynamic simulations, we propose a novel long-range regulation strategy in which midinfrared stimulation (MIRS) with a frequency of approximately 1,000 cm-1 is applied to nonthermally induce the structural transition of interfacial water from an ordered to disordered state, facilitating the access of oxygen molecules to metal surfaces at room temperature and increasing the oxygen reduction activity 50-fold. Impressively, the theoretical prediction is confirmed by the experimental observation of a significant discharge voltage increase in zinc-air batteries under MIRS. This MIRS approach can be seamlessly integrated into existing strategies, offering a new approach for accelerating heterogeneous reactions and gas sensing within the interfacial water system.

Boosted Efficiency of Fe2O3 for Photocatalytic CO2 Reduction via Engineering Fe-O-Ti Bonding

Visible light-driven photocatalytic CO2 reduction (CO2RR) offers a sustainable and promising solution to environmental and energy challenges. However, the design of efficient photocatalysts is hindered by poor interface interactions in heterojunctions and a limited understanding of reaction kinetics. A modified Fe2O3 photocatalyst, M-Fe2O3@MXene, is introduced featuring KH-550-modified M-Fe2O3 hollow nanocubes coated with MXene, constructed via an electrostatic and Fe-O-Ti bonding self-assembly method. This design achieves an unprecedented CO production rate of 240 µmol g⁻¹ h⁻¹ among non-noble metal catalysts (8.6 folds vs Fe2O3). The Fe-O-Ti sites enhance *COOH intermediate formation and CO production through higher electron deficiency of Fe3+ and rapid charge transfer. This study offers new insights on the use of functional metal oxides and high-quality Mxene layers to design efficient metal oxide-based photocatalysts.

Continuous-Flow and Scalable Synthesis of Pd@PtnL Core-Shell Nanocrystals with Enhanced Activity toward Oxygen Reduction

We report a scalable method based on continuous-flow reactors for conformally coating the surfaces of facet-controlled Pd nanocrystals with uniform, ultrathin shells made of Pt. The key to the success of such an approach is the identification of a proper polyol to generate the Pt atoms at a relatively slow rate to ensure adequate surface diffusion and thus the formation of uniform shells in a layer-by-layer fashion. We first demonstrate the concept using the production of Pd@PtnL (n = 2-5) core-shell icosahedral nanocrystals and then have the strategy successfully extended to the syntheses of Pd@PtnL cubic and octahedral nanocrystals. All these core-shell nanocrystals showed great enhancement in catalytic activity toward the oxygen reduction reaction. Our results suggest that seed-mediated growth can be combined with a continuous-flow reactor to achieve scalable production of bimetallic and even trimetallic nanocrystals with controlled sizes, shapes, compositions, and properties.

High-throughput screening of bifunctional catalysts for oxygen evolution/reduction reaction at the subnanometer regime

The development of low-cost, stable, and highly efficient electrocatalysts for the bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for advancing future renewable technologies. In this study, we systematically investigated the OER and ORR performance of subnano clusters across the 3d, 4d, and 5d transition metal (TM) series of varying sizes using first-principles calculations. The fluxional identity of these clusters in the subnanometer regime is reflected in their non-monotonic catalytic activity. We established a size-dependent scaling relationship between OER/ORR intermediates, leading to a reshaping of the activity volcano plot at the subnanometer scale. Our detailed mechanistic investigation revealed a shift in the apex of the activity volcano from the Pt(111) and IrO2 surfaces to the Au11 clusters for both OER and ORR. Late transition metal subnano clusters, specifically Au11, emerged as the best bifunctional electrocatalyst, demonstrating significantly lower overpotential values. Furthermore, we categorized our catalysts into three clusters and employed the Random Forest Regression method to evaluate the impact of non-ab initio electronic features on OER and ORR activities. Interestingly, d-band filling emerged as the primary contributor to the bifunctional activity of the subnano clusters. This work not only provides a comprehensive view of OER and ORR activities but also presents a new pathway for designing and discovering highly efficient bifunctional catalysts.

Machine-Learning-Assisted Screening of Nanocluster Electrocatalysts: Mapping and Reshaping the Activity Volcano for the Oxygen Reduction Reaction

In computational heterogeneous catalysis, Sabatier's principle-based activity volcano plots provide an intuitive guide to catalyst design but impose a fundamental constraint on the maximum achievable catalytic performance. Recently, subnano clusters have emerged as an exciting platform, offering high noble metal utilization and superior performance for various reactions compared to extended surfaces, reflecting a complex structure-activity relationship in the non-scalable regime. However, understanding their non-monotonic catalytic activity, attributed to the large configurational space and their fluxional identity, poses a formidable challenge. Here, we present a machine learning (ML) framework that captures the non-monotonic trends in oxygen reduction reaction (ORR) activity at the subnanometer scale, attributed to their dynamic fluxional characteristics. We demonstrate a size-dependent shifting and reshaping of the ORR activity volcano, with Au replacing Pt at the peak. Leveraging only upon the non-ab initio geometric and electronic properties, our trained ML model accurately captures the site-specific adsorption energies of intermediates at the subnanometer regime. To account for the inconsistent trend in activity, we analyzed the correlation between electronic and geometric properties. Our findings reveal that the d-filling and coupling matrix of the neighboring metal atom significantly influences the intermediate adsorption on the local chemical environment compared to the d-band center. Following this analysis, we utilized ML to map the catalyst distribution in the activity volcano and identified the five best sub-nano electrocatalysts, demonstrating overpotential values lower than or comparable to the Pt(111) surface for the ORR. This study provides intuitive guidelines for the rational designing of highly efficient electrocatalysts for fuel cell applications while modifying the activity volcano plots for electrocatalysts at the subnanometer regime.

Kirkendall Effect-Driven Reversible Chemical Transformation for Reconfigurable Nanocrystals

The potential universality of chemical transformation principles makes it a powerful tool for nanocrystal (NC) synthesis. An example is the nanoscale Kirkendall effect, which serves as a guideline for the construction of hollow structures with different properties compared to their solid counterparts. However, even this general process is still limited in material scope, structural complexity, and, in particular, transformations beyond the conventional solid-to-hollow process. We demonstrate in this work an extension of the Kirkendall effect that drives reversible structural and phase transformations between metastable metal chalcogenides (MCs) and metal phosphides (MPs). Starting from Ni3S4/Cu1.94S NCs as the initial frameworks, ligand-regulated sequential extractions and diffusion of host/guest (S2-/P3-) anions between Ni3S4/Cu1.94S and Ni2P/Cu3P phases enable solid-to-hollow-to-solid structural motif evolution while retaining the overall morphology of the NC. An in-depth mechanistic study reveals that the transformation between metastable MCs and MPs occurs through a combination of ligand-dependent kinetic control and anion mixing-induced thermodynamic control. This strategy provides a robust platform for creating a library of reconfigurable NCs with tunable compositions, structures, and interfaces.

Crystal-Phase-Selective Etching of Heterophase Au Nanostructures

Selective oxidative etching is one of the most effective ways to prepare hollow nanostructures and nanocrystals with specific exposed facets. The mechanism of selective etching in noble metal nanostructures mainly relies on the different reactivity of metal components and the distinct surface energy of multimetallic nanostructures. Recently, phase engineering of nanomaterials (PEN) offers new opportunities for the preparation of unique heterostructures, including heterophase nanostructures. However, the synthesis of hollow multimetallic nanostructures based on crystal-phase-selective etching has been rarely studied. Here, a crystal-phase-selective etching method is reported to selectively etch the unconventional 4H and 2H phases in the heterophase Au nanostructures. Due to the coating of Pt-based alloy and the crystal-phase-selective etching of 4H-Au in 4H/face-centered cubic (fcc) Au nanowires, the well-defined ladder-like Au@PtAg nanoframes are prepared. In addition, the 2H-Au in the fcc-2H-fcc Au nanorods and 2H/fcc Au nanosheets can also be selectively etched using the same method. As a proof-of-concept application, the ladder-like Au@PtAg nanoframes are used for the electrocatalytic hydrogen evolution reaction (HER) in acidic media, showing excellent performance that is comparable to the commercial Pt/C catalyst.

Strain-Controlled Galvanic Synthesis of Platinum Icosahedral Nanoframes and Their Enhanced Catalytic Activity toward Oxygen Reduction

The unique strain distribution on the surface of a Pd icosahedral nanocrystal is leveraged to control the sites for oxidation and reduction involved in the galvanic replacement reaction. Specifically, Pd is oxidized and dissolved from the center of each {111} facet due to its tensile strain, while the Pt(II) precursor adsorbs onto the vertices and edges featuring a compressive strain, followed by surface reduction and conformal deposition of the Pt atoms. Once the galvanic reaction is initiated, the {111} facets become more vulnerable to oxidation and dissolution, as the vertices and edges are protected by the deposited Pt atoms. The site-selected galvanic reaction naturally results in the formation of Pt icosahedral nanoframes covered by compressively strained {111} facets, which show enhanced catalytic activity and durability toward oxygen reduction relative to commercial Pt/C.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Magnetic Field Enhanced Oxygen Reduction Reaction via Oxygen Diffusion Speedup

The mass-transfer of oxygen in liquid phases (including in the bulk electrolyte and near the electrode surface) is a critical step to deliver oxygen to catalyst sites (especially immersed catalyst sites) and use the full capacity of oxygen reduction reaction (ORR). Despite the extensive efforts of optimizing the complex three-phase reaction interfaces to enhance the gaseous oxygen transfer, strong limitations remain due to oxygen's poor solubility and slow diffusion in electrolytes. Herein, a magnetic method for boosting the directional hydrodynamic pumping of oxygen toward immersed catalyst sites is demonstrated which allows the ORR to reach otherwise inaccessible catalytic regions where high currents normally would have depleted oxygen. For Pt foil electrodes without forced oxygen saturation in KOH electrolytes, the mass-transfer-limited current densities can be improved by 60% under an external magnetic field of 435 mT due to the synergistic effect between bulk- and surface-magnetohydrodynamic (MHD) flows induced by Lorentz forces. The residual magnetic fields are further used at the surface of magnetic materials (such as CoPt alloys and Pt/FeCo heterostructures) to enhance the surface-MHD effect, which helps to retain part of the ORR enhancement permanently without applying external magnetic fields.

Polytypic metal chalcogenide nanocrystals

By engineering chemically identical but structurally distinct materials into intricate and sophisticated polytypic nanostructures, which often surpass their pure phase objects and even produce novel physical and chemical properties, exciting applications in the fields of photovoltaics, electronics and photocatalysis can be achieved. In recent decades, various methods have been developed for synthesizing a library of polytypic nanocrystals encompassing IV, III-V and II-VI polytypic semiconductors. The exceptional performances of polytypic metal chalcogenide nanocrystals have been observed, making them highly promising candidates for applications in photonics and electronics. However, achieving high-precision control over the morphology, composition, crystal structure, size, homojunctions, and periodicity of polytypic metal chalcogenide nanostructures remains a significant synthetic challenge. This review article offers a comprehensive overview of recent progress in the synthesis and control of polytypic metal chalcogenide nanocrystals using colloidal synthetic strategies. Starting from a concise introduction on the crystal structures of metal chalcogenides, the subsequent discussion delves into the colloidal synthesis of polytypic metal chalcogenide nanocrystals, followed by an in-depth exploration of the key factors governing polytypic structure construction. Subsequently, we provide comprehensive insights into the physical properties of polytypic metal chalcogenide nanocrystals, which exhibit strong correlations with their applications. Thereafter, we emphasize the significance of polytypic nanostructures in various applications, such as photovoltaics, photocatalysis, transistors, thermoelectrics, stress sensors, and the electrocatalytic hydrogen evolution. Finally, we present a summary of the recent advancements in this research field and provide insightful perspectives on the forthcoming challenges, opportunities, and future research directions.

Atomic-scale strain engineering of atomically resolved Pt clusters transcending natural enzymes

Strain engineering plays an important role in tuning electronic structure and improving catalytic capability of biocatalyst, but it is still challenging to modify the atomic-scale strain for specific enzyme-like reactions. Here, we systematically design Pt single atom (Pt1), several Pt atoms (Ptn) and atomically-resolved Pt clusters (Ptc) on PdAu biocatalysts to investigate the correlation between atomic strain and enzyme-like catalytic activity by experimental technology and in-depth Density Functional Theory calculations. It is found that Ptc on PdAu (Ptc-PA) with reasonable atomic strain upshifts the d-band center and exposes high potential surface, indicating the sufficient active sites to achieve superior biocatalytic performances. Besides, the Pd shell and Au core serve as storage layers providing abundant energetic charge carriers. The Ptc-PA exhibits a prominent peroxidase (POD)-like activity with the catalytic efficiency (Kcat/Km) of 1.50 × 109 mM-1 min-1, about four orders of magnitude higher than natural horseradish peroxidase (HRP), while catalase (CAT)-like and superoxide dismutase (SOD)-like activities of Ptc-PA are also comparable to those of natural enzymes. Biological experiments demonstrate that the detection limit of the Ptc-PA-based catalytic detection system exceeds that of visual inspection by 132-fold in clinical cancer diagnosis. Besides, Ptc-PA can reduce multi-organ acute inflammatory damage and mitigate oxidative stress disorder.

Real-Time KMC Simulation of Vacancy-Mediated Intermixing in Au@Ag Octahedral Core-Cubic Shell Nanocrystals with Ab Initio-Guided Kinetics

Utilization of core-shell rather than monometallic nanocrystals (NCs) facilitates fine-tuning of NC properties for applications. However, compositional evolution via intermixing can degrade these properties prompting recent experimental studies. We develop an atomistic-level stochastic model for vacancy-mediated intermixing exploiting a formalism which allows incorporation at an ab initio density functional theory level of not just the thermodynamics of vacancy formation, but also relevant diffusion barriers for a vast number of possible local environments (in the core and in the shell, at the interface, and in the intermixed phase). This facilitates a predictive treatment and comprehensive understanding of intermixing on the relevant time scale (e.g., 101-103 s). In contrast, previous modeling at the atomistic level utilized only unrealistic generic prescriptions of barriers or employed simplified continuum treatments. For Au@Ag octahedral core-cubic shell NCs, our modeling not only captures the experimentally observed rate or time scale for intermixing of ∼100 s at 450 °C for 60 nm NCs, but also elucidates the underlying rate controlling processes and the effective intermixing barrier.

Single Entity Electrocatalysis

Making a measurement over millions of nanoparticles or exposed crystal facets seldom reports on reactivity of a single nanoparticle or facet, which may depart drastically from ensemble measurements. Within the past 30 years, science has moved toward studying the reactivity of single atoms, molecules, and nanoparticles, one at a time. This shift has been fueled by the realization that everything changes at the nanoscale, especially important industrially relevant properties like those important to electrocatalysis. Studying single nanoscale entities, however, is not trivial and has required the development of new measurement tools. This review explores a tale of the clever use of old and new measurement tools to study electrocatalysis at the single entity level. We explore in detail the complex interrelationship between measurement method, electrocatalytic material, and reaction of interest (e.g., carbon dioxide reduction, oxygen reduction, hydrazine oxidation, etc.). We end with our perspective on the future of single entity electrocatalysis with a key focus on what types of measurements present the greatest opportunity for fundamental discovery.

Designing the framework structure of noble-metal based nanoalloy catalysts driving redox electrocatalysis

Noble metal-based nanoalloys (NAs) with different entropies have great potential in the field of energy and catalysis. However, it is still very difficult for the reported synthesis strategies to achieve the universal synthesis of small-sized alloys with controllable morphology. Here we develop a general synthesis strategy that combined cation exchange and spatial confinement (CESC). We used this method to construct a library with 21 NAs having low to high entropies. Importantly, we also demonstrate that the method can controllably achieve framing of almost all the NAs obtained, which can be realized by adjusting the amount of non-precious metals, despite the differences in the number of elements. Moreover, the CESC method showed outstanding ability to suppress the sintering of NAs and regulate the particle size of NAs. In the NA library, the framed PtCu/HCN as a redox electrocatalyst shows superior properties. For the methanol oxidation reaction (MOR), the specific and mass activities (7.02 mA cm-2 and 2.81 A mgPt -1) of PtCu/HCN show 28.1- and 13.4-fold enhancement compared to those of commercial Pt/C, and the peak current density is only attenuated by 5% after 50k seconds of chronoamperometry. For the hydrogen evolution reaction (HER), it can operate at ultralow overpotential (23.5 mV and 10 mA cm-2) for 150 h, far exceeding most of the reported catalysts. Moreover, the catalyst is capable of long-term hydrogen evolution at ultra-low overpotentials. Our work offers opportunities for synthesizing framed superfine noble metal-based NAs with different entropies.

An Outlook on Platinum-Based Active Ingredients for Dermatologic and Skincare Applications

Platinum-based materials exhibit a broad spectrum of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and pro-collagen synthesis properties, making them particularly useful for various biomedical applications. This review summarizes the biological effects and therapeutic potential of platinum-based active ingredients in dermatological and skincare applications. We discuss their synthesis methods and their antioxidant, anti-inflammatory, antimicrobial, and collagen synthesis properties, which play essential roles in treating skin conditions including psoriasis and acne, as well as enhancing skin aesthetics in anti-aging products. Safety and sustainability concerns, including the need for green synthesis and comprehensive toxicological assessments to ensure safe topical applications, are also discussed. By providing an up-to-date overview of current research, we aim to highlight both the potential and the current challenges of platinum-based active ingredients in advancing dermatology and skincare solutions.

Octahedral Nanocrystals of Ru-Doped PtFeNiCuW/CNTs High-Entropy Alloy: High Performance Toward pH-Universal Hydrogen Evolution Reaction

Integrating high-entropy philosophy and nanocrystal-specific orientation into a single catalyst represents a promising strategy in development of high-performance catalysts. Nonetheless, shape-controlled synthesis of high-entropy alloy (HEA) nanocrystals is challenging owing to the distinct redox potentials and growth dynamics of metal elements. Herein, a one-pot co-reduction method is developed to fabricate ruthenium (Ru)-doped PtFeNiCuW octahedral HEA nanocrystals onto carbon nanotubes (Ru-PtFeNiCuW/CNTs). It is demonstrated that Ru dopants and W(CO)6 promote the concurrent reduction and growth of other metal precursors to obtain higher yield and larger size of HEA nanocrystals, despite low Ru content in Ru-PtFeNiCuW/CNTs. As an electrocatalyst toward hydrogen evolution reaction (HER), Ru-PtFeNiCuW/CNTs exhibits low overpotentials of 9, 16, and 34 mV at a current density of 10 mA cm-2 and Tafel slopes of 19.2, 27.9, and 23.1 mV dec-1 in acidic, alkaline, and neutral electrolytes, respectively. As a cathodic catalyst, Ru-PtFeNiCuW/CNTs operates for up to 1500 and 1200 h in acidic and alkaline electrolyte, respectively, at a current density of 50 mA cm-2 in a two-electrode system for full water splitting. Theoretical calculations reveal accelerated kinetics of H2O dissociation on W sites and *H desorption on hollow Cu-Cu-Cu and Cu-Cu-Pt sites.

Wet-Chemical Synthesis of Concave Hexoctahedral Pd and Pd@Pt Nanocrystals for Methanol Electrooxidation

Nanocrystals (NCs) exposed with high-index facets usually show enhanced electrocatalytic performances. However, it is a great challenge to persevere with high-index facets against their high surface energy during the synthesis. Herein, we successfully synthesize concave hexoctahedral (c-HOH) Pd NCs exposed with 48 high-index {741} facets using a facile one-pot wet-chemical protocol. Control experiments illustrate that l-ascorbic acid plays a critical role in the formation of the c-HOH morphology, acting as both reducing and capping agents. Moreover, we can extend the synthesis for fabricating c-HOH Pd@Pt core-shell NCs by simply introducing a Pt precursor into the reaction solution, attaining remarkably boosted electrocatalysis for methanol electrooxidation reaction (MOR). Integrating the merits of {741} facets, concave structure, and ligand and strain effect of the core-shell structure, c-HOH Pd4@Pt1 core-shell NCs showed an excellent MOR mass activity of 1.18 A mgPGM-1 or 3.60 A mgPt-1, which is 3.80 or 11.61 times higher than that of commercial Pt/C, respectively.

Spontaneous Formation of Ultrasmall Noble Metal Nanoparticles on Cobalt-Based Layered Double Hydroxide for Electrochemical and Environmental Catalysis

Supported noble metal nanoparticles (NMNPs) are appealing for energy and environment catalysis. To facilitate the loading of NMNPs, in situ reduction of Mn+ on the support with extra reductants/surfactants is adopted, but typically results in aggregated NMNPs with uneven size distributions or blocked active sites of the NMNPs. Herein, the use of cobalt layered double hydroxide (Co-LDH) is proposed as both support and reductant for the preparation of supported NMNPs with ultrasmall sizes and even distributions. The resultant Co-LDH-supported NMNPs exhibit excellent catalytic performance and stability. For example, Ir/Co-LDH displays a low overpotential of 188 mV (10 mA cm-2) for electrocatalytic oxygen evolution reaction and a long-term stability over 100 h (100 mA cm-2) in overall water splitting. Ru/Co-LDH can achieve a 4-nitrophenol reduction with high rate of 0.36 min-1 and S2- detection with low limit of detection (LOD) of 0.34 µm. Overall, this work provides a green and effective strategy to fabricate supported NMNPs with greatly improved catalytic performances.

Synergistic Ni-W Dimer Sites Induced Stable Compressive Strain for Boosting the Performance of Pt as Electrocatalyst for the Oxygen Reduction Reaction

Alloying Pt catalysts with transition metal elements is an effective pathway to enhance the performance of oxygen reduction reaction (ORR), but often accompanied with severe metal dissolution issue, resulting in poor stability of alloy catalysts. Here, instead of forming traditional alloy structure, we modify Pt surface with a novel Ni-W dimer structure by the atomic layer deposition (ALD) technique. The obtained NiW@PtC catalyst exhibits superior ORR performance both in liquid half-cell and practical fuel cell compared with initial Pt/C. It is discovered that strong synergistic Ni-W dimer structure arising from short atomic distance induced a stable compressive strain on the Pt surface, thus boosting Pt catalytic performance. This surface modification by synergistic dimer sites offers an effective strategy in tailoring Pt with excellent activity and stability, which provides a significant perspective in boosting the performance of commercial Pt catalyst modified with polymetallic atom sites.

Rational Electrochemical Design of Cuprous Oxide Hierarchical Microarchitectures and Their Derivatives for SERS Sensing Applications

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu2O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl- ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu2O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu2O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Well-dispersed Pt/Nb2O5on zeolitic imidazolate framework derived nitrogen-doped carbon for efficient oxygen reduction reaction

In this work, an advanced hybrid material was constructed by incorporating niobium pentoxide (Nb2O5) nanocrystals with nitrogen-doped carbon (NC) derived from ZIF-8 dodecahedrons, serving as a support, referred to as Nb2O5/NC. Pt nanocrystals were dispersed onto Nb2O5/NC using a simple impregnation reduction method. The obtained Pt/Nb2O5/NC electrocatalyst showed high oxygen reduction reaction (ORR) activity due to three-phase mutual contacting structure with well-dispersed Pt and Nb2O5NPs. In addition, the conductive NC benefits electron transfer, while the induced Nb2O5can regulate the electronic structure of Pt element and anchor Pt nanocrystals, thereby enhancing the ORR activity and stability. The half-wave potential (E1/2) for Pt/Nb2O5/NC is 0.886 V, which is higher than that of Pt/NC (E1/2= 0.826 V). The stability examinations demonstrated that Pt/Nb2O5/NC exhibited higher electrocatalytic durability than Pt/NC. Our work provides a new direction for synthesis and structural design of precious metal/oxides hybrid electrocatalysts.

Cu2+-Dominated Chirality Transfer from Chiral Molecules to Concave Chiral Au Nanoparticles

Foreign ions as additives are of great significance for realizing excellent control over the morphology of noble metal nanostructures in the state-of-the-art seed-mediated growth method; however, they remain largely unexplored in chiral synthesis. Here, we report on a Cu2+-dominated chiral growth strategy that can direct the growth of concave chiral Au nanoparticles with C3-dominant chiral centers. The introduction of trace amounts of Cu2+ ions in the seed-mediated chiral growth process is found to dominate the chirality transfer from chiral molecules to chiral nanoparticles, leading to the formation of chiral nanoparticles with a concave VC geometry. Both experimental and theoretical results further demonstrate the correlation between the nanoparticle structure and optical chirality for the concave chiral nanoparticle. The Cu2+ ion is found to dominate the chiral growth by selectively activating the deposition of Au atoms along the [110] and [111] directions, facilitating the formation of the concave VC. We further demonstrate that the Cu2+-dominated chiral growth strategy can be employed to generate a variety of concave chiral nanoparticles with enriched geometric chirality and desired chiroptical properties. Concave chiral nanoparticles also exhibit appealing catalytic activity and selectivity toward electrocatalytic oxidation of enantiomers in comparison to helicoidal nanoparticles. The ability to tune the geometric chirality in a controlled manner by simply manipulating the Cu2+ ions as additives opens up a promising strategy for creating chiral nanomaterials with increasing architectural diversity for chirality-dependent optical and catalytic applications.

Synthesizing Pd-based high entropy alloy nanoclusters for enhanced oxygen reduction

We report the synthesis of uniform Pd-based high-entropy alloy clusters via rapid Joule heating. The quinary PdMnFeCuNi clusters exhibit 4.95 times higher mass activity than the Commercial Pt/C for the oxygen reduction reaction, and outstanding stability with only 2 mV decay in the half-wave potential after 20 000 cycles of testing.

Highly Crystalline Iridium-Nickel Nanocages with Subnanopores for Acidic Bifunctional Water Splitting Electrolysis

Developing efficient bifunctional materials is highly desirable for overall proton membrane water splitting. However, the design of iridium materials with high overall acidic water splitting activity and durability, as well as an in-depth understanding of the catalytic mechanism, is challenging. Herein, we successfully developed subnanoporous Ir3Ni ultrathin nanocages with high crystallinity as bifunctional materials for acidic water splitting. The subnanoporous shell enables Ir3Ni NCs optimized exposure of active sites. Importantly, the nickel incorporation contributes to the favorable thermodynamics of the electrocatalysis of the OER after surface reconstruction and optimized hydrogen adsorption free energy in HER electrocatalysis, which induce enhanced intrinsic activity of the acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Together, the Ir3Ni nanocages achieve 3.72 A/mgIr(η=350 mV) and 4.47 A/mgIr(η=40 mV) OER and HER mass activity, which are 18.8 times and 3.3 times higher than that of commercial IrO2 and Pt, respectively. In addition, their highly crystalline identity ensures a robust nanostructure, enabling good catalytic durability during the oxygen evolution reaction after surface oxidation. This work provides a new revenue toward the structural design and insightful understanding of metal alloy catalytic mechanisms for the bifunctional acidic water splitting electrocatalysis.

Self-Assembly Intermetallic PtCu3 Core with High-Index Faceted Pt Shell for High-Efficiency Oxygen Reduction

Rational design of well-defined active sites is crucial for promoting sluggish oxygen reduction reactions. Herein, leveraging the surfactant-oriented and solvent-ligand effects, we develop a facile self-assembly strategy to construct a core-shell catalyst comprising a high-index Pt shell encapsulating a PtCu3 intermetallic core with efficient oxygen-reduction performance. Without undergoing a high-temperature route, the ordered PtCu3 is directly fabricated through the accelerated reduction of Cu2+, followed by the deposition of the remaining Pt precursor onto its surface, forming high-index steps oriented by the steric hindrance of surfactant. This approach results in a high half-wave potential of 0.911 V versus reversible hydrogen electrode, with negligible deactivation even after 15000-cycle operation. Operando spectroscopies identify that this core-shell catalyst facilitates the conversion of oxygen-involving intermediates and ensures antidissolution ability. Theoretical investigations rationalize that this improvement is attributed to reinforced electronic interactions around high-index Pt, stabilizing the binding strength of rate-determining OHads species.

The Recent Progress of Oxygen Reduction Electrocatalysts Used at Fuel Cell Level

Proton exchange membrane fuel cells (PEMFCs) are gaining significant interest as an attractive substitute for traditional fuel cells, with higher energy density, lower environmental pollution, and better operation efficiency. However, the cathode reaction, i.e., the oxygen reduction reaction (ORR), is widely proved to be inefficient, and therefore an obstacle to the widespread development of PEMFCs. The requirement for affordable highly-efficient ORR catalysts is extremely urgent to be met, especially at fuel cell level. Unfortunately, most previous reports focus on the ORR performance at rotating disk electrodes (RDE) level instead of membrane electrode assembly (MEA) level, making it harder to evaluate ORR catalysts operating under real vehicle conditions. Obviously, it is extremely necessary to develop an in-depth understanding of the structure-activity relationship of highly-efficient ORR catalysts applied at MEA level. In this work, an overview of the latest advances in ORR catalysts is provided with an emphasis on their performance at MEA level, hoping to cover the novel and systemic insights for innovative and efficient ORR catalyst design and applications in PEMFCs.

The role of high-resolution transmission electron microscopy and aberration corrected scanning transmission electron microscopy in unraveling the structure-property relationships of Pt-based fuel cells electrocatalysts

Platinum-based fuel cell electrocatalysts are structured on a nano level in order to extend their active surface area and maximize the utilization of precious and scarce platinum. Their performance is dictated by the atomic arrangement of their surface layers atoms via structure-property relationships. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) are the preferred methods for characterizing these catalysts, due to their capacity to achieve local atomic-level resolutions. Size, morphology, strain and local composition are just some of the properties of Pt-based nanostructures that can be obtained by (S)TEM. Furthermore, advanced methods of (S)TEM are able to provide insights into the quasi-in situ, in situ or even operando stability of these nanostructures. In this review, we present state-of-the-art applications of (S)TEM in the investigation and interpretation of structure-activity and structure-stability relationships.

Enhancing electron interaction between Pt and support for superior electrochemical performance through atomic layer deposition of tungsten oxide

The stabilization of platinum (Pt) catalysts through strong metal-support interactions is crucial for their successful implementation in fuel cell applications. Tungsten oxide (WO3) has demonstrated excellent CO tolerance and has been recognized as a promising substrate for anchoring and stabilizing Pt nanoparticles (NPs). However, the limited specific surface area of conventional tungsten oxide restricts its effectiveness in dispersing noble metal NPs. In this study, we present a pioneering approach by employing atomic layer deposition (ALD) to create a WO3 interlayer between Pt NPs and a carbon substrate. Using nitrogen-doped carbon nanotubes (NCNT) as the foundation, WO3 nanoparticles (2-5 nm) were selectively synthesized, followed by the subsequent deposition of Pt NPs using a bottom-up approach. The Pt-WO3-NCNT catalyst, with a WO3 bridge layer effectively inserted between the active site and carbon support, has displayed a notable augmentation in electrocatalytic activity and notable stability when compared to commercial Pt catalysts in oxygen reduction reaction (ORR). The detailed microstructure and the enhanced electrochemical reaction mechanism of Pt-WO3-NCNT catalyst has been investigated by X-ray adsorption spectrum and density functional theory (DFT) calculations. This work presents an innovative approach for enhancing the stability of Pt catalysts through the utilization of the ALD technique.

Identifying the distinct roles of dual dopants in stabilizing the platinum-nickel nanowire catalyst for durable fuel cell

Stabilizing active PtNi alloy catalyst toward oxygen reduction reaction is essential for fuel cell. Doping of specific metals is an empirical strategy, however, the atomistic insight into how dopant boosts the stability of PtNi catalyst still remains elusive. Here, with typical examples of Mo and Au dopants, we identify the distinct roles of Mo and Au in stabilizing PtNi nanowires catalysts. Specifically, due to the stronger interaction between atomic orbital for Ni-Mo and Pt-Au, the Mo dopant mainly suppresses the outward diffusion of Ni atoms while the Au dopant contributes to the stabilization of surface Pt overlayer. Inspired by this atomistic understanding, we rationally construct the PtNiMoAu nanowires by integrating the different functions of Mo and Au into one entity. Such catalyst assembled in fuel cell cathode thus presents both remarkable activity and durability, even surpassing the United States Department of Energy technical targets for 2025.

Machine-learning-accelerated design of high-performance platinum intermetallic nanoparticle fuel cell catalysts

Carbon supported PtCo intermetallic alloys are known to be one of the most promising candidates as low-platinum oxygen reduction reaction electrocatalysts for proton-exchange-membrane fuel cells. Nevertheless, the intrinsic trade-off between particle size and ordering degree of PtCo makes it challenging to simultaneously achieve a high specific activity and a large active surface area. Here, by machine-learning-accelerated screenings from the immense configuration space, we are able to statistically quantify the impact of chemical ordering on thermodynamic stability. We find that introducing of Cu/Ni into PtCo can provide additional stabilization energy by inducing Co-Cu/Ni disorder, thus facilitating the ordering process and achieveing an improved tradeoff between specific activity and active surface area. Guided by the theoretical prediction, the small sized and highly ordered ternary Pt2CoCu and Pt2CoNi catalysts are experimentally prepared, showing a large electrochemically active surface area of ~90 m2 gPt‒1 and a high specific activity of ~3.5 mA cm‒2.

Precisely Control Relationship between Sulfur Vacancy and H Absorption for Boosting Hydrogen Evolution Reaction

Effective and robust catalyst is the core of water splitting to produce hydrogen. Here, we report an anionic etching method to tailor the sulfur vacancy (VS) of NiS2 to further enhance the electrocatalytic performance for hydrogen evolution reaction (HER). With the VS concentration change from 2.4% to 8.5%, the H* adsorption strength on S sites changed and NiS2-VS 5.9% shows the most optimized H* adsorption for HER with an ultralow onset potential (68 mV) and has long-term stability for 100 h in 1 M KOH media. In situ attenuated-total-reflection Fourier transform infrared spectroscopy (ATR-FTIRS) measurements are usually used to monitor the adsorption of intermediates. The S- H* peak of the NiS2-VS 5.9% appears at a very low voltage, which is favorable for the HER in alkaline media. Density functional theory calculations also demonstrate the NiS2-VS 5.9% has the optimal |ΔGH*| of 0.17 eV. This work offers a simple and promising pathway to enhance catalytic activity via precise vacancies strategy.

Precise synthetic control of exclusive ligand effect boosts oxygen reduction catalysis

Ligand effect, induced by charge transfer between catalytic surface and substrate in core/shell structure, was widely proved to benefit Pt-catalyzed oxygen reduction reaction by tuning the position of d-band center of Pt theoretically. However, ligand effect is always convoluted by strain effect in real core/shell nanostructure; therefore, it remains experimentally unknown whether and how much the ligand effect solely contributes electrocatalytic activity improvements. Herein, we report precise synthesis of a kind of Pd3Ru1/Pt core/shell nanoplates with exclusive ligand effect for oxygen reduction reaction. Layer-by-layer growth of Pt overlayers onto Pd3Ru1 nanoplates can guarantee no lattice mismatch between core and shell because the well-designed Pd3Ru1 has the same lattice parameters as Pt. Electron transfer, due to the exclusive ligand effect, from Pd3Ru1 to Pt leads to a downshift of d-band center of Pt. The optimal Pd3Ru1/Pt1-2L nanoplates achieve excellent activity and stability for oxygen reduction reaction in alkaline/acid electrolyte.

Engineering Fe-N4 Electronic Structure with Adjacent Co-N2C2 and Co Nanoclusters on Carbon Nanotubes for Efficient Oxygen Electrocatalysis

Regulating the local configuration of atomically dispersed transition-metal atom catalysts is the key to oxygen electrocatalysis performance enhancement. Unlike the previously reported single-atom or dual-atom configurations, we designed a new type of binary-atom catalyst, through engineering Fe-N4 electronic structure with adjacent Co-N2C2 and nitrogen-coordinated Co nanoclusters, as oxygen electrocatalysts. The resultant optimized electronic structure of the Fe-N4 active center favors the binding capability of intermediates and enhances oxygen reduction reaction (ORR) activity in both alkaline and acid conditions. In addition, anchoring M-N-C atomic sites on highly graphitized carbon supports guarantees of efficient charge- and mass-transports, and escorts the high bifunctional catalytic activity of the entire catalyst. Further, through the combination of electrochemical studies and in-situ X-ray absorption spectroscopy analyses, the ORR degradation mechanisms under highly oxidative conditions during oxygen evolution reaction processes were revealed. This work developed a new binary-atom catalyst and systematically investigates the effect of highly oxidative environments on ORR electrochemical behavior. It demonstrates the strategy for facilitating oxygen electrocatalytic activity and stability of the atomically dispersed M-N-C catalysts.

Selective edge etching of Pd metallene for enhanced formic acid electrooxidation

We develop a facile, selective edge etching strategy to create edge sites in Pd metallene using acetic acid. The created edge sites remarkably increase the electrochemically active surface area but reduce the charge transfer resistance, resulting in significant enhancement of catalytic activity and stability toward formic acid oxidation.

Sculpting Windows onto AuAg Hollow Cubic Nanocrystals

Using surfactants in the galvanic replacement reaction (GRR) offers a versatile approach to modulating hollow metal nanocrystal (NC) morphology and composition. Among the various surfactants available, quaternary ammonium cationic surfactants are commonly utilised. However, understanding how they precisely influence morphological features, such as the size and void distribution, is still limited. In this study, we aim to uncover how adding different surfactants-CTAB, CTAC, CTApTS, and PVP-can fine-tune the morphological characteristics of AuAg hollow NCs synthesised via GRR at room temperature. Our findings reveal that the halide counterion in the surfactant significantly controls void formation within the hollow structure. When halogenated surfactants, such as CTAB or CTAC, are employed, multichambered opened nanoboxes are formed. In contrast, with non-halogenated CTApTS, single-walled closed nanoboxes with irregularly thick walls form. Furthermore, when PVP, a polymer surfactant, is utilised, changes in concentration lead to the production of well-defined single-walled closed nanoboxes. These observations highlight the role of surfactants in tailoring the morphology of hollow NCs synthesised through GRR.

Hydrogen Evolution Reaction on Single-Atom Pt Doped in Ni Matrix under Strong Alkaline Condition

Pt catalyst has been considered as the state-of-the-art catalyst for hydrogen evolution reaction (HER) under acid condition. However, its catalytic kinetics under alkaline conditions is not well-understood. Herein, we report a Ni-Pt(SAs) (SAs = single atoms) catalyst with Pt atomically dispersed in a Ni matrix, and it possesses an impressive HER performance with an overpotential as low as 210 mV at 500 mA cm-2 in strong alkaline electrolyte (7 M KOH), which is much higher than Pt nanoparticle-modified Ni catalyst (Ni-Pt(NPs)). Kinetics analysis reveals that Pt doping in the Ni matrix can accelerate the Volmer step on the Ni-Pt surface. Moreover, Ni-Pt(SAs) displays a more favorable kinetics for H2 formation reaction at high current density than Ni-Pt(NPs). Theoretical calculations reveal that atomically dispersed Pt weakens the adsorption of both H and OH on the surface of Ni-Pt electrode and promotes H2 formation from surface H on Ni-Pt(SAs).