Aging amorphous/crystalline heterophase PdCu nanosheets for catalytic reactions

Crystalline/Amorphous Interface Engineering and d-sp Orbital Hybridization Synergistically Boosting the Electrocatalytic Performance of PdCu Bimetallene toward Formic Acid-Assisted Overall Water Splitting

Advanced electrocatalysts capable of bifunctional catalysis for formic acid oxidation (FAOR) and hydrogen evolution reaction (HER) have garnered significant attention due to their exceptional energy efficiency. In this research, we have meticulously designed a PdCu bimetallene characterized by numerous crystalline/amorphous (c/a) interfaces and robust d-sp orbital hybridization, achieved by integrating the p-block metalloid boron within the PdCu matrix (B-PdCu-c/a). The B-PdCu-c/a bimetallene revealed a multitude of surface atoms and unsaturated defect sites, offering abundant catalytic active sites and an optimized electronic structure. The B2-PdCu-c/a exhibited the best performance in FAOR and HER, achieving a mass activity of 1106 mA mgcat-1 and an overpotential of 52 mV, respectively. Significantly, the two-electrode configuration of B2-PdCu-c/a∥B2-PdCu-c/a attained a low cell voltage of 0.19 V at 10 mA cm-2 during formic acid-assisted overall water splitting. Density functional theory (DFT) calculations indicated that c/a interface engineering and d-sp orbital hybridization synergistically optimized the electronic configuration of pristine PdCu bimetallene. This led to an elevation of the d-band center and an accumulation of charge at the c/a interface, which enhanced the adsorption of intermediates, facilitated C-H bond cleavage, and balanced the adsorption-desorption of hydrogen, thereby improving electrocatalytic activities for FAOR and HER, respectively. This study not only presents a viable strategy for effectively tuning the electronic configuration of bimetallene but also offers valuable insights into the development of electrocatalysts.

Discovery of Deactivation Phenomenon in NiCo2S4/NiS2 Electromagnetic Wave Absorbent and Its Reactivation Mechanism

Over the past century, extensive research has been carried out on various types of microwave absorption (MA) materials, primarily emphasizing mechanism, performance, and even toward smart device. However, the deactivation, a crucial concern for practical applications, has long been long-neglected. In this work, an in-depth exploration of the deactivation mechanism reveals a significant competition between metal and oxygen, leading to the replacement of the S-M (M = Ni and Co) bond by a new S─O bond on the surface of absorber. This substitution initiates a series of collapse effect that introduces additional defective sites and diminishes the potential for charge transport. Subsequently, passive and active anti-deactivation strategies are developed to target the deactivation. The passive strategy involved intentionally creating electron-deficient structures at the initial Ni and Co sites in the crystal through the Fe doping engineering, with the objective of preventing the generation of S─O bonds. Furthermore, the active anti-deactivation strategy allows for the precise control of absorber deactivation and reactivation by employing accelerated thermodynamic and kinetic methods, enabling a reversible transformation of S-M through competitive reactions with S─O bonds. Finally, a fast deactivation and reactivation method is first proposed promising to stimulate further innovations and breakthroughs in practical applications.

Exploring Nanozymes for Organic Substrates: Building Nano-organelles

Since the discovery of the first peroxidase nanozyme (Fe3O4), numerous nanomaterials have been reported to exhibit intrinsic enzyme-like activity toward inorganic oxygen species, such as H2O2, oxygen, and O2 -. However, the exploration of nanozymes targeting organic compounds holds transformative potential in the realm of industrial synthesis. This review provides a comprehensive overview of the diverse types of nanozymes that catalyze reactions involving organic substrates and discusses their catalytic mechanisms, structure-activity relationships, and methodological paradigms for discovering new nanozymes. Additionally, we propose a forward-looking perspective on designing nanozyme formulations to mimic subcellular organelles, such as chloroplasts, termed "nano-organelles". Finally, we analyze the challenges encountered in nanozyme synthesis, characterization, nano-organelle construction and applications while suggesting directions to overcome these obstacles and enhance nanozyme research in the future. Through this review, our goal is to inspire further research efforts and catalyze advancements in the field of nanozymes, fostering new insights and opportunities in chemical synthesis.

Defect engineered ternary metal spinel-type Ni-Fe-Co oxide as bifunctional electrocatalyst for overall electrochemical water splitting

Transition metal spinel oxides were engineered with active elements as bifunctional water splitting electrocatalysts to deliver superior intrinsic activity, stability, and improved conductivity to support green hydrogen production. In this study, we reported the ternary metal Ni-Fe-Co spinel oxide electrocatalysts prepared by defect engineering strategy with rich and deficient Na+ ions, termed NFCO-Na and NFCO, which suggest the formation of defects with Na+ forming tensile strain. The Na-rich NiFeCoO4 spinel oxide reveals lattice expansion, resulting in the formation of a defective crystal structure, suggesting higher electrocatalytic active sites. The spherical NFCO-Na electrocatalysts exhibit lower OER and HER overpotentials of 248 mV and 153 mV at 10 mA cm-2 and smaller Tafel slope values of about 78 mV dec-1 and 129 mV dec-1, respectively. Notably, the bifunctional NFCO-Na electrocatalyst requires a minimum cell voltage of about 1.67 V to drive a current density of 10 mA cm-2. The present work highlights the significant electrochemical activity of defect-engineered ternary metal oxides, which can be further upgraded as highly active electrocatalysts for water splitting applications.

Ultrafast micro/nano-manufacturing of metastable materials for energy

The structural engineering of metastable nanomaterials with abundant defects has attracted much attention in energy-related fields. The high-temperature shock (HTS) technique, as a rapidly developing and advanced synthesis strategy, offers significant potential for the rational design and fabrication of high-quality nanocatalysts in an ultrafast, scalable, controllable and eco-friendly way. In this review, we provide an overview of various metastable micro- and nanomaterials synthesized via HTS, including single metallic and bimetallic nanostructures, high entropy alloys, metal compounds (e.g. metal oxides) and carbon nanomaterials. Note that HTS provides a new research dimension for nanostructures, i.e. kinetic modulation. Furthermore, we summarize the application of HTS-as supporting films for transmission electron microscopy grids-in the structural engineering of 2D materials, which is vital for the direct imaging of metastable materials. Finally, we discuss the potential future applications of high-throughput and liquid-phase HTS strategies for non-equilibrium micro/nano-manufacturing beyond energy-related fields. It is believed that this emerging research field will bring new opportunities to the development of nanoscience and nanotechnology in both fundamental and practical aspects.

DNA Framework-Templated Fabrication of Ultrathin Electroactive Gold Nanosheets

Generally, two-dimensional gold nanomaterials have unique properties and functions that offer exciting application prospects. However, the crystal phases of these materials tend to be limited to the thermodynamically stable crystal structure. Herein, we report a DNA framework-templated approach for the ambient aqueous synthesis of freestanding and microscale amorphous gold nanosheets with ultrathin sub-nanometer thickness. We observe that extended single-stranded DNA on DNA nanosheets can induce site-specific metallization and enable precise modification of the metalized nanostructures at predefined positions. More importantly, the as-prepared gold nanosheets can serve as an electrocatalyst for glucose oxidase-catalyzed aerobic oxidation, exhibiting enhanced electrocatalytic activity (~3-fold) relative to discrete gold nanoclusters owing to a larger electrochemical active area and wider band gap. The proposed DNA framework-templated metallization strategy is expected to be applicable in a broad range of fields, from catalysis to new energy materials.

The synthesis and application of crystalline-amorphous hybrid materials

Crystalline-amorphous hybrid materials (CA-HMs) possess the merits of both pure crystalline and amorphous phases. Abundant dangling bonds, unsaturated coordination atoms, and isotropic structural features in the amorphous phase, as well as relatively high electronic conductivity and thermodynamic structural stability of the crystalline phase simultaneously take effect in CA-HMs. Furthermore, the atomic and bandgap mismatch at the CA-HM interface can introduce more defects as extra active sites, reservoirs for promoted catalytic and electrochemical performance, and induce built-in electric field for facile charge carrier transport. Motivated by these intriguing features, herein, we provide a comprehensive overview of CA-HMs on various aspects-from synthetic methods to multiple applications. Typical characteristics of CA-HMs are discussed at the beginning, followed by representative synthetic strategies of CA-HMs, including hydrothermal/solvothermal methods, deposition techniques, thermal adjustment, and templating methods. Diverse applications of CA-HMs, such as electrocatalysis, batteries, supercapacitors, mechanics, optoelectronics, and thermoelectrics along with underlying structure-property mechanisms are carefully elucidated. Finally, challenges and perspectives of CA-HMs are proposed with an aim to provide insights into the future development of CA-HMs.

Interface Engineering and Boron Modification of Pd-B/Pd Hetero-Metallene Synergistically Accelerate Oxygen Reduction Catalysis

2D metallene possess high surface area and excellent electron transport capability, thus enabling efficient application in oxygen reduction reaction (ORR). However, the interface regulation and electronic structure optimization of metallene are still great challenges. Herein, Pd-B/Pd hetero-metallene is constructed by interface engineering and B modification strategies for efficient electrocatalytic ORR. The 2D configuration of Pd-B/Pd hetero-metallene exposes a large number of surface atoms and unsaturated defect sites, thus providing abundant catalytic active sites and exhibiting high electron mobility. More importantly, interface engineering and B modification synergistically optimizing the electronic configuration of the metallene system. This work not only provides an effective strategy for the rational regulation of the electronic configuration of metallene, but also offers a reference for the construction of efficient ORR catalysts.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Seeded Synthesis of Hollow PdSn Intermetallic Nanomaterials for Highly Efficient Electrocatalytic Glycerol Oxidation

Intermetallic nanomaterials have shown promising potential as high-performance catalysts in various catalytic reactions due to their unconventional crystal phases with ordered atomic arrangements. However, controlled synthesis of intermetallic nanomaterials with tunable crystal phases and unique hollow morphologies remains a challenge. Here, a seeded method is developed to synthesize hollow PdSn intermetallic nanoparticles (NPs) with two different intermetallic phases, that is, orthorhombic Pd2 Sn and monoclinic Pd3 Sn2 . Benefiting from the rational regulation of the crystal phase and morphology, the obtained hollow orthorhombic Pd2 Sn NPs deliver excellent electrocatalytic performance toward glycerol oxidation reaction (GOR), outperforming solid orthorhombic Pd2 Sn NPs, hollow monoclinic Pd3 Sn2 NPs, and commercial Pd/C, which places it among the best reported Pd-based GOR electrocatalysts. The reaction mechanism of GOR using the hollow orthorhombic Pd2 Sn as the catalyst is investigated by operando infrared reflection absorption spectroscopy, which reveals that the hollow orthorhombic Pd2 Sn catalyst cleaves the CC bond more easily compared to the commercial Pd/C. This work can pave an appealing route to the controlled synthesis of diverse novel intermetallic nanomaterials with hollow morphology for various promising applications.

Polyethylenimine-Ethylenediamine-Induced Pd Metallene toward Alkaline Oxygen Reduction

Designing two-dimensional (2D) materials functionalized with organic molecules is an effective tactic to enhance catalytic performances for the oxygen reduction reaction (ORR). Herein, we synthesize Pd metallene with in situ modification of polyethylenimine-ethylenediamine (Pd@PEI-EDA metallene), in which PEI-EDA serves as both the structure-directing agent and modifier. Pd@PEI-EDA metallene has ample active sites and tuneable electronic structures due to ultrathin nanosheets with abundant wrinkles and interfacial structure. In contrast with commercial Pd/C and Pt/C, Pd@PEI-EDA metallene displays preferable catalytic ORR performance under alkaline conditions. This work offers an in situ interface engineering tactic for the preparation of 2D polymer-metal electrocatalysts to boost the ORR performance.

Structural Transformation of Unconventional-Phase Materials

The structural transformation of materials, which involves the evolution of different structural features, including phase, composition, morphology, etc., under external conditions, represents an important fundamental phenomenon and has drawn substantial research interest. Recently, materials with unconventional phases that are different from their thermodynamically stable ones have been demonstrated to possess distinct properties and compelling functions and can further serve as starting materials for structural transformation studies. The identification and mechanism study of the structural transformation process of unconventional-phase starting materials can not only provide deep insights into their thermodynamic stability in potential applications but also offer effective approaches for the synthesis of other unconventional structures. Here, we briefly summarize the recent research progress on the structural transformation of some typical starting materials with various unconventional phases, including the metastable crystalline phase, amorphous phase, and heterophase, induced by different approaches. The importance of unconventional-phase starting materials in the structural modulation of resultant intermediates and products will be highlighted. The employment of diverse in situ/operando characterization techniques and theoretical simulations in studying the mechanism of the structural transformation process will also be introduced. Finally, we discuss the existing challenges in this emerging research field and provide some future research directions.

Nanoarchitectonics of Metallene Materials for Electrocatalysis

Controlling the synthesis of metal nanostructures is one approach for catalyst engineering and performance optimization in electrocatalysis. As an emerging class of unconventional electrocatalysts, two-dimensional (2D) metallene electrocatalysts with ultrathin sheet-like morphology have gained ever-growing attention and exhibited superior performance in electrocatalysis owing to their distinctive properties originating from structural anisotropy, rich surface chemistry, and efficient mass diffusion capability. Many significant advances in synthetic methods and electrocatalytic applications for 2D metallenes have been obtained in recent years. Therefore, an in-depth review summarizing the progress in developing 2D metallenes for electrochemical applications is highly needed. Unlike most reported reviews on the 2D metallenes, this review starts by introducing the preparation of 2D metallenes based on the classification of the metals (e.g., noble metals, and non-noble metals) instead of synthetic methods. Some typical strategies for preparing each kind of metal are enumerated in detail. Then, the utilization of 2D metallenes in electrocatalytic applications, especially in the electrocatalytic conversion reactions, including the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, fuel oxidation reaction, CO₂ reduction reaction, and N₂ reduction reaction, are comprehensively discussed. Finally, current challenges and opportunities for future research on metallenes in electrochemical energy conversion are proposed.

Sulfur and phosphorus co-doping optimized electronic structure and modulated intermediate affinity on PdSP metallene for ethanol-assisted energy-saving H2 production

Coupling cathodic hydrogen evolution reaction (HER) and anodic electrochemical oxidation of organic small molecules in a co-electrolysis system could simultaneously realize high-value chemical generation and energy-saving hydrogen production, which, however, require high-performance electrocatalysts. In this work, we developed a one-step solvothermal method to synthesize S, P-co-doped Pd metallene (PdSP metallene) and employed it as a bifunctional electrocatalyst for both the HER and ethanol oxidation reaction (EOR). The co-doping of S and P atoms into Pd metallene could introduce multiple active sites and increase the electrochemically-active surface area. Moreover, the electronic interactions between Pd, S, and P atoms could regulate the electronic structure of the active sites and modulate the intermediate affinity on the resultant PdSP metallene, thus boosting the electrocatalytic HER and EOR performance. In the HER-EOR co-electrolysis system with bifunctional PdSP metallene electrocatalysts, only a 0.88 V of electrolysis voltage was required to fulfill 10 mA cm^-2 current density, much lower than that of pure water electrolysis (1.41 V) using the same electrocatalysts.

Defect-Rich PdIr Bimetallene Nanoribbons with Interatomic Charge Localization for Isopropanol-Assisted Seawater Splitting

Metallene with outstanding physicochemical properties is an efficient two-dimensional electrocatalysts for sustainable hydrogen (H₂ ) production applications. However, the controllable fabrication of extended atomically thin metallene nanoribbons remains a formidable challenge. Herein, this work proposes a controllable preparation strategy for atomically thin defect-rich PdIr bimetallene nanoribbons (PdIr BNRs) with a thickness of only 1.5 nm for the efficient and stable isopropanol-assisted seawater electrolytic H₂ production. When using PdIr BNRs as catalyst to build an isopropanol-assisted seawater electrolysis system, a voltage of only 0.38 V is required at @10 mA cm^-2 to achieve energy-saving H₂ production, while producing high value-added acetone at the anode. The aberration-corrected high-resolution transmission electron microscopy (HRTEM) clearly reveals that the PdIr BNRs possess abundant structural defects, which can additionally serve as highly catalytically active sites. Density functional theory (DFT) calculations combined with X-ray absorption spectroscopy studies reveal that the introduction of Ir atoms can induce the formation of a localized charge region and shift the d-band center of Pd down, thereby reducing the adsorption energy on the catalyst in favor of the rapid desorption of H₂ . This work opens the way for the controllable design and construction of defect-rich atomically thin metallene nanoribbons for efficient electrocatalytic applications.

Micron-Scale Fabrication of Ultrathin Amorphous Copper Nanosheets Templated by DNA Scaffolds

Two-dimensional (2D) amorphous materials could outperform their crystalline counterparts toward various applications because they have more defects and reactive sites and thus could exhibit a unique surface chemical state and provide an advanced electron/ion transport path. Nevertheless, it is challenging to fabricate ultrathin and large-sized 2D amorphous metallic nanomaterials in a mild and controllable manner due to the strong metallic bonds between metal atoms. Here, we reported a simple yet fast (10 min) DNA nanosheet (DNS)-templated method to synthesize micron-scale amorphous copper nanosheets (CuNSs) with a thickness of 1.9 ± 0.4 nm in aqueous solution at room temperature. We demonstrated the amorphous feature of the DNS/CuNSs by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Interestingly, we found that they could transform to crystalline forms under continuous electron beam irradiation. Of note, the amorphous DNS/CuNSs exhibited much stronger photoemission (∼62-fold) and photostability than dsDNA-templated discrete Cu nanoclusters due to the elevation of both the conduction band (CB) and valence band (VB). Such ultrathin amorphous DNS/CuNSs hold great potential for practical applications in biosensing, nanodevices, and photodevices.

Stable and Ordered Body-Centered Cubic PdCu Phase for Highly Selective Hydrogenation

Phase engineering of nanomaterials plays a crucial role for regulating the catalytic performance. Nevertheless, great challenges still remain for elucidating the structure-selectivity correlation. Herein, this study demonstrates that the body-centered cubic phase of PdCu (bcc-PdCu) can serve as a highly active and selective catalyst for 3-nitrostyrene (NS) hydrogenation under mild conditions. In particular, bcc-PdCu displays a 3-nitro-ethylbenzene (NE) selectivity of 93.8% with a turnover frequency (TOF) value of 4573 h^-1 at 30 °C in the presence of H₂ . With the assistance of NH₃ ∙BH₃ , the selectivity of 3-amino-styrene (AS) reaches 94.5% with a TOF value of 13 719 h^-1 . Detailed experimental and theoretical calculations reveal that improved NE selectivity is ascribed to the selective adsorption of the CC bond and desorption of NE on bcc-PdCu. Moreover, the presence of NH₃ ∙BH₃ facilitates the selective hydrogenation of NO₂ due to their strong interaction and thus leads to the formation of AS. This work provides an efficient selective catalyst for NS hydrogenation under mild conditions, which may attract immediate interests in the fields of materials, chemistry, and catalysis.

Photoelectric properties of the layered raspberry sandwich amorphous ZnCo2S4@MnCo2S4/CP composite counter electrode in semiconductor-sensitized solar cells

Multistage amorphous materials have promising applications in the catalytic performance of dye-sensitized solar cells (DSSCs). Herein, an amorphous sheet-raspberry sandwich-like ZnCo₂S₄@MnCo₂S₄/CP composite material was rationally designed and developed as a counter electrode (CE) for DSSCs by applying a three-step hydrothermal method. The first development of the amorphous composites as CEs resulted in lower charge transfer resistance at the CE/electrolyte interface and improved the fill factor and short-circuit current density. The excellent catalytic performance is mainly attributed to the large number of unsaturated coordination sites generated by the undirected structure of the lamellar-raspberry intercalated amorphous material, the smooth ion transport interface with a self-built corrosion-resistant layer, coupled with the dual catalytic performance of the Zn, Co, and Mn composites, and the good electrical conductivity of the C substrate. When ZnCo₂S₄@MnCo₂S₄/CP was used as the CE on a Ti substrate, the photoelectric conversion efficiency was as high as 11.68% (V_oc = 0.821, J_sc = 20.14 mA cm^-2, and FF = 0.71) under 100 mW cm^-2 light illumination. This paper provides a design idea for amorphous materials in terms of catalytic performance and a method for developing alternatives to Pt electrodes.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

Pd-Based Metallenes for Fuel Cell Reactions

Pd-based metallenes, atomically thin layers composed primarily of under-coordinated Pd atoms, have emerged as the newest members in the family of two-dimensional (2D) nanomaterials. Moreover, the unique physiochemical properties, high intrinsic activity associated with metallenes coupled with the ease of applying chemical modifications result in great potential in catalyst engineering for fuel cell reactions. Especially in recent years, interest in Pd-based metallenes is growing, as evidenced by surge in available literatures. Herein, we have reviewed the recent findings achieved in Pd-based metallenes in fuel cells by highlighting the technologies available for deriving metallenes and manifesting the modification strategies for designing them to better suit the application demand. Moreover, we also discuss the perspective insights of Pd-based metallenes for fuel cells regarding the surfactant-free synthesis method, strain engineering, constructing high-entropy alloy, and so on.

Amorphous-crystalline PdRu bimetallene for efficient hydrogen evolution electrocatalysis

In this work, PdRu bimetallene is prepared by a wet-chemical method using CO as a structure-directing agent and reductant derived from the decomposition of W(CO)₆. The PdRu bimetallene exhibits excellent catalytic activity with a small overpotential of -32 mV compared to Pd metallene (-62 mV) at -10 mA cm^-2 in acidic conditions.

Low Pt-Doped Crystalline/Amorphous Heterophase Pd12P3.2 Nanowires as Efficient Catalysts for Methanol Oxidation

Pd-based catalysts are attractive anodic electrocatalysts for direct methanol fuel cells owing to their low cost and natural abundance. However, they suffer from sluggish reaction kinetic and insufficient electroactivity in methanol oxidation reaction (MOR). In this work, we developed a facile one-pot approach to fabricate low Pt-doped Pd₁₂P_3.2 nanowires with crystalline/amorphous heterophase (termed Pt-Pd₁₂P_3.2 NWs) for MOR. The unique crystalline/amorphous heterophase structures promote the catalytic activity by the plentiful active sites at the phase boundaries and/or interfaces and the synergistic effect between different phases. Moreover, the incorporation of trace Pt into Pd lattices modifies the electronic structure and improves the electron transfer ability. Therefore, the obtained Pt-Pd₁₂P_3.2 NWs display significantly enhanced electrocatalytic performance toward MOR with the mass activity of 2.35 A mg_Pd+Pt^-1, which is 9.0, 2.9, and 2.0 times higher than those of the commercial Pd/C (0.26 A mg_Pd^-1), Pd₁₂P_3.2 NWs (0.82 A mg_Pd^-1), and commercial Pt/C (1.19 A mg_Pt^-1). The high mass activity enables the Pt-Pd₁₂P_3.2 NWs to be the promising Pd-based catalysts for MOR.

Preparation of Amorphous SnO2 -Encapsulated Multiphased Crystalline Cu Heterostructures for Highly Efficient CO2 Reduction

Controlling the architectures and crystal phases of metal@semiconductor heterostructures is very important for modulating their physicochemical properties and enhancing their application performances. Here, a facile one-pot wet-chemical method to synthesize three types of amorphous SnO₂ -encapsulated crystalline Cu heterostructures, i.e., hemicapsule, yolk-shell, and core-shell nanostructures, in which unconventional crystal phases (e.g., 2H, 4H, and 6H) and defects (e.g., stacking faults and twin boundaries) are observed in the crystalline Cu cores, is reported. The hemicapsule Cu@SnO₂ heterostructures, with voids that not only expose the Cu core with unconventional phases but also retain the interface between Cu and SnO₂ , show an excellent electrocatalytic CO₂ reduction reaction (CO₂ RR) selectivity toward the production of CO and formate with high Faradaic efficiency (FE) above 90% in a wide potential window from -1.05 to -1.55 V (vs reversible hydrogen electrode (RHE)), and the highest FE of CO₂ RR (95.3%) is obtained at -1.45 V (vs RHE). This work opens up a new way for the synthesis of new heterostructured nanomaterials with promising catalytic application.

Wet-chemical synthesis of two-dimensional metal nanomaterials for electrocatalysis

Two-dimensional (2D) metal nanomaterials have gained ever-growing research interest owing to their fascinating physicochemical properties and promising application, especially in the field of electrocatalysis. In this review, we briefly introduce the recent advances in wet-chemical synthesis of 2D metal nanomaterials. Subsequently, the catalytic performances of 2D metal nanomaterials in a variety of electrochemical reactions are illustrated. Finally, we summarize current challenges and highlight our perspectives on preparing high-performance 2D metal electrocatalysts.

Mixture Phases Engineering of PtFe Nanofoams for Efficient Hydrogen Evolution

Phase engineering is a promising but challenging approach to construct PtFe-based catalysts with efficient hydrogen evolution reaction (HER) performance. Herein, the authors successfully synthesize PtFe nanofoams with face center cubic (fcc) phase, with simple cubic crystalline (scc) phase and with the mixture phases of fcc and scc phases (PtFe-mix) by hydrogen-assisted calcination for the first time. By benchmarking the HER activity, PtFe-mix exhibits excellent activity in 1.0 m KOH, requiring an overpotential of 28 mV to achieve 10 mA cm^-2 , which is better than the commercial Pt/C (34 mV). PtFe-mix also possesses remarkable stability up to 24 h. Density functional theory calculations further verify that PtFe-mix shows a more suitable d-band center and lower energy barrier for the initial water dissociation, facilitating the HER process. This work provides a meaningful strategy to design PtFe-based catalysts with efficient activity for hydrogen evolution.

Boosting Hydrogen Evolution through the Interface Effects of Amorphous NiMoO4-MoO2 and Crystalline Cu

The rational design and synthesis of a highly efficient and cost-effective electrocatalyst for hydrogen evolution reaction (HER) are of great importance for the efficient generation of sustainable energy. Herein, amorphous/crystalline heterophase Ni-Mo-O/Cu (denoted as a/c Ni-Mo-O/Cu) was synthesized by a one-pot electrodeposition method. Thanks to the introduction of metallic Cu and the formation of amorphous Ni-Mo-O, the prepared electrocatalyst exhibits favorable conductivity and abundant active sites, which are favorable to the HER progress. Moreover, the interfaces consisting of Cu and Ni-Mo-O show electron transfers between these components, which might modify the absorption/desorption energy of H atoms, thus accelerating HER activity. As expected, the prepared a/c Ni-Mo-O/Cu possesses excellent HER performance, which affords an ultralow overpotential of 34.8 mV at 10 mA cm^-2, comparable to that of 20 wt % Pt/C (35.0 mV), and remarkable stability under alkaline conditions.

Synthesis of Pd3 Sn and PdCuSn Nanorods with L12 Phase for Highly Efficient Electrocatalytic Ethanol Oxidation

The crystal phase of nanomaterials is one of the key parameters determining their physicochemical properties and performance in various applications. However, it still remains a great challenge to synthesize nanomaterials with different crystal phases while maintaining the same composition, size, and morphology. Here, a facile, one-pot, wet-chemical method is reported to synthesize Pd₃ Sn nanorods with comparable size and morphology but different crystal phases, that is, an ordered intermetallic and a disordered alloy with L1₂ and face-centered cubic (fcc) phases, respectively. The crystal phase of the as-synthesized Pd₃ Sn nanorods is easily tuned by altering the types of tin precursors and solvents. Moreover, the approach can also be used to synthesize ternary PdCuSn nanorods with the L1₂ crystal phase. When used as electrocatalysts, the L1₂ Pd₃ Sn nanorods exhibit superior electrocatalytic performance toward the ethanol oxidation reaction (EOR) compared to their fcc counterpart. Impressively, compared to the L1₂ Pd₃ Sn nanorods, the ternary L1₂ PdCuSn nanorods exhibit more enhanced electrocatalytic performance toward the EOR, yielding a high mass current density up to 6.22 A mg_Pd ^-1 , which is superior to the commercial Pd/C catalyst and among the best reported Pd-based EOR electrocatalysts.

Ultrathin Ruthenium Nanosheets with Crystallinity-Modulated Peroxidase-like Activity for Protein Discrimination

Noble-metal-based nanozymes have attracted great interest as enzyme mimics because of their unique properties. To modulate the performance and meet the requirements of practical biosensing applications, phase engineering is promising for the design of novel noble-metal-based nanomaterials. Herein, a simple salt-assist strategy was employed for the synthesis of Ru nanosheets (NSs) with the controlled crystalline degree. The crystalline degree plays a significant role in tuning peroxidase-like activity by optimizing the affinity toward the catalytic substrate. Furthermore, the inhibition effect of mercapto molecules on the peroxidase-like activity of Ru NSs was investigated. As a proof-of-concept, the Ru NSs-based colorimetric sensing arrays were developed to distinguish mercapto molecules, and five model molecules were well classified according to the different inhibition effects. Given the complexity of practical conditions, the sensing array was further applied to discriminate proteins possessing rich mercapto groups. This work not only provides an effective strategy for the design of highly active nanozymes but also achieves promising sensing arrays for practical needs.

Recent Advances in Electrocatalysts for Alkaline Hydrogen Oxidation Reaction

With the rapid development of anion-exchange membrane technology and adequate supply of high-performance non-noble metal oxygen reduction reaction (ORR) catalysts in alkaline media, the commercialization of anion exchange membrane fuel cells (AEMFCs) become possible. However, the kinetics of the anodic hydrogen oxidation reaction (HOR) in AEMFCs is significantly decreased compared to the HOR in proton exchange membrane fuel cells (PEMFCs). Therefore, it is urgent to develop HOR catalysts with low price, high activity, and robust stability. However, comprehensive timely reviews on this specific subject do not exist enough yet and it is necessary to update reported major achievements and to point out future investigation directions. In this review, the current reaction mechanisms on HOR are summarized and deeply understood. The debates between the mechanisms are greatly harmonized. Recent advances in developing highly active and stable electrocatalysts for the HOR are reviewed. Moreover, the side reaction control is for the first time systematically introduced. Finally, the challenges and future opportunities in the field of HOR catalysis are outlined.

Heterostructuring Mesoporous 2D Iridium Nanosheets with Amorphous Nickel Boron Oxide Layers to Improve Electrolytic Water Splitting

2D heterostructures exhibit a considerable potential in electrolytic water splitting due to their high specific surface areas, tunable electronic properties, and diverse hybrid compositions. However, the fabrication of well-defined 2D mesoporous amorphous-crystalline heterostructures with highly active heterointerfaces remains challenging. Herein, an efficient 2D heterostructure consisting of amorphous nickel boron oxide (Ni-B_i ) and crystalline mesoporous iridium (meso-Ir) is designed for water splitting, referred to as Ni-B_i /meso-Ir. Benefiting from well-defined 2D heterostructures and strong interfacial coupling, the resulting mesoporous dual-phase Ni-B_i /meso-Ir possesses abundant catalytically active heterointerfaces and boosts the exposure of active sites, compared to their crystalline and amorphous mono-counterparts. The electronic state of the iridium sites is tuned favorably by hybridizing with Ni-B_i layers. Consequently, the Ni-B_i /meso-Ir heterostructures show superior and stable electrochemical performance toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte.

Sodium-Decorated Amorphous/Crystalline RuO2 with Rich Oxygen Vacancies: A Robust pH-Universal Oxygen Evolution Electrocatalyst

The oxygen evolution reaction (OER) is a key reaction for many electrochemical devices. To date, many OER electrocatalysts function well in alkaline media, but exhibit poor performances in neutral and acidic media, especially the acidic stability. Herein, sodium-decorated amorphous/crystalline RuO₂ with rich oxygen vacancies (a/c-RuO₂ ) was developed as a pH-universal OER electrocatalyst. The a/c-RuO₂ shows remarkable resistance to acid corrosion and oxidation during OER, which leads to an extremely high catalytic stability, as confirmed by a negligible overpotential increase after continuously catalyzing OER for 60 h at pH=1. Besides, a/c-RuO₂ also exhibits superior OER activities to commercial RuO₂ and most reported OER catalysts under all pH conditions. Theoretical calculations indicated that the introduction of Na dopant and oxygen vacancy in RuO₂ weakens the adsorption strength of the OER intermediates by engineering the d-band center, thereby lowering the energy barrier for OER.

Ultrathin Amorphous/Crystalline Heterophase Rh and Rh Alloy Nanosheets as Tandem Catalysts for Direct Indole Synthesis

Heterogeneous noble-metal-based catalysis plays an essential role in the production of fine chemicals. Rh-based catalysts are one of the most active candidates for indole synthesis. However, it is still highly desired to develop heterogeneous Rh-based catalysts with high activity and selectivity. In this work, a general, facile wet-chemical method is reported to synthesize ultrathin amorphous/crystalline heterophase Rh and Rh-based bimetallic alloy nanosheets (NSs), including RhCu, RhZn, and RhRu. Impressively, the amorphous/crystalline heterophase Rh NSs exhibit enhanced catalytic activity toward the direct synthesis of indole compared to the crystalline counterpart. Importantly, the obtained amorphous/crystalline heterophase RhCu alloy NSs can further enhance the selectivity to indole of >99.9% and the conversion is 100%. This work demonstrates the importance of phase engineering and metal alloying in the rational design and synthesis of tandem heterogeneous catalysts toward fine chemical synthesis.

Au-Cu@PANI Alloy Core Shells for Aerobic Fibrin Degradation under Visible Light Exposure

Fibrin plays a critical role in wound healing and hemostasis, yet it is also the main case of cardiovascular diseases and thrombosis. Here, we show the unique design of Au-Cu@PANI alloy core-shell rods for fibrin clot degradation. Microscopic (transmission electron microscopy (TEM), scanning transmission electron microscopy-energy-dispersive X-ray (STEM-EDX)) and structural characterizations (powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS)) of the Au-Cu@PANI hybrid material reveal the formation of Au-Cu heterogeneous alloy core rods (aspect ratio = 3.7) with thin Cu₂O and PANI shells that create a positive surface charge (ζ-potential = +22 mV). This architecture is supported by the survey XPS spectrum showing the presence of Cu 2p, N 1s, and C 1s features with binding energies of 934.8, 399.7, and 284.8 eV, respectively. Upon photolysis (λ ≥ 495 or 590 nm), these hybrid composite nanorods provide sufficient excited-state redox potential to generate reactive oxygen species (ROS) for degradation of model fibrin clots within 5-7 h. Detailed scanning electron microscopy (SEM) analysis of the fibrin network shows significant morphology modification including formation of large voids and strand termini, indicating degradation of fibrin protofibril by Au-Cu@PANI. The dye 1,3-diphenylisobenzofuran (DPBF) used to detect the presence of ¹O₂ shows a 27% bleaching of the absorption at λ = 418 nm within 75 min of irradiation of an aqueous Au-Cu@PANI solution in air. Moreover, electron paramagnetic resonance (EPR) spin-trapping experiments reveal a hyperfine-coupled triplet signature at room temperature with intensities 1:1:1: and g-value = 2.0057, characteristic of the reaction between the spin probe 4-Oxo-TEMP and ¹O₂ during irradiation. Controlled ¹O₂ scavenging experiments by NaN₃ show 82% reduction in the spin-trapped EPR signal area. Both DPBF bleaching and EPR spin trapping indicate that in situ generated ¹O₂ is responsible for fibrin strand scission. This unique nanomaterial function via use of ubiquitous oxygen as a reagent could open creative avenues for future in vivo biomedical applications to treat fibrin clot diseases.

Direct and indirect Z-scheme heterostructure-coupled photosystem enabling cooperation of CO2 reduction and H2O oxidation

The stoichiometric photocatalytic reaction of CO2 with H2O is one of the great challenges in photocatalysis. Here, we construct a Cu2O-Pt/SiC/IrOx composite by a controlled photodeposition and then an artificial photosynthetic system with Nafion membrane as diaphragm separating reduction and oxidation half-reactions. The artificial system exhibits excellent photocatalytic performance for CO2 reduction to HCOOH and H2O oxidation to O2 under visible light irradiation. The yields of HCOOH and O2 meet almost stoichiometric ratio and are as high as 896.7 and 440.7 μmol g-1 h-1, respectively. The high efficiencies of CO2 reduction and H2O oxidation in the artificial system are attributed to both the direct Z-scheme electronic structure of Cu2O-Pt/SiC/IrOx and the indirect Z-scheme spatially separated reduction and oxidation units, which greatly prolong lifetime of photogenerated electrons and holes and prevent the backward reaction of products. This work provides an effective and feasible strategy to increase the efficiency of artificial photosynthesis.

Synthesis of Palladium-Based Crystalline@Amorphous Core-Shell Nanoplates for Highly Efficient Ethanol Oxidation

Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core-shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu_{3- χ} P nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mg_Pd ^-1 , which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mg_Pd ^-1 ).

Phase engineering of nanomaterials

Phase has emerged as an important structural parameter - in addition to composition, morphology, architecture, facet, size and dimensionality - that determines the properties and functionalities of nanomaterials. In particular, unconventional phases in nanomaterials that are unattainable in the bulk state can potentially endow nanomaterials with intriguing properties and innovative applications. Great progress has been made in the phase engineering of nanomaterials (PEN), including synthesis of nanomaterials with unconventional phases and phase transformation of nanomaterials. This Review provides an overview on the recent progress in PEN. We discuss various strategies used to synthesize nanomaterials with unconventional phases and induce phase transformation of nanomaterials, by taking noble metals and layered transition metal dichalcogenides as typical examples. Moreover, we also highlight recent advances in the preparation of amorphous nanomaterials, amorphous-crystalline and crystal phase-based hetero-nanostructures. We also provide personal perspectives on challenges and opportunities in this emerging field, including exploration of phase-dependent properties and applications, rational design of phase-based heterostructures and extension of the concept of phase engineering to a wider range of materials.

Ultrathin Pd-based nanosheets: syntheses, properties and applications

Two-dimensional (2D) noble metal-based nanosheets (NSs) have received considerable interest in recent years due to their unique properties and widespread applications. Pd-based NSs, as a typical member of 2D noble metal-based NSs, have been most extensively studied. In this review, we first summarize the research progress on the synthesis of Pd-based NSs, including pure Pd NSs, Pd-based alloy NSs, Pd-based core-shell NSs and Pd-based hybrid NSs. The synthetic strategy and growth mechanism are systematically discussed. Then their properties and applications in catalysis, biotherapy, gas sensing and so on are introduced in detail. Finally, the challenges and opportunities towards the rational design and controlled synthesis of Pd-based NSs are proposed.

A general synthesis approach for amorphous noble metal nanosheets

Noble metal nanomaterials have been widely used as catalysts. Common techniques for the synthesis of noble metal often result in crystalline nanostructures. The synthesis of amorphous noble metal nanostructures remains a substantial challenge. We present a general route for preparing dozens of different amorphous noble metal nanosheets with thickness less than 10 nm by directly annealing the mixture of metal acetylacetonate and alkali salts. Tuning atom arrangement of the noble metals enables to optimize their catalytic properties. Amorphous Ir nanosheets exhibit a superior performance for oxygen evolution reaction under acidic media, achieving 2.5-fold, 17.6-fold improvement in mass activity (at 1.53 V vs. reversible hydrogen electrode) over crystalline Ir nanosheets and commercial IrO2 catalyst, respectively. In situ X-ray absorption fine structure spectra indicate the valance state of Ir increased to less than + 4 during the oxygen evolution reaction process and recover to its initial state after the reaction.