Carbon-Extraction-Induced Biaxial Strain Tuning of Carbon-Intercalated Iridium Metallene for Hydrogen Evolution Catalysis.

Metallene materials with atomic thicknesses are receiving increasing attention in electrocatalysis due to ultrahigh surface areas and distinctive surface strain. However, the continuous strain regulation of metallene remains a grand challenge. Herein, taking advantage of autocatalytic reduction of Cu2+ on biaxially strained, carbon-intercalated Ir metallene, we achieve control over the carbon extraction kinetics, enabling fine regulation of carbon intercalation concentration and continuous tuning of (111) in-plane (-2.0%-2.6%) and interplanar (3.5%-8.8%) strains over unprecedentedly wide ranges. Electrocatalysis measurements reveal the strain-dependent activity toward hydrogen evolution reaction (HER), where weakly strained Ir metallene (w-Ir metallene) with the smallest lattice constant presents the highest mass activity of 2.89 A mg-1Ir at -0.02 V vs reversible hydrogen electrode (RHE). Theoretical calculations validated the pivotal role of lattice compression in optimizing H binding on carbon-intercalated Ir metallene surfaces by downshifting the d-band center, further highlighting the significance of strain engineering for boosted electrocatalysis.

Recent progress in Pt and Pd-based hybrid nanocatalysts for methanol electrooxidation.

Although Pt and Pd nanocrystals are among the most popular candidates for anode catalysts in direct methanol fuel cells, their catalytic properties still need to be further improved in order to reduce the costs. In view of this, fabricating hybrid nanomaterials by integrating noble metal nanocrystals and other species turns out to be a powerful way to produce unprecedented catalysts which could combine the merits of different components and modulate the electronic states of Pt or Pd at the same time. In this review, we list recent studies in the construction of heterostructured hybrid nanocatalysts through introducing external components into the noble metal nanocrystals. The mentioned external components include heteroatom doped carbon nanomaterials, metal oxides and hydroxides, as well as transition metal carbides, nitrides, phosphides, and sulfides. The construction methodologies and functions that these introduced species played in the catalytic processes of methanol electrooxidation are discussed. The attempts to maximize the catalytically active interfaces and utilization efficiencies of noble metals are also presented. Finally, the conclusions and existing problems in relevant nanocatalysts are provided.

Water-Based Synthesis of Palladium Trigonal Bipyramidal/Tetrahedral Nanocrystals with Enhanced Electrocatalytic Oxidation Activity.

Well-defined palladium trigonal bipyramidal/tetrahedral nanocrystals were synthesized by an aqueous-phase hydrothermal method. The final products were a mixture of trigonal bipyramidal and tetrahedral nanocrystals. Statistics indicated that there were more trigonal bipyramids than tetrahedra in the products. Ethylenediamine tetraacetic acid disodium salt (EDTA-2Na) was proven to be essential in controlling the final shapes of palladium nanocrystals. Some control experiments were also conducted to investigate the shape evolution and formation mechanisms. The synthesized palladium nanocrystals showed enhanced catalytic properties for ethanol and glycerol electrooxidation in alkaline medium. This work provides a new method in preparing Pd nanomaterials with well-defined shapes.

Multifunctional PtCuTe Nanosheets with Strong ROS Scavenging and ROS-Independent Antibacterial Properties Promote Diabetic Wound Healing.

Nanozymes, as one of the most efficient reactive oxygen species (ROS)-scavenging biomaterials, are receiving wide attention in promoting diabetic wound healing. Despite recent attempts at improving the catalytic efficiency of Pt-based nanozymes (e.g., PtCu, one of the best systems), they still display quite limited ROS scavenging capacity and ROS-dependent antibacterial effects on bacteria or immunocytes, which leads to uncontrolled and poor diabetic wound healing. Hence, a new class of multifunctional PtCuTe nanosheets with excellent catalytic, ROS-independent antibacterial, proangiogenic, anti-inflammatory, and immuno-modulatory properties for boosting the diabetic wound healing, is reported. The PtCuTe nanosheets show stronger ROS scavenging capacity and better antibacterial effects than PtCu. It is also revealed that the PtCuTe can enhance vascular tube formation, stimulate macrophage polarization toward the M2 phenotype and improve fibroblast mobility, outperforming conventional PtCu. Moreover, PtCuTe promotes crosstalk between different cell types to form a positive feedback loop. Consequently, PtCuTe stimulates a proregenerative environment with relevant cell populations to ensure normal tissue repair. Utilizing a diabetic mouse model, it is demonstrated that PtCuTe significantly facilitated the regeneration of highly vascularized skin, with the percentage of wound closure being over 90% on the 8th day, which is the best among the reported comparable multifunctional biomaterials.

Lanthanide-regulating Ru-O covalency optimizes acidic oxygen evolution electrocatalysis.

Precisely modulating the Ru-O covalency in RuOx for enhanced stability in proton exchange membrane water electrolysis is highly desired. However, transition metals with d-valence electrons, which were doped into or alloyed with RuOx, are inherently susceptible to the influence of coordination environment, making it challenging to modulate the Ru-O covalency in a precise and continuous manner. Here, we first deduce that the introduction of lanthanide with gradually changing electronic configurations can continuously modulate the Ru-O covalency owing to the shielding effect of 5s/5p orbitals. Theoretical calculations confirm that the durability of Ln-RuOx following a volcanic trend as a function of Ru-O covalency. Among various Ln-RuOx, Er-RuOx is identified as the optimal catalyst and possesses a stability 35.5 times higher than that of RuO2. Particularly, the Er-RuOx-based device requires only 1.837 V to reach 3 A cm-2 and shows a long-term stability at 500 mA cm-2 for 100 h with a degradation rate of mere 37 µV h-1.

Precise Strain Tuning Boosts Electrocatalytic Hydrogen Generation.

Strain engineering has been utilized as an effective approach to regulate the binding of reaction intermediates and modify catalytic behavior on noble metal nanocatalysts. However, the continuous, precise control of strain for a depiction of strain-activity correlation remains a challenge. Herein, Pd-based nanooctahedrons coated with two Ir overlayers are constructed, and subject to different postsynthetic treatments to alter the amount of H intercalated into Pd core for achieving three different surface strains (o-Pd/Ir-1.2%, o-Pd/Ir-1.7%, and o-Pd/Ir-2.1% NPs). It is demonstrated that the catalytic performances of o-Pd/Ir NPs display a volcano-shaped curve against strains toward the hydrogen evolution reaction (HER). Specifically, o-Pd/Ir-1.7% NPs exhibit superior catalytic performance with a mass activity of 9.38 A mgIr -1 at -0.02 V versus reversible hydrogen electrode, 10.8- and 18.8-fold higher than those of commercial Pt/C and Ir/C, respectively, making it one of the most active HER electrocatalysts reported to date. Density function theory calculations verify that the moderate tensile strain on Ir(111) surfaces plays a pivotal role in optimizing the H binding energy. This work highlights a new strategy for precise control over the surface strain of nanocrystals for more efficient electrocatalysis.

Defective PtRuTe As Nanozyme with Selectively Enhanced Peroxidase-like Activity.

Noble metal based nanozymes show great potential in replacing natural enzymes; however, their development is greatly restricted by their relatively low specificity and activity. Herein, we report the synthesis of a class of amorphous/crystalline PtRuTe nanomaterials with a Pt/Te-enriched core and a Ru-enriched shell as efficient peroxidase mimics with selectively enhanced peroxidase-like activity and suppressed oxidase-like activity. We demonstrate that amorphous domains play a critical role in tuning and optimizing the catalytic properties. The PtRuTe nanozyme with high-percentage defects exhibits superior catalytic activities and kinetics, and the suppressed oxidase-like activity could diminish the interference of O2 in the glucose colorimetric assay. The high catalytic performance can be caused by amorphous phase induced electron redistribution and electronic interactions between different elements and the synergistic effect of multimetallic nanocrystals. The concurrent extraordinary peroxidase-like activity and suppressed oxidase-like activity guarantee the amorphous/crystalline PtRuTe nanozymes as promising alternatives of natural enzymes for biosensing and beyond.

Janus-like Bx C/C Quantum Sheets with Z-Scheme Mechanism Strengthen Tumor Photothermal-Immunotherapy in NIR-II Biowindow.

Carbon dots (CDs) are one of the most popular photothermal agents (PTAs) as a noninvasive strategy for tumor treatment. However, because of the inherent dominant fluorescent emission, the CDs-based PTAs hardly achieve a single photothermal conversion, which causes low photothermal conversion efficiency and poor photothermal performance. In this regard, finding a new CDs-based material system to greatly restrain its fluorescence to enhance its photothermal conversion efficiency is highly required, however, it is still a grand challenge. Herein, a kind of Z-scheme CDs-based PTAs consisting of 2D ultrathin nonmetallic Bx C/C Janus quantum sheets (Bx C/C JQSs) is reported to greatly enhance the photothermal conversion efficiency. It is demonstrated that the heterogeneous growth of Z-scheme Bx C/C JQSs enables the NIR-driven quick injection of hot electrons from C into the conjugated Bx C, realizing a single conversion of light to heat, and resulting in a high photothermal conversion of 60.0% in NIR-II. Furthermore, these new Z-scheme Bx C/C-polyethylene glycol JQSs display outstanding biocompatibility and show effective tumor elimination outcome both in vitro and in vivo through the synergistic photothermal-immunotherapy in the NIR-II biowindow with undetectable harm to normal tissues.

Rapid synthesis of Co3O4 nanosheet arrays on Ni foam by in situ electrochemical oxidization of air-plasma engraved Co(OH)2 for efficient oxygen evolution.

A novel strategy to fabricate Co3O4 nanosheet arrays for the oxygen evolution reaction (OER) was developed by electrodeposition of Co(OH)2 on nickel foam (NF) and subsequent in situ electrochemical oxidation into Co3O4 during the OER. The produced Co3O4@NF-15, which was further engraved with air plasma, exhibits the best performance and long-term stability.

Construction of surface charge-controlled reduced graphene oxide-loaded Fe3O4 and Pt nanohybrid for peroxidase mimic with enhanced catalytic activity.

Hybrid nanomaterials with synergistic effect are highly potential for developing advanced nanozymes. Herein, we designed a nanozyme assembled by polyethylenimine (PEI)-protected reduced graphene oxide anchoring iron oxide (PRGI) and Pt nanoparticle using electrostatic interaction, PRGI/Pt nanohybrid. The different ratio of PRGI nanocomposite and Pt nanoparticle could control PRGI/Pt nanohybrid's surface charge and stability, which determined PRGI/Pt nanohybrid's catalytic activity. At the mass ratio of 0.8, the as-obtained PRGI/Pt nanohybrid showed the highest catalytic ability, and was better than Pt nanoparticle at different pH and temperature, although the PRGI/Pt nanohybrid showed lower affinity for TMB than Pt nanoparticle, which maybe attributed to the fact that PRGI/Pt nanohybrid possessed better product desorption ability or larger contact area. Furthermore, PRGI/Pt nanohybrid showed much higher catalytic activity than the sum of PRGI nanocomposite and Pt nanoparticle, indicating the strong cooperation between PRGI nanocomposite and Pt nanoparticle. Our study also provided a new way to conveniently construct nanozyme based on hybrid nanomaterials.

Amorphous Co2B Grown on CoSe2 Nanosheets as a Hybrid Catalyst for Efficient Overall Water Splitting in Alkaline Medium.

In this work, we synthesized a novel hybrid catalyst (Co2B/CoSe2) by growing amorphous Co2B on the surface of CoSe2 nanosheets. Benefiting from the prominent coupled effects between Co2B and CoSe2 nanosheets, an efficient oxygen evolution reaction catalyst Co2B/CoSe2 exhibits a very low overpotential of 320 mV @ 10 mA cm-2 with a Tafel slope of 56.0 mV dec-1 in alkaline medium. An overpotential of 300 mV can also be achieved by Co2B/CoSe2 at the same condition for hydrogen evolution reaction. Notably, at the applied potential of 1.73 V, the electrocatalyst Co2B/CoSe2 demonstrates a current density of 10 mA cm-2 for overall water splitting and displays an outstanding long-term stability. The faradaic efficiencies of Co2B/CoSe2 for both hydrogen and oxygen evolution are close to 100%.

Introducing Ratiometric Fluorescence to MnO2 Nanosheet-Based Biosensing: A Simple, Label-Free Ratiometric Fluorescent Sensor Programmed by Cascade Logic Circuit for Ultrasensitive GSH Detection.

Glutathione (GSH) plays crucial roles in various biological functions, the level alterations of which have been linked to varieties of diseases. Herein, we for the first time expanded the application of oxidase-like property of MnO2 nanosheet (MnO2 NS) to fluorescent substrates of peroxidase. Different from previously reported fluorescent quenching phenomena, we found that MnO2 NS could not only largely quench the fluorescence of highly fluorescent Scopoletin (SC) but also surprisingly enhance that of nonfluorescent Amplex Red (AR) via oxidation reaction. If MnO2 NS is premixed with GSH, it will be reduced to Mn2+ and lose the oxidase-like property, accompanied by subsequent increase in SC's fluorescence and decrease in AR's. On the basis of the above mechanism, we construct the first MnO2 NS-based ratiometric fluorescent sensor for ultrasensitive and selective detection of GSH. Notably, this ratiometric sensor is programmed by the cascade logic circuit (an INHIBIT gate cascade with a 1 to 2 decoder). And a linear relationship between ratiometric fluorescent intensities of the two substrates and logarithmic values of GSH's concentrations is obtained. The detection limit of GSH is as low as 6.7 nM, which is much lower than previous ratiometric fluorescent sensors, and the lowest MnO2 NS-based fluorescent GSH sensor reported so far. Furthermore, this sensor is simple, label-free, and low-cost; it also presents excellent applicability in human serum samples.

Electrocatalytic hydrogen evolution using the MS2@MoS2/rGO (M = Fe or Ni) hybrid catalyst.

We established a three-tiered cake-like hybrid (MS2@MoS2/rGO, M = Fe or Ni) with the MS2 nanoparticles distributed over the platform of MoS2 and graphene (MoS2/rGO), which exhibits superior HER electrocatalytic activity as well as excellent electrochemical durability. The enhanced electrocatalytic activity benefits from the unique synergistic effects of graphene sheets enhancing the conductivity of the hybrid, MS2 (M = Fe or Ni) nanoparticles and MoS2 nanosheets providing abundant electrocatalytically active sites. Meanwhile, the mechanical stability is promoted by the meticulously-built cake-like structure.

Triple-enzyme mimetic activity of nickel-palladium hollow nanoparticles and their application in colorimetric biosensing of glucose.

We demonstrate that nickel-palladium hollow nanoparticles (NiPd hNPs) exhibit triple-enzyme mimetic activity: oxidase-like activity, peroxidase-like activity and catalase-like activity. As peroxidase mimetics, the catalytic activity of NiPd hNPs was investigated in detail. On this basis, a simple glucose biosensor with a wide linear range and low detection limit was developed.

Trimetallic PtCuCo hollow nanospheres with a dendritic shell for enhanced electrocatalytic activity toward ethylene glycol electrooxidation.

In this work, by utilizing galvanic replacement reaction, a simple method for the synthesis of trimetallic PtCuCo hollow nanospheres with a dendritic shell is demonstrated. The compositions of the nanospheres can be well controlled, and the electrocatalytic activity can also be modulated by adjusting their compositions. Electrocatalytic results show that all of the as-prepared trimetallic PtCuCo nanomaterials show better catalytic performance toward ethylene glycol electrooxidation than the commercial catalyst.