Manipulation of Electron Spins with Oxygen Vacancy on Amorphous/Crystalline Composite-Type Catalyst.

By substituting the oxygen evolution reaction (OER) with the anodic urea oxidation reaction (UOR), it not only reduces energy consumption for green hydrogen generation but also allows purification of urea-rich wastewater. Spin engineering of the d orbital and oxygen-containing adsorbates has been recognized as an effective pathway for enhancing the performance of electrocatalysts. In this work, we report the fabrication of a bifunctional electrocatalyst composed of amorphous RuO2-coated NiO ultrathin nanosheets (a-RuO2/NiO) with abundant amorphous/crystalline interfaces for hydrogen evolution reaction (HER) and UOR. Impressively, only 1.372 V of voltage is required to attain a current density of 10 mA cm-2 over a urea electrolyzer. The increased oxygen vacancies in a-RuO2/NiO by incorporation of amorphous RuO2 enhance the total magnetization and entail numerous spin-polarized electrons during the reaction, which speeds up the UOR reaction kinetics. The density functional theory study reveals that the amorphous/crystalline interfaces promote charge-carrier transfer, and the tailored d-band center endows the optimized adsorption of oxygen-generated intermediates. This kind of oxygen vacancy induced spin-polarized electrons toward boosting HER and UOR kinetics and provides a reliable reference for exploration of advanced electrocatalysts.

Engineering Amorphous/Crystalline Ru(OH)3/CoFe-Layered Double Hydroxide for Hydrogen Evolution at 1000 mA cm-2.

For large-scale industrial applications, it is highly desirable to create effective, economical electrocatalysts with long-term stability for the hydrogen evolution reaction (HER) at a large current density. Herein, we report a unique motif with crystalline CoFe-layered hydroxide (CoFe-LDH) nanosheets enclosed by amorphous ruthenium hydroxide (a-Ru(OH)3/CoFe-LDH) to realize the efficient hydrogen production at 1000 mA cm-2, with a low overpotential of 178 mV in alkaline media. During the continuous HER process for 40 h at such a large current density, the potential remains almost constant with only slight fluctuations, indicating good long-term stability. The remarkable HER performance can be attributed to the charge redistribution caused by abundant oxygen vacancies in a-Ru(OH)3/CoFe-LDH. The increased electron density of states lowers the charge-transfer resistance and promotes the formation and release of H2 molecules. The water-splitting electrolyzer with a-Ru(OH)3/CoFe-LDH as both an anode and a cathode in 1.0 M KOH demonstrates stable hydrogen production and a 100% faradic efficiency. The design strategy of interface engineering in this work will inspire the design of practical electrocatalysts for water splitting on an industrial scale.

Pseudopyrolysis of Metal-Organic Frameworks: A Synchronous Nucleation Mechanism to Synthesize Ultrafine Metal Compound Nanoparticles.

Metal-Organic frameworks (MOFs) are increasingly being investigated for the synthesis of carbon-supported metal-based ultrafine nanoparticles (UNPs). However, the collapse of the carbon framework and aggregation of metal particles in the pyrolysis process have severely hindered their stability and applications. Here, we report the synchronous nucleation pseudopyrolysis of MOFs to confine Fe/FeOx UNPs in intact porous carbon nanorods (IPCNs), revealed by in situ transmission electron microscopy experiments and ex situ structure analysis. The pseudopyrolysis mechanism enables strong physical and chemical confinement effects between UNPs and carbon by moderate thermal kinetics and abundant oxygen defects. Further, this strong confinement is greatly beneficial for subsequent chemical transformations to obtain different Fe-based UNPs and excellent electrochemical performance. As a proof of concept, the as-prepared FeSe UNPs in IPCNs show superior lithium storage performance with an ultrahigh and stable capacity of 815.1 mAh g-1 at 0.1 A g -1 and 379.7 mAh g-1 at 5 A g-1 for 1000 cycles.

Engineering Amorphous/Crystalline Rod-like Core-Shell Electrocatalysts for Overall Water Splitting.

The design of bifunctional electrocatalysts for hydrogen and oxygen evolution reactions delivering excellent catalytic activity and stability is highly desirable, yet challenged. Herein, we report an amorphous RuO2-encapsulated crystalline Ni0.85Se nanorod structure (termed as a/c-RuO2/Ni0.85Se) for enhanced HER and OER activities. The as-prepared a/c-RuO2/Ni0.85Se nanorods not only demonstrate splendid HER activity (58 mV@10 mA cm-2 vs RHE), OER activity (233 mV@10 mA cm-2 vs RHE), and electrolyzer activity (1.488 V@10 mA cm-2 vs RHE for overall water splitting) but also exhibit long-term stability with negligible performance decay after 50 h continuous test for overall water splitting. In addition, the variation of the d-band center (from the perspective of bonding and antibonding states) is unveiled theoretically by density functional theory calculations upon amorphous RuO2 layers coupling to clarify the increased hydrogen species adsorption for HER activity enhancement. This work represents a new pathway for the fabrication of bifunctional electrocatalysts toward green hydrogen generation.

Boosting Charge Transfer Via Heterostructure Engineering of Ti2 CTx /Na2 Ti3 O7 Nanobelts Array for Superior Sodium Storage Performance.

The poor conductivity, inert charge transmission efficiency, and irreversible Na+ trapping of Na2 Ti3 O7 result in retardant electrons/ions transportation and deficient sodium-ion storage efficiency, leading to sluggish reaction kinetics. To address these issues, an urchin-like Ti2 CTx /Na2 Ti3 O7 (Ti2 C/NTO) heterostructure sphere consisting of Ti2 C/NTO heterostructure nanobelts array is developed via a facile one-step in situ hydrothermal strategy. The Ti2 C/NTO heterostructure can obviously decrease Na+ diffusion barriers and increase electronic conductivity to improve reaction kinetics due to the built-in electric field effect and high-quantity interface region. In addition, the urchin-like vertically aligned nanobelts can reduce the diffusion distance of electrons and ions, provide favored electrolyte infiltration, adapt large volume expansion, and mitigate the aggregation to maintain structural stability during cycles, further enhancing the reaction kinetics. Furthermore, the Ti2 C/NTO heterostructure can effectively suppress many unwanted side reactions between reactive surface sites of NTO and electrolyte as well as irreversible trapping of Na+ . As a result, systematic electrochemical investigations demonstrate that the Ti2 C/NTO heterostructure as an anode material for record sodium-ion storage delivers the highest reversible capacity, the best cycling stability with 0.0065% decay rate for 4500 cycles at 2.0 A g-1 , and excellent rate capability of 172.1 mAh g-1 at 10.0 A g-1 .

Promoting photocatalytic hydrogen evolution over the perovskite oxide Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3 by plasmon-induced hot electron injection.

Exploration of highly efficient and stable photocatalysts for water splitting has attracted much attention. However, developing a facile and effective approach to enhance the photocatalytic activity for practical applications is still highly challenging. Herein, we report a newly-fabricated perovskite oxide (Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3) decorated with Au ultrafine nanoparticles for photocatalytic water splitting. An exceptionally high hydrogen evolution rate of 1618 µmol g-1 h-1 was achieved (under 2 h illumination) when the Au mass loading was optimized to 9.3 wt%, which is 540 times higher than that of the pristine one. The splendid photocatalytic activity of the sample was attributed to plasmon-excited hot electron injection from Au to Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3 (PBSCF) under illumination. The finite-difference time-domain simulations (FDTD) demonstrated that the localized strong electric field formed at the interface between Au and PBSCF under illumination, enables the hot electrons to be energetic and make the injection possible.

Ultralarge elastic deformation of nanoscale diamond.

Diamonds have substantial hardness and durability, but attempting to deform diamonds usually results in brittle fracture. We demonstrate ultralarge, fully reversible elastic deformation of nanoscale (~300 nanometers) single-crystalline and polycrystalline diamond needles. For single-crystalline diamond, the maximum tensile strains (up to 9%) approached the theoretical elastic limit, and the corresponding maximum tensile stress reached ~89 to 98 gigapascals. After combining systematic computational simulations and characterization of pre- and postdeformation structural features, we ascribe the concurrent high strength and large elastic strain to the paucity of defects in the small-volume diamond nanoneedles and to the relatively smooth surfaces compared with those of microscale and larger specimens. The discovery offers the potential for new applications through optimized design of diamond nanostructure, geometry, elastic strains, and physical properties.

Nickel-Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All-pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution.

Novel 3D Ni1-x Cox Se2 mesoporous nanosheet networks with tunable stoichiometry are successfully synthesized on Ni foam (Ni1-x Cox Se2 MNSN/NF with x ranging from 0 to 0.35). The collective effects of special morphological design and electronic structure engineering enable the integrated electrocatalyst to have very high activity for hydrogen evolution reaction (HER) and excellent stability in a wide pH range. Ni0.89 Co0.11 Se2 MNSN/NF is revealed to exhibit an overpotential (η10 ) of 85 mV at -10 mA cm-2 in alkaline medium (pH 14) and η10 of 52 mV in acidic solution (pH 0), which are the best among all selenide-based electrocatalysts reported thus far. In particular, it is shown for the first time that the catalyst can work efficiently in neutral solution (pH 7) with a record η10 of 82 mV for all noble metal-free electrocatalysts ever reported. Based on theoretical calculations, it is further verified that the advanced all-pH HER activity of Ni0.89 Co0.11 Se2 is originated from the enhanced adsorption of both H+ and H2 O induced by the substitutional doping of cobalt at an optimal level. It is believed that the present work provides a valuable route for the design and synthesis of inexpensive and efficient all-pH HER electrocatalysts.

Mesoporous SnO2 Nanostructures of Ultrahigh Surface Areas by Novel Anodization.

Here we report a novel type of hierarchical mesoporous SnO2 nanostructures fabricated by a facile anodization method in a novel electrolyte system (an ethylene glycol solution of H2C2O4/NH4F) followed by thermal annealing at a low temperature. The SnO2 nanostructures thus obtained feature highly porous nanosheets with mesoporous pores well below 10 nm, enabling a remarkably high surface area of 202.8 m2/g which represents one of the highest values reported to date on SnO2 nanostructures. The formation of this novel type of SnO2 nanostructures is ascribed to an interesting self-assembly mechanism of the anodic tin oxalate, which was found to be heavily impacted by the anodization voltage and water content in the electrolyte. The electrochemical measurements of the mesoporous SnO2 nanostructures indicate their promising applications as lithium-ion battery and supercapacitor electrode materials.

Intracellular Delivery: Diamond-Nanoneedle-Array-Facilitated Intracellular Delivery and the Potential Influence on Cell Physiology (Adv. Healthcare Mater. 10/2016).

G. Zhu, W. Zhang, X. Chen, and co-workers show on page 1157 that diamond needle arrays can efficiently deliver biomolecules into living cells. The study paves the way to a wide application of the nanonneedle treatment by systematically investigating the influence of the treatment on metabolic signal pathways.

Bactericidal activity of biomimetic diamond nanocone surfaces.

The formation of biofilms on implant surfaces and the subsequent development of medical device-associated infections are difficult to resolve and can cause considerable morbidity to the patient. Over the past decade, there has been growing recognition that physical cues, such as surface topography, can regulate biological responses and possess bactericidal activity. In this study, diamond nanocone-patterned surfaces, representing biomimetic analogs of the naturally bactericidal cicada fly wing, were fabricated using microwave plasma chemical vapor deposition, followed by bias-assisted reactive ion etching. Two structurally distinct nanocone surfaces were produced, characterized, and the bactericidal ability examined. The sharp diamond nanocone features were found to have bactericidal capabilities with the surface possessing the more varying cone dimension, nonuniform array, and decreased density, showing enhanced bactericidal ability over the more uniform, highly dense nanocone surface. Future research will focus on using the fabrication process to tailor surface nanotopographies on clinically relevant materials that promote both effective killing of a broader range of microorganisms and the desired mammalian cell response. This study serves to introduce a technology that may launch a new and innovative direction in the design of biomaterials with capacity to reduce the risk of medical device-associated infections.

Diamond-Nanoneedle-Array-Facilitated Intracellular Delivery and the Potential Influence on Cell Physiology.

Vertical arrays of nanostructures can provide access to the cell cytoplasma and probe intracellular molecules. Here, the simple combination of diamond nanoneedle arrays with centrifugation-induced supergravity is shown to efficiently deliver drugs and biomaterials into the cytosol within several minutes, negotiating the endocytososomal system. The potential influence of the technique on cell metabolism is thoroughly studied. By detecting the phosphorylated histone variant H2AX (pH2AX) in the nucleus, it is proved that the operating process will not lead to DNA double-strand breaks. However, the mechanical disruption can temporarily improve the permeability of the cell membranes. Nanoneedle treatment affects cell metabolism at multiple points. The treatment can slightly elevate the apoptotic signal in A549 cells and can significantly increase the production of reactive oxygen species (ROS) in cells, particularly if combined with anticancer drugs. Meanwhile, the activity of cytosolic glucose 6-phosphate dehydrogenase (G6PD) is also raised to counterbalance the elevated ROS content. A detected depolarization of the mitochondrial membrane potential suggests mitochondrial involvement in the intracellular redox reactions and cell apoptosis which are induced by diamond nanoneedle treatment. Overall this study provides a novel understanding on the intracellular delivery mediated by nanoneedles, especially the impact on cell physiology.

Electrochemical Energy Storage Application and Degradation Analysis of Carbon-Coated Hierarchical NiCo2S4 Core-Shell Nanowire Arrays Grown Directly on Graphene/Nickel Foam.

We developed a new electrode comprising thin carbon layer coated hierarchical NiCo2S4 core-shell nanowire arrays (NiCo2S4@C CSNAs) on graphene/Ni foam (Ni@G) substrates. The electrode showed outstanding electrochemical characteristics including a high specific capacitance of 253 mAh g(-1) at 3 A g(-1), high rate capability of 163 mAh g(-1) at 50 A g(-1) (~64.4% of that at 3 A g(-1)), and long-term cycling stability with a capacity retention of 93.9% after 5000 cycles. Comparative studies on the degradation of hierarchical NiCo2S4 CSNA electrodes with and without carbon coatings revealed that the morphology pulverization, structural separation at core/shell interface, and irretrievably chemical composition change of NiCo2S4 CSNAs electrode are major factors that deteriorate the electrochemical performance of the electrodes without carbon coating. The favorable roles of carbon coatings on hierarchical NiCo2S4 CSNAs were further clarified: (1) serving as a physical buffering layer that suppresses the structural breakdown; (2) retarding the chemical composition conversion of the NiCo2S4 CSNAs; and (3) providing extra path for charge transition in addition to the NiCo2S4 core nanowires. Understanding of the degradation mechanisms and the significance of the surface carbon coatings would provide useful guidelines for the design of new electrode materials for high-performance electrochemical devices.

Dendritic heterojunction nanowire arrays for high-performance supercapacitors.

Herein, we designed and synthesized for the first time a series of 3D dendritic heterojunction arrays on Ni foam substrates, with NiCo2S4 nanowires as cores and NiCo2O4, NiO, Co3O4, and MnO2 nanowires as branches, and studied systematically their electrochemical performance in comparison with their counterparts in core/shell structure. Attributed to the following reasons: (1) both core and branch are pseudocapacitively active materials, (2) the special dendritic structure with considerable inter-nanowire space enables easy access of electrolyte to the core and branch surfaces, and (3) the highly conductive NiCo2S4 nanowire cores provide "superhighways" for charge transition, NiCo2S4-cored dendritic heterojunction electrodes synergistically lead to ultrahigh specific capacitance, good rate capability, and excellent cycling life. These results of core/branch dentritic heterojunction arrays is universially superior to their core/shell conterparts, thus this is a significant improvement of overall electrochemical performance.