Nanostructured Architectures Research Articles

Three-Dimensional Nanostructured Architectures Enable Efficient Neural Differentiation of Mesenchymal Stem Cells via Mechanotransduction.

Cell morphology and geometry affect cellular processes such as stem cell differentiation, suggesting that these parameters serve as fundamental regulators of biological processes within the cell. Hierarchical architectures featuring micro- and nanotopographical features therefore offer programmable systems for stem cell differentiation. However, a limited number of studies have explored the effects of hierarchical architectures due to the complexity of fabricating systems with rationally tunable micro- and nanostructuring. Here, we report three-dimensional (3D) nanostructured microarchitectures that efficiently regulate the fate of human mesenchymal stem cells (hMSCs). These nanostructured architectures strongly promote cell alignment andefficient neurogenic differentiation where over 85% of hMSCs express microtubule-associated protein 2 (MAP2), a mature neural marker, after 7 days of culture on the nanostructured surface. Remarkably, we found that the surface morphology of nanostructured surface is a key factor that promotes neurogenesis and that highly spiky structures promote more efficient neuronal differentiation. Immunostaining and gene expression profiling revealed significant upregulation of neuronal markers compared to unpatterned surfaces. These findings suggest that the 3D nanostructured microarchitectures can play a critical role in defining stem cell behavior.

Recent advances in pseudocapacitor electrode materials: Transition metal oxides and nitrides

Abstract Faraday pseudocapacitors take both advantages of secondary battery with high energy density and supercapacitors with high power density, and electrode material is the key to determine the performance of Faraday pseudocapacitors. Transition metal oxides and nitrides, as the two main kinds of pseudocapacitor electrode materials, can enhance energy density while maintaining high power capability. Recent advances in designing nanostructured architectures and preparing composites with high specific surface areas based on transition metal oxides and nitrides, including ruthenium oxides, nickel oxides, manganese oxides, vanadium oxides, cobalt oxides, iridium oxides, titanium nitrides, vanadium nitrides, molybdenum nitrides and niobium nitrides, are addressed, which would provide important significances for deep researches on pseudocapacitor electrode materials.

Carbon-Based Photocathode Materials for Solar Hydrogen Production.

Hydrogen is considered a promising environmentally friendly energy carrier for replacing traditional fossil fuels. In this context, photoelectrochemical cells effectively convert solar energy directly to H2 fuel by water photoelectrolysis, thereby monolitically combining the functions of both light harvesting and electrolysis. In such devices, photocathodes and photoanodes carry out the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. Here, the focus is on photocathodes for HER, traditionally based on metal oxides, III-V group and II-VI group semiconductors, silicon, and copper-based chalcogenides as photoactive material. Recently, carbon-based materials have emerged as reliable alternatives to the aforementioned materials. A perspective on carbon-based photocathodes is provided here, critically analyzing recent research progress and outlining the major guidelines for the development of efficient and stable photocathode architectures. In particular, the functional role of charge-selective and protective layers, which enhance both the efficiency and the durability of the photocathodes, is discussed. An in-depth evaluation of the state-of-the-art fabrication of photocathodes through scalable, high-troughput, cost-effective methods is presented. The major aspects on the development of light-trapping nanostructured architectures are also addressed. Finally, the key challenges on future research directions in terms of potential performance and manufacturability of photocathodes are analyzed.

Osteogenesis by foamed and 3D-printed nanostructured calcium phosphate scaffolds: Effect of pore architecture

There is an urgent need of synthetic bone grafts with enhanced osteogenic capacity. This can be achieved by combining biomaterials with exogenous growth factors, which however can have numerous undesired side effects, but also by tuning the intrinsic biomaterial properties. In a previous study, we showed the synergistic effect of nanostructure and pore architecture of biomimetic calcium deficient hydroxyapatite (CDHA) scaffolds in enhancing osteoinduction, i.e. fostering the differentiation of mesenchymal stem cells to bone forming cells. This was demonstrated by assessing bone formation after implanting the scaffolds intramuscularly. The present study goes one step forward, since it analyzes the effect of the geometrical features of the same CDHA scaffolds, obtained either by 3D-printing or by foaming, on the osteogenic potential and resorption behaviour in a bony environment. After 6 and 12 weeks of intraosseous implantation, both bone formation and material degradation had been drastically affected by the macropore architecture of the scaffolds. Whereas nanostructured CDHA was shown to be highly osteoconductive both in the robocast and foamed scaffolds, a superior osteogenic capacity was observed in the foamed scaffolds, which was associated with their higher intrinsic osteoinductive potential. Moreover, they showed a significantly higher cell-mediated degradation than the robocast constructs, with a simultaneous and progressive replacement of the scaffold by new bone. In conclusion, these results demonstrate that the control of macropore architecture is a crucial parameter in the design of synthetic bone grafts, which allows fostering both material degradation and new bone formation.Statement of Significance3D-printing technologies open new perspectives for the design of patient-specific bone grafts, since they allow customizing the external shape together with the internal architecture of implants. In this respect, it is important to design the appropriate pore geometry to maximize the bone healing capacity of these implants. The present study analyses the effect of pore architecture of nanostructured hydroxyapatite scaffolds, obtained either by 3D-printing or foaming, on the osteogenic potential and scaffold resorption in an in vivo model. While nanostructured hydroxyapatite showed excellent osteoconductive properties irrespective of pore geometry, we demonstrated that the spherical, concave macropores of foamed scaffolds significantly promoted both material resorption and bone regeneration compared to the 3D-printed scaffolds with orthogonal-patterned struts and therefore prismatic, convex macropores.

Integrated Hierarchical Carbon Flake Arrays with Hollow P‐Doped CoSe2 Nanoclusters as an Advanced Bifunctional Catalyst for Zn–Air Batteries

AbstractHierarchical nanostructured architectures are demonstrated as an effective approach to develop highly active and bifunctional electrocatalysts, which are urgently required for efficient rechargeable metal–air batteries. Herein, a mesoporous hierarchical flake arrays (FAs) structure grown on flexible carbon cloth, integrated with the microsized nitrogen‐doped carbon (N‐doped C) FAs, nanoscaled P‐doped CoSe2 hollow clusters and atomic‐level P‐doping (P‐CoSe2/N‐C FAs) is described. The P‐CoSe2/N‐C FAs thus developed exhibit a reduced overpotential (≈230 mV at 10 mA cm−2) toward oxygen evolution reaction (OER) and large half‐wave potential (0.87 V) for oxygen reduction reactions. The excellent bifunctional electrocatalytic performance is ascribed to the synergy among the hierarchical flake arrays controlled at both micro‐ and nanoscales, and atomic‐level P‐doping. Density functional theory calculations confirm that the free energy for the potential‐limiting step is reduced by P‐doping for OER. An all‐solid‐state zinc–air battery made of the P‐CoSe2/N‐C FAs as the air‐cathode presents excellent cycling stability and mechanical flexibility, demonstrating the great potential of the hierarchical P‐CoSe2/N‐C FAs for advanced bifunctional electrocatalysis.

Morphology Engineering of Au/(PdAg alloy) Nanostructures for Enhanced Electrocatalytic Ethanol Oxidation

AbstractNoble metal nanostructures are promising electrocatalysts with their performance determined by their size, shape, and architecture. This study reports the facile preparation of Au/(PdAg alloy) electrocatalysts with diverse architectures, including nanodumbbells, yolk/shell nanoframes, and yolk/shell nanoboxes, from Au nanorod core/Ag shell bimetallic nanostructures. The fine tuning of the nanostructure architecture is realized by combining galvanic replacement reaction, etching/growth, Ostwald ripening, and coreduction processes. The adding sequence of surfactants and Pd precursors, and the Ag shell thicknesses of the starting core/shell nanocrystals, determine the growth routines and therefore the architectures of the obtained Au/(PdAg alloy) nanostructures. Electrocatalytic performances of all Au/(PdAg alloy) nanostructures toward ethanol oxidation reaction (EOR) in alkaline are examined. Compared with the commercial Pd/C electrocatalyst, the nanodumbbells (Au19Pd19Ag62) display 6.3 times higher specific activity and 4.25 times higher mass activity. The nanoframes (Au14Pd14Ag72) are superior as well, with their specific and mass activities 4.4 and 5.5 times higher than those of the Pd/C electrocatalyst, respectively. The nanoboxes also show slight improvement in electrocatalysis. Moreover, the nanodumbbells exhibit greatly improved stability toward EOR in comparison to the Pd/C electrocatalyst. These results can enrich the manufacturing techniques of noble metal nanostructure catalysts and promote their development for fuel cell applications.

Copper chalcogenide thermoelectric materials

Cu-based chalcogenides have received increasing attention as promising thermoelectric materials due to their high efficiency, tunable transport properties, high elemental abundance and low toxicity. In this review, we summarize the recent research progress on this large family compounds covering diamond-like chalcogenides and liquid-like Cu2X (X=S, Se, Te) binary compounds as well as their multinary derivatives. These materials have the general features of two sublattices to decouple electron and phonon transport properties. On the one hand, the complex crystal structure and the disordered or even liquid-like sublattice bring about an intrinsically low lattice thermal conductivity. On the other hand, the rigid sublattice constitutes the charge-transport network, maintaining a decent electrical performance. For specific material systems, we demonstrate their unique structural features and outline the structure-performance correlation. Various design strategies including doping, alloying, band engineering and nanostructure architecture, covering nearly all the material scale, are also presented. Finally, the potential of the application of Cu-based chalcogenides as high-performance thermoelectric materials is briefly discussed from material design to device development.

Capsules as ion-selective optodes – Maximizing sensitivity of ion-selective optodes

Novel type nanostructural optodes in the form of capsules are introduced. The unique feature of the proposed sensor format is presence of a liquid core within the polymeric shell, this core is loaded with classical optode system containing ion-selective receptor and optical transducer. It is shown that depending on the nanostructure architecture different responses are induced. On the contrary to the typical systems using nano- or microspheres, soft capsules with liquid core offer unique high optical signal sensitivity due to unhindered transport of ions within the bulk of the probe. The sensitivity range can be easily affected by changing the amount of ionophore present in the system.

Atomic Layer Deposition of Bismuth Vanadate Photoanodes

Bismuth vanadate (BVO) has been widely studied as one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting, owing to a bandgap of 2.4 eV and favorable band positions for water oxidation. However, while BVO has the potential for high anodic photocurrents, it is often limited by electron-hole separation, charge transport, and water oxidation kinetics, requiring development of nanostructured electrode architectures to optimize performance.1 Here we demonstrate a new method for fabricating tunable BVO photoanodes deposited by atomic layer deposition (ALD). ALD is a gas-phase thin film deposition technique with sub-nanometer thickness control, programmable film stoichiometry, and conformal coverage of 3-D nanostructured templates, enabling rational design of electrode architectures. We present the first deposition of ALD BVO using Bi(OCMe2iPr)3 as the bismuth source, vanadium(V)oxytriisopropoxide as the vanadium source, and water as the oxidant. The choice of this recently developed Bi precursor provides full control of Bi:V stoichiometry in contrast to the use of earlier Bi precursors such as triphenylbismuth3, while also providing a per cycle growth rate that is more than three times higher than previous reports. The BVO films were deposited as a nanolaminate of binary bismuth and vanadium oxides. The films were post-annealed to achieve the photoactive monoclinic BiVO4 phase. Film composition and photocurrent were investigated as a function of deposition pulse ratio and film thickness. The photoactivity of planar ALD BVO was measured in a three-electrode cell under simulated AM1.5G illumination. Sulfite oxidation was used to optimize the BVO deposition conditions independent of co-catalyst performance. We achieved the highest reported photocurrent to date for ALD photoanodes. Using a planar electrode with a 40nm thick BVO film, a photocurrent of > 2.6 mA/cm2 at 1.23 V vs. RHE was demonstrated for sulfite oxidation and a photocurrent of > 1.1 mA/cm2 at 1.23 V vs. RHE was demonstrated for water oxidation using an un-optimized cobalt oxide co-catalyst. ALD provides conformal coverage of high aspect ratio structures. The development of an ALD process for BVO enables core-shell architectures that help address the charge transport and carrier separation challenges by decoupling carrier diffusion and light absorption lengths. To demonstrate this benefit, BVO was deposited on mesoporous tin oxide (ITO) substrates to form 3-D electrode architectures with tunable absorption and charge extraction properties. The photoresponse was enhanced for both sulfite and water oxidation under illumination, demonstrating the power of ALD to improve light absorption and charge extraction in 3-D nanostructured electrode architectures. (1) Sivula, K.; van de Krol, R. Semiconducting Materials for Photoelectrochemical Energy Conversion. Nat. Rev. Mater. 2016, 1 (2), 15010. (2) Liu, C.; Dasgupta, N. P.; Yang, P. Semiconductor Nanowires for Artificial Photosynthesis. Chem. Mater. 2014, 26 (1), 415–422. (3) Stefik, M. Atomic Layer Deposition of Bismuth Vanadates for Solar Energy Materials. ChemSusChem 2016, 9 (13), 1727–1735.

Strategies to tailor the architecture of dual Ag/Fe-oxide nano-heterocrystals—interfacial and morphology effects on the magnetic behavior

Bifunctional nanostructured architectures have shown appealing properties, since a single entity can combine the diverse properties of its individual constituents. Particularly, by growing Fe-oxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be combined in a single particle. Beyond the multifunctionality of this system, there are several properties that emerge from intrinsic factors, such as: interface and/or morphology. In this study, we present the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like. In addition, the magnetization behavior of these hybrid nano-heterocrystals is investigated and discussed. These nanomaterials were built by a seed assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point, using the same batch of silver nanoparticles with a mean size of 6 nm as seeds, and tuning the electron-donor capacity of the reaction environment at the thermal decomposition of the iron precursor. Ag/Fe3O4 heterocrystals with dimer and flower-like morphologies were obtained. The synthesis protocols for generating these types of nanomaterials are discussed step-by-step. Structural and morphological properties were determined by transmission electron microscopy, x-ray diffraction and x-ray absorption fine structure. DC magnetization results suggest that the silver/magnetite coupling generates an increase of the blocking temperature in comparison to those obtained from pure magnetite. This behavior could be linked to a possible increase in the magnetic anisotropy produced by an additional disorder at the Ag–Fe3O4 interface. The higher interface area of the Ag/Fe3O4 heterocrystals with flower-like architecture leads to a higher blocking temperature and a stronger magnetic anisotropy. These results are supported by AC susceptibility data.

Improving pore-filling in TiO2 nanorods and nanotubes scaffolds for perovskite solar cells via methylamine gas healing

High performance in perovskite solar cells is often achieved using compact metal oxide layers or their mesoporous analogues. One dimensional scaffold materials such as nanorods or nanotubes are also employed in order to improve charge collection, however, perovskite pore-filling in these nanostructures is rather low. Herein, we introduce a method to more efficiently fill the pores in two most common nanostructure architectures namely, TiO2 nanorods and nanotubes. The method employs recrystallization of perovskite films in a methylamine rich environment– the so called perovskite healing. Whereas the scanning electron microscopy imaging revealed an improved pore-filling and formation of large perovskite grains upon healing, the complementary photoluminescence and electrical characterizations revealed improved charge transfer in the healed films than their pristine rivals. We also report a notable improvement in photoconversion efficiency and a better stability under continuous light soaking in the healed perovskite films.

Porous nanostructured GdFeO3 perovskite oxides and their gas response performance to NOx

Gas sensing characteristics of rare-earth-based orthoferrite (GdFeO3) mesoporous nanostructures were prepared by a facile one-step hydrothermal process. The structural analyses of the obtained materials showed sphere, leaf and flower-like nanostructured architectures. Further, the chemiresistive gas-response properties of the GdFeO3 nanostructure were investigated with various combustible gases, such as nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), ammonia (NH3), hydrogen sulfide (H2S), formaldehyde (HCHO), ethanol (C2H5OH) and gasoline, at different operating temperatures. The sphere-like GdFeO3 nanostructure shows a significantly high resistance variation to NO compared with the other architectures, exhibits a high response (91%) when exposed to 100 ppm NO, and detects a level as low as 2 ppm (7%) at an optimum operating temperature of 140 °C. The GdFeO3 nanostructure shows an excellent stability and repeatability after successive repeated cycles with a fast response and recovery time when exposed to 100 ppm NO gas. The superior response and excellent selectivity of the perovskite GdFeO3 nanostructure are due to its higher catalytic activity, large surface area, oxygen deficiency, mesoporosity, and peculiar morphology. The response mechanism of NO on the GdFeO3 nanostructured surface is also discussed in detail.

3D Architectures of Cox P Using Silk Fibroin Scaffolds: An Active and Stable Electrocatalyst for Hydrogen Generation in Acidic and Alkaline Media.

Developing nonprecious, highly active, and stable catalysts is essential for efficient electrocatalytic hydrogen evolution reaction in water splitting. In this study, the facile synthesis of a 3D flower-like Cox P/carbon architecture is proposed composed of an assembly of nanosheets interconnected by silk fibroin that acts as 3D scaffolds and a carbon source. This unique 3D architecture coupled with a carbon matrix enhances catalytic activity by exposing more active sites and increasing charge transport. The flower-like Cox P/carbon can facilitate a lower overpotential, Tafel slope, charge transfer resistance, and a higher electrochemically active surface than carbon-free and silk-free Cox P. The nanostructured architecture exhibits excellent catalytic performance with low overpotentials of 109 and 121 mV at 10 mA cm-2 and Tafel slopes of 55 and 62 mV dec-1 in acidic and alkaline media, respectively. Furthermore, it minimally degrades the overpotential and current density after long-term stability tests 10 000 cyclic voltammetry cycles and a chronoamperometric test over 40 h, respectively, in acidic media, which confirms the high durability and stability of the flower-like Cox P/carbon.

(Invited) Designing Hybrid Nanostructures for Enhancing Photon Harvest in Photocatalysis

Harvesting photons at longer wavelengths in the visible and near infrared (NIR) ranges represents an attractive approach to improve the power conversion efficiency of photocatalysis and photovoltaics. Plasmonic and upconverting nanostructures are promising in boosting and broadening photon harvesting and have been recently explored for enhancing the efficiency of solar cells and photocatalysis. Herein, I will present some of our most recent development in plasmonic and upconverting nanostructures and their applications in photocatalysis and solar cells and [1-5]. One example is shown in Figure 1. It illustrates the synthesis of novel, plasmonic Au nanoparticle decorated NaYF4:Yb3+, Er3+, Tm3+ (denoted as NYF) – core @ porous-TiO2-shell microspheres, which can harvest solar photons over a wide spectral range from ultraviolet to NIR for efficient photocatalysis, significantly better than the benchmark Degussa P25 [1]. The enhanced activity is attributed to synergistic effects from nanocomponents arranged into the nanostructured architecture in such a way that favours the efficient charge/energy transfer among nanocomponents and largely reduced charge recombination. Recently, an even simple method was developed for combing Au nanoparticles and NYF microspheres with two-dimensional graphitic C3N4 (g-C3N4) nanosheets (Au-NYF/g-C3N4) [2]. The simple one-step synthesis of NYF in the presence of g-C3N4, which was not previously reported in the literature, leads to both high NYF yield and high coupling efficiency between NYF and g-C3N4. The Au-NYF/g-C3N4 structure exhibits excellent stability, wide photoresponse from the ultraviolet, to visible and NIR regions, and prominently enhanced photocatalytic activities compared with the plain g-C3N4 sample in the degradation of methyl orange. Very recently, by constructing a complete comparative framework, based on the similar catalysts having alloy synergistic effect or plasmonic effect, or both, we compared the plasmonic and synergistic effects. It helps answers an important, yet not previously addressed question: synergistic and plasmonic effects, which can make more important contribution to photocatalysis? On the other hand, quantum dots are also promising for photon harvesting because of their size-tunable bandgaps, even in the NIR range. I may briefly introduce the use of quantum dots in photocatalysis and solar cells [6].

Thin Film Ion Transport and Morphology of Poly(ethylene oxide) and Lithium Salt Mixtures

With the ability to tune ion transport and mechanical properties, polymer electrolytes have demonstrated promise as solid electrolyte materials for lithium-metal anode batteries. In particular, polyethylene oxide (PEO) and lithium salt mixtures have been the most widely studied polymer electrolyte system.1 Moreover, block copolymer electrolytes (e.g. block polystyrene-block-PEO) have yielded more advanced nanostructured architectures with increased mechanical robustness and efficient ion transport.2 Driven by their potential applications, enormous efforts have been devoted to elucidating mechanisms for ion transport and the formation of lithium dendrites. However, majority of reported studies have focused only on thick bulk samples (100’s of microns thick films). This is significant to note as interfaces3 play a critical role in the performance of batteries, but researchers have mostly inferred interfacial effects using bulk properties. As a consequence, we focus on investigating polymer electrolytes in the (ultra)-thin film regime (5-500 nm), which can be used as a platform to directly study fundamental interfacial effects. In addition, structural characteristics limiting charge transport in polymer electrolytes such as domain orientation and interconnectivity can be more easily probed using thin films.4 Ultimately, investigating polymer electrolyte in the context of thin films will lead to better fundamental understanding of charge transport in polymer electrolytes and the charge transfer limitations at the electrode/electrolyte interfaces. Here, we report on our initial study on charge transport and morphology of a model polymer electrolyte system (mixtures of PEO and LiTFSI, lithium bis(trifluoromethanesulfonyl)imide)) in the thin film regime (<200 nm). We specifically probe the structure-property relationships as function of salt concentration, temperature, and film thickness. We utilized synchrotron-based grazing-incidence wide angle X-ray scattering (GIWAXS) to probe the effects of salt concentration and film thickness on the semicrystalline morphology. At room temperature, the PEO crystallites become more ordered, but the relative degree of crystallinity (rDoC) of PEO gradually decreases with increasing salt concentration. The film becomes completely amorphous at the highest salt concentration r = 0.15, where r is the molar ratio of lithium ions to ethylene oxide repeat units. This trend is consistent with the established theories that adding Li salt disrupts the crystallite structure of PEO and reduces the overall degree of crystallinity. Ionic transport measurements were performed using a.c. impedance spectroscopy on PEO-LiTFSI thin films on custom-designed interdigitated electrode devices (IDE). Above the melting point of PEO (≈ º60 C), the temperature dependence of ionic conductivity of all samples can be well-described using Vogel-Tammann-Fulcher (VTF) model. This suggests that segmental motion of PEO chains facilitate ionic transport in PEO-LiTFSI thin films. Ionic conductivity is found to increase with increasing salt concentration at first but decreases at high salt concentration. This is likely due to the reduced dissociation rate and increased glass transition temperature at high concentration, similar to the behavior of bulk samples.1,2 Our results have demonstrated the first successful fabrication and characterization of ionic transport in PEO-Li salt thin films. This provides an important step toward exploiting thin film configuration to reveal many morphological and interfacial effects on ion conduction mechanism of polymer electrolytes and will be subject of investigations in our future studies. REFERENCES S. Lascaud et al., Macromolecules, 27, 7469–7477 (1994).D. T. Hallinan and N. P. Balsara, Annu. Rev. Mater. Res., 43, 503–525 (2013) http://www.annualreviews.org/doi/abs/10.1146/annurev-matsci-071312-121705.E. Peled and S. Menkin, J. Electrochem. Soc., 164, A1703–A1719 (2017).Y. Kambe, C. G. Arges, S. N. Patel, M. P. Stoykovich, and P. F. Nealey, ECS Interface (2017).

Electrochemical biointerfaces based on carbon nanotubes-mesoporous silica hybrid material: Bioelectrocatalysis of hemoglobin and biosensing applications

We are reporting a novel biosensing platform based on a hybrid nanomaterial that combines the advantages of Nafion-coated multiwalled carbon nanotubes (MWCNTs) and mesoporous silica MCM41 nanoparticles functionalized with hemoglobin (Hb). MWCNTs-MCM41-Hb hybrid bioconjugate was characterized by scanning electron microscopy (SEM), UV–vis spectroscopy and electrochemical techniques after deposition at glassy carbon electrodes (GCE). The combination of the high surface area, biocompatibility and protein loading capacity of MCM41 nanoparticles and the high surface area and catalytic properties of MWCNTs allowed the direct electron transfer (DET) between Hb and the electrode surface. The electron transfer rate constant (k) and the surface coverage of electroactive Hb (ΓHb) were 5.2 s−1 and 4.7 × 10−10 mol cm−2, respectively. The GCE modified with the nanostructured architecture (GCE/MWCNTs-MCM41-Hb) was successfully used as a third-generation biosensor for the highly sensitive and selective quantification of nitrite (NO2-) and trichloroacetic acid (TCA) by taking advantage of the excellent biocatalytic activity of Hb and the efficient direct charge transfer of the heme group.

High Mass Loading MnO2 with Hierarchical Nanostructures for Supercapacitors.

Metal oxides have attracted renewed interest as promising electrode materials for high energy density supercapacitors. However, the electrochemical performance of metal oxide materials deteriorates significantly with the increase of mass loading due to their moderate electronic and ionic conductivities. This limits their practical energy. Herein, we perform a morphology and phase-controlled electrodeposition of MnO2 with ultrahigh mass loading of 10 mg cm-2 on a carbon cloth substrate to achieve high overall capacitance without sacrificing the electrochemical performance. Under optimum conditions, a hierarchical nanostructured architecture was constructed by interconnection of primary two-dimensional ε-MnO2 nanosheets and secondary one-dimensional α-MnO2 nanorod arrays. The specific hetero-nanostructures ensure facile ionic and electric transport in the entire electrode and maintain the structure stability during cycling. The hierarchically structured MnO2 electrode with high mass loading yields an outstanding areal capacitance of 3.04 F cm-2 (or a specific capacitance of 304 F g-1) at 3 mA cm-2 and an excellent rate capability comparable to those of low mass loading MnO2 electrodes. Finally, the aqueous and all-solid asymmetric supercapacitors (ASCs) assembled with our MnO2 cathode exhibit extremely high volumetric energy densities (8.3 mWh cm-3 at the power density of 0.28 W cm-3 for aqueous ASC and 8.0 mWh cm-3 at 0.65 W cm-3 for all-solid ASC), superior to most state-of-the-art supercapacitors.

A Three‐Dimensional Architecture for Hydrogen‐Evolving, Host/Guest, Hybrid Organic/Inorganic Photocathodes Based on Nanolamellar MoO3 Scaffolds

AbstractThis work reports on the synthesis and characterization of a three‐dimensional hybrid organic/inorganic photocathode host/guest architecture based on nanolamellar MoO3 scaffolds, where light absorption and charge collection are orthogonal and active surface area is maximized. The proposed nanostructured architecture combines optimized optoelectrical properties and structural–morphological features, resulting in a photocurrent density of 2 mA cm−2 at +0.18 VRHE and an onset potential of +0.65 VRHE. The nanostructured host scaffold presents efficient photon trapping and increased surface area to accommodate the thin organic absorber layer. The ensuing absorption/collection decoupling significantly improves the photoelectrochemical performance, especially when compared to the flat‐stack reference device, suggesting that out‐of‐plane film nanostructuration may provide future opportunity for the design of efficient photoelectrodes.

Surface tension driven aggregation of organic nanowires via lab in a droplet.

Directing the architecture of complex organic nanostructures is desirable and still remains a challenge in areas of materials science due to their structure-dependent collective optoelectronic properties. Herein, we demonstrate a simple and versatile solution strategy that allows surface tension to drive low-dimensional nanostructures to aggregate into complex structures via a lab in a droplet technique. By selecting a suitable combination of a solvent and an anti-solvent with controllable surface tension difference, the droplets can be automatically cracked into micro-droplets, which provides an aggregation force directed toward the centre of the droplet to drive the low-dimensional building blocks to form the special aggregations during the self-assembly process. This synthetic strategy has been shown to be universal for organic materials, which is beneficial for further optimizing the optoelectronic properties. These results contribute to gaining an insightful understanding on the detailed growth mechanism of complex organic nanostructures and greatly promoting the development of organic nanophotonics.

Progress of Cu2O/ZnO oxide heterojunction solar cells

Recent progress of low cost Cu2O/ZnO hetero-junction solar cells is reviewed in this paper. The Cu2O used as an absorbing layer in photovoltaic cells is a direct bandgap semiconductor, exhibiting natural p-type conductivity. The source material of Cu2O-based solar cells is abundant and environmentally friendly. The main device structure of Cu2O/ZnO solar cells presents a planar and nano-wire/nano-rod configuration. The nanostructured Cu2O architecture conduces to charge collection in the device. The planar Cu2O absorbing layer with large grain size, achieved through the thermal oxidation of Cu sheets, exhibits high quality of the Cu2O/ZnO solar cells. The interface buffer layer (like i-ZnO, a-ZTO and Ga2O3) and back surface field (BSF, such as p+-Cu2O) can effectively improve energy band alignment match and increase carrier transport. The Cu2O paired with a 10-nm-thick Ga2O3 layer provides a nearly ideal conduction band offset and thus reduces the interface recombination. The Ga2O3 is a highly suitable buffer layer for enhancing the Voc (Voc value reaches 1.2 V) and conversion efficiency of Cu2O-based solar cells. The p+-Cu2O like N-doped Cu2O (Cu2O:N) and Na-doped Cu2O (Cu2O:Na) can reduce back-contact resistance and create an electron-reflecting back surface field in the Cu2O based solar cells. When a p-type Cu2O: Na acts as an absorbing layer and a zinc-germanium-oxide (Zn1-xGex-O) thin film is used as an n-type layer (buffer), Cu2O hetero-junction solar cell with the device structure MgF2/Al-doped ZnO (ZnO:Al)/Zn0.38Ge0.62-O/Cu2O:Na shows an efficiency of 8.1%. The oxide hetero-junction solar cells have a great potential application in the future photovoltaic field.