Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn-Air Battery.

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn-air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn-air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63 V and good electrochemical durability for 83 h at a current density of 10 mA cm-2 in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn-air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.

Ultrathin nickel hydroxide on carbon coated 3D-porous copper structures for high performance supercapacitors.

An ultrathin nickel hydroxide layer electrodeposited on a carbon-coated three-dimensional porous copper structure (3D-C/Cu) is suggested as an additive and binder-free conductive electrode with short electron path distances, large electrochemical active sites, and improved structural stability, for high performance supercapacitors. The 3D-porous copper structure (3D-Cu) provides high electrical conductivity and facilitates electron transport between the Ni(OH)2 active materials and the current collector of the Ni-plate. A carbon coating was applied to the 3D-Cu to prevent the oxidation of Cu, without degrading the electron transport behavior of the 3D-Cu. The 3D-Ni(OH)2/C/Cu exhibited a high specific capacitance of 1860 F g-1 at 1 A g-1, and good cycling performance, with an 86.5% capacitance retention after 10 000 cycles. When tested in a two-electrode system, an asymmetric supercapacitor exhibited an energy density of 147.9 W h kg-1 and a power density of 37.0 kW kg-1. These results open a new area of ultrahigh-performance supercapacitors, supported by 3D-Cu electrodes.

Hierarchical metal/semiconductor nanostructure for efficient water splitting.

A hierarchically patterned metal/semiconductor (gold nanoparticles/ZnO nanowires) nanostructure with maximized photon trapping effects is fabricated via interference lithography (IL) for plasmon enhanced photo-electrochemical water splitting in the visible region of light. Compared with unpatterned (plain) gold nanoparticles-coated ZnO NWs (Au NPs/ZnO NWs), the hierarchically patterned Au NPs/ZnO NWs hybrid structures demonstrate higher and wider absorption bands of light leading to increased surface enhanced Raman scattering due to the light trapping effects achieved by the combination of two different nanostructure dimensions; furthermore, pronounced plasmonic enhancement of water splitting is verified in the hierarchically patterned Au NPs/ZnO NWs structures in the visible region. The excellent performance of the hierarchically patterned Au NPs/ZnO NWs indicates that the combination of pre-determined two different dimensions has great potential for application in solar energy conversion, light emitting diodes, as well as SERS substrates and photoelectrodes for water splitting.

Three-dimensional nano-foam of few-layer graphene grown by CVD for DSSC.

We report a robust and direct route to fabricate a three-dimensional nano-foam of few-layer graphene (3D-NFG) with large area coverage via a chemical vapor deposition (CVD) technique. Pyrolysis of polymer/nickel precursor film under a hydrogen environment, simply prepared by spin-coating, leads to the creation of nano-foam in the film and the reduction process of nickel ions. Carbonized-C and the nickel nano-frame formed from the pyrolysis are used as a solid carbon source and as a catalyst for the growth of graphene under CVD conditions, respectively. We investigate the use of 3D-NFG, with the advantage of large surface area and high conductivity, as an alternative to the Pt counter electrode material in dye sensitized solar cells. The excellent properties of 3D-NFG, fabricated in this simple and direct manner, suggest a great potential for interconnected graphene networks in electronic devices and photocatalytic sensors as well as in energy-related materials.

Bi-functional 3D-NiCu-Double Hydroxide@Partially Etched 3D-NiCu Catalysts for Non-Enzymatic Glucose Detection and the Hydrogen Evolution Reaction.

Hydrogen production, which is in the spotlight as a promising eco-friendly fuel, and the need for inexpensive and accurate electronic devices in the biochemistry field are important emerging technologies. However, the use of electrocatalytic devices based on expensive noble metal catalysts limits commercial applications. In recent years, to improve performance and reduce cost, electrocatalysts based on cheaper copper or nickel materials have been investigated for the non-enzymatic glucose oxidation reaction (GOR) and hydrogen evolution reaction (HER). In this study, we demonstrate a facile and easy electrochemical method of forming a cheap nickel copper double hydroxide (NiCu-DH) electrocatalyst deposited onto a three-dimensional (3D) CuNi current collector, which can effectively handle two different reactions due to its high activity for both the GOR and the HER. The as-prepared electrode has a structure comprising abundant 3D-interconnected porous dendritic walls for easy access of the electrolyte ions and highly conductive networks for fast electron transfer; additionally, it provides numerous electroactive sites. The synergistic combination of the dendritic 3D-CuNi with its abundant active sites and the self-made NiCu-DH with its excellent electrocatalytic activity toward the oxidation of glucose and HER enables use of the catalyst for both reactions. The as-prepared electrode as a glucose sensor exhibits an outstanding glucose detection limit value (0.4 µM) and a wide detection range (from 0.4 µM to 1.4 mM) with an excellent sensitivity of 1452.5 µA/cm2/mM. The electrode is independent of the oxygen content and free from chloride poisoning. Furthermore, the as-prepared electrode also requires a low overpotential of -180 mV versus reversible hydrogen electrode to yield a current density of 10 mA/cm2 with a Tafel slope of 73 mV/dec for the HER. Based on this performance, this work introduces a new paradigm for exploring cost-effective bi-functional catalysts for the GOR and HER.

Rational Design of a High Performance and Robust Solar Evaporator via 3D-Printing Technology.

Utilizing the broad-band solar spectrum for sea water desalination is a promising method that can provide fresh water without sophisticated infrastructures. However, the solar-to-vapour efficiency has been limited due to the lack of a proper design for the evaporator to deal with either a large amount of heat loss or salt accumulation. Here, these issues are addressed via two cost-effective approaches: I) a rational design of a concave shaped supporter by 3D-printing that can promote the light harvesting capacity via multiple reflections on the surface; II) the use of a double layered photoabsorber composed of a hydrophilic bottom layer of a polydopamine (PDA) coated glass fiber (GF/C) and a hydrophobic upper layer of a carbonized poly(vinyl alcohol)/polyvinylpyrrolidone (PVA/PVP) hydrogel on the supporter, which provides competitive benefit for preventing deposition of salt while quickly pumping the water. The 3D-printed solar evaporator can efficiently utilize solar energy (99%) with an evaporation rate of 1.60 kg m-2 h-1 and efficiency of 89% under 1 sun irradiation. The underlying reason for the high efficiency obtained is supported by the heat transfer mechanism. The 3D-printed solar evaporator could provide cheap drinking water in remote areas, while maintaining stable performance for a long term.

Graphitization with Suppressed Carbon Loss for High-Quality Reduced Graphene Oxide.

An efficient reduction method to obtain high-quality graphene sheets from mass-producible graphene oxide is highly desirable for practical applications. Here, we report an in situ deoxidation and graphitization mechanism for graphene oxide that allows for high-quality reduced graphene oxide sheets under the low temperature condition (<300 °C) by utilizing a well-known Fischer-Tropsch reaction catalyst (CuFeO2). By applying modified FTR conditions, where graphene oxide was reduced on the catalyst surface under the hydrogen-poor condition, deoxidation with much suppressed carbon loss was possible, resulting in high-quality graphene sheets. Our experimental data and density functional theory calculations proved that reduction which occurred on the CuFeO2 surface preferentially removed adsorbed oxygen atoms in graphene oxide sheets, leaving dissociated carbon structures to be restored to a near-perfect few-layer graphene sheet. TGA-mass data revealed that GO with catalysts released 92.8% less carbon-containing gases than GO without catalysts during the reduction process, which suggests that this process suppressed carbon loss in graphene oxide sheets, leading to near-perfect graphene. The amount of oxygen related to the epoxide group in the basal plane of GO significantly decreased to near zero (from 43.84 to 0.48 at. %) in catalyst-assisted reduced graphene oxide (CA-rGO). The average domain size and the density of defects of CA-rGO were 4 times larger and 0.1 times lower than those for thermally reduced graphene oxide (TrGO), respectively. As a result, CA-rGO had a 246 and 8 times lower electrical resistance than TrGO and CVD-graphene. With these performances, CA-rGO coated paper connected to a coin-cell battery successfully lit an LED bulb, and CA-rGO itself acted as an efficient catalyst for both the hydrogen evolution reaction and the oxygen evolution reaction.

Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries.

We report a wire-shaped three-dimensional (3D)-hybrid supercapacitor with high volumetric capacitance and high energy density due to an interconnected 3D-configuration of the electrode allowing for large number of electrochemical active sites, easy access of electrolyte ions, and facile charge transport for flexible wearable applications. The interconnected and compact electrode delivers a high volumetric capacitance (gravimetric capacitance) of 73 F cm-3 (2446 F g-1), excellent rate capability, and cycle stability. The 3D-nickel cobalt-layered double hydroxide onto 3D-nickel wire (NiCo LDH/3D-Ni)//the 3D-manganese oxide onto 3D-nickel wire (Mn3O4/3D-Ni) hybrid supercapacitor exhibits energy density of 153.3 Wh kg-1 and power density of 8810 W kg-1. The red light-emitting diode powered by the as-prepared hybrid supercapacitor can operate for 80 min after being charged for tens of seconds and exhibit excellent electrochemical stability under various deformation conditions. The results verify that such wire-shaped 3D-hybrid supercapacitors are promising alternatives for batteries with long charge-discharge times, for smart wearable and implantable devices.

Motion Sickness Prediction in Stereoscopic Videos using 3D Convolutional Neural Networks.

In this paper, we propose a three-dimensional (3D) convolutional neural network (CNN)-based method for predicting the degree of motion sickness induced by a 360° stereoscopic video. We consider the user's eye movement as a new feature, in addition to the motion velocity and depth features of a video used in previous work. For this purpose, we use saliency, optical flow, and disparity maps of an input video, which represent eye movement, velocity, and depth, respectively, as the input of the 3D CNN. To train our machine-learning model, we extend the dataset established in the previous work using two data augmentation techniques: frame shifting and pixel shifting. Consequently, our model can predict the degree of motion sickness more precisely than the previous method, and the results have a more similar correlation to the distribution of ground-truth sickness.

Highly Enhanced Raman Scattering on Carbonized Polymer Films.

We have discovered a carbonized polymer film to be a reliable and durable carbon-based substrate for carbon enhanced Raman scattering (CERS). Commercially available SU8 was spin coated and carbonized (c-SU8) to yield a film optimized to have a favorable Fermi level position for efficient charge transfer, which results in a significant Raman scattering enhancement under mild measurement conditions. A highly sensitive CERS (detection limit of 10-8 M) that was uniform over a large area was achieved on a patterned c-SU8 film and the Raman signal intensity has remained constant for 2 years. This approach works not only for the CMOS-compatible c-SU8 film but for any carbonized film with the correct composition and Fermi level, as demonstrated with carbonized-PVA (poly(vinyl alcohol)) and carbonized-PVP (polyvinylpyrollidone) films. Our study certainly expands the rather narrow range of Raman-active material platforms to include robust carbon-based films readily obtained from polymer precursors. As it uses broadly applicable and cheap polymers, it could offer great advantages in the development of practical devices for chemical/bio analysis and sensors.

p-Doped three-dimensional graphene nano-networks superior to platinum as a counter electrode for dye-sensitized solar cells.

We report CVD-grown p-doped three-dimensional graphene nano-networks (3D-GNs) that provide superior performance to Pt as a counter electrode material in dye sensitized solar cells (DSSCs). The 3D-GN based DSSC exhibits a maximum photoconversion efficiency of 8.46%, which is 6.01% greater than that exhibited by Pt based DSSCs.

Lotus leaf-inspired CVD grown graphene for a water repellant flexible transparent electrode.

By simply heating commercial copper foil under an oxygen atmosphere and subsequently annealing CuO under a hydrogen atmosphere, the 3D Cu structures in the form of double hierarchical bumps are generated. The contact angle of a lotus leaf-inspired graphene grown on the reconstructed 3D Cu structures is 154.2°.

Chemical vapor deposition of mesoporous graphene nanoballs for supercapacitor.

A mass-producible mesoporous graphene nanoball (MGB) was fabricated via a precursor-assisted chemical vapor deposition (CVD) technique for supercapacitor application. Polystyrene balls and reduced iron created under high temperature and a hydrogen gas environment provide a solid carbon source and a catalyst for graphene growth during the precursor-assisted CVD process, respectively. Carboxylic acid and sulfonic acid functionalization of the polystyrene ball facilitates homogeneous dispersion of the hydrophobic polymer template in the metal precursor solution, thus, resulting in a MGB with a uniform number of graphene layers. The MGB is shown to have a specific surface area of 508 m(2)/g and is mesoporous with a mean mesopore diameter of 4.27 nm. Mesopores are generated by the removal of agglomerated iron domains, permeating down through the soft polystyrene spheres and providing the surface for subsequent graphene growth during the heating process in a hydrogen environment. This technique requires only drop-casting of the precursor/polystyrene solution, allowing for mass-production of multilayer MGBs. The supercapacitor fabricated by the use of the MGB as an electrode demonstrates a specific capacitance of 206 F/g and more than 96% retention of capacitance after 10,000 cycles. The outstanding characteristics of the MGB as an electrode for supercapacitors verify the strong potential for use in energy-related areas.

An optimal substrate design for SERS: dual-scale diamond-shaped gold nano-structures fabricated via interference lithography.

Dual-scale diamond-shaped gold nanostructures (d-DGNs) with larger scale diamond-shaped gold nanoposts (DGNs) coupled to smaller scale gold nanoparticles have been fabricated via interference lithography as a highly reliable and efficient substrate for surface enhanced Raman scattering (SERS). The inter- and intra-particle plasmonic fields of d-DGNs are varied by changing the periodicity of the DGNs and the density of gold nanoparticles. Because of the two different length scales in the nanostructures, d-DGNs show multipole plasmonic peaks as well as dipolar plasmonic peaks, leading to a SERS enhancement factor of greater than 10(9). Simulations are carried out by finite-difference time-domain (FDTD) methods to evaluate the dependence of the inter- and intra-particle plasmonic field and the results are in good agreement with the experimentally obtained data. Our studies reveal that the combination of two different length scales is a straightforward approach for achieving reproducible and great SERS enhancement by light trapping in the diamond-shaped larger scale structures as well as efficient collective plasmon oscillation in the small size particles.

Power conversion efficiency enhancement based on the bio-inspired hierarchical antireflection layer in dye sensitized solar cells.

We have investigated the effects of the introduction of an antireflection layer consisting of a hierarchically patterned diffraction grating into a conventional TiO(2) working electrode on the power conversion efficiency (PCE) of a DSSC. High index-contrast TiO(2) nanowires (NWs) were grown in the circular holes of the two-dimensional diffraction grating prepared through the use of a polymer template fabricated via interference lithography (IL) for maximized photon trapping effects in the visible region of light. The larger scale dimension of the polymer template was determined using the beam parameters of the IL and the smaller scale dimension in the structures was controlled by the growth conditions of the TiO(2) NWs. Compared with a conventional DSSC, the hybrid nanostructure with an additional antireflection layer demonstrated higher and wider absorption bands of wavelength spectra, leading to an increased PCE due to enhanced light trapping effects achieved by the combination of antireflection and diffraction of the light on the front surface of the devices with minimum loss in the surface area of the hierarchical structure. The excellent performance of the optimized hybrid nanostructure indicates that the nanophotonic effects have strong potential for solar energy conversion, photocatalyst, and photoelectrode applications.

Identification and purification of a soluble region of BubR1: a critical component of the mitotic checkpoint complex.

The mitotic checkpoint complex (MCC) ensures the fidelity of chromosomal segregation, by delaying the onset of anaphase until all sister chromatids have been properly attached to the mitotic spindle. In essence, this MCC-induced delay is achieved via the inhibition of the anaphase-promoting complex (APC). Among the components of the MCC, BubR1 plays two major roles in the functions of the mitotic checkpoint. First, BubR1 is able to inhibit APC activity, either by itself or as a component of the MCC, by sequestering a APC coactivator, known as Cdc20. Second, BubR1 activates mitotic checkpoint signaling cascades by binding to the centromere-associated protein E, a microtubule motor protein. Obtaining highly soluble BubR1 is a prerequisite for the study of its structure. BubR1 is a multi-domain protein, which includes a KEN box motif, a mad3-like region, a Bub3 binding domain, and a kinase domain. We obtained a soluble BubR1 construct using a three-step expression strategy. First, we obtained two constructs from BLAST sequence homology searches, both of which were expressed abundantly in the inclusion bodies. We then adjusted the lengths of the two constructs by secondary structure prediction, thereby generating partially soluble constructs. Third, we optimized the solubility of the two constructs by either chopping or adding a few residues at the C-terminus. Finally, we obtained a highly soluble BubR1 construct via the Escherichia coli expression system, which allowed for a yield of 10.8 mg/L culture. This report may provide insight into the design of highly soluble constructs of insoluble multi-domain proteins.

Deacylation activity of cephalosporin acylase to cephalosporin C is improved by changing the side-chain conformations of active-site residues.

Semisynthetic cephalosporins are primarily synthesized from 7-aminocephalosporanic acid (7-ACA), mainly by environmentally toxic chemical deacylation of cephalosporin C (CPC). Thus, the enzymatic conversion of CPC to 7-ACA by cephalosporin acylase (CA) would be very interesting. However, CAs use glutaryl-7-ACA (GL-7-ACA) as a primary substrate and the enzymes have low turnover rates for CPC. The active-site residues of a CA were mutagenized to various residues to increase the deacylation activity of CPC, based on the active-site conformation of the CA structure. The aim was to generate sterically favored conformation of the active-site to accommodate the D-alpha-aminoadipyl moiety of CPC, the side-chain moiety that corresponds to the glutaryl moiety of GL-7-ACA. A triple mutant of the CA, Q50betaM/Y149alphaK/F177betaG, showed the greatest improvement of deacylation activity to CPC up to 790% of the wild-type. Our current study is an efficient method for improving the deacylation activity to CPC by employing the structure-based repetitive saturation mutagenesis.

Modifying the substrate specificity of penicillin G acylase to cephalosporin acylase by mutating active-site residues.

The penicillin G acylase (PGA) and cephalosporin acylase (CA) families, which are members of the N-terminal (Ntn) hydrolases, are valuable for the production of backbone chemicals like 6-aminopenicillanic acid and 7-aminocephalosporanic acid (7-ACA), which can be used to synthesize semi-synthetic penicillins and cephalosporins, respectively. Regardless of the low sequence similarity between PGA and CA, the structural homologies at their active-sites are very high. However, despite this structural conservation, they catalyze very different substrates. PGA reacts with the hydrophobic aromatic side-chain (the phenylacetyl moiety) of penicillin G (PG), whereas CA targets the hydrophilic linear side-chain (the glutaryl moiety) of glutaryl-7-ACA (GL-7-ACA). These different substrate specificities are likely to be due to differences in the side-chains of the active-site residues. In this study, mutagenesis of active-site residues binding the side-chain moiety of PG changed the substrate specificity of PGA to that of CA. This mutant PGA may constitute an alternative source of engineered enzymes for the industrial production of 7-ACA.

Modifying the oligomeric state of cyclic amidase and its effect on enzymatic catalysis.

A group of cyclic amidases, including hydantoinase, allantoinase, dihydropyrimidinase, and dihydroorotase, catalyze the reversible hydrolysis of cyclic ureides, such as 5-monosubstituted hydantoins and dihydropyrimidines. These four enzymes carry hydrophobic patches to form dimers. With the exception of dihydroorotase, these enzymes are further dimerized to form tetramers by hydrophobic interactions. This leads us to speculate that the hydrophobic interaction domain may be a significant factor in the catalytic property of these oligomeric cyclic amidases, for which activities are not allosterically regulated. We generated a dimeric D-hydantoinase by mutating five residues in the hydrophobic alpha-helical interface of a tetramer and analyzed the kinetic properties of the dimeric form of D-hydantoinase. The specific activity of the dimeric D-hydantoinase corresponds to 5.3% of the activity of tetrameric D-hydantoinase. This low specific activity of the dimeric D-hydantoinase indicates that the dimeric interaction to form a tetramer has a significant effect on the catalytic activity of this non-allosteric tetramer.