Three-dimensional Ordered Macroporous Flexible Electrode Design toward High-Performance Zinc-Ion Batteries.

Flexible zinc-ion batteries (ZIBs) have been considered to have huge potential in portable and wearable electronics due to their high safety, cost efficiency, and considerable energy density. Therein, the design and construction of flexible electrodes significantly determine the performance and lifespan of flexible battery devices. In this work, an ultrathin flexible three-dimensional ordered macroporous (3DOM) Sn@Zn anode (60 µm in thickness) is presented to relieve dendrite growth and expand the lifespan of flexible ZIBs. The 3DOM structure can ensure uniform electric field distribution, guide oriented zinc plating/stripping, and extend the lifespan of anodes. The rich zincophilic Sn sites on the electrode surface significantly facilitate Zn nucleation. Accordingly, a lowered nucleation overpotential of 8.9 mV and an ultralong cycling performance of 2400 h at 0.1 mA cm-2 and 0.1 mAh cm-2 are achieved in symmetric cells, and the 3DOM Sn@Zn anode can also operate in deep cycling for over 200 h at 10 mA cm-2 and 5 mAh cm-2. A flexible 3DOM MnO2/Ni cathode with a high structural stability and a high mass-specific capacity is fabricated to match with the anode to form a flexible ZIB with a total thickness of 200 µm. The flexible device delivers a high volumetric energy density of 11.76 mWh cm-3 at 100 mA gMnO2-1 and a high average open-circuit voltage of 1.5 V and exhibits high-performance power supply under deformation in practical application scenarios. This work may shed some light on the design and fabrication of flexible energy-storage devices.

Three-dimensional BiVO4-based semiconductor photocathode for high efficiency photo-assisted Zn-iodine redox flow batteries.

Aqueous Zn-iodine redox flow batteries have aroused great interest for the features of high capacity, excellent stability, low cost, and high safety, yet the dissatisfying energy efficiency still limits their future advancement. In this work, three-dimensional semiconductor BiVO4nanoparticles decorated hierarchical TiO2/SnO2arrays (BiVO4@TiO2/SnO2) were applied as photocathode in Zn-iodine redox flow batteries (ZIRFBs) for the realization of efficient photo-assisted charge/discharge process. The photogenerated carriers at the solid/liquid interfaces boosted the oxidation process of I-, and thus contributed to a significant elevation in energy efficiency of 14.9% (@0.5 mA cm-2). A volumetric discharge capacity was extended by 79.6% under light illumination, owing to a reduced polarization. The photocathode also exhibited an excellent durability, leading to a stable operation for over 80 h with a maintained high energy efficiency of ∼90% @0.2 mA cm-2. The research offers a feasible approach for the realization of high-energy-efficiency aqueous Zn-iodine batteries towards high-efficiency energy conversion and utilization.

ALD oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO arrays for high-performance self-powered solar-blind photodetectors.

The exploration of efficient self-powered solar-blind photodetectors is essential for applications in future sustainable optoelectronic systems. Herein, we demonstrate a photoelectrochemical (PEC)-type heterojunction-driven solar-blind detector constructed by atomic layer deposition (ALD) of oxygen vacancy-rich amorphous Ga2O3 on three-dimensional urchin-like ZnO nanorod arrays (3D VO-Ga2O3/ZnO). The as-fabricated device achieves excellent solar-blind photodetection performance in terms of a high photoresponsivity of 7.97 mA W-1 at 0 V bias, an ultrahigh light to dark ratio of 6.93 × 104 under 266 nm light illumination as well as fast response and recovery times. The excellent performance originates from abundant oxygen vacancies in a-Ga2O3 as donors, high specific surface area and good interface contact enabled by the 3D ordered nanostructure, and high carrier separation rates benefited from the Ga2O3/ZnO heterojunction. Our research offers a feasible and cost-effective approach towards the realization of a high-performance self-powered photodetection system for various applications.

Light output enhancement of scintillators by using mixed-scale microstructures.

Scintillators play an important role in the field of nuclear radiation detection. However, the light output of the scintillators is often limited by total internal reflection due to the high refractive indices of the scintillators. Furthermore, the light emission from scintillators typically has an approximately Lambertian profile, which is detrimental to the collection of the light. In this paper, we demonstrate a promising method to achieve enhancement of the light output from scintillators through use of mixed-scale microstructures that are composed of a photonic crystal slab and a microlens array. Simulations and experimental results both show significant improvements in the scintillator light output. The X-ray imaging characteristics of scintillators are improved by the application of the mixed-scale microstructures. The results presented here suggest that the application of the proposed mixed-scale microstructures to scintillators will be beneficial in the nuclear radiation detection field.

Ultrathin Co(OH)2 Nanosheets@Nitrogen-Doped Carbon Nanoflake Arrays as Efficient Air Cathodes for Rechargeable Zn-Air Batteries.

Developing highly active, cost-effective, and durable bifunctional oxygen electrocatalysts is an important step for the advancement of rechargeable Zn-air batteries (ZABs). Herein, an efficient bifunctional oxygen electrocatalyst of ultrathin Co(OH)2 nanosheets supported on nitrogen-doped carbon nanoflake arrays (named as Co(OH)2 @NC), is reported, which yields excellent bifunctional activity, i.e., a low overpotential of 285 mV to reach 10 mA cm-2 for oxygen evolution reaction (OER), a high half-wave potential (0.83 V) for oxygen reduction reaction (ORR), and a low potential gap (ΔE) of 0.69 V. The excellent bifunctional catalytic performance can be ascribed to the concerted efforts of cobalt hydroxide toward OER and nitrogen-doped carbon for ORR. The Co(OH)2 @NC nanoflake arrays is further used as binder-free air cathodes for rechargeable Zn-air batteries, exhibiting a high specific capacity of 798.3 mAh gZn -1 , improved stability (a working life of >70 h at 5 mA cm-2 ), as well as a reduced long-term charging voltage, which outperforms the counterparts of NC nanoflake arrays and Pt/C-based air cathodes. One step further, the Co(OH)2 @NC nanoflake arrays on carbon cloth are directly used as binder-free air cathodes for flexible, solid-state ZABs, showing excellent performance under deformation as well.

Hollow nanosphere arrays with a high-index contrast for enhanced scintillating light output from ß-Ga2O3 crystals.

ß-Ga2O3 is a new type of fast scintillator with potential applications in medical imaging and nuclear radiation detection with high count-rate situations. Because of the severe total internal reflection with its high refractive index, the light extraction efficiency of ß-Ga2O3 crystals is rather low, which would limit the performance of detection systems. In this paper, we use hollow nanosphere arrays with a high-index contrast to enhance the light extraction efficiency of ß-Ga2O3 crystals. We can increase the transmission diffraction efficiency and reduce the reflection diffraction efficiency through controlling the refractive index and the thickness of the shell of the hollow nanospheres, which can lead to a significant increase in the light extraction efficiency. The relationships between the light extraction efficiency and the refractive index and thickness of the shell of the hollow nanospheres are investigated by both numerical simulations and experiments. It is found that when the refractive index of the shell of the hollow nanospheres is higher than that of ß-Ga2O3, the light extraction efficiency is mainly determined by the diffraction efficiency of light transmitted from the surface with the hollow nanosphere arrays. When the refractive index of the shell is less than that of ß-Ga2O3, the light extraction efficiency is determined by the ratio of the diffraction efficiency of the light transmitted from the surface with the hollow nanosphere arrays to the diffraction efficiency of the light that can escape from the lateral surface.

Ultrafine Ru nanoclusters supported on N/S doped macroporous carbon spheres for efficient hydrogen evolution reaction.

The construction of highly-active and stable electrocatalysts for the hydrogen evolution reaction (HER) is significant for efficient water splitting processes. Herein, we develop an efficient HER catalyst of ultrafine Ru nanoclusters supported on a N/S doped macroporous hollow carbon sphere (Ru/H-S,N-C). The N/S co-doping strategy not only facilitates the reduction of the Ru nanocluster sizes, but also regulates the electronic structure of metallic Ru, improving the HER activity of the metallic Ru catalyst. Due to the structural advantages of N/S-doped macroporous carbon spheres that provide a fast mass transfer process and the high intrinsic activity of Ru nanoclusters, the optimized Ru/H-S,N-C catalyst exhibits excellent HER performance in alkaline medium, with a low overpotential of 32 mV to reach 10 mA cm-2, fast HER kinetics (a Tafel slope of 24 mV dec-1) and excellent durability, superior to the performances of the Ru/H-N-C sample and commercial Pt/C catalyst. Our work offers some guidance on the design of efficient Ru-based electrocatalysts.

Recent Advances on Self-Supported Arrayed Bifunctional Oxygen Electrocatalysts for Flexible Solid-State Zn-Air Batteries.

Flexible solid-state Zn-air batteries have been rapidly developed benefiting from the uprising demand for wearable electronic devices, wherein the air electrode integrated with efficient bifunctional oxygen electrocatalysts plays an important role to achieve high performance. Binder-free self-supported bifunctional catalysts can provide large active surface area, fast electron transport path, easy ion diffusion, and excellent structural stability and flexibility, thus acting as promising flexible air cathodes. In this review, recent advances on the application of nanoarrayed electrocatalysts as air cathodes in flexible Zn-air batteries are reviewed. Especially, various types of bifunctional oxygen electrocatalysts, including carbonaceous material arrays, transition metal compound arrays, transition metal/carbon arrays, transition metal compound/carbon arrays, and other hybrid arrays, are discussed. The applications of flexible Zn-air batteries with two configurations (i.e., planar stacks and cable fibers) are also introduced. Finally, perspectives on the optimization of arrayed air cathodes for future development to achieve high-performance flexible Zn-air batteries are shared.

Directional Control and Enhancement of Light Output of Scintillators by Using Microlens Arrays.

Scintillators play an important role in the field of nuclear radiation detection, such as nuclear medical imaging, dark matter detection, nuclear physics experiments, and national security. However, the light extraction efficiency of a scintillator with a high refractive index is severely restricted because of the total internal reflection. In this paper, microlens arrays have been applied onto the surface of a cerium-doped lutetium-yttrium oxyorthosilicate scintillator to improve the light extraction efficiency and to control the directivity of the light output. Compared to that of a reference sample, a 3.26-fold enhancement with an emission angle of 45° has been obtained by using microlens arrays with optimal parameters. It was also found that the enhancement ratio can be affected by the refractive index of the microlens, the spacing of individual microlens. The control mechanism of microlens arrays is revealed by a combination of simulations and experiments. X-ray imaging characteristics exhibit an improved gray scale amplitude without any loss of the spatial resolution. The present results suggest that the application of microlens arrays to scintillators is beneficial to the field of nuclear radiation detection.

Convenient method for improving the light output of scintillators by using buffer layers coated with photonic crystals.

The low light-extraction efficiency of scintillators is due to total internal reflection and has led to the extensive use of photonic crystals to improve the light output. However, in some applications, photonic crystals cannot be fabricated directly on scintillators. Here, we demonstrate a promising method to improve the light output of scintillators by using a buffer layer coated with photonic crystals and then fixed to the scintillator. Through both numerical simulations and experiments, we investigate how the refractive indexes of the buffer layer and photonic crystal affect the light output from scintillators. The experimental results indicate that the light output of (Lu,Y)2SiO5:Ce scintillators is enhanced 1.9 times by using a sapphire buffer layer coated with an array of polystyrene nanospheres. This method can be used to improve the detection efficiency of radiation-detection systems when photonic crystals cannot be fabricated directly on the scintillator.

Nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays as a bifunctional catalyst for efficient overall water splitting.

Development of high-efficiency and Earth-abundant bifunctional catalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is desirable to realize an efficient overall water splitting process. In this work, a highly active and durable bifunctional catalyst of coral-like nickel iron phosphide ultrathin nanosheets anchored on nitrogen-doped carbon nanoflake arrays on carbon cloth (CC-NC-NiFeP) was fabricated by using metal organic framework (MOF) derived nitrogen-doped carbon nanoflake arrays as catalyst supports. Combined with the electronic structure regulation by bimetallic phosphides and using three dimensional nitrogen-doped carbon nanoflakes as supports that provide a large specific surface area as well as fast charge/mass transport, the as-prepared CC-NC-NiFeP yields excellent bifunctional electrocatalytic activity in both the HER and OER in an alkaline medium with an overpotential of 94 mV and 145 mV to reach a current density of 10 mA cm-2, respectively. Meanwhile, the CC-NC-NiFeP can behave as both a cathode and anode simultaneously for overall water splitting, achieving a low cell voltage of 1.54 V to reach a current density of 10 mA cm-2, which outperforms that of most of the non-precious metal based catalysts.

RuP nanoparticles on ordered macroporous hollow nitrogen-doped carbon spheres for efficient hydrogen evolution reaction.

The design of highly active, Earth-abundant and stable electrocatalysts is important for efficient water splitting. In this work, we report the fabrication of RuP and Ru2P nanoparticles supported on ordered macroporous N-doped carbon hollow spheres (RuP/H-NC and Ru2P/H-NC) through a facile and scalable space-confined pyrolysis process. The RuP/H-NC catalyst exhibits Pt-like activity in alkaline electrolyte, by means of the macroporous structure with a larger specific area and more exposed active sites, as well as the synergistic effect between the RuP nanoparticles and N-doped carbon. Specifically, the RuP/H-NC catalyst yields superior hydrogen evolution reaction activity in terms of low overpotential of 19 mV in 1 M KOH to achieve a current density of 10 mA cm-2 and excellent durability, outperforming Ru2P/H-NC and most of the reported non-Pt catalysts. Further density function theory calculation reveals that RuP is more intrinsically active with favorable hydrogen adsorption Gibbs free energy than that of Ru2P.

Rational Design of 3D Hierarchical Ternary SnO2/TiO2/BiVO4 Arrays Photoanode toward Efficient Photoelectrochemical Performance.

BiVO4 as a promising semiconductor absorber is widely investigated as photoanode in photoelectrochemical water splitting. Herein, the rational design of 3D hierarchical ternary SnO2/TiO2/BiVO4 arrays is reported as photoanode for photoelectrochemical application, in which the SnO2 hierarchically hollow microspheres core/nanosheets shell arrays act as conductive skeletons, while the sandwiched TiO2 and surface BiVO4 are working as hole blocking layer and light absorber, respectively. Arising to the hierarchically ordered structure and synergistic effect between each component in the composite, the ternary SnO2/TiO2/BiVO4 photoanode enables high light harvesting efficiency as well as enhanced charge transport and separation efficiency, yielding a maximum photocurrent density of ≈5.03 mA cm-2 for sulfite oxidation and ≈3.1 mA cm-2 for water oxidation, respectively, measured at 1.23 V versus reversible hydrogen electrode under simulated air mass (AM) 1.5 solar light illumination. The results reveal that electrode design and interface engineering play important roles on the overall PEC performance.

Au nanoparticles embedded in BiVO4 films photoanode with enhanced photoelectrochemical performance.

In this work, we report the fabrication of Au nanoparticles embedded in BiVO4 films photoanode for photoelectrochemical (PEC) application by a facile electrochemical deposition and sputtering process. The Au NPs/BiVO4 films photoanode decorated with Co-Pi yields significantly improved PEC performance with a maximum photocurrent density of ∼3.1 mA cm-2 at 1.23 V versus RHE. The significantly enhanced performance could be attributed to the introduction of Au nanoparticles, which leads to enhancement of light absorption arising from surface plasmon resonance effect of nanosized Au and improved charge transfer and separation efficiency resulted by increased carrier density and charge transport property by the Au metal doping effect.

3D Brochosomes-Like TiO2 /WO3 /BiVO4 Arrays as Photoanode for Photoelectrochemical Hydrogen Production.

An ideal photoelectrochemical (PEC) anode should process effective light absorption, charge transport, and separation efficiency. Here, a novel 3D brochosomes-like TiO2 /WO3 /BiVO4 array as an efficient photoanode by combining a colloid polystyrene sphere template and electrochemical deposition routes for PEC hydrogen generation is reported. The as-fabricated 3D TiO2 /WO3 /BiVO4 brochosomes photoanode yields excellent PEC performance with photocurrent densities of ≈3.13 and ≈4.27 mA cm-2 with FeOOH/NiOOH catalyst, respectively, measured in 0.5 m Na2 SO4 solution with 0.1 m Na2 SO3 at 1.23 V versus reversible hydrogen electrode (RHE) under simulated AM1.5 light illumination, which is ≈6 times the reference sample of a planar WO3 /BiVO4 film electrode. The significantly improved performance could be benefited from the ordered hollow porous structure that provides enhanced light absorption and efficient charge transport as well as improved charge separation efficiency by WO3 /BiVO4 "host-guest" heterojunctions.

Three-dimensional macroporous W2C inverse opal arrays for the efficient hydrogen evolution reaction.

The development of a low-cost and durable non-precious metal-based electrocatalyst for the hydrogen evolution reaction (HER) is important to realize highly efficient overall water splitting. Here, we report the design and fabrication of a binder-free electrocatalyst of three-dimensional macroporous ditungsten carbide (W2C) inverse opal (W2C IO) arrays by a facile thermal carburization process with WO3 IO as a template. The as-fabricated W2C IO exhibits superior electrocatalytic performance in 0.5 M H2SO4 solution in terms of a low overpotential of 146 mV to reach a current density of 10 mA cm-2, a low Tafel slope of 78 mV dec-1 and excellent long-term stability. The superior performance can be attributed to the favorable electronic structure and hydrogen adsorption Gibbs free energy of W2C evidenced by theory calculations and the enhancement of the charge/mass transfer process by the 3D macroporous arrayed electrode design.

Multiscale porous molybdenum phosphide of honeycomb structure for highly efficient hydrogen evolution.

The hydrogen evolution reaction (HER) based on electrochemical water splitting is considered a promising strategy to produce clean and sustainable hydrogen energy. Searching for non-noble metal based electrocatalysts with high efficiency and durability toward the HER is vitally necessary. In this work, we report a novel method for synthesizing molybdenum phosphide (MoP) supported on multiscale porous honeycomb carbon (MoP@HCC) and the application of this catalyst material in acidic media for water electrolysis. Due to the unique structure of the catalyst material, the as-prepared MoP@HCC shows remarkable electrocatalytic activity and stability in 0.5 M H2SO4 aqueous solution. The hybrid catalyst could deliver a current density of 10 mA cm-2 at a low overpotential of 129 mV, with an onset overpotential of 69 mV and a Tafel slope of 48 mV dec-1, outperforming most of the current noble-metal-free electrocatalysts. This study demonstrates an effective way for multiscale control of the MoP structure via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites toward the HER.

Hyperbranched TiO2-CdS nano-heterostructures for highly efficient photoelectrochemical photoanodes.

Quasi-1D-hyperbranched TiO2 nanostructures are grown via pulsed laser deposition and sensitized with thin layers of CdS to act as a highly efficient photoelectrochemical photoanode. The device properties are systematically investigated by optimizing the height of TiO2 scaffold structure and thickness of the CdS sensitizing layer, achieving photocurrent values up to 6.6 mA cm-2 and reaching saturation with applied biases as low as 0.35 VRHE. The high internal conversion efficiency of these devices is to be found in the efficient charge generation and injection of the thin CdS photoactive film and in the enhanced charge transport properties of the hyperbranched TiO2 scaffold. Hence, the proposed device represents a promising architecture for heterostructures capable of achieving high solar-to-hydrogen efficiency.

Hollow Co3 O4 Nanosphere Embedded in Carbon Arrays for Stable and Flexible Solid-State Zinc-Air Batteries.

Highly active and durable air cathodes to catalyze both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for rechargeable metal-air batteries. In this work, an efficient bifunctional oxygen catalyst comprising hollow Co3 O4 nanospheres embedded in nitrogen-doped carbon nanowall arrays on flexible carbon cloth (NC-Co3 O4 /CC) is reported. The hierarchical structure is facilely derived from a metal-organic framework precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC-Co3 O4 /CC can be used as an additive-free air cathode for flexible all-solid-state zinc-air batteries, which present high open circuit potential (1.44 V), high capacity (387.2 mAh g-1 , based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt- and Ir-based zinc-air batteries.

Modified timing characteristic of a scintillation detection system with photonic crystal structures.

It is intuitively expected that an enhanced light extraction of a scintillator can be easily achieved by photonic crystal structures. Here, we demonstrate a modified timing characteristic for a detection system induced by enhanced light extraction with photonic crystal structures. Such improvement is due to the enhanced light extraction which can be clearly proven by the independent measurements of the light output and the timing resolution. The present investigation is advantageous to promote the development of a scintillation detection system performance based on the time-of-flight measurement.