Ni3S2 nanorods growing directly on Ni foam for all-solid-state asymmetric supercapacitor and efficient overall water splitting

Transition metal compounds are attractive for their significant applications in supercapacitors and as non-noble metal catalysts for electrochemical water splitting.Herein,we develop Ni3 S2 nanorods growing directly on Ni foam,which act as multifunctional additive-free Ni3 S2@Ni electrode for supercapacitor and overall water splitting.Based on PVA-KOH gel electrolyte,the assembled all-solid-state Ni3 S2@Ni//AC asymmetric supercapacitor delivers a high areal energy density of 0.52 mWh cm^-2 at an areal power density of 9.02 MW cm^-2,and exhibits an excellent cycling stability with a capacitance retention ratio of 89%after 10000 GCD cycles at a current density of 30 mA cm^-2.For hydrogen evolution reaction and oxygen evolution reaction in 1 M KOH,Ni3 S2@Ni electrode achieves a benchmark of 10 mA cm^-2at overpotentials of 82 mV and 310 mV,respectively.Furthermore,the assembled Ni3 S2@Ni‖Ni3 S2@Ni electrolyzer for overall water splitting attains a current density of 10 mA cm^-2 at 1.61 V.The in-situ synthesis of Ni3 S2@Ni electrode enriches the applications of additive-free transition metal compounds in high-performance energy storage devices and efficient electrocatalysis.

Controllable Hydrothermal Synthesis of MnO₂Nanostructures

Various MnO2 nanostructures with controlling phases and morphologies, like α-MnO2 nanorods, nanotubes, nanocubes, nanowires and β-MnO2 cylinder/spindle-like nanosticks have been successfully prepared by hydrothermal method, which is simply tuned by changing the ratio of Mn precursor solution to HCl, Mn(Ac)2·4H2O or C6H12O6·H2O, surfactants and reaction temperature and time. The study found out that temperature is a crucial key to get a uniform and surface-smooth nanorod. High ratio of KMnO4 to HCl leads to well dispersed MnO2 nanorods and changing the precursor of HCl into Mn(Ac)2·4H2O or C6H12O6·H2O results in forming nanowires or nanocubes. Different shapes such as cylinder/spindle-like nanosticks could be obtained by adding surfactants. Since the properties rely on the structure of materials firmly, these MnO2 products would be potentially used in supercapacitor and other energy storage applications.

Electrically programmable phase-change photonic memory for optical neural networks with nanoseconds in situ training capability

Optical neural networks (ONNs), enabling low latency and high parallel data processing withoutelectromagnetic interference, have become a viable player for fast and energy-efficient processing andcalculation to meet the increasing demand for hash rate. Photonic memories employing nonvolatile phase-change materials could achieve zero static power consumption, low thermal cross talk, large-scale, andhigh-energy-efficient photonic neural networks. Nevertheless, the switching speed and dynamic energyconsumption of phase-change material-based photonic memories make them inapplicable for in situ training.Here, by integrating a patch of phase change thin film with a PIN-diode-embedded microring resonator,a bifunctional photonic memory enabling both 5-bit storage and nanoseconds volatile modulation wasdemonstrated. For the first time, a concept is presented for electrically programmable phase-changematerial-driven photonic memory integrated with nanosecond modulation to allow fast in situ training and zerostatic power consumption data processing in ONNs. ONNs with an optical convolution kernel constructedby our photonic memory theoretically achieved an accuracy of predictions higher than 95% when testedby the MNIST handwritten digit database. This provides a feasible solution to constructing large-scalenonvolatile ONNs with high-speed in situ training capability.

Passive devices at 2 μm wavelength on 200 mm CMOS-compatible silicon photonics platform [Invited]

As a promising spectral window for optical communication and sensing, it is of great significance to realize on-chip devices at the 2 μm waveband.The development of the 2 μm silicon photonic platform mainly depends on the performance of passive devices.In this work, the passive devices were fabricated in the silicon photonic multi-project wafer process.The designed micro-ring resonator with a 0.6 μm wide silicon ridge waveguide based on a 220 nm silicon-on-insulator platform achieves a high intrinsic quality factor of 3.0 × 105.The propagation loss is calculated as 1.62 d B/cm.In addition,the waveguide crossing, multimode interferometer, and Mach–Zehnder interferometer were demonstrated at 2 μm with good performances.

Facile synthesis of porous nitrogen-doped holey graphene as an efficient metal-free catalyst for the oxygen reduction reaction

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions （ORRs）. The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene （PHNG） via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale （5-15 nm） holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.

Recent developments of infrared photodetectors with lowdimensional inorganic nanostructures

Low-dimensional inorganic nanostructures such as quantum dots as well as one-and two-dimensional nanostructures are widely studied and already used in high-performance infrared photodetectors.These structures feature large surface-to-volume ratios,tunable light absorption,and electron-limiting effects.This article reviews the state-of-the-art research of low-dimensional inorganic nanostructures and their application for infrared photodetection.Thanks to nano-structuring,a narrow bandgap,hybrid systems,surface-plasmon resonance,and doping,many common semiconductors have the potential to be used for infrared detection.The basic approaches towards infrared detection are summarized.Furthermore,a selection of very important and special nanostructured materials and their remarkable infrared-detection properties are introduced(e.g.,black phosphorus,graphene-based,MoX_(2)-based,Ⅲ-Ⅶ group).Each section in this review describes the corresponding photosensitive properties in detail.The article concludes with an outlook of anticipated future developments in the field.

An adjustable multi-color detector based on regulating TiO_(2)surface adsorption and multi-junction synergy

A TiO_(2)-based multi-color photodetector with controlled photoelectric response to ultraviolet(UV)and visible light is developed by using band regulation technologies such as multi-junction synergy and surface adsorption.This photodetector is manufactured via a continuous process including magnetron sputtering,hydrothermal growth,hydrogen annealing,spin coating and thermal evaporation assembly to form a structure of N-doped TiO_(2)/hydrogenated-TiO_(2)/p-Si heterojunction.These synergistic effects form electronic potential wells in the device to control the electrical transport and spectral response of photo-generated carriers.In the air,the device exhibits a controllable photodetection ability that responds to visible light at positive voltages and UV light at negative voltages.But in vacuum(<0.1 Pa),the photodetection ability of the device at negative voltages is greatly reduced due to the lack of barrier effect caused by surface adsorption.On the contrary,the photodetection ability at positive voltage(e.g.,4 V)has been greatly improved,and the quantum efficiency reaches 206.6%under the 480 nm wavelength light.The device has a controllable ability to detect UV and visible light depending on the environments,which is very useful in the fields of environmental detection,chemical sensing and multi-color communication,etc.