Underwater images suffer from blurring effects, low contrast, and grayed out colors due to the absorption and scattering effects under the water. Many image enhancement algorithms for improving the ...visual quality of underwater images have been developed. Unfortunately, no well-accepted objective measure exists that can evaluate the quality of underwater images similar to human perception. Predominant underwater image processing algorithms use either a subjective evaluation, which is time consuming and biased, or a generic image quality measure, which fails to consider the properties of underwater images. To address this problem, a new nonreference underwater image quality measure (UIQM) is presented in this paper. The UIQM comprises three underwater image attribute measures: the underwater image colorfulness measure (UICM), the underwater image sharpness measure (UISM), and the underwater image contrast measure (UIConM). Each attribute is selected for evaluating one aspect of the underwater image degradation, and each presented attribute measure is inspired by the properties of human visual systems (HVSs). The experimental results demonstrate that the measures effectively evaluate the underwater image quality in accordance with the human perceptions. These measures are also used on the AirAsia 8501 wreckage images to show their importance in practical applications.
The electrochemical method of combining N2 and H2O to produce ammonia (i.e., the electrochemical nitrogen reduction reaction E‐NRR) continues to draw attention as it is both environmentally friendly ...and well suited for a progressively distributed farm economy. Despite the multitude of recent works on the E‐NRR, further progress in this field faces a bottleneck. On the one hand, despite the extensive exploration and trial‐and‐error evaluation of E‐NRR catalysts, no study has stood out to become the stage protagonist. On the other hand, the current level of ammonia production (microgram‐scale) is an almost insurmountable obstacle for its qualitative and quantitative determination, hindering the discrimination between true activity and contamination. Herein i) the popular theory and mechanism of the NRR are introduced; ii) a comprehensive summary of the recent progress in the field of the E‐NRR and related catalysts is provided; iii) the operational procedures of the E‐NRR are addressed, including the acquisition of key metrics, the challenges faced, and the most suitable solutions; iv) the guiding principles and standardized recommendations for the E‐NRR are emphasized and future research directions and prospects are provided.
Ammonia represents the blood of industry; and agriculture, crop growth, green energy fuels, and industry production are inseparable from it. The electrochemical synthesis of ammonia is expected to replace the harsh and environmentally unfriendly Harber–Bosch process. A timely and comprehensive review of the booming ambient electrochemical ammonia synthesis is presented to promote its rapid and healthy development.
Electrocatalytic nitrogen fixation is considered a promising approach to achieve NH3 production. However, due to the chemical inertness of nitrogen, it is necessary to develop efficient catalysts to ...facilitate the process of nitrogen reduction. Here, molybdenum carbide nanodots embedded in ultrathin carbon nanosheets (Mo2C/C) are developed to serve as a catalyst candidate for highly efficient and robust N2 fixation through an electrocatalytic nitrogen reduction reaction (NRR). The as‐synthesized Mo2C/C nanosheets show excellent catalytic performance with a high NH3 yield rate (11.3 µg h−1 mg−1
Mo2C) and Faradic efficiency (7.8%) for NRR under ambient conditions. More importantly, the isotopic experiments using 15N2 as a nitrogen source confirm that the synthesized ammonia is derived from the direct supply of nitrogen. This result also demonstrates the possibility of high‐efficiency nitrogen reduction even though accompanied with vigorous hydrogen evolution.
An effective size‐control synthesis strategy is proposed to endow the nitrogen reduction reaction (NRR) performance of Mo2C nanodots by boosting nitrogen adsorption and activation. The Mo2C nanodots show excellent NRR catalytic performance with a high NH3 yield rate (11.3 µg h−1 mg−1
Mo2C) under ambient conditions. This result demonstrates the possibility of high‐efficiency nitrogen reduction even though accompanied with vigorous hydrogen evolution.
Constructing efficient catalysts for the N2 reduction reaction (NRR) is a major challenge for artificial nitrogen fixation under ambient conditions. Herein, inspired by the principle of “like ...dissolves like”, it is demonstrated that a member of the nitrogen family, well‐exfoliated few‐layer black phosphorus nanosheets (FL‐BP NSs), can be used as an efficient nonmetallic catalyst for electrochemical nitrogen reduction. The catalyst can achieve a high ammonia yield of 31.37 μg h−1 mg−1cat. under ambient conditions. Density functional theory calculations reveal that the active orbital and electrons of zigzag and diff‐zigzag type edges of FL‐BP NSs enable selective electrocatalysis of N2 to NH3 via an alternating hydrogenation pathway. This work proves the feasibility of using a nonmetallic simple substance as a nitrogen‐fixing catalyst and thus opening a new avenue towards the development of more efficient metal‐free catalysts.
Well‐exfoliated few‐layer black phosphorus nanosheets (FL‐BP NSs) were developed as an efficient nonmetallic catalyst for electrochemical nitrogen reduction. The catalyst can achieve a high ammonia yield of 31.37 μg h−1 mg−1cat. under ambient conditions. DFT calculations show that the zigzag and diff‐zigzag edges of the FL‐BP NSs are the active centers, which enable selective electroreduction of N2 to NH3 via an alternating hydrogenation pathway.
Development of easy‐to‐make, highly active, and stable bifunctional electrocatalysts for water splitting is important for future renewable energy systems. Three‐dimension (3D) porous Ni/Ni8P3 and ...Ni/Ni9S8 electrodes are prepared by sequential treatment of commercial Ni‐foam with acid activation, followed by phosphorization or sulfurization. The resultant materials can act as self‐supported bifunctional electrocatalytic electrodes for direct water splitting with excellent activity toward oxygen evolution reaction and hydrogen evolution reaction in alkaline media. Stable performance can be maintained for at least 24 h, illustrating their versatile and practical nature for clean energy generation. Furthermore, an advanced water electrolyzer through exploiting Ni/Ni8P3 as both anode and cathode is fabricated, which requires a cell voltage of 1.61 V to deliver a 10 mA cm−2 water splitting current density in 1.0 m KOH solution. This performance is significantly better than that of the noble metal benchmark—integrated Ni/IrO2 and Ni/Pt–C electrodes. Therefore, these bifunctional electrodes have significant potential for realistic large‐scale production of hydrogen as a replacement clean fuel to polluting and limited fossil‐fuels.
Three‐dimension nickel‐based electrocatalytic electrodes (Ni/Ni8P3 and Ni/Ni9S8) are developed for application in water splitting. The as‐obtained Ni/Ni8P3 catalytic electrode, particularly exhibiting excellent electrocatalytic activity and stability due to its advanced structure effects, can serve as a highly efficient and stable bifunctional catalyst for overall water splitting.
In this article, the fault-tolerant consensus control problem is investigated for multiagent systems with sensor faults. A first-order difference equation is utilized to describe the sensor fault, ...and an observer is designed to estimate the state and the fault simultaneously. For security enhancement and/or congestion mitigation purposes, the estimated state is first encrypted into a series of finite-level codewords by an encryption algorithm and, then, transmitted to other agents through a directed topology. After being received, the codewords are then decrypted by the corresponding decryption algorithm and subsequently utilized to design the consensus controller. By constructing a novel matrix norm along with its compatible vector norm, we obtain a necessary and sufficient condition, which serves as an index in the observer and the controller design. In the end, a simulation example is given to demonstrate the validity of the results in this article.
The aqueous electrocatalytic reduction of NO3− into NH3 (NitrRR) presents a sustainable route applicable to NH3 production and potentially energy storage. However, the NitrRR involves a directly ...eight‐electron transfer process generally required a large overpotential (<−0.2 V versus reversible hydrogen electrode (vs. RHE)) to reach optimal efficiency. Here, inspired by biological nitrate respiration, the NitrRR was separated into two stages along a 2+6‐electron pathway to alleviate the kinetic barrier. The system employed a Cu nanowire catalyst produces NO2− and NH3 with current efficiencies of 91.5 % and 100 %, respectively at lower overpotentials (>+0.1 vs. RHE). The high efficiency for such a reduction process was further explored in a zinc‐nitrate battery. This battery could be specified by a high output voltage of 0.70 V, an average energy density of 566.7 Wh L−1 at 10 mA cm−2 and a power density of 14.1 mW cm−2, which is well beyond all previously reported similar concepts.
For the efficient electrocatalytic conversion of NO3− to NH3, a two‐stage process following the 2+6‐electron pathway is proposed inspired by biological nitrate respiration. This system produces NO2− and NH3 at low overpotentials (>+0.1 vs. RHE), resulting in a low energy consumption of 17.7 kWh kg−1 for NH3 production and high energy density of 566.7 Wh L−1 at 10 mA cm−2 for Zn−NO3− battery.
The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton ...delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(ii) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.Pt(ii) complexes allow the fabrication of efficient near-infrared organic light-emitting diodes that operate beyond the 900 nm region.
The electrochemical reduction of nitrogen into ammonia under ambient conditions is a potential strategy for sustainable ammonia production. At present, one of the main research directions in the ...field of electrochemical nitrogen fixation is to improve the current efficiency and ammonia yield by developing efficient nitrogen reduction catalysts. To optimise the selectivity and catalytic activity of nitrogen reduction catalysts more efficiently, herein, we systematically summarise the progress of research on nitrogen reduction catalysts in recent years and present some general catalyst design strategies. Considering that it is difficult for metal‐based catalysts to balance the competitive reactions of nitrogen activation and hydrogen evolution, we discuss in detail the advantages and application prospects of non‐metallic catalysts in electrochemical nitrogen fixation. Moreover, both the design strategy of surface or interface defects, and how this atomic‐level control of functionalisation helps to promote selectivity and catalytic activity are also discussed by theoretical and experimental electrochemistry. On this basis, we also discussed the future development direction, opportunities and challenges of nitrogen reduction electrocatalysts.
Herding cats: This review provides a comprehensive and critical summary of the progress of research on nitrogen reduction catalysts and some general catalyst design strategies. Considering that it is difficult for metal‐based catalysts to balance the competitive reactions of nitrogen activation and hydrogen evolution, the advantages and application prospects of non‐metallic catalysts in electrochemical nitrogen fixation are summarized and discussed.
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