North University of China

Fluorescent carbon nanoparticles (CNPs) were synthesized by laser irradiation of a suspension of carbon powders in organic solvent. The surface modification on the CNPs was fulfilled simultaneously with the formation of the CNPs, and tunable light emission could be generated by selecting appropriate solvents. The origin of the luminescence was attributed to carboxylate ligands on the surface of the CNPs.

Abstract The antioxidant activities of 18 typical phenolic acids were investigated using 2, 2′-diphenyl-1-picrylhydrazyl (DPPH) and ferric ion reducing antioxidant power (FRAP) assays. Five thermodynamic parameters involving hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton-loss electron transfer (SPLET) mechanisms were calculated using density functional theory with the B3LYP/UB3LYP functional and 6–311++G (d, p) basis set and compared in the phenolic acids. Based on the same substituents on the benzene ring, -CH 2 COOH and -CH = CHCOOH can enhance the antioxidant activities of phenolic acids, compared with -COOH. Methoxyl (-OCH 3 ) and phenolic hydroxyl (-OH) groups can also promote the antioxidant activities of phenolic acids. These results relate to the O-H bond dissociation enthalpy of the phenolic hydroxyl group in phenolic acids and the values of proton affinity and electron transfer enthalpy (ETE) involved in the electron donation ability of functional groups. In addition, we speculated that HAT, SET-PT, and SPLET mechanisms may occur in the DPPH reaction system. Whereas SPLET was the main reaction mechanism in the FRAP system, because, except for 4-hydroxyphenyl acid, the ETE values of the phenolic acids in water were consistent with the experimental results.

Intrinsically conducting polymers (ICP) and conductive fillers incorporated conductive polymer-based composites (CPC) greatly facilitate the research in electromagnetic interference (EMI) shielding because they not only provide excellent EMI shielding but also have advantages of electromagnetic wave absorption rather than reflection. In this review, the latest developments in ICP and CPC based EMI shielding materials are highlighted. In particular, existing methods for adjusting the morphological structure, electric and magnetic properties of EMI shielding materials are discussed along with the future opportunities and challenges in developing ICP and CPC for EMI shielding applications.

Although reports have shown shifts in carbon dot emission wavelengths resulting from varying the excitation wavelength, this excitation-dependent emission does not constitute true tuning, as the shifted peaks have much weaker intensity than their dominant emission, and this is often undesired in real world applications. We report for the first time the synthesis and photoluminescence properties of carbon dots whose peak fluorescence emission wavelengths are tunable across the entire visible spectrum by simple adjustment of the reagents and synthesis conditions, and these carbon dots are excited by white light. Detailed material characterization has revealed that this tunable emission results from changes in the carbon dots' chemical composition, dictated by dehydrogenation reactions occurring during carbonization. These significantly alter the nucleation and growth process, resulting in dots with either more oxygen-containing or nitrogen-containing groups that ultimately determine their photoluminescence properties, which is in stark contrast to previous observations of carbon dot excitation-dependent fluorescence. This new ability to synthesize broadband excitable carbon dots with tunable peak emissions opens up many new possibilities, particularly in multimodal sensing, in which multiple analytes and processes could be monitored simultaneously by associating a particular carbon dot emission wavelength to a specific chemical process without the need for tuning the excitation source.

It is vitally essential to design highly efficient and cost-effective bifunctional electrocatalysts toward water splitting. Herein, we report the development of P-doped Co 3 O 4 nanowire array on nickel foam (P-Co 3 O 4 /NF) from Co 3 O 4 nanowire array through low-temperature annealing, using NaH 2 PO 2 as the P source. As a 3D catalyst, such P-Co 3 O 4 /NF demonstrates superior performance for oxygen evolution reaction with a low overpotential (260 mV at 20 mA cm –2 ), a small Tafel slope (60 mV dec –1 ), and a satisfying durability in 1.0 M KOH. Density functional theory calculations indicate that P-Co 3 O 4 has a reaction free-energy value that is much smaller than that of pristine Co 3 O 4 for the potential determining step of the oxygen evolution reaction. Such P-Co 3 O 4 /NF also performs efficiently for hydrogen evolution reaction, and a two-electrode alkaline electrolyzer assembled by P 8.6 -Co 3 O 4 /NF as both anode and cathode needs only 1.63 V to reach a water-splitting current of 10 mA cm –2 .

With the widespread application of electronic communication technology, the resulting electromagnetic radiation pollution has been significantly increased. Metal matrix electromagnetic interference (EMI) shielding materials have disadvantages such as high density, easy corrosion, difficult processing and high price, etc. Polymer matrix EMI shielding composites possess light weight, corrosion resistance and easy processing. However, the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance. This review firstly discusses the key concept, loss mechanism and test method of EMI shielding. Then the current development status of EMI shielding materials is summarized, and the research progress of polymer matrix EMI shielding composites with different structures is illustrated, especially for their preparation methods and evaluation. Finally, the corresponding key scientific and technical problems are proposed, and their development trend is also prospected.

Searching for the highly active, stable, and high-efficiency bifunctional electrocatalysts for overall water splitting, e.g., for both oxygen evolution (OER) and hydrogen evolution (HER), is paramount in terms of bringing future renewable energy systems and energy conversion processes to reality. Herein, three-dimensional (3D) Ni 3 FeN nanoparticles/reduced graphene oxide (r-GO) aerogel electrocatalysts were fabricated using precursors of (Ni,Fe)/r-GO alginate hydrogels through an ion-exchange process, followed by a convenient one-step nitrogenization treatment in NH 3 at 700 °C. The resultant materials exhibited excellent electrocatalytic performance for OER and HER in alkaline media, with only small overpotentials of 270 and 94 mV at a current density of 10 mA cm –2, respectively. The good performance was attributed to abundant active sites and high electrical conductivity of the bimetallic nitrides and efficient mass transport of the 3D r-GO aerogel framework. Furthermore, an alkaline electrolyzer was set up using Ni 3 FeN/r-GO as both the cathode and the anode, which achieved a 10 mA cm –2 current density at 1.60 V with durability of 100 h for overall water splitting. Density functional theory calculations support that Ni 3 FeN (111)/r-GO is more favorable for overall water splitting since the surface electronic structure of Ni 3 FeN is tuned by transferring electrons from Ni 3 FeN cluster to the r-GO through interaction of two metal species. Thus, the currently developed Ni 3 FeN/r-GO with superior water-splitting performance may potentially serve as a material for use in industrial alkaline water electrolyzers.

Metal–organic frameworks (MOFs) have attracted intensive attention for high-performance supercapacitors owing to their large specific surface area and tunable pore structure. Herein, ultrathin NiCo-MOF nanosheets are fabricated by a facile ultrasonication at room temperature and employed as a supercapacitor electrode material. The unique nanosheet-like structure of NiCo-MOF provides more electroactive sites and a shorter pathway for electron transfer and electrolyte diffusion, resulting in excellent electrochemical performance with a high specific capacitance of 1202.1 F g –1 at 1 A g –1 . In addition, an asymmetric supercapacitor of NiCo-MOF//activated carbon was assembled in 2 M KOH electrolyte. It delivers an energy density of 49.4 W h kg –1 at a power density of 562.5 W h kg –1 in a voltage window of 1.5 V. The results demonstrate a new method to fabricate ultrathin MOF nanosheets for high-performance supercapacitor electrode materials.

Supercapacitors as one of the most promising energy storage systems have been extensively studied due to the unique merits such as long-term cycling stability, fast charge rate, and low maintenance cost. It is widely known that the electrochemical performances of supercapacitors are closely related to the structure and specific surface area of the electrode materials. Therefore, many researches are focused on the design and synthesis of the electrode materials with novel shapes and large surface area. CuCo2O4 has recently attracted enormous research interests as the electrode materials for supercapacitors owing to its inherent advantages including high theoretical capacity, environmental friendliness, natural abundance, and low cost. In the practical applications the CuCo2O4 still suffers from some drawbacks, for instance, poor conductivity, relatively low specific capacity, and poor cycling durability. Hence, a comprehensive summary about the recent progress of CuCo2O4-based materials is necessary and significant to better understand the opportunity and challenge that such material faces. In this work, the progress of preparation methods and electrochemical performances of CuCo2O4-based materials is comprehensively reviewed. The aim of this review is to highlight some of the advances made by CuCo2O4-based electrode materials for supercapacitors and guide future research toward closing the gap between achieved and theoretical capacity, without limiting the loading mass.

Surrogate models have shown to be effective in assisting metaheuristic algorithms for solving computationally expensive complex optimization problems. The effectiveness of existing surrogate-assisted metaheuristic algorithms, however, has only been verified on low-dimensional optimization problems. In this paper, a surrogate-assisted cooperative swarm optimization algorithm is proposed, in which a surrogate-assisted particle swarm optimization (PSO) algorithm and a surrogate-assisted social learning-based PSO (SL-PSO) algorithm cooperatively search for the global optimum. The cooperation between the PSO and the SL-PSO consists of two aspects. First, they share promising solutions evaluated by the real fitness function. Second, the SL-PSO focuses on exploration while the PSO concentrates on local search. Empirical studies on six 50-D and six 100-D benchmark problems demonstrate that the proposed algorithm is able to find high-quality solutions for high-dimensional problems on a limited computational budget.

Abstract Organic electrochemical transistors (OECTs) and OECT-based circuitry offer great potential in bioelectronics, wearable electronics and artificial neuromorphic electronics because of their exceptionally low driving voltages (<1 V), low power consumption (<1 µW), high transconductances (>10 mS) and biocompatibility 1–5 . However, the successful realization of critical complementary logic OECTs is currently limited by temporal and/or operational instability, slow redox processes and/or switching, incompatibility with high-density monolithic integration and inferior n-type OECT performance 6–8 . Here we demonstrate p- and n-type vertical OECTs with balanced and ultra-high performance by blending redox-active semiconducting polymers with a redox-inactive photocurable and/or photopatternable polymer to form an ion-permeable semiconducting channel, implemented in a simple, scalable vertical architecture that has a dense, impermeable top contact. Footprint current densities exceeding 1 kA cm −2 at less than ±0.7 V, transconductances of 0.2–0.4 S, short transient times of less than 1 ms and ultra-stable switching (>50,000 cycles) are achieved in, to our knowledge, the first vertically stacked complementary vertical OECT logic circuits. This architecture opens many possibilities for fundamental studies of organic semiconductor redox chemistry and physics in nanoscopically confined spaces, without macroscopic electrolyte contact, as well as wearable and implantable device applications.

This review paper summarizes the categories, sensing mechanisms, and affecting factors of flexible conductive polymer composite-based stretchable strain sensors.

Existing state-of-health (SOH) data-driven prediction techniques for lithium-ion batteries are subject to mass training data, which leads to limited application. To face the challenge, in this article, we propose a novel SOH prediction method based on transfer learning. The long short-term memory (LSTM) combined with fully connected (FC) layers is designed as the base model. The LSTM can learn the long-term dependencies of battery aging to reduce the noise sensitivity of the prediction model, and the FC layers serve as the “firewall” during the transferring process. A feature expression scoring (FES) rule is developed to assess the relevance of multiple prediction tasks. Different from traditional transfer learning, we select the task with the highest FES score to obtain the base model with superior generalization performance. During transfer learning, the fine-tuning strategy is executed for the tasks with high scores, but rebuilding strategy for the low score one. Only using the first 25% of a dataset for transfer training, our technique can predict more phases compared to traditional data-driven methods, which will avoid more unreasonable operations from users. The experimental results verify that the proposed method can achieve accurate, fast, and steady SOH prediction. Compared to some existing data-driven methods, our method obtains optimal performance.

Strengthening of magnesium (Mg) is known to occur through dislocation accumulation, grain refinement, deformation twinning, and texture control or dislocation pinning by solute atoms or nano-sized precipitates. These modes generate yield strengths comparable to other engineering alloys such as certain grades of aluminum but below that of high-strength aluminum and titanium alloys and steels. Here, we report a spinodal strengthened ultralightweight Mg alloy with specific yield strengths surpassing almost every other engineering alloy. We provide compelling morphological, chemical, structural, and thermodynamic evidence for the spinodal decomposition and show that the lattice mismatch at the diffuse transition region between the spinodal zones and matrix is the dominating factor for enhancing yield strength in this class of alloy.

An ultraefficient EMI shielding WPU composite foam with extremely low reflection is achieved <italic>via</italic> ingenious asymmetric conductive network design.

As one of the most promising new energy sources, the lithium-ion battery (LIB) and its associated safety concerns have attracted great research interest. Herein, a comprehensive review on the thermal hazards of LIBs and the corresponding countermeasures is provided. In general, the thermal hazards of the LIB can be caused or aggravated by several factors including physical, electrical and thermal factors, manufacturing defect and even battery aging. Due to the activity and combustibility of traditional battery components, they usually possess a relatively high thermal hazard and a series of side reactions between electrodes and electrolytes may occur under abusive conditions, which would further lead to the thermal failure of LIBs. Besides, the thermal hazards generally manifest as the thermal runaway behaviors such as high-temperature, ejection, combustion, explosion and toxic gases for a single battery, and it can even evolve to thermal failure propagation within a battery pack. To decrease these hazards, some countermeasures are reviewed including the application of safety devices, fire-retardant additives, battery management systems, hazard warnings and firefighting should a hazard occur.

In this work, bundlelike CuCo 2 O 4 microstructures (CuCo 2 O 4 BMs) assembled with ultrathin nanosheets were fabricated through employing an easy and scalable hydrothermal method along with an extra thermal treatment in air. These CuCo 2 O 4 BMs possessed a specific surface area as large as 114.36 m 2 g –1 and a mean pore size of 10.99 nm with pore size distribution at 1.88 nm. The electrochemical behavior was evaluated in 2 M KOH solution. It demonstrated that the CuCo 2 O 4 BMs exhibited the typical features of battery-type electrode material with a specific capacity up to 303.22 C g –1 at 1 A g –1, a rate capability of 69.77% at 10 A g –1, and 71.8% capacity retention after 5000 cycles at 5 A g –1 . A hybrid supercapacitor (HSC) was assembled with CuCo 2 O 4 BMs as the cathode and activated carbon as the anode, respectively. The HSC exhibited a specific capacity of 152.25 C g –1 at 1 A g –1 with 111.75% retention over 5000 cycles and delivered a remarkable energy density of 39.95 W h kg –1 at 944.63 W kg –1 and still maintained 27.06 W h kg –1 even at 8.06 kW kg –1 . By virtue of these impressive electrochemical performances, the CuCo 2 O 4 BMs can serve as a promising battery-type electrode material toward high-performance hybrid supercapacitors and other energy-storage systems.

Developing diatomic catalysts (DACs) for the CO 2 reduction reaction (CO 2 RR) has emerged as a promising leading-edge research area owing to their maximum atomic utility and more sophisticated functionalities. However, the proper design of DACs at an atomic level and an understanding of the synergistic mechanism of binary sites remain challenging. Herein, an N-rich carbon matrix with precisely controlled Ni/Cu dual sites is synthesized through the assistance of metal–organic frameworks. The as-prepared catalyst presents high CO Faradaic efficiency of over 95% from −0.39 to −1.09 V vs reversible hydrogen electrode (RHE) with the maximum value of 99.2% at −0.79 V vs RHE and long-term durability of 60 h electrolysis. Density functional theory studies reveal that the electronic redistribution and band gap narrowing induced by the adjacent NiN 4 and CuN 4 moieties enhance the electron conductivity and strengthen the bonding interactions between *COOH intermediates and Ni centers, thus lowering the overall reaction barriers and promoting CO generation.

Highly efficient electromagnetic shielding materials entailing strong electromagnetic wave absorption and low reflection have become an increasing requirement for next-generation communication technologies and high-power electronic instruments. In this study, a new strategy is employed to provide flexible waterborne polyurethane composite films with an ultra-efficient electromagnetic shielding effectiveness (EMI SE) and low reflection by constructing gradient shielding layers with a magnetic ferro/ferric oxide deposited on reduced graphene oxide (rGO@Fe 3 O 4 ) and silver-coated tetraneedle-like ZnO whisker (T-ZnO/Ag) functional nanoparticles. Because of the differences in density between rGO@Fe 3 O 4 and T-ZnO/Ag, a gradient structure is automatically formed during the film formation process. The gradient distribution of rGO@Fe 3 O 4 over the whole thickness range forms an efficient electromagnetic wave absorption network that endows the film with a strong absorption ability on the top side, while a thin layer of high-density T-ZnO/Ag at the bottom constructs a highly conductive network that provides an excellent electromagnetic reflection ability for the film. This specific structure results in an “absorb–reflect–reabsorb” process when electromagnetic waves penetrate into the composite film, leading to an excellent EMI shielding performance with an extremely low reflection characteristic at a very low nanofiller content (0.8 vol % Fe 3 O 4 @rGO and 5.7 vol % T-ZnO/Ag): the EMI SE reaches 87.2 dB against the X band with a thickness of only 0.5 mm, while the shielding effectiveness of reflection (SE R ) is only 2.4 dB and the power coefficient of reflectivity ( R ) is as low as 0.39. This result means that only 39% of the microwaves are reflected in the propagation process when 99.9999998% are attenuated, which is the lowest value among the reported references. This composite film with remarkable performance is suitable for application in portable and wearable smart electronics, and this method offers an effective strategy for absorption-dominated EMI shielding.

In recent years, the development and research of flexible sensors have gradually deepened, and the performance of wearable, flexible devices for monitoring body temperature has also improved. For the human body, body temperature changes reflect much information about human health, and abnormal body temperature changes usually indicate poor health. Although body temperature is independent of the environment, the body surface temperature is easily affected by the surrounding environment, bringing challenges to body temperature monitoring equipment. To achieve real-time and sensitive detection of various parts temperature of the human body, researchers have developed many different types of high-sensitivity flexible temperature sensors, perfecting the function of electronic skin, and also proposed many practical applications. This article reviews the current research status of highly sensitive patterned flexible temperature sensors used to monitor body temperature changes. First, commonly used substrates and active materials for flexible temperature sensors have been summarized. Second, patterned fabricating methods and processes of flexible temperature sensors are introduced. Then, flexible temperature sensing performance are comprehensively discussed, including temperature measurement range, sensitivity, response time, temperature resolution. Finally, the application of flexible temperature sensors based on highly delicate patterning are demonstrated, and the future challenges of flexible temperature sensors have prospected.