Wearable electronics have received considerable attention in recent years. These devices have penetrated every aspect of our daily lives and stimulated interest in futuristic electronics. Thus, flexible batteries that can be bent or folded are desperately needed, and their electrochemical functions should be maintained stably under the deformation states, given the increasing demands for wearable electronics. Carbon nanomaterials, such as carbon nanotubes, graphene, and/or their composites, as flexible materials exhibit excellent properties that make them suitable for use in flexible batteries. Herein, the most recent progress on flexible batteries using carbon nanomaterials is discussed from the viewpoint of materials fabrication, structure design, and property optimization. Based on the current progress, the existing advantages, challenges, and prospects are outlined and highlighted.

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area efficiency by mimicking human neurons, synapses, and their networks. [3,4] Memristors are known as promising candidates for artificial synapses, constituting a key building block for neuromorphic computing. Moreover, crossbar array (CBA) made of memristors is promising to construct neural networks due to its fast and highly parallelized computing capability that utilizes multiply-and-accumulate (MAC) operation based on Ohm's law and Kirchhoff 's law. [5,6] However, state-of-the-art memristive CBA using transition metal oxide (TMO) is suffering from challenges such as limited resistive switching (RS) ratio and considerable temporal (cycle-to-cycle) and spatial (device-todevice) variability, [7][8][9] which necessitates alternative material platforms with better switching reliability.Memristors based on 2D materials have emerged as a promising option over TMObased memristors [10,11] due to their unique properties and superior device performance, including large RS ratio, [12] low switching voltage, [12,13] small device variation, [14] as well as, capability of transition between the threshold and bipolar RS. [12,15] However, conventional 2D material-based memristive devices are fabricated using mechanical exfoliation, which lacks a good control of flake thickness and poor spatial variation. [16][17][18][19] Moreover, due to the single crystallinity of the exfoliated flake, post-treatments are required to decorate defects for creating switching pathways, such as, ion and electron beam irradiation, which hinder the implementation of circuits and computing hardware. [15,[20][21][22] To address these inherent limitations caused by mechanical exfoliation, considerable efforts have been dedicated to develop scalable fabrication processes. One such approach is liquid-phase exfoliation and spin-coating, which can produce large quantities of materials, but at the expense of crosspoint area scaling and nanoflake orientation control, resulting in poor endurance and low array density. [23][24][25] Another scalable approach is wafer-scale 2D material synthesis that by far has been primarily driven by logic applications which demand monolayer, high mobility, and single crystallinity. [26,27] Recently, memristors based on chemical vapor deposition (CVD) grown 2D materials with intrinsic defects have been demonstrated with the potential for wafer-scale device fabrication capability with low device Memristor crossbar with programmable conductance could overcome the energy consumption and speed limitations of neural networks when executing core computing tasks in image processing. However, the implementation of crossbar array (CBA) based on ultrathin 2D materials is hindered by challenges associated with large-scale material synthesis and device integration. Here, a memristor CBA is demonstrated using wafer-scale (2-inch) polycrystalline hafnium diselenide (HfSe 2 ) grown by molecular beam epitaxy, and a metal-assisted van der Waals transfer technique. The memristor exhibits small switching voltage (0.6 V), low switching energy...

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In this paper, we reported that oxygen vacancies could be introduced in tungsten oxide hierarchical nanostructures through air treatment at certain temperatures. The production of oxygen vacancies may be due to two mechanisms, i.e., critical phase transition and nanoscale inhomogeneous deformation, depending on the annealing temperature or time and the size of the building block. The oxygen vacancies can be introduced at 300 and 350 °C when critical phase transformation from orthorhombic WO3·0.33H2O to hexagonal WO3 takes place or 350 and 400 °C when nanoscale inhomogeneous deformation occurs in the nanobelts. Moreover, the oxygen vacancy concentration is also influenced by the annealing time. For comparison, the oxygen vacancies are also introduced by hydrogen treatment. It is found that a certain amount of oxygen vacancies introduced by air treatment could trap and transfer electrons, thus decreasing the electron–hole recombination rate and improving the conductivity, while an abundance of oxygen vacancies introduced by hydrogen treatment could facilitate the electron–hole pair recombination and destroy the hexagonal tunnel structure, resulting in lower photocatalytic activity and electrochemical performance. Through air treatment, the constant rate of photocatalytic performance in degrading rhodamine B under visible light irradiation can reach 0.0300 min–1, and the specific capacitance can improve to 166.7 F/g. It is suggested that both photocatalytic activity and electrochemical performance can be greatly improved by introducing a proper concentration of oxygen vacancies through air treatment.