packaging, account for a large fraction of the total weight of the device, the use of thin electrodes results in a signifi cantly lower energy density than what could be attained using thicker electrodes. [ 3 ] Therefore, the development of thick electrodes for supercapacitors represents an important direction for making high-energy supercapacitors for practical applications.We recently developed a class of pseudocapacitive anode materials for asymmetric supercapacitors composed of interpenetrating networks of carbon nanotubes (CNTs) and V 2 O 5 nanowires. [ 16 ] The CNTs and nanowires were intimately intertwined into a hierarchically porous structure, enabling effective electrolyte access to the electrochemically active materials without limiting charge transport. Such composites exhibited high specifi c capacitance ( > 300 F g − 1 ) at high current density (1 A g − 1 ) in aqueous electrolyte. In this paper we report the fabrication of high energy density asymmetric supercapacitors containing thick-fi lm electrodes (over 100 μ m thick) of the CNT/V 2 O 5 nanowire composite in combination with an organic electrolyte, which allows for a higher initial cell potential. The excellent conductivity, high specifi c capacitance, and large voltage window of the CNT/V 2 O 5 nanocomposite enable the fabrication of devices with an energy density as high as 40 Wh kg − 1 at a power density of 210 W kg − 1 . Even at a high power density of 6 300 W kg − 1 , the device possesses an energy density of nearly 7.0 Wh kg − 1 . Moreover, the resulting devices exhibit excellent cycling stability. This work demonstrates that the nanowire composite approach is an effective strategy towards high-energy and high power density supercapacitors. Figure 1 A shows a representative scanning electron microscopy (SEM) image of a nanocomposite with 18 wt% of CNTs, demonstrating a continuous fi brous structure (Figure 1 A). The intertwined networks of the CNTs and nanowires exhibit an electrical conductivity of ≈ 3.0 S cm − 1 , which is 80 times higher than that of V 2 O 5 nanowires (0.037 S cm − 1 ). Figure 1 B is a transmission electron microscopy (TEM) image of a V 2 O 5 nanowire with a diameter of around 50 nm. The high-resolution TEM (HRTEM) image (inset) suggests the nanowire contains a layered crystalline structure; the small nanowire dimension allows effective Li + diffusion. Moreover, nitrogen sorption isotherms ( Figure S1, Supporting Information) and higher resolution SEM images of the etched composite fi lm (Figure 1 A, inset) show that the composite possesses a hierarchically porous structure; the presence of large pores enables rapid electrolyte transport while the small pores effectively increase the surface area available for electrochemical reactions. These small pores are responsible for the surface area of 125 m 2 g − 1 determined for the composite.An ideal electrical energy storage device provides both high energy and power density. [ 1 , 2 ] Supercapacitors exhibit signifi cantly higher power densities compared to batteries and ...

A morphotropic phase boundary driven by epitaxial strain has been observed in lead‐free multiferroic BiFeO3 thin films and the strain‐driven phase transitions have been widely reported as iso‐symmetric Cc‐Cc by recent works. In this paper, it is suggested that the tetragonal‐like BiFeO3 phase identified in epitaxial films on (001) LaAlO3 single crystal substrates is monoclinic MC. This MC phase is different from the MA type monoclinic phase reported in BiFeO3 films grown on low mismatch substrates, such as SrTiO3. This is confirmed not only by synchrotron X‐ray studies but also by piezoresponse force microscopy measurements. The polarization vectors of the tetragonal‐like phase lie in the (100) plane, not the (110) plane as previously reported. A phenomenological analysis is proposed to explain the formation of MC Phase. Such a low‐symmetry MC phase, with its linkage to MA phase and the multiphase coexistence open an avenue for large piezoelectric response in BiFeO3 films and shed light on a complete understanding of possible polarization rotation paths and enhanced multiferroicity in BiFeO3 films mediated by epitaxial strain. This work may also aid the understanding of developing new lead‐free strain‐driven morphotropic phase boundary in other ferroic systems.

Ir‐based binary and ternary alloys are effective catalysts for the electrochemical oxygen evolution reaction (OER) in acidic solutions. Nevertheless, decreasing the Ir content to less than 50 at% while maintaining or even enhancing the overall electrocatalytic activity and durability remains a grand challenge. Herein, by dealloying predesigned Al‐based precursor alloys, it is possible to controllably incorporate Ir with another four metal elements into one single nanostructured phase with merely ≈20 at% Ir. The obtained nanoporous quinary alloys, i.e., nanoporous high‐entropy alloys (np‐HEAs) provide infinite possibilities for tuning alloy's electronic properties and maximizing catalytic activities owing to the endless element combinations. Particularly, a record‐high OER activity is found for a quinary AlNiCoIrMo np‐HEA. Forming HEAs also greatly enhances the structural and catalytic durability regardless of the alloy compositions. With the advantages of low Ir loading and high activity, these np‐HEA catalysts are very promising and suitable for activity tailoring/maximization.

The combination of epitaxial strain and defect engineering facilitates the tuning of the transition temperature of BaTiO3 to >800 °C. Advances in thin-film deposition enable the utilization of both the electric and elastic dipoles of defects to extend the epitaxial strain to new levels, inducing unprecedented functionality and temperature stability in ferroelectrics.