anodic aluminum oxide (AAO) molds. Our model electrodes are based on thin gold (Au) fi lms on which AuNWs are grown directly from, and aligned vertically to the fi lm surface. The 1D structure and alignment of the NWs give short path lengths for ion and electron transport. The NWs are seamlessly integrated with the underlying fi lms in an attempt to prevent electrons from scattering at the NW-fi lm interface. Moreover, the proposed method does not require current collectors, binders, and conductive additives. The monolithic feature of the NW-array electrodes effectively circumvents the interfacial resistance typically observed for agglomerated electrodes composed of granular materials. Due to the high electrical conductivity of the metal (>10 5 S cm −1 [ 9 ] , NW-array electrodes designed in this way can suppress internal resistance involved in charge transport, leading to SCs with superior rate performance. More importantly, defects in the NW-array electrode considerably infl uence the internal resistance of the SCs, so device performance is enhanced by creating the electrode structure utilizing a homemade, defect-free AAO mold, effectively reducing the internal resistance and increasing the electroactive area. Figure 1 a illustrates the method used to fabricate the NWarray electrodes. Thin Au fi lms with ≈1.8 µm thickness were fi rst prepared on one side of AAO molds via Au sputtering, followed by electrodeposition of Au. Following this procedure, AuNWs were electrodeposited and grown from the pre-formed Au fi lms through cylindrical pores in the AAO molds, and the height of the NW arrays was uniform at ≈19 µm. After removing the AAO, this method produced fl exible and free-standing monolithic NW-array electrodes as displayed in Figure 1 b. In our approach, the pore structure of the AAO molds can be directly transferred to the structure of the NW-array electrodes. Using this method, we tested two different molds in order to design the electrodes with a desirable structure for SCs. Figure 1 c shows the surface and cross-sectional scanning electron microscope (SEM) images of a commercial AAO mold we tested. The pores had a diameter d = 37.5 ± 9.9 nm (relative standard deviation, RSD = 0.26), and were randomly distributed with the center-to-center spacing of nearest-neighbor pores, r = 129.3 ± 27.4 nm (RSD = 0.21). The large RSDs of d and r refl ect an irregularity in pore size and pore spacing. Additionally, the mold contained defects, both inside the pores and on its surface. The resulting NW-array electrode (henceforth, AuNW D ) had analogous defects (e.g., branched, bottlenecked, and disconnected NWs shown in the top portion of Figure 1 e). We also prepared and tested a homemade, defect-free AAO Incorporation of ionic and electronic charges with nanostructured materials can give rise to interesting conduction phenomena and new device properties. [ 1 ] Supercapacitors (SCs), also called electrochemical capacitors, store energy via the formation of electric double layers (EDLs) within porous electrodes presentin...

In this study, we demonstrate that vertically aligned gold nanowire array electrodes provide rapid ion and electron transport to the electrode–electrolyte interface. The charge-transport properties of the nanowire electrodes were investigated through cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy under a constant-volume device configuration. The total charge stored in the corresponding devices increases monotonically with the length of the nanowires owing to the concomitant increase in the electroactive real surface area of the electrode. A remarkable feature of the electrodes is that the internal resistance associated with charge transport decreases with increasing nanowire length. The electric double-layer capacitance per unit electroactive surface area remains constant up to high charge/discharge rates. Our results demonstrate that charge migration occurs rapidly on the surfaces of the nanowires regardless of their length and the charge/discharge rate used. Thus, vertically aligned nanowire array electrodes show promise as current collectors for next-generation electrochemical energy-storage devices.

Pseudocapacitors have been widely studied in the context of their potential applications in portable electronics and energy regeneration. However, the internal resistance within these devices hampers charge transport and limits their performance. As a result, maximum charge/discharge rates are typically limited to a few hundred mV s for pseudocapacitors. Beyond this limit, capacitance rapidly decreases and devices become incapable of storing energy. Here, we design electrodes in which coaxial nanowires made of highly conductive metal cores and pseudocapacitive organic shells are fabricated into a seamless, monolithic, and vertically aligned structure. The design of this structure reduces its internal resistance, and devices fabricated using these electrodes exhibit excellent energy capacity even when charged/discharged at high rates of more than a few hundred mV s . The energy density obtained in these devices corresponds to the maximum energy density predicted by the Trasatti method, and the coaxial-nanowire structure of the electrodes enhances the charge storage capacity and rate capability simultaneously.

The reduction of internal resistance in supercapacitors is essential for storing and delivering a large amount of energy at high speed. In article number 1500354, H. Nakanishi and co‐workers have developed all‐metal monolithic nanowire array supercapacitor electrodes that allow for ultrafast charge/discharge rates of up to 300 V s−1. Defects in nanowire arrays greatly influence device performance. Supercapacitor electrodes prepared from defect‐free molds lower the internal resistance, providing superior performance at higher energy and power densities.

The Inside Cover picture shows a gold nanowire electrode (top), and a coaxial nanowire electrode with nanowires that have a gold core and a polypyrrole shell (bottom). The coaxial nanowire electrode has the ability to store a large amount of energy through the pseudocapacitance of the outer polypyrrole layer, and charge can be transferred to the inner gold core at fast rates, making it ideal for use in pseudocapacitors. This coaxial structure is effective at reducing the internal resistance of the electrode and the energy density is increased without a noticeable deterioration of power density. More details can be found in the Full Paper by Nakanishi et al. on page 701 in Issue 4, 2017 (DOI: 10.1002/cssc.201601310).