properties assisted in moisture absorption. The Namib Desert beetles and Texas horned lizard collect dew using their bumpy body surface with alternating regions of hydrophilic and hydrophobic, and the honeycomb structures on the scale increase condensation foci. [3][4][5][6] These excellent water harvesting creatures elucidate the critical role of wettability irregularity and hierarchical structure gradient in guiding water transport. [7] Inspired by nature, researchers have developed artificial water harvesters, [7][8][9][10][11][12][13][14][15][16][17][18] such as water collecting filaments and hydrophobichydrophilic patterned fog collectors. [19][20][21][22] However, most of the water harvesters developed so far are based on either a 2D surface or a 1D filament.Recently, researchers have uncovered that porous membranes with wettability gradient or wettability contrast in thickness direction can have a "smart" directional wicking effect, which enables water to transfer automatically across the membrane just in one direction. [23][24][25][26][27][28][29][30] Our previous works have reported the preparation of hydrophobic-to-hydrophilic gradient fabrics that can guide directional water-transport from the hydrophobic to the hydrophilic side. [31,32] Such a unidirectional water penetration phenomenon was also reported by other researchers. In research literatures, the directional water transport was also termed "one-way water transport," "directional wicking," [33][34][35] or "water diode." [36][37][38][39][40] Almost all the directional water transport membranes have a hydrophobic layer on one side and a hydrophilic layer on the other, a typical feature of Janus membranes. However, not all Janus membranes have a directional wicking property because Janus membranes might have bidirectional or nonwicking properties, depending on the hydrophobic/hydrophilic combination layout. [36,38,39] Despite the reports about the preparation and applications of directional wicking porous media, limited attention has been devoted to using them for water harvesting.Herein, we report a novel finding about harvesting water from air using hydrophobic/superhydrophilic directional wicking nanofibrous membranes. A two-step electrospinning method was employed to prepare directional wicking fibrous membranes using polyacrylonitrile (PAN) as a starting material. The directional wicking membranes were found to have much larger water harvesting capacity than those with homogeneous wettability and the same fibrous structure. The porous structure and pore dimension also contributed to water harvesting.Previous studies about water harvesting from airborne moisture, which is driven by a directional water transport principle, are based on either a 2D surface or a 1D filament. Porous membranes with a directional water transport capability are seldom used for water harvesting. Herein, a novel hydrophobic/ hydrophilic directional-wicking nanofibrous membrane is reported showing enhanced water harvesting ability. In comparison to the hydrophobic or hy...

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nitride (InN) nanowire energy harvesters [8][9][10][11][12][13][14] ; 2) triboelectric-based generators with multiple electrification pairs or a sliding Schottky nanocontact [15][16][17] ; 3) conducting polymer-metal Schottky diodes. [18,19] In our previous studies, we have demonstrated that a conducting polymer film when forming a Schottky contact with a metal (such as Al or Al alloy) can produce DC outputs under compressive deformations. [18,19] The devices showed a large energy density. They are easy to fabricate, offering great potential for applications in various self-powered electronic devices.Polyaniline (PANI) is a major conducting polymer possessing high conductivity and processing ability. [20] It has shown vast application potential in the fields of supercapacitors, batteries, sensors, EMI shielding, and gas separation. [21][22][23] PANI can be easily doped and de-doped. The dopant and doping state have a great effect on the electrical properties of PANI. [24] For example, PANI emeraldine base (PANI-EB), i.e., non-doped PANI, is almost nonconductive with an electrical resistivity as high as 10 10 Ω cm −1 . [25] The conductivity is largely enhanced when doped with a protonic acid. [26] The dopant effect was attributed to the change of PANI crystallinity, interchain distance, and energy bandgap, hence leading to change in chemical and physical properties (e.g., electrochemical, spectroscopic, and modulus). [24,27,28] However, how dopant affects the energy conversion property of PANI-metal Schottky diodes has not been reported in research literature.In this study, we have for the first time demonstrated the effect of dopants on the mechanical-to-electrical energy conversion behavior of a conducting polymer-metal Schottky power generator. PANI was used as a conducting polymer model, which was doped with four protonic acids; orthophosphoric acid (H 3 PO 4 ), sulfuric acid (H 2 SO 4 ), perchloric acid (HClO 4 ), and hydrochloric acid (HCl). The dopants showed a great effect on energy conversion property. The device made of nondoped PANI only produced up to 1.5 mV and 0.55 nA cm −2 electrical outputs. The one from HCl-doped PANI generated much higher outputs (0.9 V and 33.9 µA cm −2 ) than those from PANI doped with other protonic acids. The change in electrical outputs was attributed to the effect of dopant on barrier height and conductivity. For Al/PANI-HCl/Au, the barrier height decreased significantly from 0.87 to 0.78 eV when the Conducting polymer-metal Schottky diodes show an interesting mechanical energy-to-electricity conversion ability to generate direct current (DC) power without rectification. However, little is reported about how dopants in conducting polymer affect the energy conversion behavior of Schottky diodes. In this study, a novel effect of dopants on mechanical energy-to-DC electricity conversion of conducting polymer-metal Schottky devices is demonstrated. Using polyaniline (PANI) as a model, conducting polymers doped with a series of protonic acids is prepared. Without dopant, the dev...

based on their structures: (1) fiber electrode wrapped fiber devices (FEWFDs), [1] (2) twisted fiber devices (TFDs), [2] (3) sheath-core single fiber device (SCSFDs), [2b,3] and (4) parallel coil electrode in single fiber devices (PCFDs). These fiber-shaped electronic devices are schematically illustrated in Figure S1 (Supporting Information). TFDs are prepared by twisting two fibrous electrodes, which can be prepared either by metallic wires or electrically conductive fiber. FEWFDs are set asymmetrically by wrapping a fibrous electrode onto another fiber electrode. The electrode arrangement in both TFD and FEWFD can be adjusted by changing the screw pitch or twisting tightness of the fibrous electrodes. SCSFDs have a multiple layer structure with a similar configuration to sandwich structured flat electronic devices, where the electroactive layers are deposited layer-by-layer between the internal and the external electrodes. PCFDs were later developed than other types of the fiber devices. PCFDs combine the structure features of FEWFDs and SCSFDs. The parallel coil electrodes resemble wrapping structure in appearance, but the electrode substances are deposited either chemically or physically, rather than being wrapped onto the fiber substrates, hence adhering on the fiber surface with a reasonable adhesion. Therefore, PCFDs are structurally stable and adjustable.Electrochromic materials change their optical properties (e.g., absorbance and transmittance) in response to the change of electrical potential applied. [4] The coloration and decoloration stem from their redox states which have different colors. By changing the electric potential, doping or de-doping takes place in the electrochromic materials. Electrochromism is conventionally used for making smart windows and antiglare mirrors. Wearable electrochromic devices are expected to find applications in the fields of displaying, decoration, safety warning, and sensors.Multiple color electrochromic devices offer potential in showing material state based on voltage applied. In combination with optical devices, such as optical attenuators, [5] multiple color can be used to tune light wavelength hence regulating signal transmittance as well. In addition, multiple colors driven by voltage make it possible to develop displaying devices with a simple device structure. [6] Wearable electrochromic devices were reported recently. [7] However, most of the flexible electrochromic devices adopted either a planar sandwiched device Wearable electrochromic devices with a multiple color changing effect have shown great potential for applications in the fields of displaying, decoration, safety warning, and sensors. However, limited attention is paid toward the preparation of multicolor electrochromic fiber devices. In this study, a set of electrochromic fibers which can change their color between dark red, green, and gold is prepared. The fiber devices are prepared by forming dual helix metal electrodes along a plastic fiber substrate and by subsequently depositing tung...

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