Colloid probe atomic force microscopy (AFM) force measurements are used to elucidate the effect of variation in the cation alkyl chain length and the anion species on IL nanostructure at Au(111) surfaces as a function of potential. Four ionic liquids (ILs) are examined: 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), 1-butyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([BMIM] FAP), 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP) and 1-butyl-3-methylimidazolium iodide ([BMIM] I). The step-wise force-distance profiles show the ILs adopt a multilayered morphology, with stronger near surface structure present at more biased potentials. The results suggest that the innermost (interfacial) layer is enriched in counter ions strongly bound to the Au(111) surface. For ILs with FAP(-) anions, the cations in the interfacial layer at negative potentials pack more neatly than the anions at positive potentials, and thus more effectively template structure in subsequent layers. [BMIM] FAP has the weakest interfacial structure. [EMIM] FAP has stronger interfacial structure because the imidazolium rings of [EMIM](+) cations in the interfacial layer are orientated towards the Au(111) surface, and this more parallel orientation is favourable for templating structure. [HMIM] FAP is more strongly structured than [BMIM] FAP because the longer cation alkyl chain increases solvophobic interactions which lead to better defined near surface structure. The response of [BMIM] I to changes in potential is opposite to that of the FAP(-) ILs. [BMIM] I interfacial nanostructure is stronger at positive potentials, because I(-) anions pack more neatly at the Au(111) surface than [BMIM](+) cations, which templates stronger structure in subsequent layers.

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We present an in situ reduction method to synthesize a novel structured MnO(2)/mesoporous carbon (MnC) composite. MnO(2) nanoparticles have been synthesized and embedded into the mesoporous carbon wall of CMK-3 materials by the redox reaction between permanganate ions and carbons. Thermogravimetric analysis (TG), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), and cyclic voltammetry were employed to characterize these composite materials. The results show that different MnO(2) contents could be introduced into the pores of CMK-3 treated with different concentrations of potassium permanganate aqueous solution, while retaining the ordered mesostructure and larger surface area. Increasing the MnO(2) content did not result in a decrease in pore size from the data of nitrogen sorption isotherms, indicating that MnO(2) nanoparticles are embedded in the pore wall, as evidenced by TEM observation. We obtained a large specific capacitance over 200 F/g for the MnC composite and 600 F/g for the MnO(2), and these materials have high electrochemical stability and high reversibility.

Solid-state fiber-based supercapacitors have been considered promising energy storage devices for wearable electronics due to their lightweight and amenability to be woven into textiles. Efforts have been made to fabricate a high performance fiber electrode by depositing pseudocapacitive materials on the outer surface of carbonaceous fiber, for example, crystalline manganese oxide/multiwalled carbon nanotubes (MnO/MWCNTs). However, a key challenge remaining is to achieve high specific capacitance and energy density without compromising the high rate capability and cycling stability. In addition, amorphous MnO is actually preferred due to its disordered structure and has been proven to exhibit superior electrochemical performance over the crystalline one. Herein, by incorporating amorphous MnO onto a well-aligned MWCNT sheet followed by twisting, we design an amorphous MnO@MWCNT fiber, in which amorphous MnO nanoparticles are distributed in MWCNT fiber uniformly. The proposed structure gives the amorphous MnO@MWCNT fiber good mechanical reliability, high electrical conductivity, and fast ion-diffusion. Solid-state supercapacitor based on amorphous MnO@MWCNT fibers exhibits improved energy density, superior rate capability, exceptional cycling stability, and excellent flexibility. This study provides a strategy to design a high performance fiber electrode with microstructure control for wearable energy storage devices.

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Monodispersed monoclinic BiVO4 nanorods grown along the [010] direction were prepared using a one-step low temperature hydrothermal method in the presence of the low-cost, nontoxic sodium oleate serving as a chelating agent. The BiVO4 nanorods with diameters of 15-20 nm possess a huge specific surface area as large as 28.2 m(2) g(-1), which can endow them with high photocatalytic activity and strong adsorption of reactants. Meanwhile, the specific [010] growth direction is capable of facilitating efficient electron-hole separation by accumulating electrons on {010} facets. Thus, the highly efficient photocatalytic activity of the as-prepared BiVO4 nanorods under visible light, which far surpasses that of commercial P25, is demonstrated by the degradation of rhodamine B and phenol. Plentiful V(4+) species, which can create oxygen vacancies, is detected implying that the as-obtained nanorods are self-doped BiVO4. Significantly, 61% of rhodamine B is adsorbed by the BiVO4 nanorods before irradiation owing to the appearance of plentiful O(2-) and OH(-) species on the surface adsorbed by oxygen vacancies. More excitingly, the excellent visible-light-driven photocatalytic activity of the as-obtained BiVO4 nanorods can be further elevated to an unprecedented level, roughly doubled, after applying a low temperature heat treatment process at 230 °C for 2 h and this improvement could primarily be ascribed to their optimized charge-carrier transport characteristics resulting from elevated crystallinity and decreased V(4+) species.

Atomic force microscopy (AFM) force measurements elucidate the effect of cation alkyl chain length and the anion species on ionic liquid (IL) interfacial structure at highly ordered pyrolytic graphite (HOPG) surfaces as a function of potential. Three ILs are examined: 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIM] FAP), 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMIM] FAP), and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] TFSA). The step-wise force-distance profiles indicate the ILs adopt a multilayered morphology near the surface. When the surface is biased positively or negatively versus Pt quasireference electrode, both the number of steps, and the force required to rupture each step increase, indicating stronger interfacial structure. At all potentials, push-through forces for [HMIM] FAP are the highest, because the long alkyl chain results in strong cohesive interactions between cations, leading to well-formed layers that resist the AFM tip. The most layers are observed for [EMIM] FAP, because the C2 chains are relatively rigid and the dimensions of the cation and anion are similar, facilitating neat packing. [EMIM] TFSA has the smallest push-through forces and fewest layers, and thus the weakest interfacial structure. Surface-tip attractive forces are measured for all ILs. At the same potential, the attractions are the strongest for [EMIM] TFSA and the weakest for [HMIM] FAP because the interfacial layers are better formed for the longer alkyl chain cation. This means interfacial forces are stronger, which masks the weak attractive forces.

Stimulus-responsive hydrogels, such as conductive hydrogels and thermoresponsive hydrogels, have been explored extensively and are considered promising candidates for smart materials such as wearable devices and artificial muscles. However, most of the existing studies on stimulus-responsive hydrogels have mainly focused on their single stimulus-responsive property and have not explored multistimulus-responsive or multifunction properties. Although some works involved multifunctionality, the prepared hydrogels were incompatible. In this work, a multistimulus-responsive and multifunctional hydrogel system (carboxymethyl cellulose/poly acrylic-acrylamide) with good elasticity, superior flexibility, and stable conductivity was prepared. The prepared hydrogel not only showed excellent human motion detection and physiological signal response but also possessed the ability to respond to environmental temperature changes. By integrating a conductive hydrogel with a thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel to form a bilayer hydrogel, the prepared bilayer also functioned as two kinds of actuators owing to the different degrees of swelling and shrinking under different thermal stimuli. Furthermore, the different thermochromic properties of each layer in the bilayer hydrogel endowed the hydrogel with a thermoresponsive “smart” feature, the ability to display and conceal information. Therefore, the prepared hydrogel system has excellent prospects as a smart material in different applications, such as ionic skin, smart info-window, and soft robotics.