The oxygen, O, in air interferes with the detection of H by palladium (Pd)-based H sensors, including Pd nanowires (NWs), depressing the sensitivity and retarding the response/recovery speed in air-relative to N or Ar. Here, we describe the preparation of H sensors in which a nanofiltration layer consisting of a Zn metal-organic framework (MOF) is assembled onto Pd NWs. Polyhedron particles of Zn-based zeolite imidazole framework (ZIF-8) were synthesized on lithographically patterned Pd NWs, leading to the creation of ZIF-8/Pd NW bilayered H sensors. The ZIF-8 filter has many micropores (0.34 nm for gas diffusion) which allows for the predominant penetration of hydrogen molecules with a kinetic diameter of 0.289 nm, whereas relatively larger gas molecules including oxygen (0.345 nm) and nitrogen (0.364 nm) in air are effectively screened, resulting in superior hydrogen sensing properties. Very importantly, the Pd NWs filtered by ZIF-8 membrane (Pd NWs@ZIF-8) reduced the H response amplitude slightly (ΔR/R = 3.5% to 1% of H versus 5.9% for Pd NWs) and showed 20-fold faster recovery (7 s to 1% of H) and response (10 s to 1% of H) speed compared to that of pristine Pd NWs (164 s for response and 229 s for recovery to 1% of H). These outstanding results, which are mainly attributed to the molecular sieving and acceleration effect of ZIF-8 covered on Pd NWs, rank highest in H sensing speed among room-temperature Pd-based H sensors.

In this work, we prepared a well-aligned palladium oxide nanowire (PdO NW) array using the lithographically patterned Pd nanowire electrodeposition (LPNE) method followed by subsequent calcination at 500 °C. Sensitization with platinum (Pt) nanoparticles (NPs), which were functionalized on PdO NWs through a simple reduction process, significantly enhanced the detection capability of the Pt-loaded PdO NWs (Pt-PdO NWs) sensors toward hydrogen gas (H2) at room temperature. The well-distributed Pt NPs, which are known chemical sensitizers, activated the dissociation of H2 and oxygen molecules through the spillover effect with subsequent diffusion of these products to the PdO surface, thereby transforming the entire surface of the PdO NWs into reaction sites for H2. As a result, at a high concentration of H2 (0.2%), the Pt-PdO NWs showed an enhanced sensitivity of 62% (defined as ΔR/R air × 100%) compared to that (6.1%) of pristine PdO NWs. The Pt-PdO NWs exhibited a response time of 166 s, which was 2.68-fold faster than that of pristine PdO NWs (445 s). In addition, the Pt-PdO NWs responded to a very low concentration of H2 (10 ppm) with a sensitivity of 14%, unlike the pristine PdO NWs, which did not exhibit any response at that concentration. These outstanding results are mainly attributed to a homogeneous decoration of Pt NPs on the surface of well-aligned PdO NWs. In this work, we demonstrated the potential suitability of Pt-PdO NWs as a highly sensitive H2 sensing layer at room temperature.

Palladium (Pd) nanoparticle (NP)-decorated carbon nanotube (CNT) ropes (or CNT@PdNP) are used as the sensing element for hydrogen gas (H) chemiresistors. In spite of the fact that Pd NPs have a mean diameter below 6 nm and are highly dispersed on the CNT surfaces, CNT@PdNP ropes produce a relative resistance change 20-30 times larger than is observed at single, pure Pd nanowires. Thus, CNT@PdNP rope sensors improve upon all H sensing metrics (speed, dynamic range, and limit-of-detection), relative to single Pd nanowires which heretofore have defined the state-of-the-art in H sensing performance. Specifically, response and recovery times in air at [H] ≈ 50 ppm are one-sixth of those produced by single Pd nanowires with cross-sectional dimensions of 40 × 100 nm Pd. The LOD is <10 ppm versus 300 ppm, and the dynamic range (10 ppm -4%) is nearly twice that afforded by the Pd nanowire. CNT@PdNP rope sensors are prepared by the dielectrophoretic deposition of a single semiconducting CNT rope followed by the electrodeposition of Pd nanoparticles with mean diameters ranging from 4.5 (±1) nm to 5.8 (±3) nm. The diminutive mean diameter and the high degree of diameter monodispersity for the deposited Pd nanoparticles are distinguishing features of the CNT@PdNP rope sensors described here, relative to prior work on similar systems.

Pd based alloy materials with hollow nanostructures are ideal hydrogen (H) sensor building blocks because of their double-H sensing active sites (interior and exterior side of hollow Pd alloy) and fast response. In this work, for the first time, we report a simple fabrication process for preparing hollow Pd-Ag alloy nanowires (Pd@Ag HNWs) by using the electrodeposition of lithographically patterned silver nanowires (NWs), followed by galvanic replacement reaction (GRR) to form palladium. By controlling the GRR time of aligned Ag NWs within an aqueous Pd-containing solution, the compositional transition and morphological evolution from Ag NWs to Pd@Ag HNWs simultaneously occurred, and the relative atomic ratio between Pd and Ag was controlled. Interestingly, a GRR duration of 17 h transformed Ag NWs into Pd@Ag HNWs that showed enhanced H response and faster sensing response time, reduced 2.5-fold, as compared with Ag NWs subjected to a shorter GRR period of 10 h. Furthermore, Pd@Ag HNWs patterned on the colorless and flexible polyimide (cPI) substrate showed highly reversible H sensing characteristics. To further demonstrate the potential use of Pd@Ag HNWs as sensing layers for all-transparent, wearable H sensing devices, we patterned the Au NWs perpendicular to Pd@Ag HNWs to form a heterogeneous grid-type metallic NW electrode which showed reversible H sensing properties in both bent and flat states.

Here, we propose heterogeneous nucleation-assisted hierarchical growth of metal-organic frameworks (MOFs) for efficient particulate matter (PM) removal. The assembly of two-dimensional (2D) Zn-based zeolite imidazole frameworks (2D-ZIF-L) in deionized water over a period of time produced hierarchical ZIF-L (H-ZIF-L) on hydrophilic substrates. During the assembly, the second nucleation and growth of ZIF-L occurred on the surface of the first ZIF-L, leading to the formation of flowerlike H-ZIF-L on the substrate. The flowerlike H-ZIF-L was easily synthesized on various substrates, namely, glass, polyurethane three-dimensional foam, nylon microfibers, and nonwoven fabrics. We demonstrated H-ZIF-L-assembled polypropylene microfibers as a washable membrane filter with highly efficient PM removal property (92.5 ± 0.8% for PM and 99.5 ± 0.2% for PM), low pressure drop (10.5 Pa at 25 L min), long-term stability, and superior recyclability. These outstanding particle filtering properties are mainly attributed to the unique structure of the 2D-shaped H-ZIF-L, which is tightly anchored on individual fibers comprising the membrane.

The preparation by electrodeposition of transverse nanowire electroluminescent junctions (tn-ELJs) is described, and the electroluminescence (EL) properties of these devices are characterized. The lithographically patterned nanowire electrodeposition process is first used to prepare long (millimeters), linear, nanocrystalline CdSe nanowires on glass. The thickness of these nanowires along the emission axis is 60 nm, and the width, wCdSe, along the electrical axis is adjustable from 100 to 450 nm. Ten pairs of nickel-gold electrical contacts are then positioned along the axis of this nanowire using lithographically directed electrodeposition. The resulting linear array of nickel-CdSe-gold junctions produces EL with an external quantum efficiency, EQE, and threshold voltage, Vth, that depend sensitively on wCdSe. EQE increases with increasing electric field and also with increasing wCdSe, and Vth also increases with wCdSe and, therefore, the electrical resistance of the tn-ELJs. Vth down to 1.8(±0.2) V (for wCdSe ≈ 100 nm) and EQE of 5.5(±0.5) × 10(-5) (for wCdSe ≈ 450 nm) are obtained. tn-ELJs produce a broad EL emission envelope, spanning the wavelength range from 600 to 960 nm.

Nb 2 O 5 is a Li + intercalation metal oxide that is of current interest for lithium ion battery electrodes. The electrophoretic deposition (ED) of Nb 2 O 5 thin-films from aqueous, NbO x colloidal solutions is reported here. For films ranging in thickness from 38 to 144 nm, the mass loading of Nb 2 O 5 on the electrode is correlated with the coulometry of ED using quartz crystal microbalance gravimetry. Crystalline, phase pure films of orthorhombic, T-Nb 2 O 5 , are obtained by postdeposition calcination. These films exhibit unusually high specific capacities for Li +-based energy storage as a consequence of ≈70% porosity. For example, a 60 nm thick film displays a specific capacity, C sp , of 420 mAh/g at 5 A/g and 220 mAh/g at 50 A/g, which can be compared with the theoretical Faradaic capacity of 202 mAh/g. T-Nb 2 O 5 films also have a specific energy density in the range from 770−486 Wh/kg, and a specific power density in the range from 9 to 90 kW/kg. These excellent energy storage metrics are attributed to augmentation of the Faradaic capacity by high double-layer capacities enabled by the mesoporous structure of these films. 37 of a few k B T, for Li + transport in this material, as measured 38 using nuclear magnetic resonance. 39 T-Nb 2 O 5 is most often synthesized by hydrothermal 40 methods, 1,2,4,13,14 and highly dispersed T-Nb 2 O 5 on carbon 41 has demonstrated specific capacities of up to 590 F/g. 14 Other 42 methods for preparing Nb 2 O 5 films include electrospinning 43 followed by thermal annealing, 16 spray pyrolysis, 17 sol−gel 44 processing methods, 9,10,18 electrospinning, 19 and reactive 45 sputtering. 11 46 Electrodeposition has hardly been attempted, in spite of the 47 fact that it is an attractive method for both electrochromics and 48 battery/capacitor materials because it promotes an electrically 49 intimate contact with an electrode that can also serve as a 50 current collector. The reason is that electrodeposition of 51 Nb 2 O 5 is difficult: the cathodic electrodeposition of niobium 52 oxides (NbO x) is complicated by the very negative reduction 53 potential for Nb 3+ (−1.1 V vs NHE) which makes disruptive

Nb 2 O 5 is a Li + intercalation transition metal oxide that is of current interest for lithium ion battery and capacitor electrodes. For orthorhombic (T) Nb 2 O 5 films prepared by electrophoretic deposition (EPD) and subjected to lithiation/ delithiation cycling, a remarkably reproducible degradation process is observed. It is characterized by the onset of irreversible capacity loss from a baseline specific capacity, C sp , of 400 (±50) F/g at 1000 (± 500) cycles. A gradual reduction of C sp occurs during the ensuing 9000 cycles after which the C sp stabilizes at 200 (±25) F/ g. We investigate this degradation using six ex situ instrumental methods and more than 100 individual Nb 2 O 5 films to characterize and understand the composition, atomic scale structure, chemical bonding, electrochemical, and electrical properties of these films during these 10,000 cycles. What emerges is a multidimensional picture of the degradation process in which the decline in C sp occurs concurrently with an increase in the charge transfer resistance, a loss of crystalline order, and the dissolution of niobium from the film.