Flexible humidity sensor based on light-scribed graphene oxide

Journal of Materials Science: Materials in Electronics - The light scribe (LS) technique has been applied to reduce graphene oxide (LSGO) over a flexible substrate to be used as a humidity sensor....     

Microstructural investigation of friction stir welded 7050-T651 aluminium

The grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal. The various regions were studied in detail to better understand the microstructural evolution during friction stir welding (FSW). The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Using the combination of structural characteristics observed in each weld region, a new dynamic recrystallization model has been proposed. The precipitation phenomena in different weld regions are also discussed.     

Enhanced Electro-catalytic Activity of Nitrogen-doped Reduced Graphene Oxide Supported PdCu Nanoparticles for Formic Acid Electro-oxidation

Successful commercialization of direct formic acid fuel cells (DFAFCs) is restricted because of its apparent instability in acidic medium and high cost of typically noble metal based anode catalyst. To adequately address these key issues, in this work, a series of palladium-copper alloy catalyst supported on nitrogen-doped reduced graphene oxide (N-rGO) were synthesized via wet chemical reduction process. Several microscopic and spectroscopic techniques were employed to determine the crystal pattern, particle size, composition and morphology of the synthesized material. Electro-catalytic performance of the synthesized catalysts was carefully verified with respect to formic acid oxidation. All N-doped reduced graphene oxide (N-rGO) supported catalyst show enhanced catalytic activity in comparison to commercial Pd/C catalyst. Electrochemical study reveals precisely that Pd₇₅Cu₂₅/N-rGO catalysts have highest electro catalytic activity 1738 mA mg⁻¹_pd among all synthesized catalyst which is 3.67 times higher than commercial Pd/C catalyst. Pd₇₅Cu₂₅/N-rGO catalyst show lowest Tafel slope (119 mV dec⁻¹) and excellent stability after 250 potential cycles. These extensive studies signify that N-rGO support material can remarkably improve the catalytic activity and stability of the catalysts which may be due to outstanding electron transfer capability and synergy between PdCu metallic and N-rGO support. This work helps further design of alloy nanoparticles on N-rGO support as a highly active and stable catalyst for application in the fuel cell.     

Palladium-zirconia diffusion bonds: Mechanical properties and interface reactions

High strength and toughness diffusion bonds have been fabricated using palladium foils between TZP zirconia blocks at temperatures above 1000°C in vacuum. Bonds fabricated below 1000°C in vacuum and under all conditions in air showed negligible strength. Strong, vacuum made bonds lost almost all their strength on annealing in air above 1000°C, anneals in vacuum also resulted in a decrease in bond strength but with a much less marked effect. PdZrO₂ interfaces have been characterised by cross-sectional TEM and a thin reaction zone identified. Microanalysis identified the presence of Pd, Zr and O in a ratio of approximately 30:52:18 in the reaction interlayer. This composition has a Pd:Zr ratio close to that of a steep eutectic in the PdZr binary system and evidence for the presence of a liquid phase at the PdZrO₂ interface during bonding is presented. The strength and toughness of the bonds are shown to be strongly dependent on the perfection of the bonded interface with the presence of a small fraction of voids causing a significant reduction in bond strength and toughness. Simple slip-line field methods are used to illustrate the influence of interface voids on the plastic constraint of bonded thin ductile layers.     

Electro-oxidation mechanisms of methanol and formic acid on Pt-Ru alloy surfaces

Voltammetry combined with single-potential alteration infrared spectroscopy (SPAIRS) were used to study the extent of adsorbed CO produced at Pt, Ru and Pt-Ru alloy electrodes during methanol and formic acid oxidation in acidic supporting electrolyte. The addition of even small atomic fractions of Ru to Pt surfaces caused a decrease in the quasi-steady-state level of CO on the surface for both reactions. This result is consistent with the bifunctional mechanism proposed previously: Ru sites nucleate oxygen containing species at ≈0.2-0.3 V lower potential than on the pure Pt surface; the adsorption of methanol occurs on Pt ensembles producing adsorbed CO; in the case of formic acid, adsorption is equally facile at Pt-Pt, Pt-Ru and Ru-Ru sites, with dehydration producing adsorbed CO; the further electro-oxidation of CO is catalyzed by oxygen-containing species nucleated onto nearby by Ru atoms. The improved efficiency of the alloy surfaces for oxidation of adsorbed CO at low potential shifts the rate limiting step to the adsorption step, which results in very low coverages of the surfaces by adsorbed CO.     

Assessing the optoelectronic behavior of soiled silicon photovoltaic cell under harsh environmental conditions

In the current study, a monocrystalline Si photovoltaic(PV) cell was modeled using solar cell capacitance simulator(SCAPS) to demonstrate the optoelectronic performance of the cell under harsh environmental conditions. Harsh conditions are simulated in terms of wind speed and temperature fluctuations within the presence of a dust layer. All models are evaluated with respect to a bare model with no dust layer accumulated and operating under standard test conditions(STC). Accordingly, the PV under...     

Flow and heat transfer from a continuous surface in a parallel free stream of micropolar fluid

Boundary layer solutions are presented to investigate the steady now and heat transfer characteristics from a continuous flat surface moving in a parallel free stream of micropolar fluid. Numerical results are presented for the distribution of velocity, micro-rotation and temperature profiles within the boundary layer. The groupings of the material properties of the fluid were allowed to vary over a wide range.     

Lead-free multilayer ceramic capacitors with ultra-wide temperature dielectric stability based on multifaceted modification

The rapid development of high technology—such as space exploration and electric vehicles—urgently requires ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to achieve reliable operation of electronic circuits in harsh environments. However, simultaneously achieving high dielectric permittivity, low dielectric loss, and ultrahigh thermal stability has been a major challenge for practical dielectric ceramics. The co-firing matching of the internal electrode and the dielectric ceramic is also an important factor that affects the reliability of UWT MLCCs. Herein, through multifaceted modification—i.e., composition design related to the modulation of the local polar nanoregions (PNRs) and optimizing device sintering in the context of the compatibility of the heterogeneous interface—these concerns have been well-addressed. A new lead-free dielectric system (1-x) (0.56Na_0.5Bi_0.5TiO₃-0.14K_0.5Bi_0.5TiO₃-0.3NaNbO₃)-xCaZrO₃ (NKBTNN-xCZ) dominated by P4bm PNRs was designed and corresponding UWT MLCCs with reliable Pt internal electrode interface bonding were fabricated by optimizing the sintering temperature. A record-high dielectric permittivity (ε_r = 839 ± 15 %) and low dielectric loss (tanδ ≤0.02) was achieved over an ultra-wide temperature range from -70 °C to 337 °C for NKBTNN-0.063CZ UWT MLCCs. This work suggests that multifaceted modification should be generalized for construction of high-performance UWT MLCCs.     

Carbon supported PdM (M = Fe,Co) electrocatalysts for formic acid oxidation. Influence of the Fe and Co precursors

Pd and PdM (M = Fe or Co) nanostructured electrocatalysts were synthesized by the impregnation method and supported on carbon black Vulcan XC-72R for the formic acid oxidation reaction, FAOR, in acid medium. Nitrates or chlorides were used as Fe and Co precursors to study the counter ion role on the physicochemical features and electrochemical performance of the electrocatalysts. TEM analysis showed that PdM was deposited on the carbon material with a particle size around 2–3 nm. From XRD, peaks associated with the fcc palladium planes were observed along with evidence of PdM alloy formation, particularly when the nitrate salts were used as metal precursors. Furthermore, XPS analyses indicated that nitrates promote the metal oxide formation to a greater extent than chlorides, mainly for Pd. PdCo electrocatalyst obtained from nitrates exhibited the highest performance for FAOR with a steady state current density of 451 and 313 μA cm⁻² at 200 and 400 mV respectively, which is in both cases, 3 times larger than that developed for a commercial Pd/C catalyst.