Hydrogen sensing characteristics of a Pd/Nickel oxide/GaN-based Schottky diode

Hydrogen sensing characteristics of a novel metal-oxide-semiconductor (MOS) Schottky diode are thoroughly investigated. The MOS structure consists of a gallium nitride (GaN)-based semiconductor system, a nickel oxide (NiO) layer, and palladium (Pd) catalytic materials. A well-prepared Pd/NiO/GaN-based diode shows several advantages in relation to hydrogen sensing, including a simple structure, high sensing speed, wide flexibility for operation under both forward and reverse applied voltages, and a good sensing response of 8.1 × 10³ under an applied forward voltage of 0.25 V, at 300 K in a 1% H₂/air ambience. Furthermore, under an applied reverse voltage of −2 V and at a high temperature of 573 K, this MOS diode shows a response as high as 1.8 × 10⁴ towards 1% H₂/air mixture gas. The Schottky diode sensor with a novel Pd/NiO/GaN structure demonstrated in this study is a promising candidate for high-performance hydrogen sensing applications.     

Influence of nanoadditives on ignition characteristics of Kusum (Schleichera oleosa) biodiesel

Biodiesel obtained from inedible sources emerged as a productive approach in Indian energy scenario due to the scarcity of food resources come up with extensive usage of edible crops. Kusum (Schleichera oleosa) oil is abundantly available in India and can be used as feedstock to produce biodiesel. However, issues such as higher viscosity, poor stability, and lower calorific value result in poor ignition characteristics, hence limiting its use in combustion applications. An improvement in performance and emission characteristics can be achieved by doping nanoparticles in Kusum biodiesel (KBD). The present work examines the impact of a metal compound and carbon‐primarily based nanoparticles on the evaporation time and ignition probability of the KBD. During the experimental process, different fuel samples of KBD were prepared by amalgamating nanoparticles; then, a sequence of hot plate (stainless steel) ignition test was conducted on these test fuels. The comparative assessment of neat biodiesel and the biodiesel fuel doped with 30 ppm each of alumina (Al2O3), and multiwalled carbon nanotubes (MWCNTs) nanoparticles were carried out. The Kusum oil was converted to biodiesel using two‐stage transesterification process. In the initial stage, refined oil was gone through the acid catalyst esterification process followed by the transesterification reaction. The prepared methyl ester was confirmed and characterized using GC‐MS technique. The thermophysical and spray properties of the test fuels including density, viscosity, calorific value, cloud/pour point, Sauter mean diameter (SMD), and specific surface area (SSA) were also calculated. The experimental result showed a significant increase in ignition probability and heat conduction properties due to improved surface area/volume ratio. Also, lower evaporation time was noted for metal/carbon‐based nanoparticles doped biodiesel as compared with neat biodiesel.     

Localized surface plasmon resonance (LSPR) detection of hydrogen gas by Pd2+/Au core/shell like colloidal nanoparticles

A hydrogen detector colloidal solution based on the plasmonic properties of gold nanoparticles (GNPs) is presented. GNPs were prepared by pulsed laser ablation (PLA) of gold target in DI water. PdCl₂ solution with different concentration was added to the obtained GNPs colloidal solutions. X-ray diffraction (XRD) confirmed the formation of metallic gold and presence of PdCl₂ phases. Transmission electron microscope (TEM) images along with X-ray photoelectron spectroscopy (XPS) revealed formation of the core-shell-like structures of Pd²⁺/Au NPs. After hydrogenation, TEM revealed that the core-shell morphology changes into free NPs and XPS revealed formation of the metallic Pd phase. Voltammetry analysis showed a well absorption and desorption capability of hydrogen in this gold-PdCl₂ plasmonic system. After adding PdCl₂ aqueous solution, a red-shift from 522 to 526 nm was observed which was attributed to Pd²⁺ ion attraction by the negative surface charge of bare GNPs and formation a core-shell like morphology. The optical absorption peaks of PdCl₂ (the range 207–236 nm) as well as the LSPR peak of GNPs were traced during diluted hydrogen (0.3–10%) injection in colloidal samples with different Au:Pd molar ratio. It was found that the PdCl₂ peaks drop due to Pd²⁺→Pd⁰ conversion and more importantly, the gold peak undergoes blue shift due to change in chemical properties of GNPs surrounding. A good correlation between PdCl₂ absorption intensity and gold LSPR peak position was found when hydrogen concentration was varied. In this correlation, a desirable detection capability for low concentrations of hydrogen (<4% range, the limit of hydrogen explosion) with a possible large number of points was observed. Finally, a model for the hydrogen sensing mechanism based on the LSPR effect was presented.     

Temperature effect on the electrical properties of pyrolytic MnO2 thin films prepared from Mn(C2H3O2)2·4H2O

Spray deposited MnO₂ thin films onto glass substrate were subjected to a post-deposition heat treatment and the effects of temperature on electrical transport properties were studied in details. The heating and cooling cycles of the samples are reversible after successive heat-treatments in air and vacuum. The films were polycrystalline in structure and the oxygen chemisorption–desorption process was found to play an important role in controlling the electronic properties. Various grain-boundary and energy band parameters were calculated by taking conventional extrinsic semiconductor theory and grain boundary trapping models into account. The samples were non-degenerate n-type semiconductors. The transport properties are interpreted in terms of Seto's model which was proposed for polycrystalline semiconducting films. The inter-crystallite boundaries of the thin films play an important role in the transport properties.     

Optimization of Process Parameters for the Preparation of CaO/CaSO4/Coal Fly Ash Sorbent for Sulfur Dioxide (SO2) Removal: Part II

A two-step optimization strategy was employed to optimize the surface area of sorbent prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO₄) for flue gas desulfurization. In the first step, a 3 level full factorial design of experiment was used to develop a regression model equation to correlate the significant experimental sorbent preparation variables to the surface area of the resulting sorbent. The three experimental sorbent preparation variables studied are hydration period (x ₁), ratio of CaO to fly ash (x ₂) and amount of CaSO₄ (x ₃). In the subsequent step, response surface methodology was used to identify the experimental sorbent preparation variables that maximize the surface area of the sorbent. Through this two-step optimization strategy, it was found that at a hydration period of 10 hrs and drying temperature of 100°C, optimum surface area of 67.0 m²/g could be attained by using 5 grams of CaO, 13.7 grams of fly ash, and 7.4 grams of CaSO₄ in the preparation mixture. The prediction was verified with experimental runs.     

Numerical analysis on influence of hydrogen peroxide (H2O2) addition on the combustion and emissions characteristics of NH3/CH4-air (O2/N2)/ H2O2 mixture

In this work, extensive chemical kinetic modeling is performed to analyze the combustion and emissions characteristics of premixed NH₃/CH₄–O₂/N₂/H₂O₂ mixtures at different replacement percentages of air with hydrogen peroxide (H₂O₂). This work is comprehensively discusses the ignition delay time, flame speed, heat release rate, and NOx & CO emissions of premixed NH₃/CH₄–O₂/N₂/H₂O₂ mixtures. Important intermediate crucial radicals such as OH, HO₂, HCO, and HNO effect on the above-mentioned parameters is also discussed in detail. Furthermore, correlations were obtained for the laminar flame speed, NO, and CO emissions with important radicals such as OH, HO₂, HCO, and HNO. The replacement of air with H₂O₂ increases flame speed and decreases the ignition delay time of the mixture significantly. Also, increases the CO and NOx concentration in the products. The CO and NOx emissions can be controlled by regulating the H₂O₂ concentration and equivalence ratios. Air replacement with H₂O₂ enhances the reactions rate and concentration of intermediate radicals such as O/H, HO₂, and HCO in the mixture. These intermediate radicals closely govern the combustion chemistry of the NH₃/CH₄– O₂/N₂/H₂O₂ mixture. A linear correlation is observed between the flame speed and peak mole fraction of OH + HO₂ radicals, and 2nd degree polynomial correlation is observed for the peak mole fraction of NO and CO with HNO + OH and HCO + OH radicals, respectively.     

Hydrogen production through autothermal reforming of CH4: Efficiency and action mode of noble (M = Pt,Pd) and non-noble (M = Re,Mo, Sn) metal additives in the composition of Ni-M/Ce0.5Zr0.5O2/Al2O3 catalysts

Hydrogen production through autothermal reforming of methane (ATR of CH₄) over promoted Ni catalysts was studied. The control of the ability to self-activation and activity of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was achieved by tuning their reducibility through the application of different types (M = Pt, Pd, Re, Mo or Sn) and content (molar ratio M/Ni = 0.003, 0.01 or 0.03) of additive. The comparison of the efficiency and action mode of noble (M = Pt, Pd) and non-noble (M = Re, Mo, Sn) metal additives in the composition of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was performed using X-ray fluorescence analysis, N₂ adsorption, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction with hydrogen, and thermal analysis. The composition-characteristics-activity correlations were determined. It was shown that the introduction of a promoter does not affect the textural and structural properties of catalysts but influences their reducibility and performance in ATR of CH₄. At the similar dispersion of NiO active component (11 ± 2 nm), the Ni²⁺ reduction is intensified in the following order of additives: Mo < Sn < Re ≤ Pd < Pt. It was found that for the activation of Ni and Ni–Sn catalysts before ATR of CH₄ tests, the pre-reduction is required. On the contrary, the introduction of Pt, Pd and Re additives leads to the self-activation of catalysts under the reaction conditions and an increase of the H₂ yield due to the enhanced reducibility of Ni²⁺. The efficient and stable catalyst for hydrogen production has been developed: in ATR of CH₄ at 850 °C over an optimum 10Ni-0.9Re/Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst the H₂ yield of 70% is attained. The designed catalyst has enhanced stability against oxidation and sintering of Ni active component as well as high resistance to coking.