Ultra-fast response and highly selectivity hydrogen gas sensor based on Pd/SnO2 nanoparticles

It is still a challenging task to achieve the rapid detection of hydrogen (H₂) with the rapid development of hydrogen energy sector. In this work, the H₂ sensing capabilities of pristine and Pd-modified SnO₂ nanoparticles with the size of ～7 nm were systematically evaluated. The SnO₂ nanoparticles were synthesized via hydrothermal method and Pd modification was performed using impregnation route. Pd modification remarkably upgraded the H₂ sensing performances compared with the pristine SnO₂ gas sensor. The working temperature of SnO₂ decreased from 300 °C to 125 °C after Pd loading. Among the prepared Pd/SnO₂ gas sensors, 0.50 at.% Pd/SnO₂ sensor exhibited the highest response magnitude of 254 toward 500 ppm H₂ and rapid response/recovery time of 1/22 s at 125 °C. The enhanced H₂ sensing capabilities by Pd modification may be related to the catalytic effect and the resistance modulation.     

Evaluating hydrogen detection performance of an electrospun CuZnFe2O4 nanofiber sensor

CuZnFe₂O₄ nanoparticles (<50 nm) are successfully synthesized and incorporated in polyvinyl alcohol (PVA) to fabricate nanofibers via electrospinning technique followed by calcination process under various temperatures. Scanning electron microscopy (SEM) is used to observe the morphological characteristics of both nanoparticles and nanofibers. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric (TG) analyses along with energy dispersive X-ray spectrometer (EDX) analysis are conducted to evaluate structure and composition of the nanofibers, respectively. The results exhibit that the calcination temperature is substantially effective on nanofiber morphology and sensing performance in the context of forming grains (beads) on the nanofibers. The highest response and recovery performance values (response and recovery time of about 6.5 s) are obtained at the calcination temperature of 500 °C and sensor working temperature of 250 °C at 500 ppm of H2 gas concentration which also corresponds to 30% increment in detection performance compared to 300 °C-calcined nanofiber sensor. The sensor selectivity against various gases is also analyzed to compare the detection performance in air.     

Electrical and hydrogen gas sensing properties of Co1-xZnxFe2O4 nanoparticles; effect of the sputtered palladium thin layer

Hydrogen gas sensing of Co_1-xZn_xFe₂O₄ (x = 0–0.45) nanoparticles synthesized by a simple hydrothermal process has been investigated. An n→p crossover in the electrical conductivity toward hydrogen gas was observed. However, no such charge carrier reversal is noticed at higher x values. In both cases, the related mechanisms are proposed. It has been found that reversal is temperature and doping ratio dependent. In this regard, the more compatible and realistic model is presented which explains the nature of our observations. By analyzing the adsorption kinetics of the surface, it is identified that at a higher percentage of Zn (x = 0.45) the sensor response deviates from the Freundlich isotherm and falls under the category of the Langmuir adsorption model toward H₂ gas exposure. These strong correlations between the results of gas sensing measurements and those calculated based on the DC electric resistivity would pave the way for further investigation of the gas sensors from a fundamental point of view. Deposition of Palladium nano-structures (possibly island-like) on the surface of the CoFe₂O₄ sensor appeared to be effective in speeding up the response time and increasing the sensitivity. The remarkable response time, as low as 3 s, is obtained after modifying the sensor surface with the palladium deposition.     

Flower-shaped magnetically recyclable ZnS/ZnIn2S4/Fe2O3 nanocomposites towards decolorization of colored pollutants

Innovation the photocatalysts with acceptable performance, and facile recycle ability with magnetic separation is one of the most important challenges for researchers because of they are the promising materials can help to environmental health. Fe₂O₃ nanostructures with different ration loaded on ZnS/ZnIn₂S₄ nanocomposite were efficaciously provided through glycothermal procedure. The effect of amount of Fe₂O₃ nanostructures on structural, physical, magnetic and photocatalytic attributes of the resultant nanocomposite was explored. Morphology, uniformity and size of magnetic recyclable photocatalysts were detected, and present a flower shaped microstructures with assembling the nanosheets. Based on magnetic hysteresis, ternary ZnS/ZnIn₂S₄/Fe₂O₃ nanocomposite exposed the maximum saturation magnetization of 0.5481 emu/g which is higher than binary ZnS/ZnIn₂S₄ nanocomposite. Photocatalytic decolorization of ZnS/ZnIn₂S₄/Fe₂O₃ nanocomposites was conducted in Rhodamine B (RhB) and Methyl orange (MO) solutions illuminated under a 400 W Osram lamp. The outcomes discovered that 95.07% and 56.42% of RhB and MO was removed for the ZnS/ZnIn₂S₄/Fe₂O₃ nanocomposites with ratio of 1:1 from Fe₂O₃:Zn. Moreover, it can be simply separated and recycled after being used five times and the degradation efficiency remains 60.83%. Compared to the other catalysts, the magnetic ZnS/ZnIn₂S₄/Fe₂O₃ nanocomposites is suitable for large scale requests in industrial water treatment system.     

Effect of copper phthalocyanine (CuPc) on electrochemical hydrogen storage capacity of BaAl2O4/BaCO3 nanoparticles

A green synthesis method, solution combustion, were performed to synthesize BaAl₂O₄/BaCO₃ nanoparticles by using stoichiometric amount of cations, Ba²⁺ and Al³⁺, in rational fraction of a fuel (maltose). Single fuel led to the formation of combustion reaction required further annealing at 700 °C in order to achieve pure crystals. The average crystallite sizes of the BaAl₂O₄/BaCO₃ nanopowders were obtained about 36 nm using modified Scherrer equation. In order to improve the electrochemical hydrogen storage capacity of BaAl₂O₄/BaCO₃ nanoparticles, a novel admixture was designed by introducing copper phthalocyanine (CuPc) into an inorganic phase. The reaction profiles of BaAl₂O₄/BaCO₃-CuPc nanocomposites were confirmed by FTIR analysis. The structural and elemental analysis were confirmed the formation of nanocomposites. Morphological analysis confirmed the nanoscale formation of the host material. In addition, TEM results clearly confirmed the morphology of BaAl₂O₄/BaCO₃ sample and its nanocomposites. The Band gap energy was calculated for host, CuPc and its respective nanocomposites using Tauc method obtained at 4.95, 2.10 and 2.54/4.89 eV, respectively. Electrochemical performances of the materials were confirmed a large I_pa for BaAl₂O₄/BaCO₃-CuPc nanocomposites as compare to the host materials. This was directly reflected in hydrogen storage capacities of the materials (900 mA h/g discharge capacity for BaAl₂O₄/BaCO₃ (～3.17%) and >1500 mA h/g for BaAl₂O₄/BaCO₃-CuPc nanocomposites (～5.3%)).     

Database of thermophysical properties of H2/CO2/CO/CH4/H2O mixtures

As a potential alternative to fossil fuel, hydrogen has attracted much attention due to its renewable and environmentally friendly properties. Systems built for hydrogen-production and hydrogen-application tend to be larger, more integrated and more complex. In order to more efficiently design the vital components of hydrogen energy systems, accurate estimations of the thermodynamic and thermophysical properties of hydrogen-containing mixtures involved is essential. In this study, we introduced methods typically for calculating the thermodynamic and thermophysical properties of H₂/CO₂/CO/CH₄/H₂O mixtures, and established the technical database covering a wide range of mole fractions, pressures and temperatures. Moreover, a user-friendly software integrating all the calculation methods called H2MixThermoDatabase is compiled, whose code has been made available on the GitHub page for other researchers to effectually facilitate the further developments of hydrogen energy system.     

An efficient ternary Mn0.2Cd0.8S/MoS2/Co3O4 heterojunction for visible-light-driven photocatalytic H2 evolution

An efficient ternary Mn_0.2Cd_0.8S/MoS₂/Co₃O₄ heterojunction was prepared and displayed excellent photocatalytic performance. The ternary Mn_0.2Cd_0.8S/MoS₂/Co₃O₄ heterojunction with 0.62 wt% of MoS₂ and 1.51 wt% of Co₃O₄ achieved the highest H₂ evolution activity (16.45 mmol g⁻¹ h⁻¹), which was well above Mn_0.2Cd_0.8S (2.72 mmol g⁻¹ h⁻¹). The improved H₂ evolution activity was ascribed to the synergistic effect of the Mn_0.2Cd_0.8S/Co₃O₄ p–n heterojunction and the modification of MoS₂ as a co-catalyst. This work can offer a new perspective for the application of Mn_xCd_1−xS-based ternary heterojunction towards solar energy conversion.     

Magnetically recyclable ZnCo2O4/Co3O4 nano-photocatalyst: Green combustion preparation,characterization and its application for enhanced degradation of contaminated water under sunlight

Finding the appropriate photocatalyst for elimination of organic contaminants is a challenge for remediation of environment. Herein, we tried to synthesis of ZnCo₂O₄/Co₃O₄ nanocomposite using the Stevia extract as a natural reagent that can act as green fuel in auto-combustion sol-gel method and control the size of product by steric-hindrance induced by its structure. The chelating role of this natural reagent was investigated by changing the amount of this extract for synthesis of different samples. Analyses confirmed the effect of this parameter on morphology and size of products. The photocatalytic activities of different samples under visible irradiation were investigated and the effect of size of photocatalyst on degradation percent of dye was studied. The good performance of ZnCo₂O₄/Co₃O₄ nanocomposite was detected by degradation of Acid violet 7 about 93.5% in 70 min and 2-phenol about 100% in 18 min. Photocatalyst was easily recycled through magnetic properties of products and stability of it under irradiation was confirmed by degradation of dye after 10 times recycling.     

Much enhanced electrocatalysis of Pt/PtO2 and low platinum loading Pt/PtO2-Fe3O4 dumbbell nanoparticles

Pt/PtO₂ nanoparticles (NPs) have been prepared by a simple synthetic strategy, easily able to control nanoparticles (NPs) size, consisting in the thermolysis of a suitable precursor in organic solvent under a low oxygen enriched atmosphere. An excellent combination of a low tafel slope of 31 mV/dec with a negligible overpotential was measured for our Pt/PtO₂ NPs, due to PtO₂ resulting in electron rich Pt island, showing activity higher than that of common Pt. Additionally, the paper proves that it is possible to improve platinum/platinum oxide activity through control of NPs size and reduce platinum loading through its junction and interaction with a further metal oxide. Very high hydrogen production rate of 3.35 mL cm^?2 h^?1 at ?0.024 V, obtained by means of an on-line mass spectrometry analysis, to corroborate the results with a realistic hydrogen production estimation, was measured for Pt/PtO₂ electrode. Moreover, Pt/PtO₂ was stable in corrosive acidic solution during electrolysis under high current density.     

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 gas sensor based on mesoporous In2O3 with fast response/recovery and ppb level detection limit

Hydrogen gas sensors were fabricated using mesoporous In₂O₃ synthesized using hydrothermal reaction and calcination processes. Their best performance for the hydrogen detection was found at a working temperature of 260 °C with a high response of 18.0 toward 500 ppm hydrogen, fast response/recovery times (e.g. 1.7 s/1.5 s for 500 ppm hydrogen), and a low detection limit down to 10 ppb. Using air as the carrier gas, the mesoporous In₂O₃ sensors exhibited good reversibility and repeatability towards hydrogen gas. They also showed a good selectivity for hydrogen compared to other commonly investigated gases including NH₃, CO, ethyl alcohol, ethyl acetate, styrene, CH₂Cl₂ and formaldehyde. In addition, the sensors showed good long-term stability. The good sensing performance of these hydrogen sensors is attributed to the formation of mesoporous structures, large specific surface areas and numerous chemisorbed oxygen ions on the surfaces of the mesoporous In₂O₃.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Cooperation of Fe2O3@C and Co3O4/C subunits enhances the cyclic stability of Fe2O3@C/Co3O4 electrodes for lithium‐ion batteries

A Fe₂O₃@C/Co₃O₄ hybrid composite anode is synthesized via a two‐step hydrothermal method in which the acetylene carbon black component serves as a conductive matrix and as an effective elastic buffer to relieve the stress from Fe₂O₃@C and Co₃O₄/C during the electrochemical testing. The crystallinity, structure, morphology, and electrochemical performance of the composites are systematically characterized. Galvanostatic charge/discharge measurements of Fe₂O₃@C/Co₃O₄ present the excellent rate performance and cyclic stability. Its reversible capacity reaches 1478 mAh·g^?1 after 45 cycles, and it is equal to 1035 mAh·g^?1 after 350 cycles at a current density of 200 mA·g^?1. Furthermore, the changes after 30, 45, 60, 90, and 120 cycles are investigated. It is found that the electrochemical performance varies with the morphological change of the electrode surface. Correspondingly, the microstructure, cyclic voltammetry curves, and Nyquist plots significantly change as a consequence of cycling. The results of this study provide an understanding of the increased capacity and excellent cyclic performance of a new anodic material for Li‐ion batteries.     

Sono-synthesis and characterization of Ho2O3 nanostructures via a new precipitation way for photocatalytic degradation improvement of erythrosine

For the first time, Ho₂O₃ nanostructures have been successfully produced through a facile sonochemical way. In this way, diethylenetriamine (dien) as a new precipitator and holmium nitrate were employed to fabricate Ho₂O₃ products. To optimize the grain size, morphology and photocatalytic efficiency of Ho₂O₃ samples, the kind of capping agents has been changed. The formed Ho₂O₃ products have been characterized by means of FT-IR, TEM, EDX, XRD, FESEM and DRS. It was observed that the grain size, morphology and photocatalytic efficiency of the sonochemically produced Ho₂O₃ were largely dependent on the kind of capping agent. The photocatalytic behaviors of Ho₂O₃ nano and bulk structures have been compared through decomposition of erythrosine contaminant under ultraviolet irradiation.     

Combustion features of CH4/NH3/H2 ternary blends

The use of so-called “green” hydrogen for decarbonisation of the energy and propulsion sectors has attracted considerable attention over the last couple of decades. Although advancements are achieved, hydrogen still presents some constraints when used directly in power systems such as gas turbines. Therefore, another vector such as ammonia can serve as a chemical to transport and distribute green hydrogen whilst its use in gas turbines can limit combustion reactivity compared to hydrogen for better operability. However, pure ammonia on its own shows slow, complex reaction kinetics which requires its doping by more reactive molecules, thus ensuring greater flame stability. It is expected that in forthcoming years, ammonia will replace natural gas (with ^～90% methane in volume) in power and heat production units, thus making the co-firing of ammonia/methane a clear path towards replacement of CH₄ as fossil fuel. Hydrogen can be obtained from the pre-cracking of ammonia, thus denoting a clear path towards decarbonisation by the use of ammonia/hydrogen blends. Therefore, ammonia/methane/hydrogen might be co-fired at some stage in current combustion units, hence requiring a more intrinsic analysis of the stability, emissions and flame features that these ternary blends produce. In return, this will ensure that transition from natural gas to renewable energy generated e-fuels such as so-called “green” hydrogen and ammonia is accomplished with minor detrimentals towards equipment and processes. For this reason, this work presents the analysis of combustion properties of ammonia/methane/hydrogen blends at different concentrations. A generic tangential swirl burner was employed at constant power and various equivalence ratios. Emissions, OH1/NH1/NH₂1/CH1 chemiluminescence, operability maps and spectral signatures were obtained and are discussed. The extinction behaviour has also been investigated for strained laminar premixed flames. Overall, the change from fossils to e-fuels is led by the shift in reactivity of radicals such as OH, CH, CN and NH₂, with an increase of emissions under low and high ammonia content. Simultaneously, hydrogen addition improves operability when injected up to 30% (vol), an amount at which the hydrogen starts governing the reactivity of the blends. Extinction strain rates confirm phenomena found in the experiments, with high ammonia blends showing large discrepancies between values at different hydrogen contents. Finally, a 20/55/25% (vol) methane/ammonia/hydrogen blend seems to be the most promising at high equivalence ratios (1.2), with no apparent flashback, low emissions and moderate formation of NH₂/OH radicals for good operability.     

TmVO4/Fe2O3 nanocomposites: Sonochemical synthesis,characterization, and investigation of photocatalytic activity

Today, a unique method of treating environmental contaminants is drawing considerable attention. Organic dyes are significant wastes from myriad industries, including paper, food, and textiles, which have become a serious environmental concern and have the potential to be toxic to humans and living organisms. This study demonstrates the fabrication and characterization of thulium vanadate (TmVO₄) nanostructures and TmVO₄/Fe₂O₃ nanocomposites that were effectively applied in the photodecomposition efficiency of cationic and anionic organic contaminants. The TmVO₄/Fe₂O₃ nanocomposites were prepared through a sonochemical method, and triethylenetetramine (TETA) was employed as a precipitating and capping agent. The tests were performed using a probe as a sonication source (60 W, 18 kHz). The impact of TmVO₄ content (5, 10, 15, and 30%) on the modification of binary nanocomposites was studied in terms of morphological, optical, and photocatalytic properties. The recyclable magnetic TmVO₄/Fe₂O₃ nanocomposites with 15% TmVO₄ achieve 68.3% of eriochrome black t (EBT) utilizing visible origin. More notably, the binary TmVO₄/Fe₂O₃ nanocomposites reveal higher photocatalytic activity than the pure TmVO₄ and Fe₂O₃ nanoparticles.     

Numerical approach to evaluate performance of porous SiC5/4O3/2 as potential high temperature hydrogen gas sensor

Porous silicon oxycarbide (SiCO) is a novel class of nano-porous material with superior gas sensing performance. In this work, the amorphous porous structure of SiC_5/4O_3/2 is successfully reproduced by simulating the experimental etching process, and the gas sensing performance of porous SiCO at high temperature is investigated. The calculation results show porous SiC_5/4O_3/2 exhibits a much higher sensitivity towards H₂ than CO, NO₂ and acetone at 773 K. Compared with the other three gases, H₂ absorbed system show shorter adsorption distance and more obvious increasing in density of states around Fermi level. Therefore, porous SiC_5/4O_3/2 shows a highly selective sensitivity toward H₂ at high temperature. Moreover, our results show the Si–C/O units are the major sensing sites of H₂ at high temperature, and the large diffusion coefficient of H₂ in SiC_5/4O_3/2 is related to the fast response of porous SiCO gas sensor.     

Enhanced electrochemical activity of Co3O4/Co9S8 heterostructure catalyst for water splitting

The dearth of efficient, robust, and economical electrocatalysts for water oxidation is dubiously the key obstacle for renewable energy devices, so synthesis of efficient, and cost-effective metal-based water oxidation catalysts is vital. Herein, Co₃O₄, Co₉S₈ catalysts and their heterostructure Co₃O₄/Co₉S₈ were synthesized and evaluated as water oxidation electrocatalysts. The characterization of Co₃O₄, Co₉S₈, and Co₃O₄/Co₉S₈ electrocatalysts was performed using Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction techniques. The heterostructure Co₃O₄/Co₉S₈ (1.46 V) exhibited water oxidation electrocatalysis at extremely low onset potential compared to Co₃O₄ (1.58 V), and Co₉S₈ (1.48 V) catalysts. A 281 mV overpotential required to attain a current density of 50 mA cm^?2 in alkaline solution (1 M KOH), outperforming most of Co-based benchmark electrocatalysts. Further, the Co₃O₄/Co₉S₈ heterojunction demonstrated catalytic activity with small Tafel slope of 37 mV dec^?1. The finding of electrochemical studies involving controlled potential electrolysis and long-term stability are projected to steer the future advancement in constructing efficient, economical, stable, and earth-abundant metal-based water oxidation catalysts.     

Thermal desorption processes of H2 and CH4 from Li2ZrO3 and Li4SiO4 materials absorbed H2O and CO2 in air at room temperature

The thermal desorption processes of hydrogen (H₂) and methane (CH₄) from lithium-based materials, Li₂ZrO₃ and Li₄SiO₄, exposed to air at room temperature of 293 K with a relative humidity of 80%, were investigated using gas chromatography (GC). The GC analysis revealed that the absolute values of the released H₂ and CH₄ gases at 523 K were approximately 7.42 × 10^?6 and 1.54 × 10^?6 ml/g for Li₂ZrO₃, and 3.24 × 10^?6 and 0 ml/g for Li₄SiO₄. The amounts of H₂ and CH₄ released increased with increase in annealing temperatures and considerably depended on absorption properties of water (H₂O) and carbon dioxide (CO₂) present in air at room temperature. The production of CH₄ at low temperature is due to the intermediate species including CH_x precursors produced by the reaction between H split from H₂O and Li₂CO₃ resulting in the CO₂ absorption of Li₂ZrO₃ and Li₄SiO₄ materials.