Low power consumption, fast response and quick recovery times are important parameters for gas sensors performance. Herein, we report the experimental and theoretical studies of ZnO and Cr doped ZnO nanostructures used in low temperature (50 °C) sensors for the detection of CO. The synthesized films were characterized by XRD, UV-Vis, FE-SEM and EDX. The XRD patterns for the ZnO and 0.5 wt% Cr/ZnO films confirm the formation of a single-phase hexagonal wurtzite structure. The reduction of the ZnO optical band gap from 3.12 eV to 2.80 eV upon 0.5 wt% Cr doping is well correlated with the simulation data. The FE-SEM images of the films show spherical morphology with the estimated particle sizes of about ~40 nm and ~ 25 nm were recorded for the ZnO and 0.5 wt% Cr/ZnO films, respectively. Enhanced gas sensing performance is achieved with Cr doping and the sensitivity of ZnO increases from 9.65% to 65.45%, and simultaneously decreasing the response and recovery times from 334.5 s to 172.3 s and from 219 s to 37.2 s, respectively. These improvements in gas sensing performance are due to the reduction in particle size and optical band gap, and an increase in specific surface area.
carrier, in addition to the application of fuel cells operating on hydrogen-rich fuel. Water electrolysis driven by renewable energy is a promising technology [1][2][3] for hydrogen production with zero emission. Water electrolysis can be classified into the following types: alkaline, [4] proton exchange membrane (PEM), [5,6] and anion exchange membrane (AEM). [7,8] Compared to the other types, PEM-type water electrolysis is considered to be more ecofriendly and efficient because it generates no waste, produces highly pure H 2 gas (>99.9999 vol%), [9] and displays a high discharge H 2 pressure (3.0-7.6 MPa) [10] and a high current density (1.0-4.0 A cm −2 ) at low overpotentials (1.5-1.9 V). [3,6,10,11] In contrast, alkaline-and AEM-type water electrolysis produces H 2 with >99.5 vol% and >99.99 vol% purities, respectively. However, efficient electrocatalytic reactions in these systems require considerable amounts of noble metals, for example, 300 kg of Pt in the cathode and 700 kg of Ir in the anode per 1.0 GW of power input of the PEM-type electrolyzer. [11] The serious scarcity of noble metals, especially that of Ir (global production: ≈7 ton year −1 ), [11] To realize a sustainable hydrogen economy, corrosion-resistant non-noblemetal catalysts are needed to replace noble-metal-based catalysts. The combination of passivation elements and catalytically active elements is crucial for simultaneously achieving high corrosion resistance and high catalytic activity. Herein, the self-selection/reconstruction characteristics of multielement (nonary) alloys that can automatically redistribute suitable elements and rearrange surface structures under the target reaction conditions during the oxygen evolution reaction are investigated. The following synergetic effect (i.e., cocktail effect), among the elements Ti, Zr, Nb, and Mo, significantly contributes to passivation, whereas Cr, Co, Ni, Mn, and Fe enhance the catalytic activity. According to the practical water electrolysis experiments, the self-selected/reconstructed multi-element alloy demonstrates high performance under a similar condition with proton exchange membrane (PEM)-type water electrolysis without obvious degradation during stability tests. This verifies the resistance of the alloy to corrosion when used as an electrode under a practical PEM electrolysis condition.
Bimetallic alloys are important catalysts with enhanced catalytic activities and product selectivities. However, the phase dependence of catalytic activity in bimetallic alloys afford contradictory characters in that one phase catalyzes the main reaction and the other catalyzes the side reaction; this aspect of bimetallic alloy catalysts has not been investigated. In this study, we systematically synthesized NiSn alloys from Ni, which is catalytically active in hydrogen generation, and Sn, which is catalytically active in electrochemical CO2 reduction. The thus-prepared alloys were applied in catalyzing the phase-dependent electrochemical CO2 reduction, and the formate generation mechanism was elucidated. The Faradaic efficiency of formate was found to increase with increasing Sn atomic concentration, and Ni3Sn4 showed higher catalytic activity than only Sn for electrochemical CO2 reduction. Density functional theory calculations revealed that Ni can additionally provide catalytically active sites for formate generation in a suitable phase. Thus, our investigation brings a better understanding of the catalytic activities of bimetallic alloys prepared from metals with different characters for electrochemical CO2 reduction.
In this investigation, the use of phosphotungstic acid (PWA) and phosphomolybdic acid (PMA) as well as Zn2+ containing kaolin and bentonite explored for chemical recycling of post-consumer poly(ethyleneterephathalate) (PET) wastes have been explored. The clay supported catalysts containing 5wt% of the metals and heteropolyacids (HPAs) are synthesized using wet impregnation method. The effect of metal ions and HPAs loading on the surface area, pore volume, elemental composition and crystalline nature of the kaolin and bentonite has been evaluated by nitrogen adsorption and desorption studies, SEM-EDX mapping, powder XRD, FTIR and XPS analysis. The total surface area of BET increased with a loading of 5 wt% of Zn2+, PWA and PMA on kaolin and bentonite, while the pore volume and pore diameter remain unchanged. SEM and EDAX mapping images showed that the heteropolyacids crystals are well dispersed on the surface and occupied interlayer spaces of the clay support. SEM-EDX showed that bentonite showed a better loading of PWA and PMA compared with kaolin. PET waste water bottles collected from the local market used for the chemical recycling process. The aminolysis reaction using Zn2+ and PWA loaded on bentonite showed complete depolymerisation of PET wastes to produce 87-98% of BHETA. The glycolysis reaction using the above catalysts showed complete depolymerisation at 180-210 °C and yielded 78-90% of BHET. When comparing the clay, bentonite performed well in terms of heteropolyacid loading and afforded a higher yield of BHET and BHETA due to higher loading of Zn and HPA as supported by SEM-EDX and XPS. Reusability of the catalysts were also examined for glycolysis.
In this investigation, the use of phosphotungstic acid (PWA) and phosphomolybdic acid (PMA) as well as Zn 2+ containing kaolin and bentonite explored for chemical recycling of post-consumer poly(ethyleneterephathalate) (PET) wastes have been explored. The clay supported catalysts containing 5wt% of the metals and heteropolyacids (HPAs) are synthesized using wet impregnation method. The effect of metal ions and HPAs loading on the surface area, pore volume, elemental composition and crystalline nature of the kaolin and bentonite has been evaluated by nitrogen adsorption and desorption studies, SEM-EDX mapping, powder XRD, FTIR and XPS analysis. The total surface area of BET increased with a loading of 5 wt% of Zn 2+ , PWA and PMA on kaolin and bentonite, while the pore volume and pore diameter remain unchanged. SEM and EDAX mapping images showed that the heteropolyacids crystals are well dispersed on the surface and occupied interlayer spaces of the clay support. SEM-EDX showed that bentonite showed a better loading of PWA and PMA compared with kaolin. PET waste water bottles collected from the local market used for the chemical recycling process. The aminolysis reaction using Zn 2+ and PWA loaded on bentonite showed complete depolymerisation of PET wastes to produce 87-98% of BHETA. The glycolysis reaction using the above catalysts showed complete depolymerisation at 180-210 °C and yielded 78-90% of BHET. When comparing the clay, bentonite performed well in terms of heteropolyacid loading and afforded a higher yield of BHET and BHETA due to higher loading of Zn and HPA as supported by SEM-EDX and XPS. Reusability of the catalysts were also examined for glycolysis.
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