In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results i...In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.展开更多
The photocatalytic oxidation of methane(CH_(4)) to valuable chemicals like low alcohols(CH_(3)OH and C_(2)H_(5)OH) represents a significant technological advancement with implications for energy conversion and environ...The photocatalytic oxidation of methane(CH_(4)) to valuable chemicals like low alcohols(CH_(3)OH and C_(2)H_(5)OH) represents a significant technological advancement with implications for energy conversion and environmental purification.A major challenge in this field is the chemical inertness of methane and the strong oxidizing nature of photogenerated holes,which can lead to over-oxidation and reduced selectivity and efficiency.To address these issues,we have developed a sodium-doped zinc oxide(Na-ZnO) modified with cobalt oxide(CoO) catalyst.This catalyst has demonstrated excellent performance in converting methane to low alcohols,achieving a yield of 130 μmol g^(-1)h^(-1) and a selectivity of up to 96 %.The doping of Na in ZnO significantly enhances methane adsorption,while the surface-modified CoO effectively captures photogenerated holes,activates water molecules,and uses hydroxyl radicals to activate methane,thus controlling the dehydrogenation degree of methane and preventing the formation of over-oxidized products.This strategy has successfully improved the efficiency and selectivity of photocatalytic methane oxidation to low alcohols,offering a new perspective for the application of photocatalytic technology in energy and environmental fields.展开更多
The development of ZnO-based composites with high charge separation and effective inhibition of toxic by-products is admirable for effective photocatalysis of nitrogen oxides(NO_(x))oxidation.In this study,carbon quan...The development of ZnO-based composites with high charge separation and effective inhibition of toxic by-products is admirable for effective photocatalysis of nitrogen oxides(NO_(x))oxidation.In this study,carbon quan-tum dots(CQDs)/ZnO hollow microspheres,synthesized through a rapid microwave-assisted method,achievedover a 30-fold higher NO_(x) removal efficiency compared to ZnO,with complete inhibition of NO_(2) by-products andgood durability.The enhanced photocatalytic activity was ascribed to the unique role of CQDs,as revealed byin-situ photoelectric techniques.Results demonstrated that the electron directional migration from ZnO to CQDsat the composite interface accounts for the enhanced charge separation.Active free radicals for NO_(x) oxidationwere identified,and in-situ diffuse reflectance infrared Fourier transform spectroscopy analysis elucidated theconversion pathways of NO_(x) oxidation under visible light irradiation.This work sheds light on the mechanismsof electron transfer and charge separation at the composite interface,offering guidance for designing superiorZnO-based photocatalysts for complete NO_(x) removal.展开更多
文摘In modern ZnO varistors,traditional aging mechanisms based on increased power consumption are no longer relevant due to reduced power consumption during DC aging.Prolonged exposure to both AC and DC voltages results in increased leakage current,decreased breakdown voltage,and lower nonlinearity,ultimately compromising their protective performance.To investigate the evolution in electrical properties during DC aging,this work developed a finite element model based on Voronoi networks and conducted accelerated aging tests on commercial varistors.Throughout the aging process,current-voltage characteristics and Schottky barrier parameters were measured and analyzed.The results indicate that when subjected to constant voltage,current flows through regions with larger grain sizes,forming discharge channels.As aging progresses,the current focus increases on these channels,leading to a decline in the varistor’s overall performance.Furthermore,analysis of the Schottky barrier parameters shows that the changes in electrical performance during aging are non-monotonic.These findings offer theoretical support for understanding the aging mechanisms and condition assessment of modern stable ZnO varistors.
基金support from the Zhejiang Provincial Natural Science Foundation of China (No.LQ24B030011)the Ningbo Natural Science Foundation (No.2023J181)+4 种基金the Open Research Fund of Key Laboratory of Functional Inorganic Materials Chemistry of the Ministry of Education (Heilongjiang University)the Start-up Funding offered by Ningbo University of Technology to J.D.LiNational Natural Science Foundation of China (No.U24A2071)Postdoctoral Research Start-up Fund (No.2111224002)Harbin Normal University Talent Plan (No.1305124213) to Y.D.Liu。
文摘The photocatalytic oxidation of methane(CH_(4)) to valuable chemicals like low alcohols(CH_(3)OH and C_(2)H_(5)OH) represents a significant technological advancement with implications for energy conversion and environmental purification.A major challenge in this field is the chemical inertness of methane and the strong oxidizing nature of photogenerated holes,which can lead to over-oxidation and reduced selectivity and efficiency.To address these issues,we have developed a sodium-doped zinc oxide(Na-ZnO) modified with cobalt oxide(CoO) catalyst.This catalyst has demonstrated excellent performance in converting methane to low alcohols,achieving a yield of 130 μmol g^(-1)h^(-1) and a selectivity of up to 96 %.The doping of Na in ZnO significantly enhances methane adsorption,while the surface-modified CoO effectively captures photogenerated holes,activates water molecules,and uses hydroxyl radicals to activate methane,thus controlling the dehydrogenation degree of methane and preventing the formation of over-oxidized products.This strategy has successfully improved the efficiency and selectivity of photocatalytic methane oxidation to low alcohols,offering a new perspective for the application of photocatalytic technology in energy and environmental fields.
基金supported by the National Natural Science Foundation of China(No.42403080)the Youth Innovation Promotion Asso-ciation of the Chinese Academy of Sciences(No.2022415)+1 种基金the Key Research and Development Program of Shaanxi Province(No.S2023-YF-LLRH-QCYK-0263)the Key Research and Development Programof Shaanxi Province(No.2023QCY-LL-16).
文摘The development of ZnO-based composites with high charge separation and effective inhibition of toxic by-products is admirable for effective photocatalysis of nitrogen oxides(NO_(x))oxidation.In this study,carbon quan-tum dots(CQDs)/ZnO hollow microspheres,synthesized through a rapid microwave-assisted method,achievedover a 30-fold higher NO_(x) removal efficiency compared to ZnO,with complete inhibition of NO_(2) by-products andgood durability.The enhanced photocatalytic activity was ascribed to the unique role of CQDs,as revealed byin-situ photoelectric techniques.Results demonstrated that the electron directional migration from ZnO to CQDsat the composite interface accounts for the enhanced charge separation.Active free radicals for NO_(x) oxidationwere identified,and in-situ diffuse reflectance infrared Fourier transform spectroscopy analysis elucidated theconversion pathways of NO_(x) oxidation under visible light irradiation.This work sheds light on the mechanismsof electron transfer and charge separation at the composite interface,offering guidance for designing superiorZnO-based photocatalysts for complete NO_(x) removal.
