The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in Al...The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.展开更多
The fabrication of bifunctional electrocatalysts for hydrogen and oxygen evolution in aqueous environment has far-reaching significance.Especially,reasonable interface process regulation toward heterogeneous composite...The fabrication of bifunctional electrocatalysts for hydrogen and oxygen evolution in aqueous environment has far-reaching significance.Especially,reasonable interface process regulation toward heterogeneous composites can make full use of the active sites and improve the electrocatalytic activity.In this study,we designed and synthesized NiS_(2)-MoS_(2)-based heterogeneous composites as efficient and stable electrocatalysts for hydrogen and oxygen evolution in alkaline electrolyte.The heterostructure was obtained by one-step hydrothermal ulfurization operation towards polymolybdate-based metal-organic complex.The composition and nanostructures can be tailored by modulating experiment parameter,realizing the phase-controlled synthesis and interface regulation:(1)High-percentage of 1T-MoS_(2)can be achieved via selecting appropriate vulcanization time and thiourea concentration,benifiting for the higher electroconductivity and more active sites;(2)Regular and orderly vulcanization time promotes the gradual growth and aggregation of nanosheets;(3)The existence of nickel hydroxide improves the electrocatalytic stability for oxygen production performance.The optimized heterogeneous interfaces provide sufficient active sites and accelerate electron transfer.Consequently,the optimal heterogeneous nanosheets present low overpotentials of 33 and 122 m V at the catalytic current densities of 10 m A/cm2for HER and OER,respectively.展开更多
基金the National Key Research and Development Program of China(Grant No.2018YFB1802100)the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2020JM-191 and 2018HJCG-20)+2 种基金the National Natural Science Foundation of China(Grant Nos.61904135,61704124,and 61534007)the China Postdoctoral Science Foundation(Grant Nos.2018M640957 and 2019M663930XB)the Wuhu and Xidian University Special Fund for Industry-University-Research Cooperation,China(Grant No.XWYCXY-012019007).
文摘The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.
基金financially supported by the National Natural Science Foundation of China(Nos.22271021,21971024)Liao Ning Revitalization Talents Program(No.XLYC1902011)Research Foundation of Education Bureau of Liaoning Province(No.LJKQZ20222290)。
文摘The fabrication of bifunctional electrocatalysts for hydrogen and oxygen evolution in aqueous environment has far-reaching significance.Especially,reasonable interface process regulation toward heterogeneous composites can make full use of the active sites and improve the electrocatalytic activity.In this study,we designed and synthesized NiS_(2)-MoS_(2)-based heterogeneous composites as efficient and stable electrocatalysts for hydrogen and oxygen evolution in alkaline electrolyte.The heterostructure was obtained by one-step hydrothermal ulfurization operation towards polymolybdate-based metal-organic complex.The composition and nanostructures can be tailored by modulating experiment parameter,realizing the phase-controlled synthesis and interface regulation:(1)High-percentage of 1T-MoS_(2)can be achieved via selecting appropriate vulcanization time and thiourea concentration,benifiting for the higher electroconductivity and more active sites;(2)Regular and orderly vulcanization time promotes the gradual growth and aggregation of nanosheets;(3)The existence of nickel hydroxide improves the electrocatalytic stability for oxygen production performance.The optimized heterogeneous interfaces provide sufficient active sites and accelerate electron transfer.Consequently,the optimal heterogeneous nanosheets present low overpotentials of 33 and 122 m V at the catalytic current densities of 10 m A/cm2for HER and OER,respectively.
