Planar micro-supercapacitors （MSCs） have drawn extensive research attention owing to their unique structural design and size compatibility for microelectronic devices. Graphene has been widely used to improve the pe...Planar micro-supercapacitors （MSCs） have drawn extensive research attention owing to their unique structural design and size compatibility for microelectronic devices. Graphene has been widely used to improve the performance of microscale electrochemical capacitors. However, investigations of an intrinsic electrochemical mechanism for graphene-based microscale devices are still not sufficient. Here, micro-supercapacitors with various typical architectures are fabricated as models to study the graphene effect, and their electrochemical performance is also evaluated. The results show that ionic accessibility and adsorption are greatly improved after the introduction of the holey graphene intermediate layer. This study provides a new route to understand intrinsic electrochemical behaviors and possesses exciting potential for highly efficient on-chip micro-energy storage.展开更多
Due to its abundant sodium content and low cost,sodium-ion battery(SIB)has become an effective substitute and supplement for lithium-ion batteries,which has a broad development prospect in largescale energy storage sy...Due to its abundant sodium content and low cost,sodium-ion battery(SIB)has become an effective substitute and supplement for lithium-ion batteries,which has a broad development prospect in largescale energy storage systems.Na-super-ionic conductor(NASICON)structural materials have stable 3D skeleton structures and open Na+transport channels,which is a very promising SIB cathode material.But in the typical NASICON material Na_(3)V_(2)(PO_(4))_(3)(NVP),the number of electrons involved in NVP per formula unit is less than 2 at the stable voltage window,which limits the further improvement of battery performance.In this work,we report another NASICON structured Na_(3)V_(4/3)Cr_(2/3)(PO_(4))_(3)@C(NVCP@C),which is obtained by Cr-doped NVP through spray drying.By taking full advantage of the voltage platforms of V^(5+/4+),V^(4+/3+),and V^(3+/2+)in the window of 1.5-4.4 V,NVCP@C delivered a high discharge capacity(175 mAh g^(-1))and durable cyclability(86%capacity retention for 2000 cycles).In-situ X-ray diffraction results demonstrate that the reversible structural evolution accompanies by solid-solution reaction and two-phase reaction mechanisms co-exist during charge/discharge processes.When coupled with Na^(+)preembedded hard carbon(HC),the assembled NVCP@C//HC full cell delivers a high capacity(105 mAh g^(-1))and long cycling performance(70%after 1000 cycles).This Cr-doped NVP method offers new insights into the design of high-energy NASICON-structured cathode materials.展开更多
In the last decade, pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors. Although various methods have been investigated to improve the performance of pyroly...In the last decade, pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors. Although various methods have been investigated to improve the performance of pyrolyzed carbons, such as conductivity, energy storage density and cycling performance, effective methods for the integration and mass-production of pyrolyzed-carbon- based composites on a large scale are lacking. Here, we report the development of an optimized photolithographic technique for the fine micropatterning of photoresist/chitosan-coated carbon nanotube （CHIT-CNT） composite. After subsequent pyrolysis, the fabricated carbon/CHIT-CNT microelectrode-based micro-supercapacitor has a high capacitance （6.09 mF.cm-2） and energy density （4.5 mWh.cm-3） at a scan rate of 10 mV.s-L Additionally, the micro-supercapacitor has a remarkable long-term cyclability, with 99.9% capacitance retention after 10,000 cyclic voltammetry cycles. This design and microfabrication process allow the application of carbon microelectromechanical system （C-MEMS）-based micro-supercapacitors due to their high potential for enhancing the mechanical and electrochemical performance of micro-supercapacitors.展开更多
Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices. Asymmetric structures have been widely inves- tigated in micro-supercapacitors, and carbon-based materia...Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices. Asymmetric structures have been widely inves- tigated in micro-supercapacitors, and carbon-based materials are commonly applied in the electrodes. To integrate different metal oxides in both electrodes in micro-supercapacitors, the critical challenge is the pairing of different faradic metal oxides. Herein, we propose a strategy of matching the voltage and capadtance of two faradic materials that are fully integrated into one high-performance asymmetric micro-supercapacitor by a facile and controllable fabrication process. The fabricated micro-supercapacitors employ MnO2 as the positive active material and Fe203 as the negative active material, respectively. The planar asymmetric micro-supercapacitors possess a high capacitance of 60 F-cm-3, a high energy density of 12 mW.h.cm-3, and a broad operation voltage range up to 1.2 V.展开更多
Molybdenum disulfide （MoS2） is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced a...Molybdenum disulfide （MoS2） is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced after modification due to higher conductivity and enriched active sites. However, the underlying mechanism of the influence of the resistance of electrode material and contact resistance on the hydrogen evolution reaction （HER） process is unclear. Herein, we present a systematic study to understand the relationship between HER performance and electrode conductivity, which is bi-tuned through the electric field and photoelectrical effect. It was found that the onset overpotential consistently decreased with the increase of electrode conductivity. In addition, the reduction of the contact resistance resulted in a quicker electrochemical reaction process than enhancing the conductivity of the MoS2 nanosheet. An onset overpotential of 89 mV was achieved under 60 mW/cm^2 sunlight illumination （0.6 sun） and a simultaneous gate voltage of 3 V. These physical strategies can also be applied to other catalysts, and offer new directions to improve HER catalytic performance of semiconductor materials.展开更多
Hybrid or composite heterostructured electrode materials have been widely studied for their potential application in electrochemical energy storage. Whereas their physical or chemical properties could be affected sign...Hybrid or composite heterostructured electrode materials have been widely studied for their potential application in electrochemical energy storage. Whereas their physical or chemical properties could be affected significantly by modulating the heterogeneous interface, the underlying mechanisms are not yet fully understood. In this work, we fabricated an electrochemical energy storage device with a MoS2 nanosheet/MnO2 nanowire heterostructure and designed two charge/discharge channels to study the effect of the heterogeneous interface on the energy storage performances. Electrochemical measurements show that a capadty improvement of over 50% is achieved when the metal current collector was in contact with the MnO2 instead of the MoS2 side. We propose that this enhancement is due to the unidirectional conductivity of the MoS2/MnO2 heterogeneous interface, resulting from the unimpeded electrical transport in the MnO2-MoS2 channel along with the blocking effect on the electron transport in the MoS2-MnO2 channel, which leads to reaction kinetics optimization. The present study thus provides important insights that will improve our understanding of heterostructured electrode materials for electrochemical energy storage.展开更多
Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials.Characterizing the minute-variations in complementary aspects such as crystal structure,chemical bonds,...Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials.Characterizing the minute-variations in complementary aspects such as crystal structure,chemical bonds,and electron/ion conductivity will give an in-depth understanding on the reaction mechanism of electrode materials,as well as revealing pathways for optimization.Here,vanadium pentoxide (V2O5),a typical cathode material suffering from severe capacity decay during cycling,is characterized by in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy combined with electrochemical tests.The phase transitions of V2O5 within the 0-1 LiN ratio are characterized in detail.The V--O and V-V distances became more extended and shrank compared to the original ones after charge/discharge process,respectively.Combined with electrochemical tests,these variations are vital to the crystal structure cracking,which is linked with capacity fading.This work demonstrates that chemical bond changes between the transition metal and oxygen upon cycling serve as the origin of the capacity fading.展开更多
基金This work was supported by the National Basic Research Program of China （Nos. 2013CB934103 and 2012CB933003）, the International Science ＆ Technology Cooperation Program of China （No. 2013DFA50840）, the National Natural Science Foundation of China （Nos. 51522001 and 51272197）, the National Science Fund for Hubei Provincial Natural Science Young Scholars （No. 51425204）, the Hubei Science Fund for Distinguished Young Scholars （No. 2014CFA035）, the Fundamental Research Funds for the Central Universities （WUT： 2015-PY-2, 2015-CL-A1-03）. We are deeply thankful to Prof. Charles M. Lieber of Harvard University, Prof. Dongyuan Zhao of Fudan University, and Prof. Jun Liu of Pacific Northwest National Laboratory for their stimulating discussion and kind help.
文摘Planar micro-supercapacitors （MSCs） have drawn extensive research attention owing to their unique structural design and size compatibility for microelectronic devices. Graphene has been widely used to improve the performance of microscale electrochemical capacitors. However, investigations of an intrinsic electrochemical mechanism for graphene-based microscale devices are still not sufficient. Here, micro-supercapacitors with various typical architectures are fabricated as models to study the graphene effect, and their electrochemical performance is also evaluated. The results show that ionic accessibility and adsorption are greatly improved after the introduction of the holey graphene intermediate layer. This study provides a new route to understand intrinsic electrochemical behaviors and possesses exciting potential for highly efficient on-chip micro-energy storage.
基金the National Natural Science Foundation of China(No.52102299)the Guangdong Basic and Applied Basic Research Foundation(Nos.2021A1515110059,2020A1515110250,and 2021B1515120041)+1 种基金the National Key Research and Development Program of China(No.2020YFA0715000)the Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(Grant No.2021JJLH0058).
文摘Due to its abundant sodium content and low cost,sodium-ion battery(SIB)has become an effective substitute and supplement for lithium-ion batteries,which has a broad development prospect in largescale energy storage systems.Na-super-ionic conductor(NASICON)structural materials have stable 3D skeleton structures and open Na+transport channels,which is a very promising SIB cathode material.But in the typical NASICON material Na_(3)V_(2)(PO_(4))_(3)(NVP),the number of electrons involved in NVP per formula unit is less than 2 at the stable voltage window,which limits the further improvement of battery performance.In this work,we report another NASICON structured Na_(3)V_(4/3)Cr_(2/3)(PO_(4))_(3)@C(NVCP@C),which is obtained by Cr-doped NVP through spray drying.By taking full advantage of the voltage platforms of V^(5+/4+),V^(4+/3+),and V^(3+/2+)in the window of 1.5-4.4 V,NVCP@C delivered a high discharge capacity(175 mAh g^(-1))and durable cyclability(86%capacity retention for 2000 cycles).In-situ X-ray diffraction results demonstrate that the reversible structural evolution accompanies by solid-solution reaction and two-phase reaction mechanisms co-exist during charge/discharge processes.When coupled with Na^(+)preembedded hard carbon(HC),the assembled NVCP@C//HC full cell delivers a high capacity(105 mAh g^(-1))and long cycling performance(70%after 1000 cycles).This Cr-doped NVP method offers new insights into the design of high-energy NASICON-structured cathode materials.
基金This work was supported by the National Basic Research Program of China （No. 2013CB934103）, the National Natural Science Fund for Distinguished Young Scholars （No. 51425204）, the National Natural Science Foundation of China （Nos. 51521001 and 51502227）, the China Postdoctoral Science Foundation （No. 2015T80845）, and the Fundamental Research Funds for the Central Universities （WUT： Nos. 2014- IV-062, 2014-IV-147, 2014-YB-002, and 2016III005）.
文摘In the last decade, pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors. Although various methods have been investigated to improve the performance of pyrolyzed carbons, such as conductivity, energy storage density and cycling performance, effective methods for the integration and mass-production of pyrolyzed-carbon- based composites on a large scale are lacking. Here, we report the development of an optimized photolithographic technique for the fine micropatterning of photoresist/chitosan-coated carbon nanotube （CHIT-CNT） composite. After subsequent pyrolysis, the fabricated carbon/CHIT-CNT microelectrode-based micro-supercapacitor has a high capacitance （6.09 mF.cm-2） and energy density （4.5 mWh.cm-3） at a scan rate of 10 mV.s-L Additionally, the micro-supercapacitor has a remarkable long-term cyclability, with 99.9% capacitance retention after 10,000 cyclic voltammetry cycles. This design and microfabrication process allow the application of carbon microelectromechanical system （C-MEMS）-based micro-supercapacitors due to their high potential for enhancing the mechanical and electrochemical performance of micro-supercapacitors.
基金This work was supported by the National Key Research and Development Program of China （No. 2016YFA0202603）, the National Basic Research Program of China （No. 2013CB934103）, the Programme of Introducing Talents of Discipline to Universities （No. B17034）, the National Natural Science Foundation of China （Nos. 51521001, 51502227, 51579198, and 51302203）, the National Natural Science Fund for Distinguished Young Scholars （No. 51425204）, and the Fundamental Research Funds for the Central Universities （WUT： 2016III001, 2016III005, 2016III006）.
文摘Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices. Asymmetric structures have been widely inves- tigated in micro-supercapacitors, and carbon-based materials are commonly applied in the electrodes. To integrate different metal oxides in both electrodes in micro-supercapacitors, the critical challenge is the pairing of different faradic metal oxides. Herein, we propose a strategy of matching the voltage and capadtance of two faradic materials that are fully integrated into one high-performance asymmetric micro-supercapacitor by a facile and controllable fabrication process. The fabricated micro-supercapacitors employ MnO2 as the positive active material and Fe203 as the negative active material, respectively. The planar asymmetric micro-supercapacitors possess a high capacitance of 60 F-cm-3, a high energy density of 12 mW.h.cm-3, and a broad operation voltage range up to 1.2 V.
文摘Molybdenum disulfide （MoS2） is an earth-abundant and low-cost hydrogen evolving electrocatalyst with the potential to replace traditional noble metal catalysts. The catalytic activity can be significantly enhanced after modification due to higher conductivity and enriched active sites. However, the underlying mechanism of the influence of the resistance of electrode material and contact resistance on the hydrogen evolution reaction （HER） process is unclear. Herein, we present a systematic study to understand the relationship between HER performance and electrode conductivity, which is bi-tuned through the electric field and photoelectrical effect. It was found that the onset overpotential consistently decreased with the increase of electrode conductivity. In addition, the reduction of the contact resistance resulted in a quicker electrochemical reaction process than enhancing the conductivity of the MoS2 nanosheet. An onset overpotential of 89 mV was achieved under 60 mW/cm^2 sunlight illumination （0.6 sun） and a simultaneous gate voltage of 3 V. These physical strategies can also be applied to other catalysts, and offer new directions to improve HER catalytic performance of semiconductor materials.
基金This work was supported by the National Key Research and Development Program of China （No. 2016YFA0202603）, the National Basic Research Program of China （No. 2013CB934103）, the Programme of Introducing Talents of Discipline to Universities （No. B17034）, the National Natural Science Foundation of China （No. 51521001）, the National Natural Science Fund for Distinguished Young Scholars （No. 51425204）, and the Fundamental Research Funds for the Central Universities （WUT： 2016III001, 2017III009）, Prof. Liqiang Mai gratefully acknowledged financial support from China Scholarship Council （No. 201606955096）.
文摘Hybrid or composite heterostructured electrode materials have been widely studied for their potential application in electrochemical energy storage. Whereas their physical or chemical properties could be affected significantly by modulating the heterogeneous interface, the underlying mechanisms are not yet fully understood. In this work, we fabricated an electrochemical energy storage device with a MoS2 nanosheet/MnO2 nanowire heterostructure and designed two charge/discharge channels to study the effect of the heterogeneous interface on the energy storage performances. Electrochemical measurements show that a capadty improvement of over 50% is achieved when the metal current collector was in contact with the MnO2 instead of the MoS2 side. We propose that this enhancement is due to the unidirectional conductivity of the MoS2/MnO2 heterogeneous interface, resulting from the unimpeded electrical transport in the MnO2-MoS2 channel along with the blocking effect on the electron transport in the MoS2-MnO2 channel, which leads to reaction kinetics optimization. The present study thus provides important insights that will improve our understanding of heterostructured electrode materials for electrochemical energy storage.
文摘Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials.Characterizing the minute-variations in complementary aspects such as crystal structure,chemical bonds,and electron/ion conductivity will give an in-depth understanding on the reaction mechanism of electrode materials,as well as revealing pathways for optimization.Here,vanadium pentoxide (V2O5),a typical cathode material suffering from severe capacity decay during cycling,is characterized by in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy combined with electrochemical tests.The phase transitions of V2O5 within the 0-1 LiN ratio are characterized in detail.The V--O and V-V distances became more extended and shrank compared to the original ones after charge/discharge process,respectively.Combined with electrochemical tests,these variations are vital to the crystal structure cracking,which is linked with capacity fading.This work demonstrates that chemical bond changes between the transition metal and oxygen upon cycling serve as the origin of the capacity fading.
