Advanced Energy Materials

/Advanced Energy Materials

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

2018-11-18T00:32:36+00:00November 17th, 2018|Categories: Publications|Tags: , |

The defects in graphene are deactivated by the coverage of Al2O3 nanoclusters, which suppress the irreversible decomposition of the sodium conductive salt in sodium‐ion battery electrolytes. An ion‐conducting, thin and homogenous solid electrolyte interphase is formed, resulting in high initial Coulombic efficiency, good rate capability, and cyclic stability for sodium‐ion storage. Abstract Carbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon

Published in: "Advanced Energy Materials".

Deactivating Defects in Graphenes with Al2O3 Nanoclusters to Produce Long‐Life and High‐Rate Sodium‐Ion Batteries

2018-11-16T04:36:45+00:00November 16th, 2018|Categories: Publications|Tags: , |

The defects in graphene are deactivated by the coverage of Al2O3 nanoclusters, which suppress the irreversible decomposition of the sodium conductive salt in sodium‐ion battery electrolytes. An ion‐conducting, thin and homogenous solid electrolyte interphase is formed, resulting in high initial Coulombic efficiency, good rate capability, and cyclic stability for sodium‐ion storage. Abstract Carbon materials are the most promising anodes for sodium‐ion batteries (SIBs), but low initial Coulombic efficiency (ICE) and poor cyclic stability hinder their practical use. It is shown herein, that an effective but simple remedy for these problems can be achieved by deactivating defects in the carbon with Al2O3 nanocluster coverage. A 3D porous graphene monolith (PGM) is used as the model material and Al2O3 nanoclusters around 1 nm are grown on the defects of graphene. It is shown that these Al2O3 nanoclusters suppress the decomposition of conductive sodium salt in the electrolyte, resulting in the formation of a thin and homogenous solid electrolyte interphase (SEI). In addition, Al2O3 nanoclusters appear to reduce the detrimental etching of the SEI by hydrogen fluoride (HF) and improve its stability. Therefore, after the introduction of Al2O3 nanoclusters, the ICE, cyclic stability, and rate capability of the PGM are greatly improved. A higher ICE (70.2%) and capacity retention (82.9% after 500 cycles at 0.5 A g−1) than those of normally reported for large surface area carbons are achieved. This work indicates a new way to deactivate defects and modify the SEI of carbon materials, and hopefully accelerate the commercialization of carbon

Published in: "Advanced Energy Materials".

Pseudomorphic Transformation of Interpenetrated Prussian Blue Analogs into Defective Nickel Iron Selenides for Enhanced Electrochemical and Photo‐Electrochemical Water Splitting

2018-11-11T00:33:06+00:00November 10th, 2018|Categories: Publications|Tags: |

A defect‐rich porous selenide‐based framework is obtained from an interpenetrated Prussian blue analog network. The resulting structure displays an interconnected porous conductive network at the microscopic level and exposes excess reactive crystal boundary defects in the form of unsaturated atoms at the edges and interfaces at the atomic level. It delivers highly reactive and durable photo(electro)chemical energy conversion functionalities. Abstract A significant methodology gap remains in the construction of advanced electrocatalysts, which has collaborative defective functionalities and structural coherence that maximizes electrochemical redox activity, electrical conductivity, and mass transport characteristics. Here, a coordinative self‐templated pseudomorphic transformation of an interpenetrated metal organic compound network is conceptualized into a defect‐rich porous framework that delivers highly reactive and durable photo(electro)chemical energy conversion functionalities. The coordinative‐template approach enables previously inaccessible synthesis routes to rationally accomplish an interconnected porous conductive network at the microscopic level, while exposing copious unsaturated reactive sites at the atomic level without electronic or structural integrity trade‐offs. Consequently, porous framework, interconnected motifs, and engineered defects endow remarkable electrocatalytic hydrogen evolution reaction and oxygen evolution reaction activity due to intrinsically improved turnover frequency, electrochemical surface area, and charge transfer. Moreover, when the hybrid is coupled with a silicon photocathode for solar‐driven water splitting, it enables photon assisted redox reactions, improved charge separation, and enhanced carrier transport via the built‐in heterojunction and additive co‐catalyst functionality, leading to a promising photo(electro)chemical hydrogen generation performance. This work signifies a viable and generic approach to prepare other functional interconnected metal organic coordinated compounds, which can

Published in: "Advanced Energy Materials".

High Performance Lithium Metal Batteries Enabled by Surface Tailoring of Polypropylene Separator with a Polydopamine/Graphene Layer

2018-11-11T00:33:04+00:00November 10th, 2018|Categories: Publications|Tags: |

A multifunctional trilayer separator is designed by depositing a dual layer of a polydopamine and a graphene‐carboxymethyl cellulose on top of a polypropylene separator. When the designed membrane is employed in each Li/Cu half‐cell and Li/LiFePO4 full‐cell, the electrochemical performance is dramatically improved, due to the reduced local current density and the improved electrochemical kinetics. Abstract Lithium (Li) metal batteries suffer from the intrinsic issues associated with poor Coulombic efficiency and dendritic Li growth. Herein, a multifunctional trilayer membrane is reported first by depositing a dual layer of a polydopamine (PDA) and a graphene‐carboxymethyl cellulose (Gr‐CMC) on top of the standard polypropylene separator in order to enhance the cycle performance and electrochemical stabilities of Li metal electrodes. The Gr‐CMC layer of the designed separator has an excellent electrolyte wettability, enhanced electrical conductivity, and additional capacity for Li storage. These strong benefits facilitate the excellent and effective electrochemical reactions and kinetics in both the Li/Cu half‐cell and the Li/LiFePO4 (LFP) full cell. When the PDA/Gr‐CMC separator is employed in both systems, the cycle stability and Coulombic efficiency are dramatically improved and the interfacial impedance between the electrode and the separator is significantly reduced. Electrochemical stability tests at 0 °C further demonstrate the positive potential of the designed separator for facilitating the stable operation of Li metal batteries. The approach not only serves as an effective way of enhancing the life‐time and capacity of Li metal batteries but also can broaden the material options for the development of advanced Li metal

Published in: "Advanced Energy Materials".

Pseudomorphic Transformation of Interpenetrated Prussian Blue Analogs into Defective Nickel Iron Selenides for Enhanced Electrochemical and Photo‐Electrochemical Water Splitting

2018-11-10T00:33:34+00:00November 9th, 2018|Categories: Publications|Tags: |

A defect‐rich porous selenide‐based framework is obtained from an interpenetrated Prussian blue analog network. The resulting structure displays an interconnected porous conductive network at the microscopic level and exposes excess reactive crystal boundary defects in the form of unsaturated atoms at the edges and interfaces at the atomic level. It delivers highly reactive and durable photo(electro)chemical energy conversion functionalities. Abstract A significant methodology gap remains in the construction of advanced electrocatalysts, which has collaborative defective functionalities and structural coherence that maximizes electrochemical redox activity, electrical conductivity, and mass transport characteristics. Here, a coordinative self‐templated pseudomorphic transformation of an interpenetrated metal organic compound network is conceptualized into a defect‐rich porous framework that delivers highly reactive and durable photo(electro)chemical energy conversion functionalities. The coordinative‐template approach enables previously inaccessible synthesis routes to rationally accomplish an interconnected porous conductive network at the microscopic level, while exposing copious unsaturated reactive sites at the atomic level without electronic or structural integrity trade‐offs. Consequently, porous framework, interconnected motifs, and engineered defects endow remarkable electrocatalytic hydrogen evolution reaction and oxygen evolution reaction activity due to intrinsically improved turnover frequency, electrochemical surface area, and charge transfer. Moreover, when the hybrid is coupled with a silicon photocathode for solar‐driven water splitting, it enables photon assisted redox reactions, improved charge separation, and enhanced carrier transport via the built‐in heterojunction and additive co‐catalyst functionality, leading to a promising photo(electro)chemical hydrogen generation performance. This work signifies a viable and generic approach to prepare other functional interconnected metal organic coordinated compounds, which can

Published in: "Advanced Energy Materials".

High Performance Lithium Metal Batteries Enabled by Surface Tailoring of Polypropylene Separator with a Polydopamine/Graphene Layer

2018-11-10T00:33:33+00:00November 9th, 2018|Categories: Publications|Tags: |

A multifunctional trilayer separator is designed by depositing a dual layer of a polydopamine and a graphene‐carboxymethyl cellulose on top of a polypropylene separator. When the designed membrane is employed in each Li/Cu half‐cell and Li/LiFePO4 full‐cell, the electrochemical performance is dramatically improved, due to the reduced local current density and the improved electrochemical kinetics. Abstract Lithium (Li) metal batteries suffer from the intrinsic issues associated with poor Coulombic efficiency and dendritic Li growth. Herein, a multifunctional trilayer membrane is reported first by depositing a dual layer of a polydopamine (PDA) and a graphene‐carboxymethyl cellulose (Gr‐CMC) on top of the standard polypropylene separator in order to enhance the cycle performance and electrochemical stabilities of Li metal electrodes. The Gr‐CMC layer of the designed separator has an excellent electrolyte wettability, enhanced electrical conductivity, and additional capacity for Li storage. These strong benefits facilitate the excellent and effective electrochemical reactions and kinetics in both the Li/Cu half‐cell and the Li/LiFePO4 (LFP) full cell. When the PDA/Gr‐CMC separator is employed in both systems, the cycle stability and Coulombic efficiency are dramatically improved and the interfacial impedance between the electrode and the separator is significantly reduced. Electrochemical stability tests at 0 °C further demonstrate the positive potential of the designed separator for facilitating the stable operation of Li metal batteries. The approach not only serves as an effective way of enhancing the life‐time and capacity of Li metal batteries but also can broaden the material options for the development of advanced Li metal

Published in: "Advanced Energy Materials".

Spray‐Dried Mesoporous Mixed Cu‐Ni [email protected] Nanocomposite Microspheres for High Power and Durable Li‐Ion Battery Anodes

2018-11-07T14:33:15+00:00November 7th, 2018|Categories: Publications|Tags: , |

High‐performance exfoliated graphene‐wrapped mesoporous mixed oxide nanocomposites are synthesized using a straightforward nanostructure engineering strategy. They show significantly improved specific capacity with unprecedented reversible cycling stability exceeding 3000 charge/discharge cycles even at very high current regimes (up to effective 1280 mA) and, thus, can be used as superior alternative anodes in the next generation of high‐performing and long‐lasting Li‐ion batteries. Abstract Exfoliated graphene‐wrapped mesoporous Cu‐Ni oxide (CNO) nanocast composites are developed using a straightforward nanostructure engineering strategy. The synergistic effect of hierarchical mesoporous CNO nanobuilding blocks that are homogeneously wrapped by graphene nanosheets (GNSs) using a rapid spray drying technique effectively preserves the electroactive species against the volume changes resulting from the charge/discharge process. Owing to the intriguing structural/morphological features arising from the caging effect of exfoliated graphene sheets, these 3D/2D [email protected] nanocomposite microspheres are promising as high‐performance Li‐ion battery anode materials. They exhibit unprecedented electrochemical behavior, such as high reversible specific capacity (initial discharge capacities exceeding 1700 mAh g−1 at low 0.1 mA g−1, stable 850 and 730 mAh g−1 at 1 and 5 mA g−1 after 800 and 1300 cycles, respectively, and higher than 400 mAh g−1 at very high current density of 10 mA g−1 after more than 2000 cycles), excellent coulombic efficiency and long‐term stability (more than 3000 cycles with >55% capacity retention) at high current density that are remarkable compared to most transition metal oxides and nanocomposites prepared by conventional techniques. This simple, yet innovative, material design is inspiring to develop advanced conversion materials

Published in: "Advanced Energy Materials".

Unsaturated Sulfur Edge Engineering of Strongly Coupled MoS2 Nanosheet–Carbon Macroporous Hybrid Catalyst for Enhanced Hydrogen Generation

2018-11-07T14:33:13+00:00November 7th, 2018|Categories: Publications|Tags: , |

A class of strongly coupled MoS2 nanosheet–carbon macroporous hybrids with engineered unsaturated sulfur edges has been developed as excellent hydrogen evolution reaction (HER) electrocatalysts. Both experimental analysis and first‐principles calculations verify that the resultant catalysts exhibit high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, greatly boosting the HER activity and durability in acidic and alkaline media. Abstract The low hydrogen adsorption free energy and strong acid/alkaline resistance of layered MoS2 render it an excellent pH‐universal electrocatalyst for hydrogen evolution reaction (HER). However, the catalytic activity is dominantly suppressed by its limited active‐edge‐site density. Herein, a new strategy is reported for making a class of strongly coupled MoS2 nanosheet–carbon macroporous hybrid catalysts with engineered unsaturated sulfur edges for boosting HER catalysis by controlling the precursor decomposition and subsequent sodiation/desodiation. Both surface chemical state analysis and first‐principles calculations verify that the resultant catalysts exhibit a desirable valence‐electron state with high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, significantly improving the intrinsic HER catalytic activity. Such an electrocatalyst exhibits superior and stable catalytic activity toward HER with small overpotentials of 136 mV in 0.5 m H2SO4 and 155 mV in 1 m KOH at 10 mA cm−2, which is the best report for MoS2–C hybrid electrocatalysts to date. This work paves a new avenue to improve the intrinsic catalytic activity of 2D materials for hydrogen generation.

Published in: "Advanced Energy Materials".

Exploring Indium‐Based Ternary Thiospinel as Conceivable High‐Potential Air‐Cathode for Rechargeable Zn–Air Batteries

2018-11-07T14:33:10+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A novel and promising bifunctional oxygen electrocatalyst (CoIn2S4) is demonstrated, with S‐doped reduced graphene oxide as an electronic conductor. Both experimental and theoretical investigations demonstrate that the introduction of indium can effectively promote the reversible oxygen electrode reactions. A rechargeable Zn–air battery with this catalyst exhibits a high voltaic efficiency and long cycling life, outperforming the costlier Pt/C+RuO2 mixture catalyst. Abstract Reversible oxygen reactions in Zn–air batteries require cost‐effective and highly‐active bifunctional electrocatalysts to substitute traditional noble‐metal based catalysts. Herein, a new and promising electrocatalytic material, ternary CoIn2S4 thiospinel, is demonstrated for effectively catalyzing oxygen reduction and oxygen evolution reactions (ORR and OER) with S‐doped reduced graphene oxide (S‐rGO) as an electronic conductor. Compared with Co9S8/S‐rGO (without In doping), the newly developed CoIn2S4/S‐rGO reveals superior electrocatalytic properties for the ORR (half‐wave potential of 0.83 V) and OER (overpotential of 0.37 V at 10 mA cm−2), demonstrating that the introduction of In can promote the reversible oxygen electrode reactions of CoIn2S4. The superior experimentally‐observed electrocatalytic properties are corroborated via density function theory investigations. Meanwhile, the synergistic improvements in the bifunctional activities resulting from the combination of CoIn2S4 and S‐rGO are also confirmed. As a proof of concept, home‐made Zn–air cells are assembled with CoIn2S4/S‐rGO as an air‐cathode. The developed Zn–air cells exhibit a high peak power density (133 mW cm−2) with an energy density of 951 Wh kgZn−1 and robust cycling stability over 150 cycles for 50 h, exceeding of those commercial Pt/C+RuO2 which highlights the practical viability of CoIn2S4/S‐rGO

Published in: "Advanced Energy Materials".

Nickel–Cobalt Double Hydroxide as a Multifunctional Mediator for Ultrahigh‐Rate and Ultralong‐Life Li–S Batteries

2018-11-07T14:33:06+00:00November 7th, 2018|Categories: Publications|Tags: , |

The nickel–cobalt double hydroxide composite can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of lithium polysulfides. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting lithium–sulfur battery exhibits a superior capacity, ultrahigh rate performance, and ultralong life with a decay rate of 0.015% per cycle. The mechanism is investigated in detail. Abstract The performance of lithium–sulfur (Li–S) batteries is largely hindered by the shuttle effect caused by the dissolution of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of LiPSs. Here, it is demonstrated that the nickel–cobalt double hydroxide (NiCo‐DH) shells that encapsulate sulfur nanoparticles can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of LiPSs by combining with graphene and carbon nanotubes to construct the conductive networks. The NiCo‐DH shell that intimately contacts with sulfur physically confines the loss of sulfur and promotes the charge transfer and ion diffusion. More importantly, it can react with LiPSs to produce the surface‐bound intermediates, which are able to anchor the soluble LiPSs and accelerate the redox kinetics. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting Li–S battery exhibits a superior capacity (1348.1 mAh g−1 at 0.1 C), ultrahigh rate performance (697.7 mAh g−1 at 5 C), and ultralong cycle life (1500 cycles) with a decay rate of 0.015% per cycle.

Published in: "Advanced Energy Materials".

Fast Na‐Ion Intercalation in Zinc Vanadate for High‐Performance Na‐Ion Hybrid Capacitor

2018-11-07T14:33:02+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A composite of reduced graphene oxide and Zn0.25V2O5·nH2O nanobelts is reported as a new type of Na+ intercalation material with high pseudocapacitance, enabling fast sodium storage. Combination of this material as an anode with a capacitive cathode composed of an ordered mesoporous carbon gives access to a high‐performance Na‐ion hybrid capacitor. Abstract Na‐ion hybrid capacitors are an emerging class of inexpensive and sustainable devices that combine the high energy of batteries with the high power of capacitors. However, their development is strongly impeded by a limited choice of electrode materials that display good electrochemical kinetics and long‐term cyclability. Here, a reduced graphene oxide–Zn0.25V2O5·nH2O nanobelt composite is introduced as a high power anode for Na‐ion batteries and Na‐ion hybrid capacitors. The composite material possesses fast Na‐ion intercalation kinetics, high electronic conductivity, and small volume change during Na‐ion storage, which lead to outstanding rate capability and cycling stability in half‐cell tests. Pairing it with a hard salt–templated, highly ordered mesoporous carbon as a high‐performance capacitive cathode results in a Na‐ion hybrid capacitor, which delivers a high energy density (88.7 Wh kg−1 at 223 W kg−1), a high power density (12552 W kg−1 with 13.2 Wh kg−1 retained), and an impressive cycling performance (31.7 Wh kg−1 (i.e., 87%) retained after 2000 cycles at 1 A g−1). This work explores zinc vanadate, a typical example of a layered metal vanadate, as an intercalation anode material with high pseudocapacitance for Na‐ion hybrid capacitors, which may open a promising direction for high‐rate Na‐ion storage.

Published in: "Advanced Energy Materials".

Exploring Indium‐Based Ternary Thiospinel as Conceivable High‐Potential Air‐Cathode for Rechargeable Zn–Air Batteries

2018-11-07T02:37:40+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A novel and promising bifunctional oxygen electrocatalyst (CoIn2S4) is demonstrated, with S‐doped reduced graphene oxide as an electronic conductor. Both experimental and theoretical investigations demonstrate that the introduction of indium can effectively promote the reversible oxygen electrode reactions. A rechargeable Zn–air battery with this catalyst exhibits a high voltaic efficiency and long cycling life, outperforming the costlier Pt/C+RuO2 mixture catalyst. Abstract Reversible oxygen reactions in Zn–air batteries require cost‐effective and highly‐active bifunctional electrocatalysts to substitute traditional noble‐metal based catalysts. Herein, a new and promising electrocatalytic material, ternary CoIn2S4 thiospinel, is demonstrated for effectively catalyzing oxygen reduction and oxygen evolution reactions (ORR and OER) with S‐doped reduced graphene oxide (S‐rGO) as an electronic conductor. Compared with Co9S8/S‐rGO (without In doping), the newly developed CoIn2S4/S‐rGO reveals superior electrocatalytic properties for the ORR (half‐wave potential of 0.83 V) and OER (overpotential of 0.37 V at 10 mA cm−2), demonstrating that the introduction of In can promote the reversible oxygen electrode reactions of CoIn2S4. The superior experimentally‐observed electrocatalytic properties are corroborated via density function theory investigations. Meanwhile, the synergistic improvements in the bifunctional activities resulting from the combination of CoIn2S4 and S‐rGO are also confirmed. As a proof of concept, home‐made Zn–air cells are assembled with CoIn2S4/S‐rGO as an air‐cathode. The developed Zn–air cells exhibit a high peak power density (133 mW cm−2) with an energy density of 951 Wh kgZn−1 and robust cycling stability over 150 cycles for 50 h, exceeding of those commercial Pt/C+RuO2 which highlights the practical viability of CoIn2S4/S‐rGO

Published in: "Advanced Energy Materials".

Nickel–Cobalt Double Hydroxide as a Multifunctional Mediator for Ultrahigh‐Rate and Ultralong‐Life Li–S Batteries

2018-11-07T02:37:26+00:00November 7th, 2018|Categories: Publications|Tags: , |

The nickel–cobalt double hydroxide composite can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of lithium polysulfides. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting lithium–sulfur battery exhibits a superior capacity, ultrahigh rate performance, and ultralong life with a decay rate of 0.015% per cycle. The mechanism is investigated in detail. Abstract The performance of lithium–sulfur (Li–S) batteries is largely hindered by the shuttle effect caused by the dissolution of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of LiPSs. Here, it is demonstrated that the nickel–cobalt double hydroxide (NiCo‐DH) shells that encapsulate sulfur nanoparticles can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of LiPSs by combining with graphene and carbon nanotubes to construct the conductive networks. The NiCo‐DH shell that intimately contacts with sulfur physically confines the loss of sulfur and promotes the charge transfer and ion diffusion. More importantly, it can react with LiPSs to produce the surface‐bound intermediates, which are able to anchor the soluble LiPSs and accelerate the redox kinetics. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting Li–S battery exhibits a superior capacity (1348.1 mAh g−1 at 0.1 C), ultrahigh rate performance (697.7 mAh g−1 at 5 C), and ultralong cycle life (1500 cycles) with a decay rate of 0.015% per cycle.

Published in: "Advanced Energy Materials".

Nickel–Cobalt Double Hydroxide as a Multifunctional Mediator for Ultrahigh‐Rate and Ultralong‐Life Li–S Batteries

2018-11-07T02:37:26+00:00November 7th, 2018|Categories: Publications|Tags: , |

The nickel–cobalt double hydroxide composite can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of lithium polysulfides. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting lithium–sulfur battery exhibits a superior capacity, ultrahigh rate performance, and ultralong life with a decay rate of 0.015% per cycle. The mechanism is investigated in detail. Abstract The performance of lithium–sulfur (Li–S) batteries is largely hindered by the shuttle effect caused by the dissolution of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of LiPSs. Here, it is demonstrated that the nickel–cobalt double hydroxide (NiCo‐DH) shells that encapsulate sulfur nanoparticles can play multiple roles in suppressing the shuttle effect and accelerating the redox kinetics of LiPSs by combining with graphene and carbon nanotubes to construct the conductive networks. The NiCo‐DH shell that intimately contacts with sulfur physically confines the loss of sulfur and promotes the charge transfer and ion diffusion. More importantly, it can react with LiPSs to produce the surface‐bound intermediates, which are able to anchor the soluble LiPSs and accelerate the redox kinetics. Such composite electrodes can load high contents of sulfur (>85 wt%) and the resulting Li–S battery exhibits a superior capacity (1348.1 mAh g−1 at 0.1 C), ultrahigh rate performance (697.7 mAh g−1 at 5 C), and ultralong cycle life (1500 cycles) with a decay rate of 0.015% per cycle.

Published in: "Advanced Energy Materials".

Fast Na‐Ion Intercalation in Zinc Vanadate for High‐Performance Na‐Ion Hybrid Capacitor

2018-11-07T02:37:21+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A composite of reduced graphene oxide and Zn0.25V2O5·nH2O nanobelts is reported as a new type of Na+ intercalation material with high pseudocapacitance, enabling fast sodium storage. Combination of this material as an anode with a capacitive cathode composed of an ordered mesoporous carbon gives access to a high‐performance Na‐ion hybrid capacitor. Abstract Na‐ion hybrid capacitors are an emerging class of inexpensive and sustainable devices that combine the high energy of batteries with the high power of capacitors. However, their development is strongly impeded by a limited choice of electrode materials that display good electrochemical kinetics and long‐term cyclability. Here, a reduced graphene oxide–Zn0.25V2O5·nH2O nanobelt composite is introduced as a high power anode for Na‐ion batteries and Na‐ion hybrid capacitors. The composite material possesses fast Na‐ion intercalation kinetics, high electronic conductivity, and small volume change during Na‐ion storage, which lead to outstanding rate capability and cycling stability in half‐cell tests. Pairing it with a hard salt–templated, highly ordered mesoporous carbon as a high‐performance capacitive cathode results in a Na‐ion hybrid capacitor, which delivers a high energy density (88.7 Wh kg−1 at 223 W kg−1), a high power density (12552 W kg−1 with 13.2 Wh kg−1 retained), and an impressive cycling performance (31.7 Wh kg−1 (i.e., 87%) retained after 2000 cycles at 1 A g−1). This work explores zinc vanadate, a typical example of a layered metal vanadate, as an intercalation anode material with high pseudocapacitance for Na‐ion hybrid capacitors, which may open a promising direction for high‐rate Na‐ion storage.

Published in: "Advanced Energy Materials".

Fast Na‐Ion Intercalation in Zinc Vanadate for High‐Performance Na‐Ion Hybrid Capacitor

2018-11-07T02:37:20+00:00November 7th, 2018|Categories: Publications|Tags: , , |

A composite of reduced graphene oxide and Zn0.25V2O5·nH2O nanobelts is reported as a new type of Na+ intercalation material with high pseudocapacitance, enabling fast sodium storage. Combination of this material as an anode with a capacitive cathode composed of an ordered mesoporous carbon gives access to a high‐performance Na‐ion hybrid capacitor. Abstract Na‐ion hybrid capacitors are an emerging class of inexpensive and sustainable devices that combine the high energy of batteries with the high power of capacitors. However, their development is strongly impeded by a limited choice of electrode materials that display good electrochemical kinetics and long‐term cyclability. Here, a reduced graphene oxide–Zn0.25V2O5·nH2O nanobelt composite is introduced as a high power anode for Na‐ion batteries and Na‐ion hybrid capacitors. The composite material possesses fast Na‐ion intercalation kinetics, high electronic conductivity, and small volume change during Na‐ion storage, which lead to outstanding rate capability and cycling stability in half‐cell tests. Pairing it with a hard salt–templated, highly ordered mesoporous carbon as a high‐performance capacitive cathode results in a Na‐ion hybrid capacitor, which delivers a high energy density (88.7 Wh kg−1 at 223 W kg−1), a high power density (12552 W kg−1 with 13.2 Wh kg−1 retained), and an impressive cycling performance (31.7 Wh kg−1 (i.e., 87%) retained after 2000 cycles at 1 A g−1). This work explores zinc vanadate, a typical example of a layered metal vanadate, as an intercalation anode material with high pseudocapacitance for Na‐ion hybrid capacitors, which may open a promising direction for high‐rate Na‐ion storage.

Published in: "Advanced Energy Materials".

Spray‐Dried Mesoporous Mixed Cu‐Ni [email protected] Nanocomposite Microspheres for High Power and Durable Li‐Ion Battery Anodes

2018-11-07T00:33:10+00:00November 6th, 2018|Categories: Publications|Tags: , |

High‐performance exfoliated graphene‐wrapped mesoporous mixed oxide nanocomposites are synthesized using a straightforward nanostructure engineering strategy. They show significantly improved specific capacity with unprecedented reversible cycling stability exceeding 3000 charge/discharge cycles even at very high current regimes (up to effective 1280 mA) and, thus, can be used as superior alternative anodes in the next generation of high‐performing and long‐lasting Li‐ion batteries. Abstract Exfoliated graphene‐wrapped mesoporous Cu‐Ni oxide (CNO) nanocast composites are developed using a straightforward nanostructure engineering strategy. The synergistic effect of hierarchical mesoporous CNO nanobuilding blocks that are homogeneously wrapped by graphene nanosheets (GNSs) using a rapid spray drying technique effectively preserves the electroactive species against the volume changes resulting from the charge/discharge process. Owing to the intriguing structural/morphological features arising from the caging effect of exfoliated graphene sheets, these 3D/2D [email protected] nanocomposite microspheres are promising as high‐performance Li‐ion battery anode materials. They exhibit unprecedented electrochemical behavior, such as high reversible specific capacity (initial discharge capacities exceeding 1700 mAh g−1 at low 0.1 mA g−1, stable 850 and 730 mAh g−1 at 1 and 5 mA g−1 after 800 and 1300 cycles, respectively, and higher than 400 mAh g−1 at very high current density of 10 mA g−1 after more than 2000 cycles), excellent coulombic efficiency and long‐term stability (more than 3000 cycles with >55% capacity retention) at high current density that are remarkable compared to most transition metal oxides and nanocomposites prepared by conventional techniques. This simple, yet innovative, material design is inspiring to develop advanced conversion materials

Published in: "Advanced Energy Materials".

Unsaturated Sulfur Edge Engineering of Strongly Coupled MoS2 Nanosheet–Carbon Macroporous Hybrid Catalyst for Enhanced Hydrogen Generation

2018-11-07T00:33:09+00:00November 6th, 2018|Categories: Publications|Tags: , |

A class of strongly coupled MoS2 nanosheet–carbon macroporous hybrids with engineered unsaturated sulfur edges has been developed as excellent hydrogen evolution reaction (HER) electrocatalysts. Both experimental analysis and first‐principles calculations verify that the resultant catalysts exhibit high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, greatly boosting the HER activity and durability in acidic and alkaline media. Abstract The low hydrogen adsorption free energy and strong acid/alkaline resistance of layered MoS2 render it an excellent pH‐universal electrocatalyst for hydrogen evolution reaction (HER). However, the catalytic activity is dominantly suppressed by its limited active‐edge‐site density. Herein, a new strategy is reported for making a class of strongly coupled MoS2 nanosheet–carbon macroporous hybrid catalysts with engineered unsaturated sulfur edges for boosting HER catalysis by controlling the precursor decomposition and subsequent sodiation/desodiation. Both surface chemical state analysis and first‐principles calculations verify that the resultant catalysts exhibit a desirable valence‐electron state with high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, significantly improving the intrinsic HER catalytic activity. Such an electrocatalyst exhibits superior and stable catalytic activity toward HER with small overpotentials of 136 mV in 0.5 m H2SO4 and 155 mV in 1 m KOH at 10 mA cm−2, which is the best report for MoS2–C hybrid electrocatalysts to date. This work paves a new avenue to improve the intrinsic catalytic activity of 2D materials for hydrogen generation.

Published in: "Advanced Energy Materials".

Redox‐Active Organic Sodium Anthraquinone‐2‐Sulfonate (AQS) Anchored on Reduced Graphene Oxide for High‐Performance Supercapacitors

2018-11-07T00:33:06+00:00November 6th, 2018|Categories: Publications|Tags: , , |

Redox active organic sodium anthraquinone‐2‐sulfonate (AQS) is successfully anchored on highly conductive reduced graphene oxide sheets with the formation of a space‐charge layer, which greatly facilitates the pseudocapacitance of AQS molecules for supercapacitor applications. Abstract Redox active organic quinones are potentially low cost, sustainable, and high‐energy pseudocapacitive materials due to their fast and reversible redox reactivity. However, their electrically insulating nature prevents any practical application. Herein, for the first time, sodium anthraquinone‐2‐sulfonate (AQS) is examined as an organic redox‐active compound and highly conductive graphene nanosheets are incorporated to enhance the electronic conductivity. The SO3− functional group of AQS offers excellent hydrophilicity, which promotes the molecular level binding of AQS with reduced graphene oxide (rGO) and leads to a 3D interconnected xerogel ([email protected]). The composite exhibits a high specific capacitance of 567.1 F g−1 at 1 A g−1 with a stable capacity retention of 89.1% over 10 000 cycles at 10 A g−1. More importantly, the optimized composite maintains a high capacitance of 315.1 F g−1 even at 30 A g−1 due to the high pseudocapacitance of AQS and the capacitive contribution of rGO. First‐principles calculations further elucidate that AQS offers strong adhesion to rGO sheets with the formation of a space‐charge layer, which is favorable for the pseudocapacitance of AQS. This work opens a new avenue for developing high‐performance supercapacitors though rational combination of redox organic molecules with highly conductive graphene.

Published in: "Advanced Energy Materials".

Exploring Indium‐Based Ternary Thiospinel as Conceivable High‐Potential Air‐Cathode for Rechargeable Zn–Air Batteries

2018-11-07T00:33:03+00:00November 6th, 2018|Categories: Publications|Tags: , , |

A novel and promising bifunctional oxygen electrocatalyst (CoIn2S4) is demonstrated, with S‐doped reduced graphene oxide as an electronic conductor. Both experimental and theoretical investigations demonstrate that the introduction of indium can effectively promote the reversible oxygen electrode reactions. A rechargeable Zn–air battery with this catalyst exhibits a high voltaic efficiency and long cycling life, outperforming the costlier Pt/C+RuO2 mixture catalyst. Abstract Reversible oxygen reactions in Zn–air batteries require cost‐effective and highly‐active bifunctional electrocatalysts to substitute traditional noble‐metal based catalysts. Herein, a new and promising electrocatalytic material, ternary CoIn2S4 thiospinel, is demonstrated for effectively catalyzing oxygen reduction and oxygen evolution reactions (ORR and OER) with S‐doped reduced graphene oxide (S‐rGO) as an electronic conductor. Compared with Co9S8/S‐rGO (without In doping), the newly developed CoIn2S4/S‐rGO reveals superior electrocatalytic properties for the ORR (half‐wave potential of 0.83 V) and OER (overpotential of 0.37 V at 10 mA cm−2), demonstrating that the introduction of In can promote the reversible oxygen electrode reactions of CoIn2S4. The superior experimentally‐observed electrocatalytic properties are corroborated via density function theory investigations. Meanwhile, the synergistic improvements in the bifunctional activities resulting from the combination of CoIn2S4 and S‐rGO are also confirmed. As a proof of concept, home‐made Zn–air cells are assembled with CoIn2S4/S‐rGO as an air‐cathode. The developed Zn–air cells exhibit a high peak power density (133 mW cm−2) with an energy density of 951 Wh kgZn−1 and robust cycling stability over 150 cycles for 50 h, exceeding of those commercial Pt/C+RuO2 which highlights the practical viability of CoIn2S4/S‐rGO

Published in: "Advanced Energy Materials".

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