Energy

/Tag: Energy

Sulfur-doped graphene for efficient electrocatalytic N2-to-NH3 fixation

2019-02-22T12:43:10+00:00February 22nd, 2019|Categories: Publications|Tags: , |

Chem. Commun., 2019, Accepted ManuscriptDOI: 10.1039/C9CC00602H, CommunicationLi Xia, Jia-Jia Yang, Huanbo Wang, Runbo Zhao, hongyu chen, Wei-hai Fang, Abdullah M. Asiri, Fengyu Xie, Ganglong Cui, Xuping SunIndustrial NH3 synthesis mainly relies on the carbon-emitting Haber–Bosch process operating under severe conditions. Electrocatalytic N2-to-NH3 fixation at ambient conditions is an attractive approach to reduce energy consumption and avoid…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Toward High Power‐High Energy Sodium Cathodes: A Case Study of Bicontinuous Ordered Network of 3D Porous Na3(VO)2(PO4)2F/rGO with Pseudocapacitance Effect

2019-02-22T10:45:17+00:00February 22nd, 2019|Categories: Publications|Tags: , , |

A bicontinuous ordered network of 3D porous Na3(VO)2(PO4)2F/reduced graphene oxide (NVOPF/rGO) is prepared by a two‐step strategy (solvothermal plus electrostatic spray deposition method). Such electrodes exhibit excellent rate capability and cycling stability for both half cell and full cell, as well as a significant contribution of pseudocapacitance, resulting in real high power‐high energy sodium batteries. Abstract Developing high power‐high energy electrochemical energy storage systems is an ultimate goal in the energy storage field, which is even more difficult but significant for low‐cost sodium ion batteries. Here, fluoride is successfully prepared by the electrostatic spray deposition (ESD) technique, which greatly expands the application scope of ESD. A two‐step strategy (solvothermal plus ESD method) is proposed to construct a bicontinuous ordered network of 3D porous Na3(VO)2(PO4)2F/reduced graphene oxide (NVOPF/rGO). This two‐step strategy makes sure that NVOPF can be prepared by ESD, since it avoids the loss of F element during synthesis. The obtained NVOPF particles are as small as 15 nm, and the carbon content is only 3.5% in the final nanocomposite. Such a bicontinuous ordered network and small size of electroactive particles lead to the significant contribution of the pseudocapacitance effect to sodium storage, resulting in real high power‐high energy sodium cathodes. The cathode exhibits excellent rate capability and cycling stability, whose rate performance is one of the best ever reported in both half cells and full cells. Moreover, this work provides a general and promising strategy for developing high power‐high energy electrode materials for various electrochemical energy storage systems.

Published in: "Small".

Efficient and Robust Carbon Dioxide Electroreduction Enabled by Atomically Dispersed Snδ+ Sites

2019-02-22T06:37:14+00:00February 22nd, 2019|Categories: Publications|Tags: , |

A positively charged single‐atom metal electrocatalyst to largely reduce the overpotentials for carbon dioxide electroreduction is fabricated. Synchrotron‐radiation X‐ray absorption fine structure and high‐angle annular dark‐field scanning transmission electron microscopy demonstrate that atomically dispersed tin atoms are positively charged, which enables carbon dioxide activation and protonation proceed spontaneously, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Abstract Electrocatalytic CO2 reduction at considerably low overpotentials still remains a great challenge. Here, a positively charged single‐atom metal electrocatalyst to largely reduce the overpotentials is designed and hence CO2 electroreduction performance is accelerated. Taking the metal Sn as an example, kilogram‐scale single‐atom Sn δ + on N‐doped graphene is first fabricated by a quick freeze–vacuum drying–calcination method. Synchrotron‐radiation X‐ray absorption fine structure and high‐angle annular dark‐field scanning transmission electron microscopy demonstrate the atomically dispersed Sn atoms are positively charged, which enables CO2 activation and protonation to proceed spontaneously through stabilizing CO2•−* and HCOO−*, affirmed by in situ Fourier transform infrared spectra and Gibbs free energy calculations. Furthermore, N‐doping facilitates the rate‐limiting formate desorption step, verified by the decreased desorption energy from 2.16 to 1.01 eV and the elongated SnHCOO− bond length. As an result, single‐atom Sn δ + on N‐doped graphene exhibits a very low onset overpotential down to 60 mV for formate production and shows a very large turnover frequency up to 11930 h−1, while its electroreduction activity proceeds without deactivation even after 200 h. This work offers a new pathway for manipulating electrocatalytic performance.

Published in: "Advanced Materials".

Monolithic Integration of All‐in‐One Supercapacitor for 3D Electronics

2019-02-22T04:38:17+00:00February 22nd, 2019|Categories: Publications|Tags: , , |

An all‐in‐one asymmetrical supercapacitor is prepared by integrating a 2D MnO2 cathode, a holey reduced graphene oxide/carbon nanotube anode, Ni/Au current collector, and a separator into one monolithic glass fiber (GF) membrane. The all‐in‐one supercapacitror is embedded into GF/polydimethylsiloxane substrate to realize the integration with the 3D electronic system. Abstract A supercapacitor is usually stacked in the configuration of a layered sandwiched architecture, and has been adopted as discrete energy storage device or circuit component. However, this stacked structure decreases mechanical integrity, leads to low specific capacity, and prevents high‐density monolithic integration. Here all‐in‐one supercapacitors are fabricated by integrating cathode, anode, current collector, and separator into one monolithic glass fiber (GF) substrate together with other circuit components through matured and scalable fabrication techniques, the all‐in‐one supercapacitor is embedded as a component for 3D electronics. This all‐in‐one architecture demonstrates its effectiveness in the prevention of the delamination of the sandwiched supercapacitor and the minimization of the proportion of inactive materials. The supercapacitor delivers high power density (320 mW cm−3) and energy density (2.12 mWh cm−3), and exhibits a capacitance retention of 100% even after a continuous cycling of 431 h. Furthermore, a 3D polydimethylsiloxane/GF architecture is constructed for driving a flash light emitting diode system, where the all‐in‐one supercapacitor is monolithically integrated in the 3D system, and each layer is connected via vertical through‐holes. This all‐in‐one device can be constructed with a macroscopically available membrane and readily integrated into 3D systems without secondary packaging, providing the potential for high‐density heterogeneous 3D

Published in: "Advanced Energy Materials".

High‐Performance Solid Polymer Electrolytes Filled with Vertically Aligned 2D Materials

2019-02-22T04:33:44+00:00February 22nd, 2019|Categories: Publications|Tags: |

Vertically aligned 2D materials filler for solid polymer electrolytes is demonstrated. The aligned, continuous, run‐through polymer‐filler interfaces enhance the ionic conductivity, Li+ transference number, mechanical modulus, and electrochemical stability of solid polymer electrolytes. LiFePO4 in lithium metal batteries with the electrolyte could deliver a specific capacity of 167 mAh g−1 at 0.1 C at 35 °C. Abstract Solid state lithium metal batteries are the most promising next‐generation power sources owing to their high energy density and safety. Solid polymer electrolytes (SPE) have gained wide attention due to the excellent flexibility, manufacturability, lightweight, and low‐cost processing. However, fatal drawbacks of the SPE such as the insufficient ionic conductivity and Li+ transference number at room temperature restrict their practical application. Here vertically aligned 2D sheets are demonstrated as an advanced filler for SPE with enhanced ionic conductivity, Li+ transference number, mechanical modulus, and electrochemical stability, using vermiculite nanosheets as an example. The vertically aligned vermiculite sheets (VAVS), prepared by the temperature gradient freezing, provide aligned, continuous, run‐through polymer‐filler interfaces after infiltrating with polyethylene oxide (PEO)‐based SPE. As a result, ionic conductivity as high as 1.89 × 10−4 S cm−1 at 25 °C is achieved with Li+ transference number close to 0.5. Along with their enhanced mechanical strength, Li|Li symmetric cells using VAVS–CSPE are stable over 1300 h with a low overpotential. LiFePO4 in all‐solid‐state lithium metal batteries with VAVS–CSPE could deliver a specific capacity of 167 mAh g−1 at 0.1 C at 35 °C and 82% capacity retention after 200 cycles at

Published in: "Advanced Functional Materials".

Ab-initio calculations of carbon and boron nitride allotropes and their structural phase transitions using periodic coupled cluster theory. (arXiv:1902.08100v1 [cond-mat.mtrl-sci])

2019-02-22T02:29:25+00:00February 22nd, 2019|Categories: Publications|Tags: , |

We present an ab-initio study of boron nitride as well as carbon allotropes. Their relative thermodynamic stabilities and structural phase transitions from low- to high-density phases are investigated. Pressure-temperature phase diagrams are calculated and compared to experimental findings. The calculations are performed using quantum chemical wavefunction based as well as density functional theories. Our findings reveal that predicted energy differences often depend significantly on the choice of the employed method. Comparison between calculated and experimental results allows for benchmarking the accuracy of various levels of theory. The produced results show that quantum chemical wavefunction based theories allow for achieving systematically improvable estimates. We find that on the level of coupled cluster theories the low- and high-density phases of boron nitride become thermodynamically degenerate at 0 K. This is in agreement with recent experimental findings, indicating that cubic boron nitride is not the thermodynamically stable allotrope at ambient conditions. Furthermore we employ the calculated results to assess transition probabilities from graphitic low-density to diamond-like high-density phases in an approximate manner. We conclude that the stacking order of the parent graphitic material is crucial for the possible formation of meta-stable wurtzite boron nitride and hexagonal carbon diamond also known as lonsdaleite.

Published in: "arXiv Material Science".

Dramatically Enhanced Ambient Ammonia Electrosynthesis Performance by In‐Operando Created Li–S Interactions on MoS2 Electrocatalyst

2019-02-21T06:38:44+00:00February 21st, 2019|Categories: Publications|Tags: , |

The ambient NH3 electrosynthesis performance of MoS2 is dramatically enhanced by in‐operando created Li–S interactions through effectively suppressed hydrogen evolution reaction activity at S‐edge/Mo‐edge sites, and simultaneously increased N2 adsorption capability and boosted N2 reduction reaction catalytic activity on Mo‐edge sites. The reported in‐operando formation of catalytic active structures via catalyst–electrolyte interactions opens a new way to develop catalysts and catalysis systems. Abstract The Haber‐Bosch process can be replaced by the ambient electrocatalytic N2 reduction reaction (NRR) to produce NH3 if suitable electrocatalysts can be developed. However, to develop high performance N2 fixation electrocatalysts, a key issue to be resolved is to achieve efficient hydrogenation of N2 without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, in‐operando created strong Li–S interactions are reported to empower the S‐rich MoS2 nanosheets with superior NRR catalytic activity and HER suppression ability. The Li+ interactions with S‐edge sites of MoS2 can effectively suppress hydrogen evolution reaction by reducing H* adsorption free energy from 0.03 to 0.47 eV, facilitate N2 adsorption by increasing N2 adsorption free energy from –0.32 to –0.70 eV and enhance electrocatalytic N2 reduction activity by decreasing the activation energy barrier of the reaction control step (*N2 → *N2H) from 0.84 to 0.42 eV. A NH3 yield rate of 43.4 μg h−1 mg−1 MoS2 with a faradaic efficiency (FE) of 9.81% can be achieved in presence of strong Li–S interactions, more than 8 and 18 times by the same electrocatalyst in the absence of Li–S interactions. This report opens a

Published in: "Advanced Energy Materials".

Trifunctional Electrocatalysis on Dual‐Doped Graphene Nanorings–Integrated Boxes for Efficient Water Splitting and Zn–Air Batteries

2019-02-21T06:38:23+00:00February 21st, 2019|Categories: Publications|Tags: , |

An easy yet robust route, for the first time, is developed to craft N, O‐codoped graphene‐integrated boxes by employing hybrids containing polymers and Prussian blue analogue cubes as precursors. Benefiting from the hierarchically porous nanostructures and highly active N, O‐codoped graphene, the resulting electrocatalysts display excellent performance on the overall water splitting and Zn–air battery. Abstract Despite the exciting achievements made in synthesis of monofunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), or hydrogen evolution reaction (HER), it is challenging to develop trifunctional electrocatalysts for both ORR/OER/HER. Herein, N, O‐codoped graphene nanorings‐integrated boxes (denoted NOGB) are crafted via high‐temperature pyrolysis and following acid etching of hybrid precursors containing polymers and Prussian blue analogue cubes. The electrochemical results signified that the resulting NOGB‐800 (800 refers to pyrolysis temperature) is highly active for trifunctional electrocatalysis of ORR/OER/HER. This can be reasonably attributed to the advanced nanostructures (i.e., the hierarchically porous nanostructures on the hollow nanorings) and unique chemical compositions (i.e., N, O‐codoped graphene). More attractively, the rechargeable Zn–air battery based on NOGB‐800 displays maximum power density of 111.9 mW cm−2 with small charge–discharge potential of 0.72 V and excellent stability of 30 h, comparable with the Pt/C+Ir/C counterpart. The NOGB‐800 could also be utilized as bifunctional electrocatalysts for overall water splitting to yield current density of 10 mA cm−2 at a voltage of 1.65 V, surpassing most reported electrocatalysts. Therefore, the NOGB‐800 is a promising candidate instead of precious metal–based electrocatalysts for the efficient Zn–air battery and water splitting.

Published in: "Advanced Energy Materials".

Valley filtering effect of phonons in graphene with a grain boundary. (arXiv:1902.07372v1 [cond-mat.mes-hall])

2019-02-21T04:30:34+00:00February 21st, 2019|Categories: Publications|Tags: , |

Due to their possibility to encode information and realize low-energy-consumption quantum devices, control and manipulation of the valley degree of freedom have been widely studied in electronic systems. In contrast, the phononic counterpart–valley phononics–has been largely unexplored, despite the importance in both fundamental science and practical applications. In this work, we demonstrate that the control of “valleys” is also applicable for phonons in graphene by using a grain boundary. In particular, perfect valley filtering effect is observed at certain energy windows for flexural modes and found to be closely related to the anisotropy of phonon valley pockets. Moreover, valley filtering may be further improved using Fano-like resonance. Our findings reveal the possibility of valley phononics, paving the road towards purposeful phonon engineering and future valley phononics.

Published : "arXiv Mesoscale and Nanoscale Physics".

Room-temperature giant Stark effect of single photon emitter in van der Waals material. (arXiv:1902.07340v1 [cond-mat.mes-hall])

2019-02-21T04:30:32+00:00February 21st, 2019|Categories: Publications|Tags: , |

Single photon emitters (SPEs) are critical building blocks needed for quantum science and technology. For practical applications, large-scale room-temperature solid-state platforms are required. Color centers in layered hexagonal boron nitride (hBN) have recently been found to be ultra-bright and stable SPEs at room temperature. Yet, to scale up solid-state quantum information processing, large tuning range of single photon energy is demanded for wavelength division multiplexing quantum key distribution, where indistinguishability is not required, and for indistinguishable single-photon production from multi-emitters. Stark effect can tune the single photon energy by an electric field, which however, has been achieved only at cryogenic temperature so far. Here we report the first room-temperature Stark effect of SPEs by exploiting hBN color centers. Surprisingly, we observe a giant Stark shift of single photon more than 30 meV, about one order of magnitude greater than previously reported in color center emitters. Moreover, for the first time, the orientation of the electric permanent dipole moment in the solid-state SPE is determined via angle-resolved Stark effect, revealing the intrinsic broken symmetries at such a color center. The remarkable Stark shift discovered here and the significant advance in understanding its atomic structure pave a way towards the scalable solid-state on-chip quantum communication and computation at room temperature.

Published : "arXiv Mesoscale and Nanoscale Physics".

Scalable Production of Graphene Inks via Wet‐Jet Milling Exfoliation for Screen‐Printed Micro‐Supercapacitors

2019-02-21T02:32:35+00:00February 21st, 2019|Categories: Publications|Tags: , |

Single‐/few‐layer graphene flakes, produced via scalable wet‐jet milling exfoliation of graphite, are used as the active material for micro‐supercapacitors (MSCs). The formulation of aqueous‐alcohol graphene inks, as well as the addition of carbon nanotubes, allows interdigitated structure to be screen‐printed on plastic substrates for metal‐free, flexible, solid‐state, and washable MSCs with high areal performance. Abstract The miniaturization of energy storage units is pivotal for the development of next‐generation portable electronic devices. Micro‐supercapacitors (MSCs) hold great potential to work as on‐chip micro‐power sources and energy storage units complementing batteries and energy harvester systems. Scalable production of supercapacitor materials with cost‐effective and high‐throughput processing methods is crucial for the widespread application of MSCs. Here, wet‐jet milling exfoliation of graphite is reported to scale up the production of graphene as a supercapacitor material. The formulation of aqueous/alcohol‐based graphene inks allows metal‐free, flexible MSCs to be screen‐printed. These MSCs exhibit areal capacitance (C areal) values up to 1.324 mF cm−2 (5.296 mF cm−2 for a single electrode), corresponding to an outstanding volumetric capacitance (C vol) of 0.490 F cm−3 (1.961 F cm−3 for a single electrode). The screen‐printed MSCs can operate up to a power density above 20 mW cm−2 at an energy density of 0.064 µWh cm−2. The devices exhibit excellent cycling stability over charge–discharge cycling (10 000 cycles), bending cycling (100 cycles at a bending radius of 1 cm) and folding (up to angles of 180°). Moreover, ethylene vinyl acetate‐encapsulated MSCs retain their electrochemical properties after a home‐laundry cycle, providing waterproof and

Published in: "Advanced Functional Materials".

Exploring Approaches for the Synthesis of Few‐Layered Graphdiyne

2019-02-21T00:38:30+00:00February 20th, 2019|Categories: Publications|Tags: , |

The state‐of‐art research of graphdiyne (GDY) and focus on exploring approaches for few‐layered GDY synthesis are critically summarized. The obstacles and challenges of GDY synthesis are also analyzed in detail. The advantages and limitations of different methods are analyzed comprehensively. These synthetic methods provide considerable inspiration to approaching the synthesis of single/few‐layered GDY film. Abstract Graphdiyne (GDY) is an emerging carbon allotrope in the graphyne (GY) family, demonstrating extensive potential applications in the fields of electronic devices, catalysis, electrochemical energy storage, and nonlinear optics. Synthesis of few‐layered GDY is especially important for both electronic applications and structural characterization. This work critically summarizes the state‐of‐art of GDY and focuses on exploring approaches for few‐layered GDY synthesis. The obstacles and challenges of GDY synthesis are also analyzed in detail. Recently developed synthetic methods are discussed such as i) the copper substrate‐based method, ii) the chemical vapor deposition (CVD) method, iii) the interfacial construction method, and iv) the graphene‐templated method. Throughout the discussion, the superiorities and limitations of different methods are analyzed comprehensively. These synthetic methods have provided considerable inspiration approaching synthesis of few‐layered or single‐layered GDY film. The work concludes with a perspective on promising research directions and remaining barriers for layer‐controlled and morphology‐controlled synthesis of GDY with higher crystalline quality.

Published in: "Advanced Materials".

Progress and Prospects of Graphdiyne‐Based Materials in Biomedical Applications

2019-02-21T00:38:27+00:00February 20th, 2019|Categories: Publications|Tags: |

Current research progress indicates that graphdiyne‐based materials are useful in the biomedical field, including biosensing, radiation protection, and cancer therapy. In these applications, graphdiyne (GDY) is proven to be better than other carbon‐based materials. Though the biomedical applications of GDY are still rare and some difficulties need to be solved, graphdiyne has great potential in its future applications. Abstract Graphdiyne is a new member of the family of carbon‐based nanomaterials that possess two types of carbon atoms, sp‐ and sp2‐hybridized carbon atoms. As a novel 2D carbon‐based nanomaterial with unique planar structure, such as uniformly distributed nanopores and large conjugated structure, graphdiyne has shown many fascinating properties in mechanics, electronics, and optics since it was first experimentally synthesized in 2010. Up to now, graphdiyne and its derivatives have been reported to be successfully applied in many areas, such as catalysis, energy, environment, and biomedicine, due to these excellent properties. Herein, the current research progress of graphdiyne‐based materials in biomedical fields is summarized, including biosensing, biological protection, cancer therapy, tissue engineering, etc. The advantages of graphdiyne and its derivatives are presented and compared with other carbon‐based materials. Considering the potential biomedical and clinical applications of graphdiyne‐based materials, the toxicity and biocompatibility are also discussed based on current studies. Finally, future perspectives and possible biomedical applications of graphdiyne‐based materials are also discussed.

Published in: "Advanced Materials".

Ultrathin Cobalt Oxide Layers as Electrocatalysts for High‐Performance Flexible Zn–Air Batteries

2019-02-21T00:37:54+00:00February 20th, 2019|Categories: Publications|Tags: , |

Ultrathin cobalt oxide layers on the surface of a metallic cobalt/N‐doped graphene substrate synergistically enhance the electrical conductivity and catalytic activity, leading to high performance in oxygen reactions under alkaline conditoins. A flexible Zn‐air battery built with this electrocatalyst has an ultrahigh output power capability and a record‐high specific power of 300 W gcat−1, which is essential for portable devices. Abstract Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal–air batteries. In this study, one‐nanometer‐scale ultrathin cobalt oxide (CoOx) layers are fabricated on a conducting substrate (i.e., a metallic Co/N‐doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn–air batteries. Specifically, at the atomic scale, the ultrathin CoOx layers effectively accelerate electron conduction and provide abundant active sites. X‐ray absorption spectroscopy reveals that the metallic Co/N‐doped graphene substrate contributes to electron transfer toward the ultrathin CoOx layer, which is beneficial for the electrocatalytic process. The as‐obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half‐wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm−2 for OER. The flexible Zn–air battery built with this catalyst exhibits an ultrahigh specific power of 300 W gcat−1, which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high‐performance rechargeable metal–air battery systems.

Published in: "Advanced Materials".

Bundled Defect‐Rich MoS2 for a High‐Rate and Long‐Life Sodium‐Ion Battery: Achieving 3D Diffusion of Sodium Ion by Vacancies to Improve Kinetics

2019-02-20T22:34:38+00:00February 20th, 2019|Categories: Publications|Tags: , |

Bundled defect‐rich MoS2 is achieved by quenching MoS2 sheet. Na+ can cross MoS2 layers by vacancies and is not limited to diffusion along the layer, realizing 3D diffusion for high rate capability. The bundled architecture reduces the stack of sheets with a superior cycle life, illustrating the capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles. Abstract Molybdenum disulfide (MoS2), a 2D‐layered compound, is regarded as a promising anode for sodium‐ion batteries (SIBs) due to its attractive theoretical capacity and low cost. The main challenges associated with MoS2 are the low rate capability suffering from the sluggish kinetics of Na+ intercalation and the poor cycling stability owning to the stack of MoS2 sheets. In this work, a unique architecture of bundled defect‐rich MoS2 (BD‐MoS2) that consists of MoS2 with large vacancies bundled by ultrathin MoO3 is achieved via a facile quenching process. When employed as anode for a SIB, the BD‐MoS2 electrode exhibits an ultrafast charge/discharge due to the pseudocapacitive‐controlled Na+ storage mechanism in it. Further experimental and theoretical calculations show that Na+ is able to cross the MoS2 layer by vacancies, not only limited to diffusion along the layer, thus realizing a 3D Na+ diffusion with faster kinetics. Meanwhile, the bundling architecture reduces the stack of sheets with a superior cycle life illustrating the highly reversible capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles.

Published in: "Small".

Dramatically Enhanced Ambient Ammonia Electrosynthesis Performance by In‐Operando Created Li–S Interactions on MoS2 Electrocatalyst

2019-02-20T22:33:43+00:00February 20th, 2019|Categories: Publications|Tags: , |

The ambient NH3 electrosynthesis performance of MoS2 is dramatically enhanced by in‐operando created Li–S interactions through effectively suppressed hydrogen evolution reaction activity at S‐edge/Mo‐edge sites, and simultaneously increased N2 adsorption capability and boosted N2 reduction reaction catalytic activity on Mo‐edge sites. The reported in‐operando formation of catalytic active structures via catalyst–electrolyte interactions opens a new way to develop catalysts and catalysis systems. Abstract The Haber‐Bosch process can be replaced by the ambient electrocatalytic N2 reduction reaction (NRR) to produce NH3 if suitable electrocatalysts can be developed. However, to develop high performance N2 fixation electrocatalysts, a key issue to be resolved is to achieve efficient hydrogenation of N2 without interference by the thermodynamically favored hydrogen evolution reaction (HER). Herein, in‐operando created strong Li–S interactions are reported to empower the S‐rich MoS2 nanosheets with superior NRR catalytic activity and HER suppression ability. The Li+ interactions with S‐edge sites of MoS2 can effectively suppress hydrogen evolution reaction by reducing H* adsorption free energy from 0.03 to 0.47 eV, facilitate N2 adsorption by increasing N2 adsorption free energy from –0.32 to –0.70 eV and enhance electrocatalytic N2 reduction activity by decreasing the activation energy barrier of the reaction control step (*N2 → *N2H) from 0.84 to 0.42 eV. A NH3 yield rate of 43.4 μg h−1 mg−1 MoS2 with a faradaic efficiency (FE) of 9.81% can be achieved in presence of strong Li–S interactions, more than 8 and 18 times by the same electrocatalyst in the absence of Li–S interactions. This report opens a

Published in: "Advanced Energy Materials".

Trifunctional Electrocatalysis on Dual‐Doped Graphene Nanorings–Integrated Boxes for Efficient Water Splitting and Zn–Air Batteries

2019-02-20T22:33:34+00:00February 20th, 2019|Categories: Publications|Tags: , |

An easy yet robust route, for the first time, is developed to craft N, O‐codoped graphene‐integrated boxes by employing hybrids containing polymers and Prussian blue analogue cubes as precursors. Benefiting from the hierarchically porous nanostructures and highly active N, O‐codoped graphene, the resulting electrocatalysts display excellent performance on the overall water splitting and Zn–air battery. Abstract Despite the exciting achievements made in synthesis of monofunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), or hydrogen evolution reaction (HER), it is challenging to develop trifunctional electrocatalysts for both ORR/OER/HER. Herein, N, O‐codoped graphene nanorings‐integrated boxes (denoted NOGB) are crafted via high‐temperature pyrolysis and following acid etching of hybrid precursors containing polymers and Prussian blue analogue cubes. The electrochemical results signified that the resulting NOGB‐800 (800 refers to pyrolysis temperature) is highly active for trifunctional electrocatalysis of ORR/OER/HER. This can be reasonably attributed to the advanced nanostructures (i.e., the hierarchically porous nanostructures on the hollow nanorings) and unique chemical compositions (i.e., N, O‐codoped graphene). More attractively, the rechargeable Zn–air battery based on NOGB‐800 displays maximum power density of 111.9 mW cm−2 with small charge–discharge potential of 0.72 V and excellent stability of 30 h, comparable with the Pt/C+Ir/C counterpart. The NOGB‐800 could also be utilized as bifunctional electrocatalysts for overall water splitting to yield current density of 10 mA cm−2 at a voltage of 1.65 V, surpassing most reported electrocatalysts. Therefore, the NOGB‐800 is a promising candidate instead of precious metal–based electrocatalysts for the efficient Zn–air battery and water splitting.

Published in: "Advanced Energy Materials".

Valley filtering effect of phonons in graphene with a grain boundary

2019-02-20T14:39:01+00:00February 20th, 2019|Categories: Publications|Tags: , |

Author(s): Xiaobin Chen, Yong Xu, Jian Wang, and Hong GuoDue to their possibility to encode information and realize low-energy-consumption quantum devices, control and manipulation of the valley degree of freedom have been widely studied in electronic systems. In contrast, the phononic counterpart—valley phononics—has been largely unexplored, despite the …[Phys. Rev. B 99, 064302] Published Wed Feb 20, 2019

Published in: "Physical Review B".

Interfacial and electronic properties of heterostructures of MXene and graphene

2019-02-20T14:38:37+00:00February 20th, 2019|Categories: Publications|Tags: , , |

Author(s): Rui Li, Weiwei Sun, Cheng Zhan, Paul R. C. Kent, and De-en JiangMXene-based heterostructures have received considerable interest owing to their unique properties. Herein, we examine various heterostructures of the prototypical MXene Ti3C2T2 (T=O, OH, F; terminal groups) and graphene using density-functional theory. We find that the adhesion energy, charge transf…[Phys. Rev. B 99, 085429] Published Wed Feb 20, 2019

Published in: "Physical Review B".

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