Xiaocong Tian

Nanowire electrodes for electrochemical energy storage devices.

Liqiang Mai,*,† Xiaocong Tian,† Xu Xu,† Liang Chang,‡ and Lin Xu†,§ †State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, WUT-Harvard Joint Nano Key Laboratory, Wuhan University of Technology, Wuhan 430070, China ‡Department of Materials Science and Engineering, Michigan Technological University, Houghton, Michigan 49931-1295, United States Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States

Synergistic interaction between redox-active electrolyte and binder-free functionalized carbon for ultrahigh supercapacitor performance

Development of supercapacitors with high-energy density and high-power density is a tremendous challenge. Although the use of conductive carbon materials is promising, other methods are needed to reach high cyclability, which cannot be achieved by fully utilizing the surface-oxygen redox reactions of carbon. Here we introduce an effective strategy that utilizes Cu(2+) reduction with carbon-oxygen surface groups of the binder-free electrode in a new redox-active electrolyte. We report a 10-fold increase in the voltammetric capacitance (4,700 F g(-1)) compared with conventional electrolyte. We measured galvanostatic capacitances of 1,335 F g(-1) with a retention of 99.4% after 5,000 cycles at 60 A g(-1) in a three-electrode cell and 1,010 F g(-1) in a two-electrode cell. This improvement is attributed to the synergistic effects between surface-oxygen molecules and electrolyte ions as well as the low charge transfer resistance (0.04 Ω) of the binder-free porous electrode. Our strategy provides a versatile method for designing new energy storage devices and is promising for the development of high-performance supercapacitors for large-scale applications.

Nanoscroll Buffered Hybrid Nanostructural VO2 (B) Cathodes for High‐Rate and Long‐Life Lithium Storage

Hybrid nanostructural VO2 (B) composed of nanoscrolls, nanobelts and nanowires is synthesized through a hydrothermal-driven splitting and self-rolled method. The hybrid nanostructure with nanoscroll buffered effect provides facile strain relaxation for swelling during lithiation/delithiation, resulting in the excellent structural stability and cyclability. The interior of nanoscrolls and the interconnected voids shorten the ion diffusion pathway, which greatly enhances the rate performance.

Synergistic Effect of Hierarchical Nanostructured MoO2/Co(OH)2 with Largely Enhanced Pseudocapacitor Cyclability

Pseudocapacitors have demonstrated an ability to deliver high energy and power densities. The main limitation is their poor cyclability and for this reason the architectural design of electrode materials has attracted considerable attention. Here we report the synthesis of hierarchical nanostructured material by growing Co(OH)2 nanoflakes onto MoO2 thin film. The electrode material exhibits a high capacitance of 800 F g(-1) at 20 A g(-1) with only 3% capacitance loss after 5000 cycles and high rate capability with increasing current density from 2 to 40 A g(-1), which are better than those of individual component. The enhanced pseudocapacitor performances benefit from the synergistic effect of the hierarchical nanostructure: (1) faster ion diffusion and electron transport at electrode/electrolyte interface, and (2) mitigation of the electrode destruction caused by ion insertion/deinsertion during charge-storage process. This facile design and rational synthesis offers an effective strategy to enhance the electrochemical performance of pseudocapacitors and shows promising potential for large-scale application in energy storage.

Porous Nickel–Iron Selenide Nanosheets as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction

Exploring non-noble and high-efficiency electrocatalysts is critical to large-scale industrial applications of electrochemical water splitting. Currently, nickel-based selenide materials are promising candidates for oxygen evolution reaction due to their low cost and excellent performance. In this work, we report the porous nickel-iron bimetallic selenide nanosheets ((Ni0.75Fe0.25)Se2) on carbon fiber cloth (CFC) by selenization of the ultrathin NiFe-based nanosheet precursor. The as-prepared three-dimensional oxygen evolution electrode exhibits a small overpotential of 255 mV at 35 mA cm(-2) and a low Tafel slope of 47.2 mV dec(-1) and keeps high stability during a 28 h measurement in alkaline solution. The outstanding catalytic performance and strong durability, in comparison to the advanced non-noble metal catalysts, are derived from the porous nanostructure fabrication, Fe incorporation, and selenization, which result in fast charge transportation and large electrochemically active surface area and enhance the release of oxygen bubbles from the electrode surface.

Hydrated vanadium pentoxide with superior sodium storage capacity

Sodium ion batteries (SIBs), as potential candidates for large-scale energy storage systems, have attracted great attention from researchers. Herein, a V2O5·nH2O xerogel composed of thin acicular interconnected nanowire networks has been synthesized via a facile freeze-drying process. The interlayer spacing of V2O5·nH2O is larger than that of orthorhombic V2O5 due to the intercalation of water molecules into the layer structure. As the cathode of a SIB, V2O5·nH2O exhibits a high initial capacity of 338 mA h g−1 at 0.05 A g−1 and a high-rate capacity of 96 mA h g−1 at 1.0 A g−1. On the basis of combining ex-situ XRD and FTIR spectroscopy, the Na+ ion intercalation storage reactions are discussed in detail. By modeling calculations, the pseudocapacitive behavior makes a great contribution to the high capacities. Our work demonstrates that V2O5·nH2O with large interlayer spacing is a promising candidate for high capacity sodium-based energy storage.

Graphene Oxide Templated Growth and Superior Lithium Storage Performance of Novel Hierarchical Co2V2O7 Nanosheets

Hierarchical Co2V2O7 nanosheets consisted of interconnected nanoparticles are synthesized by a facile method using graphene oxide as the template. The electrochemical reaction mechanism of the Co2V2O7 nanosheets is thoroughly investigated by in situ XRD and ex situ TEM. The initial Co2V2O7 transforms into CoO nanoparticles and vanadium oxides in the first cycle, and the following reversible conversion reaction mainly occurs between CoO and Co and lithiation/delithiation of the vanadium oxides. The Co2V2O7 nanosheet displays a high reversible capacity (962 mAh/g at 0.5 A/g) and remarkable high rate capability. When cycled at 5.0 A/g, a reversible capacity of 441 mAh/g can be retained after 900 cycles. The stable high capacity and excellent rate capability make the hierarchical Co2V2O7 nanosheets a promising anode material for lithium-ion batteries.

Facile synthesis of a Co3V2O8 interconnected hollow microsphere anode with superior high-rate capability for Li-ion batteries

Hollow microspheres with a high surface area, sufficient void space, and short ion/electron transport distance have attracted much attention as a superior electrode structure for high-rate lithium-ion batteries. In this work, a facile and low-cost hydrothermal approach followed by annealing is developed to synthesize Co3V2O8 interconnected hollow microspheres, which are able to endure an extremely high current density of 20 A g−1 and achieve a reversible discharge capacity of 320 mA h g−1. Furthermore, a stable capacity of 424 mA h g−1 can be obtained after 300 cycles at 10 A g−1. Such remarkable rate capability and cycling performance make the Co3V2O8 interconnected hollow microspheres a promising anode material for lithium-ion batteries.

Arbitrary Shape Engineerable Spiral Micropseudocapacitors with Ultrahigh Energy and Power Densities.

Inspired by the Archimedean spiral, a new integrated design of micropseudocapacitors is presented. The fabricated micropseudocapacitors deliver an energy density of 34.9 mW h cm(-3) and a power density of 193.4 W cm(-3). Meanwhile, this spiral design can be engineered into arbitrary microshapes and unconventional series/parallel combinations with symmetrical electrodes.

In Situ Investigation of Li and Na Ion Transport with Single Nanowire Electrochemical Devices

In the past decades, Li ion batteries are widely considered to be the most promising rechargeable batteries for the rapid development of mobile devices and electric vehicles. There arouses great interest in Na ion batteries, especially in the field of static grid storage due to their much lower production cost compared with Li ion batteries. However, the fundamental mechanism of Li and Na ion transport in nanoscale electrodes of batteries has been rarely experimentally explored. This insight can guide the development and optimization of high-performance electrode materials. In this work, single nanowire devices with multicontacts are designed to obtain detailed information during the electrochemical reactions. This unique platform is employed to in situ investigate and compare the transport properties of Li and Na ions at a single nanowire level. To give different confinement for ions and electrons during the electrochemical processes, two different configurations of nanowire electrode are proposed; one is to fully immerse the nanowire in the electrolyte, and the other is by using photoresist to cover the nanowire with only one end exposed. For both configurations, the conductivity of nanowire decreases after intercalation/deintercalation for both Li and Na ions, indicating that they share the similar electrochemical reaction mechanisms in layered electrodes. However, the conductivity degradation and structure destruction for Na ions is more severe than those of Li ions during the electrochemical processes, which mainly results from the much larger volume of Na ions and greater energy barrier encountered by the limited layered spaces. Moreover, the battery performances of coin cells are compared to further confirm this conclusion. The present work provides a unique platform for in situ electrochemical and electrical probing, which will push the fundamental and practical research of nanowire electrode materials for energy storage applications.