Jinping Liu

Co3O4 Nanowire@MnO2 Ultrathin Nanosheet Core/Shell Arrays: A New Class of High‐Performance Pseudocapacitive Materials

With the ever-increasing power and energy needs in applications ranging from next-generation plug-in hybrid electric vehicles (PHEVs) and modern consumer electronics to microand nanoelectromechanical systems, recent research and development has focused on new electrode materials for advanced energy storage devices. [ 1–5 ] Of the various power source devices, supercapacitors, also known as electrochemical capacitors (ECs), have attracted great interest due to a number of desirable properties, including fast charging and discharging, long cycle life, and the ability to deliver up to ten times more power than conventional batteries. [ 6–10 ] In addition, ECs play an important role in complementing fuel cells in future all-electric vehicles based on clean and renewable energy media. [ 11 ] There are three major types of electrode materials reported for ECs: carbonaceous materials, [ 12 ] metal oxides/hydroxides, [ 13 ] and conducting polymers. [ 14 ] Carbon-based materials store charge electrostatically from the reversible adsorption of ions onto their surfaces, leading to high power delivery at the cost of low energy density. By contrast, metal oxides/hydroxides and conducting polymers store charge in a faradic or redox-type process similar to batteries, which enables high energy density but is in general kinetically unfavorable. To bridge the performance gap between these materials, attempts at novel electrode design have been extensively made. Despite a huge number of publications, nearly all of them can be clarifi ed into one general concept, that is, the use of pseudocapacitive material–conductive matrix hybrid nanostructures. [ 15 , 16 ] In this regard, materials presenting high pseudocapacitence (metal oxides) are incorporated directly into highly conductive nanostructured carbons (carbon nanotubes, [ 17–20 ]

Three-dimensional tubular arrays of MnO2–NiO nanoflakes with high areal pseudocapacitance

Transition metal oxide nanostructures are current research focus for energy storage applications. We herein report the synthesis of MnO2–NiO nanoflake-assembled tubular array on stainless steel substrate to function as pseudocapacitor electrode by programmed three-dimensional (3D) interfacial reactions, in which the ZnO nanowire array is employed as the low-cost in situ sacrificial template. In this 3D nanoelectrode, MnO2 and NiO nanoflakes share the same “root” and form an integrated hierarchical structure, which adheres robustly to the substrate. Importantly, both MnO2 and NiO contribute to the charge storage. The highly porous structure, which allows easy penetration of the electrolyte, gives additional merits. Detailed electrochemical characterization reveals that the assembled MnO2–NiO array exhibits good rate performance and cycle life. In particular, it displays an areal capacitance that is four orders of magnitude higher than that of carbonaceous materials and significantly superior to those of previous directly-grown pseudocapacitive nanostructure films.

A general strategy toward graphene@metal oxide core–shell nanostructures for high-performance lithium storage

We demonstrate a simple, efficient, yet versatile method for the realization of core–shell assembly of graphene around various metal oxide (MO) nanostructures, including nanowires (NWs) and nanoparticles (NPs). The process is driven by (i) the ring-opening reaction between the epoxy groups and amine groups in graphene oxide (GO) platelets and amine-modified MO nanostructures, respectively, and (ii) electrostatic interaction between these two components. Nearly every single NW or NP is observed to be wrapped by graphene. To the best of our knowledge, this is the first report that substrate-supported MO NWs are fully coated with a graphene shell. As an example of the functional properties of these compound materials, the graphene@α-Fe2O3 core–shell NPs are investigated as the lithium-ion battery (LIB) electrode, which show a high reversible capacity, improved cycling stability, and excellent rate capability with respect to the pristine α-Fe2O3. The superior performance of the composite electrode is presumably attributed to the effectiveness of the graphene shell in preventing the aggregation, buffering the volume change, maintaining the integrity of NPs, as well as improving the conductivity of the electrode.

Fabrication of Co3O4-reduced graphene oxide scrolls for high-performance supercapacitor electrodes

A new type of scrolled structure of Co(3)O(4)/reduced graphene oxide (r-GO) is facilely prepared through a two-step surfactant-assisted method. This assembly enables almost every single Co(3)O(4) scroll to connect with the r-GO platelets, thus leading to remarkable electrochemical performances in terms of high specific capacitance and good rate capability.

Quantum‐Dot‐Sensitized TiO2 Inverse Opals for Photoelectrochemical Hydrogen Generation

A new nanoarchitecture photoelectrode design comprising CdS quantum-dot-sensitized, optically and electrically active TiO(2) inverse opals is developed for photoelectrochemical water splitting. The photoelectrochemical performance shows high photocurrent density (4.84 mA cm(-2) at 0 V vs. Ag/AgCl) under simulated solar-light illumination.

CNT/Ni hybrid nanostructured arrays: synthesis and application as high-performance electrode materials for pseudocapacitors

CNT/Ni hybrid nanostructured arrays (NSAs) are synthesized on a stainless steel substrate through a one-step chemical-vapor-deposition (CVD) method using nullaginite NSAs as starting materials. During the CVD process, the nullaginite NSAs are transformed into Ni NSAs, which can further act as the catalysts to initiate the simultaneous in situ growth of CNTs on their surface, leading to an intriguing three-dimensional (3D) hybrid nanostructure. The resulting ordered CNT/Ni NSAs are highly porous and conductive, which are believed to be quite favorable for electrochemical applications. As a proof-of-concept demonstration of the functions of such a well-designed architecture in energy storage, the CNT/Ni NSAs are tested as the working electrodes of electrochemical capacitors (ECs). After being activated, the composite electrode exhibits both well-defined pseudo-capacitive and electrical double-layer behavior with high areal capacitance (up to ∼0.901 F cm−2), excellent cyclability (nearly 100% capacitance retention after 5000 cycles), and outstanding rate capability. The unique interconnected hybrid structure and virtues inherited from the conductive CNT network and porous NSAs are believed to be responsible for the excellent performance.

ZnO nanowire array-templated LbL self-assembled polyelectrolyte nanotube arrays and application for charged drug delivery

Vertically oriented and robust polyelectrolyte nanotube arrays with high density, large area and high uniformity were successfully grown on substrates by a ZnO nanowire array-templated layer-by-layer (LbL) self-assembly approach for the first time, and were further used to deliver charged drugs, showing that they not only possess pH-responsive loading property, but also significantly enhance the loading capacity and sustained release time. This work could be extended to fabricate polyelectrolyte nanotube arrays with different polyelectrolyte combinations, including weak polyelectrolyte/weak polyelectrolyte, weak polyelectrolyte/strong polyelectrolyte and strong polyelectrolyte/strong polyelectrolyte. With the great versatility to use various substrates and building blocks, the polyelectrolyte nanotube arrays may have great potential for broad applications such as biosensor arrays, bioreactor arrays and optoelectronics.