Utilizing a Photocatalysis Process to Achieve a Cathode with Low Charging Overpotential and High Cycling Durability for a Li-O2 Battery.

The practical applications of non-aqueous lithium-oxygen batteries are impeded by large overpotentials and unsatisfactory cycling durability. Reported here is that commonly encountered fatal problems can be efficiently solved by using a carbon- and binder-free electrode of titanium coated with TiO2 nanotube arrays (TNAs) and gold nanoparticles (AuNPs). Ultraviolet irradiation of the TNAs generates positively charged holes, which efficiently decompose Li2 O2 and Li2 CO3 during recharging, thereby reducing the overpotential to one that is near the equilibrium potential for Li2 O2 formation. The AuNPs promote Li2 O2 formation, resulting in a large discharge capacity. The electrode exhibits excellent stability with about 100 % coulombic efficiency during continuous cycling of up to 200 cycles, which is due to the carbon- and binder-free composition. This work reveals a new strategy towards the development of highly efficient oxygen electrode materials for lithium-oxygen batteries.

Free-Standing Crystalline@Amorphous Core-Shell Nanoarrays for Efficient Energy Storage.

Structures comprising high capacity active material are highly desirable in the development of advanced electrodes for energy storage devices. However, the structure degradation of such material still remains a challenge. The construction of amorphous and crystalline heterostructure appears to be a novel and effectual strategy to figure out the problem, owing to the distinct properties of the amorphous protective layer. Herein, crystalline-Co3 O4 @amorphous-TiO2 core-shell nanoarrays directly grown on the carbon cloth substrate are rationally designed to construct the free-standing electrode. In the unique structure, the 3D porous nanoarrays provide increased availability of electrochemical active sites, and the array with a unique heterostructure of crystalline Co3 O4 core and amorphous TiO2 shell exhibits intriguing synergistic properties. Besides, the amorphous TiO2 protective layer shows elastic behavior to mitigate the volume effect of Co3 O4 . Benefiting from these structural advantages, the as-prepared free-standing electrode exhibits superior lithium storage properties, including high coulombic efficiency, outstanding cyclic stability, and rate capability. Pouch cells with high flexibility are also fabricated and show remarkable electrochemical performances, holding great potential for flexible electronic devices in the future.

Stabilization of binder-free vanadium oxide-based oxygen electrodes using Pd clusters for Li-O2 batteries.

A binder-free electrode consisting of Pd clusters and vanadium oxide (VO) has been prepared via gas-phase-cluster beam deposition on carbon cloth. The Pd clusters largely improve the stability of the VO-Pd-based electrode, which can be reversibly and continuously cycled for more than 120 cycles in a Li-O2 based battery.

Hierarchical Ta-Doped TiO2 Nanorod Arrays with Improved Charge Separation for Photoelectrochemical Water Oxidation under FTO Side Illumination.

TiO2 is one of the most attractive semiconductors for use as a photoanode for photoelectrochemical (PEC) water oxidation. However, the large-scale application of TiO2 photoanodes is restricted due to a short hole diffusion length and low electron mobility, which can be addressed by metal doping and surface decorating. In this paper we report the successful synthesis of hierarchical Ta doped TiO2 nanorod arrays, with nanoparticles on the top (Ta:TiO2), on F-doped tin oxide (FTO) glass by a hydrothermal method, and its application as photoanodes for photoelectrochemical water oxidation. It has been found that the incorporation of Ta5+ in the TiO2 lattice can decrease the diameter of surface TiO2 nanoparticles. Ta:TiO2-140, obtained with a moderate Ta concentration, yields a photocurrent of ∼1.36 mA cm-2 at 1.23 V vs. a reversible hydrogen electrode (RHE) under FTO side illumination. The large photocurrent is attributed to the large interface area of the surface TiO2 nanoparticles and the good electron conductivity due to Ta doping. Besides, the electron trap-free model illustrates that Ta:TiO2 affords higher transport speed and lower electron resistance when under FTO side illumination.

Ta-Doped porous TiO2 nanorod arrays by substrate-assisted synthesis: efficient photoelectrocatalysts for water oxidation.

Owing to its excellent chemical stability and low cost, titanium dioxide (TiO2) has been widely studied as a photoanode for photoelectrochemical (PEC) water splitting. However, TiO2's practical applications in solar energy-to-synthetic fuel conversion processes have been constrained by its inherently poor ability to transport photogenerated electrons and holes. In this paper, we report Ta-doped porous TiO2 nanorod arrays on Ta foil (Ta-PTNA) that do not possess this issue and that can thus efficiently photoelectrocatalyze water oxidation, helping the production of H2 (a clean fuel) from water at the expense of solar light. The materials are synthesized by a new, facile synthetic approach involving the hydrothermal treatment of a TiO2 precursor with Ta foil, without seeds and templates, and followed by calcination of the product. Besides serving as a source of Ta dopant atoms, Ta foil is found to play a vital role in the formation of nanopores in the materials. The material obtained with hydrothermal treatment at 180 °C for 10 h (Ta-PTNA-10), in particular, affords very large photocurrent density and very high photoconversion efficiency (0.32% at 0.79 V vs. RHE, which is better than those of many previously reported photocatalysts and ∼4 times larger than that of undoped TiO2 nanorod arrays). Ta-PTNAs' remarkable PEC catalytic performance is found to be due to their nanoporous structure and high electronic conductivity.

Facile and scalable carbon- and binder-free electrode materials for ultra-stable and highly improved Li-O2 batteries.

A carbon- and binder-free Ti@Ru material is synthesized through a facile and controllable strategy. A Ti@Ru based Li-O2 battery can effectively avoid the subsidiary reactions, and can be reversibly and continuously cycled for more than 500 cycles with an efficiency ca. 100%, exhibiting an ultra-cycling stability.

Growth of Black Phosphorus Nanobelts and Microbelts.

Black phosphorus nanobelts are fabricated with a one-step solid-liquid-solid reaction method under ambient pressure, where red phosphorus is used as the precursor instead of white phosphorus. The thickness of the as-fabricated nanobelts ranges from micrometers to tens of nanometers as studied by scanning electron microscopy. Energy dispersive X-ray spectroscopy and X-ray diffraction indicate that the nanobelts have the composition and the structure of black phosphorus, transmission electron microscopy reveals a typical layered structure stacked along the b-axis, and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy analysis demonstrates the doping of bismuth into the black phosphorus structure. The nanobelt can be directly measured in scanning tunneling microscopy in ambient conditions.

Chestnut-Like TiO2@α-Fe2O3 Core-Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage.

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO2@α-Fe2O3 core-shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO2 and α-Fe2O3 are observed and supposed to provide synergistic effect. The TiO2 microsphere framework significantly improves the mechanical stability, while the α-Fe2O3 provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g-1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g-1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe0 phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe2O3-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs.

Research on Effective Oxygen Window Influencing the Capacity of Li-O2 Batteries.

Li-O2 batteries have attracted extensive attention recently due to the extremely huge specific energy. Similar to research mode of Li-ion batteries, nowadays specific capacity based on the mass of cathode material is widely adopted to evaluate the electrochemical performance of Li-O2 batteries. However, the prerequisite of linear correlation between the delivered capacity and active mass is easily neglected. In this paper, we demonstrate the rationality of specific capacity adopted in Li-ion batteries with classic LiCoO2 cathode by confirming the linear correlation between cell capacity and LiCoO2 mass. Delivered capacities of Li-O2 batteries with different cathode masses are simultaneously measured and nonlinear correlation is obtained. The discharge and charge products are identified by X-ray diffraction and in situ gas chromatography-mass spectrometry analysis to ensure reaction mechanism. Discharge capacities of Li-O2 batteries with various areas of oxygen window are further studied, which shows that cell capacity increases linearly with the area of oxygen window. Scanning electron microscopy is employed to observe the discharged electrode and shows that Li2O2 deposition during discharge mainly occurs in the electrode area exposure to the oxygen, which is consequently defined as effective area for accommodating Li2O2. Moreover, a plausible route for formation of effective area in the oxygen electrode is proposed. These results provide evidence that effective area is an equally important factor determining cell capacity.

Ordered mesoporous TiC-C composites as cathode materials for Li-O2 batteries.

Ordered mesoporous TiC-C (OMTC) composites were prepared and served as catalysts for nonaqueous Li-O2 batteries. The OMTC cathodes showed high specific capacity, low overpotential and good cyclability. Furthermore, the reaction mechanism of Li-O2 batteries during charge and discharge processes was investigated extensively by XRD, XPS and in situ GC-MS methods.

Binder-free carbonized bacterial cellulose-supported ruthenium nanoparticles for Li-O2 batteries.

Network structured carbonized bacterial cellulose-supported Ru nanoparticles (CBC/Ru), which provide sufficient space for Li2O2 deposition without a significant volume effect and improve the transport of oxygen and electrons, were used as the binder-free oxygen electrode in a Li-O2 battery. The CBC/Ru exhibited high activities and good stability during discharge-recharge processes.

Three-dimensional network films of electrospun copper oxide nanofibers for glucose determination.

Copper oxide nanofibers (CuO-NFs) prepared by electrospinning and subsequent thermal treatment processes were demonstrated for the first time for glucose non-enzymatic determination. The structures and morphologies of CuO-NFs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction spectrum (XRD). Different dispersants were utilized for the suspension preparation and effects of ultrasonic time on the films electrode fabrication were investigated in detail. The assay performances to glucose were evaluated by cyclic voltammetry (CV) and chronoamperometry (I-t). Results revealed a high sensitivity (431.3 microAmM(-1)cm(-2)), fast response (about 1s), long-term stability and excellent resistance towards electrode fouling in the glucose determination at +0.40V. The improved performances of CuO-NFs films electrode for electro-oxidation glucose were ascribed to the high surface-to-volume ratio, complex pore structure, extremely long length of the as-prepared CuO-NFs, and the excellent three-dimensional network structure after immobilization. Results in this study suggest that electrospun CuO-NFs is a promising 1-D nanomaterial for further design and microfabrication of bioelectrochemical nanodevices for glucose determination.

Investigations on copper-titanate intercalation materials for amperometric sensor.

Copper-based titanate intercalation electrode materials (referred as Cu-TO) were achieved by electrochemical reduction of the intercalated cupric ions that were ion exchanged on the layer structured titanate films by using n-propylamine as an exfoliating agent. The copper-based titanate intercalation electrode materials were characterized by X-ray diffraction (XRD), electrochemical techniques and inductive coupled plasma-atomic emission spectroscopy (ICP-AES). These copper-based titanate materials were exploited to fabricate the enzymeless glucose sensors, and their assay performances to glucose were evaluated by conventional electrochemical techniques. Cyclic voltammetry (CV) and chronoamperometry (I-t) revealed a high sensitivity, fast response, excellent stability, and good reproducibility in the glucose determination at +0.55 V. Under optimal conditions, the electrocatalytic response of the sensor was proportional to the glucose concentration in the range of 2.5x10(-7) M to 8.0x10(-3) M with a detection limit of 5.0x10(-8) M (signal-to-noise=3). Moreover, the intercalated copper electrode materials exhibited high stability and improved selectivity for glucose compared with the more apparently accessible copper. This work also provides a simply controlled test-bed for electrochemical functionalization of layered titanate for sensor applications.