in reversible oxidation/reduction reaction to achieve a high energy density. (ii) Fast charge transport and high exchanging current density of materials dramatically reduce the polarization and further provide a high power density. (iii) Uniform micro/nanostructures are associated with increased specific surfaces areas and decreased ionic diffusion over distance and time, resulting in a long lifetime and a good cycling stability.Among various energy sources in history, rechargeable cells are lead (Pb)-acid, nickel-chromium (Ni-Cr), nickel-metal hydride (Ni-MH), redox flow, lithiumion, fuel cells and metal-air batteries. [2] In particular, rechargeable metal-air batteries have received great interest due to a huge theoretical specific energy density, deriving from a unique cell structure. In this system, only the metal (Li, Na, Mg, Al, Zn, Si, Fe, Sn, etc.) anode is assembled in the cell, while the active cathode material is oxygen (O 2 ), directly obtained from the atmosphere. [12][13][14][15][16][17] Figure 1a presents a summary of basic theoretical properties and electrochemical reactions in typical metal-air batteries. For instance, rechargeable Li-air batteries can provide a theoretical cell voltage of 2.96 V and a theoretical specific energy density of 3.4 kW h kg −1 . In this particular battery, the decomposition of lithium peroxide (Li 2 O 2 ), despite being an explosive and poisonous compound, plays a vital role in the improved charge transport because it demonstrates a highly reversible reaction between the discharge and charge process. [18,19] The maximum specific capacity of secondary Li-air batteries reaches an initial discharge capacity of 14000 mA h g −1 at a current density of 140 mA g −1 , using Co 3 O 4 /reduced graphene oxide nanocomposites as electrocatalysts. [20] Unfortunately, although they are the focus of numerous investigations, lithium-air batteries are still accompanied by the major drawbacks of the high price of metallic lithium (The USD $160000-180000/ton as of May 2017) and safety issues in an organic electrolyte.Magnesium provides a number of improvements compared to metallic Li, including its abundance in the earth's crust (2.08% for Mg vs 0.0065% for Li) and environmental friendliness. Moreover, rechargeable Mg-O 2 battery allows a theoretical volumetric density and a specific energy density of 14 kW h L −1 and 3.9 kW h kg −1 , respectively, assuming MgO is formed as the discharge product. [21,22] These values are much larger than those of Li-O 2 cells on the basis of Li 2 O 2 (8.0 kW h L −1 and 3.4 kW h kg −1 ). Though a great number of efforts have focused on the widespread studies of Li-air Rechargeable Mg-air batteries are a promising alternative to Li-air cells owing to the safety, low price originating from the abundant resource on the earth, and high theoretical volumetric density (3832 A h L −1 for Mg anode vs 2062 A h L −1 for Li). Only a few works are related to the highly reversible Mg-air batteries. The fundamental scientific difficulties hindering the rapid developmen...

Li-richl ayered oxides with high capacity are expected to be the next generation of cathode materials. However,t he irreversible and sluggish anionic redox reaction leads to the O 2 loss in the surface as well as the capacity and voltage fading.I nt he present study,asimple gas-solid treatment with ferrous oxalate has been proposed to uniformly coat at hin spinel phase layer with oxygen vacancy and simultaneously realize Fe-ion substitution in the surface.T he integration of oxygen vacancy and spinel phase suppresses irreversible O 2 release,p revents electrolyte corrosion, and promotes Li-ion diffusion. In addition, the surface doping of Fe-ion can further stabilizet he structure.A ccordingly,t he treated Feox-2 %c athode exhibits superior capacity retention of 86.4 %a nd 85.5 %a t1Ca nd 2C to that (75.3 %a nd 75.0 %) of the pristine sample after 300 cycles,r espectively. Then, the voltage fading is significantly suppressed to 0.0011 V per cycle at 2Cespecially.T he encouraging results may play asignificant role in paving the practical application of Li-rich layered oxides cathode.

In this paper, we report on the shape-controlled synthesis of monoclinic (m-) ZnV 2 O 6 micro/ nanostructures through a simple hydrothermal approach and their highly reversible lithium storage for anode materials in lithium-ion batteries. m-ZnV 2 O 6 structures with different diameters were selectively explored by changing the critical experimental parameters of dwell time and reaction temperatures. A novel ''dissolution recrystalizaion-Ostwald ripening-splitting'' combination mechanism for uniform nanowires is proposed by further monitoring the time-dependent evolution of morphologies and phases. Furthermore, these m-ZnV 2 O 6 nanowires with high aspect ratio exhibit a better reversible capacity and a much excellent cyclic retention than that of as-obtained mesostructures and bulk counterparts because of better contact behavior and a shorter diffusion length for Li + , implying a promising candidate for the application in high-energy batteries.

Due to the energy crisis, it is necessary to develop clean and renewable energy sources. In this study, we report an efficient and economical technology to produce hydrogen from solar energy by splitting water in a two-compartment photoelectrochemical (PEC) cell without any external applied voltage. To enhance the solar conversion efficiency, highly ordered TiO2 nanotube arrays with 4 μm in length were synthesized by a rapid anodization process in ethylene glycol electrolyte. Crystal phase and morphology of the TiO2 nanotubes (NTs) samples annealed at various temperatures were characterized by XRD and FESEM. Transient photocurrent response and linear sweep voltammetry curves were measured using electrochemical working station under solar light illumination. The photocatalytic activity was evaluated by the hydrogen production in the PEC cell. The results indicated that the crystal phase and morphology of TiO2 NTs had no great changes at low annealing temperatures. Anatase phase and tubular structure of TiO2 NTs were stable up to 450 °C. With further increase in temperature, the crystallization transformation from anatase to rutile phase appeared, accompanied by the destruction of tubular structures. Due to the excellent crystallization and the maintenance of tubular structures, TiO2 NTs annealed at 450 °C exhibited the highest photoconversion efficiency of 4.49% and maximum hydrogen production rate of 122 μmol/(h·cm2), which is superior to most of those reported so far.