We report on the evolution of a hollow sphere secondary structure of spherical nanoparticles by a solubilization-reprecipitation mechanism based on the difference of solubility products (K(sp)) of two different precipitates. Carbon-coated nanoparticles of olivine structure LiFePO(4) served as the primary nano-blocks to build the secondary nano-architecture.

Dye-sensitized photo-rechargeable battery (DSPB) harvests and stores dim light efficiently, realizing indoor-light-harvesting battery to operate IoT devices successfully without sun light.

No abstract

Nitrogen-containing electrocatalysts, such as metal-nitrogen-carbon (M-N-C) composites and nitrogen-doped carbons, are known to exhibit high activities for an oxygen reduction reaction (ORR).Moreover, even if the mechanism by which nitrogen improves the activities is not completely understood, a strong electronic interaction between nitrogen and active sites has been found in these composites.Herein, we demonstrate a case in which nitrogen improves the electroactivity, but in the absence of a strong interaction with other components. The overpotentials of the ORR and oxygen evolution reaction (OER) on perovskite oxide catalysts were significantly reduced simply by mixing the catalyst particles with polypyrrole/carbon composites (pPy/C). Any strong interactions between pPy (a nitrogen-containing compound) and active sites of the catalysts are not confirmed. A scenario based on the sequential task allocation between pPy and oxide catalysts for the ORR was proposed: (1) molecular oxygen is incorporated into pPy as a form of superoxide (pPy + O 2 À ), (2) the superoxide is transferred to the active sites of perovskite catalysts, and (3) the superoxide is completely reduced along the 4e ORR process.Oxygen-related electrochemistry is important for next-generation energy conversion and storage. Oxygen reduction reactions (ORR) are used as cathodic processes of fuel cells and metal air batteries for the generation of electricity. 1-5 Its reverse reaction, oxygen evolution reaction (OER), is the anodic process for splitting water and charging process of metal air batteries. 6,7 High reversibility between the ORR and OER should be guaranteed in the rechargeable metal air batteries, 2-5 whereas fuel cells and water splitting are based on either forward or backward reactions of the oxygen-to-water conversion. Although platinum is known as the best ORR catalyst, the oxide layer formed on its surface under oxidative conditions seriously deteriorates its catalytic activity for the OER. [8][9][10] Iridium or ruthenium oxides have been regarded as the best OER catalysts. 11 However, their electrocatalytic activities for the ORR are not as high as those for the OER and are significantly inferior to those of the other catalysts. Iridium alloys with transition metals, as another form of iridium-containing catalysts (not the oxide form), efficiently catalyzed the ORR, whereas other forms of ruthenium did not work as ORR catalysts. 12 Therefore, it is challenging to develop a catalyst with high electroactivities for both ORR and OER.Perovskite oxides have been studied as catalysts for oxygenrelated electrochemistry. Simple perovskite oxides (ABO 3 ; A = alkaline and/or rare earth metals, B = transition metals) have been suggested as mono-functional catalysts for OER or ORR 13-15 and bifunctional catalysts. [16][17][18] Material candidates were extended from the simple perovskites to double or layered perovskites. A series of double perovskites have been reported to be more stable during OER than their simple perovskite counterpart BS...

As high rate charge and discharge characteristics of energy storage devices become more important with the market of electric vehicles intensively growing, the kinetics of lithiation or delithiation of electrode materials for lithium ion batteries require enhancement. Graphites, the most widely used anode materials, have a limited power density at high discharge rates, while their alternatives, such as silicon and transition metal oxides, show even inferior rate capability. This work was motivated from an idea of what if the edge opening of graphite was zipped more open to lithium ions in the electrolyte. By edge-selective functionalization, the peripheral d-spacing of graphite (d(0)) was locally controlled. Larger values of d(0) led to higher capacity especially at high discharge rates. Around 2-fold enhancement of capacity or energy density was achieved at 50C discharge rate from 110 to 190 mAh g(-1) by exfoliating graphite locally in its edge region. Also, the d(0) dependency of delithiation kinetics confirmed that the electrochemical step of Li(+) influx into or efflux out of the interlayer space of graphite is possibly the rate-determining step of lithiation or delithiation.