In the present study, an in-depth investigation on the structural transformation in a mesoporous γ-MnO2 cathode during electrochemical reaction in a zinc-ion battery (ZIB) has been undertaken. A combination of in situ Synchrotron XANES and XRD studies reveal that the tunnel-type parent γ-MnO2 undergoes a structural transformation to spinel-type Mn­(III) phase (ZnMn2O4) and two new intermediary Mn­(II) phases, namely, tunnel-type γ-Zn x MnO2 and layered-type L-Zn y MnO2, and that these phases with multioxidation states coexist after complete electrochemical Zn-insertion. On successive Zn-deinsertion/extraction, a majority of these phases with multioxidation states is observed to revert back to the parent γ-MnO2 phase. The mesoporous γ-MnO2 cathode, prepared by a simple ambient temperature strategy followed by low-temperature annealing at 200 °C, delivers an initial discharge capacity of 285 mAh g–1 at 0.05 mA cm–2 with a defined plateau at around 1.25 V vs Zn/Zn2+. Ex situ HR-TEM studies of the discharged electrode aided to identify the lattice fringe widths corresponding to the Mn­(III) and Mn­(II) phases, and the stoichiometric composition estimated by ICP analysis appears to be concordant with the in situ findings. Ex situ XRD studies also confirmed that the same electrochemical reaction occurred on repeated discharge/charge cycling. Moreover, the present synthetic strategy offers solutions for developing cost-effective and environmentally safe nanostructured porous electrodes for cheap and eco-friendly batteries.

In response to the ever-increasing global demand for viable energy-storage systems, sodium and potassium batteries appear to be promising alternatives to lithium ion batteries because of the abundance, low cost and environmental benignity of sodium/ potassium. Electrical energy storage via ion-intercalation reactions in crystalline electrodes is critically dependent on the sizes of the guest ions. Herein, we report on the use of a porous amorphous iron phosphate synthesized using ambient temperature strategies as a potential host that stores electrical energy through the feasible insertion of mono-/di-/tri-valent ions. A combination of ex situ studies reveals the existence of a reversible amorphous-to-crystalline transition in this versatile electrode during electrochemical reactions with monovalent sodium, potassium and lithium. This reconstitutive reaction contributes to realizing specific capacities of 179 and 156 mAhg − 1 versus sodium and potassium at current densities of 10 and 5 mAg − 1 , respectively. This finding facilitates the feasible development of several amorphous electrodes with similar phase behavior for energy-storage applications. NPG Asia Materials (2014) 6, e138; doi:10.1038/am.2014.98; published online 17 October 2014 INTRODUCTIONSince 1990, the global demand for electricity has increased twice as much as the demand for energy overall, and the demand for electricity is expected to further increase by more than two-thirds over the next 20 years. Energy storage/conversion technologies have therefore become a crucial research topic as we seek to make society sustainable. In particular, electrical energy storage is critical not only for supporting electronic, vehicular and load-leveling applications but also for efficiently commercializing renewable solar and wind power. Rechargeable Li-ion batteries with an output energy exceeding 90% have emerged as one of the most effective electrochemical energystorage technologies, and these batteries power most modern-day electronic devices. 1 Despite substantial research to enhance Li-ion batteries for high-power applications, aspects such as their availability, cost and safety still remain to be fully addressed. 2 The controversies surrounding the accessible global lithium reserves and the anticipated energy demand may greatly impact the cost of Li-ion batteries in the long term. 3 Although advancing Li-ion battery technologies for electric vehicle applications is attractive, the quest for alternative energy sources for smart grid-scale storage applications has recently gained significant momentum. Rechargeable sodium and potassium batteries offer tremendous potential because they utilize inexpensive, abundant and environmentally benign sodium/potassium elements. [4][5][6][7][8][9] However,

No abstract

Fully activated Li 2 MnO 3 nanoparticles were prepared by a chemical based oxidation reaction. All of the diffraction peaks of the prepared samples were well matched to a monoclinic phase (space group: C2/m) with no impurity peaks and refined using the General Structure Analysis System (GSAS) program. The activated Li 2 MnO 3 sample showed homogeneously well-dispersed nanoparticles with a size of $10 nm. The oxidation state of Mn was confirmed by XPS. The activated Li 2 MnO 3 nanoparticles delivered a high charge capacity of 302 mA h g À1 above 4.5 V and discharge capacity of 236 mA h g À1 during the first cycle. Interestingly, the cycle performance of the activated Li 2 MnO 3 nanoparticles during extended cycles exhibited somewhat stable discharge capacities without any drastic capacity fading, even when cycled in the high voltage range of 2.0-4.9 V and after the phase transition to spinel. In terms of the rate performance, the activated Li 2 MnO 3 sample exhibited significantly superior properties compared to the bulk Li 2 MnO 3 sample, probably due to the nano-size particles with high crystallinity.

No abstract

Organic–inorganic hybrid perovskites (OHPs) are promising emitters for light‐emitting diodes (LEDs) due to the high color purity, low cost, and simple synthesis. However, the electroluminescent efficiency of polycrystalline OHP LEDs (PeLEDs) is often limited by poor surface morphology, small exciton binding energy, and long exciton diffusion length of large‐grain OHP films caused by uncontrolled crystallization. Here, crystallization of methylammonium lead bromide (MAPbBr3) is finely controlled by using a polar solvent‐soluble self‐doped conducting polymer, poly(styrenesulfonate)‐grafted polyaniline (PSS‐g‐PANI), as a hole injection layer (HIL) to induce granular structure, which makes charge carriers spatially confined more effectively than columnar structure induced by the conventional poly(3,4‐ethylenedioythiphene):polystyrenesulfonate (PEDOT:PSS). Moreover, lower acidity of PSS‐g‐PANI than PEDOT:PSS reduces indium tin oxide (ITO) etching, which releases metallic In species that cause exciton quenching. Finally, doubled device efficiency of 14.3 cd A‐1 is achieved for PSS‐g‐PANI‐based polycrystalline MAPbBr3 PeLEDs compared to that for PEDOT:PSS‐based PeLEDs (7.07 cd A‐1). Furthermore, PSS‐g‐PANI demonstrates high efficiency of 37.6 cd A‐1 in formamidinium lead bromide nanoparticle LEDs. The results provide an avenue to both control the crystallization kinetics and reduce the migration of In released from ITO by forming OIP films favorable for more radiative luminescence using the polar solvent‐soluble and low‐acidity polymeric HIL.

No abstract

Here we present CVD growth of graphene on Ni and investigate the growth mechanism using isotopically labeled (13)C-ethanol as the precursor. Results show that during low-pressure alcohol catalytic CVD (LP-ACCVD), a growth time of less than 30 s yields graphene films with high surface coverage (>80%). Moreover, when isotopically labeled ethanol precursors were sequentially introduced, Raman mapping revealed that both (12)C and (13)C graphene flakes exist. This shows that even at high temperature (∼900 °C) the graphene flakes form independently, suggesting a different growth mechanism for ethanol-derived graphene on Ni from the segregation process for methane-derived graphene. We interpret this growth mechanism using a direct surface-adsorptive growth model in which small carbon fragments catalyzed from ethanol decomposition products first nucleate at metal step edges or grain boundaries to initiate graphene growth, and then expand over the entire metal surface.