Sharad B. Patil

Composition‐Tailored 2 D Mn1−xRuxO2 Nanosheets and Their Reassembled Nanocomposites: Improvement of Electrode Performance upon Ru Substitution

Composition-tailored Mn1-x Rux O2 2 D nanosheets and their reassembled nanocomposites with mesoporous stacking structure are synthesized by a soft-chemical exfoliation reaction and the subsequent reassembling of the exfoliated nanosheets with Li(+) cations, respectively. The tailoring of the chemical compositions of the exfoliated Mn1-x Rux O2 2 D nanosheets and their lithiated nanocomposites can be achieved by adopting the Ru-substituted layered manganese oxides as host materials for exfoliation reaction. Upon the exfoliation-reassembling process, the substituted ruthenium ions remain stabilized in the layered Mn1-x Rux O2 lattice with mixed Ru(3+) /Ru(4+) oxidation state. The reassembled Li-Mn1-x Rux O2 nanocomposites show promising pseudocapacitance performance with large specific capacitances of approximately 330 F g(-1) for the second cycle and approximately 360 F g(-1) for the 500th cycle and excellent cyclability, which are superior to those of the unsubstituted Li-MnO2 homologue and many other MnO2 -based materials. Electrochemical impedance spectroscopy analysis provides strong evidence for the enhancement of the electrical conductivity of 2 D nanostructured manganese oxide upon Ru substitution, which is mainly responsible for the excellent electrode performance of Li-Mn1-x Rux O2 nanocomposites. The results underscore the powerful role of the composition-controllable metal oxide 2 D nanosheets as building blocks for exploring efficient electrode materials.

Phase Tuning of Nanostructured Gallium Oxide via Hybridization with Reduced Graphene Oxide for Superior Anode Performance in Li-Ion Battery: An Experimental and Theoretical Study

The crystal phase of nanostructured metal oxide can be effectively controlled by the hybridization of gallium oxide with reduced graphene oxide (rGO) at variable concentrations. The change of the ratio of Ga2O3/rGO is quite effective in tailoring the crystal structure and morphology of nanostructured gallium oxide hybridized with rGO. This is the first example of the phase control of metal oxide through a change of the content of rGO hybridized. The calculations based on density functional theory (DFT) clearly demonstrate that the different surface formation energy and Ga local symmetry of Ga2O3 phases are responsible for the phase transition induced by the change of rGO content. The resulting Ga2O3-rGO nanocomposites show promising electrode performance for lithium ion batteries. The intermediate Li-Ga alloy phases formed during the electrochemical cycling are identified with the DFT calculations. Among the present Ga2O3-rGO nanocomposites, the material with mixed α-Ga2O3/β-Ga2O3/γ-Ga2O3 phase can deliver the largest discharge capacity with the best cyclability and rate characteristics, highlighting the importance of the control of Ga2O3/rGO ratio in optimizing the electrode activity of the composite materials. The present study underscores the usefulness of the phase-control of nanostructured metal oxides achieved by the change of rGO content in exploring novel functional nanocomposite materials.

Recent Applications of 2D Inorganic Nanosheets for Emerging Energy Storage System

Among many types of nanostructured inorganic materials, highly anisotropic 2D nanosheets provide unique advantages in designing and synthesizing efficient electrode and electrocatalyst materials for novel energy storage technologies. 2D inorganic nanosheets boast lots of unique characteristics such as high surface area, short ion diffusion path, tailorable compositions, and tunable electronic structures. These merits of 2D inorganic nanosheets render them promising candidate materials as electrodes for diverse secondary batteries and supercapacitors, and electrocatalysts. A wide spectrum of examples is presented for inorganic nanosheet-based electrodes and electrocatalysts. Future perspectives in research about 2D nanosheet-based functional materials are discussed to provide insight for the development of next-generation energy storage systems using 2D nanostructured materials.

Understanding the crucial role of local crystal order in the electrocatalytic activity of crystalline manganese oxide

The structure–property relationship in transition metal oxides is of crucial importance in designing and synthesizing economically feasible high-performance electrocatalysts. Since cation substitution allows to finely tailor the atomic arrangement, structural distortion, and electrocatalytic performance of transition metal oxides, a relationship between local structural order and electrocatalytic activity in crystalline manganese oxide can be systematically investigated by in situ X-ray absorption, electron paramagnetic resonance, and electrochemical impedance spectroscopic analyses for unsubstituted and Fe-substituted α-Mn1−xFexO2 during the oxygen evolution reaction (OER). The substitution of Mn with Fe is quite effective in improving the OER activity of α-MnO2 to reach a small overpotential of 0.40 V at 10 mA cm−2. Under OER conditions, the Fe substitution improves the local structural order of MnO6 octahedra in the α-MnO2 lattice, thus leading to a significant enhancement of charge transport kinetics. Since the Fe substitution induces only a limited alteration of the electronic structure and the substituted Fe ion itself shows only a negligible contribution to the OER activity, the excellent OER functionality of Fe-substituted α-Mn1−xFexO2 is attributable mainly to the improvement of local structural ordering upon Fe substitution. The present study underscores the crucial role of local structural order in optimizing the electrocatalytic functionality of crystalline transition metal oxides.

Improvement of Na Ion Electrode Activity of Metal Oxide via Composite Formation with Metal Sulfide

The composite formation with a conductive metal sulfide domain can provide an effective methodology to improve the Na-ion electrode functionality of metal oxide. The heat treatment of TiO2(B) under CS2 flow yields an intimately coupled TiO2(B)-TiS2 nanocomposite with intervened TiS2 domain, since the reaction between metal oxide and CS2 leads to the formation of metal sulfide and CO2. The negligible change in lattice parameters and significant enhancement of visible light absorption upon the reaction with CS2 underscore the formation of conductive metal sulfide domains. The resulting TiO2(B)-TiS2 nanocomposites deliver greater discharge capacities with better rate characteristics for electrochemical sodiation-desodiation process than does the pristine TiO2(B). The 23Na magic angle spinning nuclear magnetic resonance analysis clearly demonstrates that the electrode activities of the present nanocomposites rely on the capacitive storage of Na+ ions, and the TiS2 domains in TiO2(B)-TiS2 nanocomposites play a role as mediators for Na+ ions to and from TiO2(B) domains. According to the electrochemical impedance spectroscopy, the reaction with CS2 leads to the significant enhancement of charge transfer kinetics, which is responsible for the accompanying improvement in electrode performance. The present study provides clear evidence for the usefulness in composite formation between the semiconducting metal oxide and metal sulfide in exploring new efficient NIB electrode materials.