Transparent and flexible energy storage devices have received immense attention due to their suitability for innovative electronics and displays. However, it remains a great challenge to fabricate devices with high storage capacity and high degree of transmittance. This study describes a simple process for fabrication of supercapacitors with ≈75% of visible transparency and areal capacitance of ≈3 mF cm with high stability tested over 5000 cycles of charging and discharging. The electrodes consist of Au wire networks obtained by a simple crackle template method which are coated with MnO nanostructures by electrodeposition process. Importantly, the membrane separator itself is employed as substrate to bring in the desired transparency and light weight while additionally exploiting its porous nature in enhancing the interaction of electrolyte with the active material from both sides of the substrate, thereby enhancing the storage capacity. The method opens up new ways for fabricating transparent devices.
Tuning of crystal structures and shapes of submicrometer-sized noble metals have revealed fascinating catalytic, optical, electrical, and magnetic properties that enable developments of environmentally friendly and durable nanotechnological applications. Several attempts have been made to stabilize Au, knowing its extraordinary stability in its conventional face-centered cubic (fcc) lattice, into different lattices, particularly to develop Au-based catalysis for industry. Here, we report the results from scanning X-ray diffraction microscopy (SXDM) measurements on an ambient-stable penta-twinned bipyramidal Au microcrystallite (about 1.36 μm in length and 230 nm in diameter) stabilized in noncubic lattice, exhibiting catalytic properties. With more than 82% of the crystal volume, the majority crystallite structure is identified as body-centered orthorhombic (bco), while the remainder is the standard fcc. A careful analysis of the diffraction maps reveals that the tips are made up of fcc, while the body contains mainly bco with very high strain. The reported structural imaging technique of representative single crystallite will be useful to investigate the growth mechanism of similar multiphase nano- and micrometer-sized crystals.
Conventional gold comprising the cubic lattice is universally known for its stability. However, well known to chemists and metallurgists, this nobility is challenged by reagents such as aqua regia, which dissolve gold to form a salt solution. Among metals, mercury blends with gold to form amalgam, otherwise transition metals such as copper tend to interact with gold surfaces in electrochemical media. Herein, we report a combined experimental and theoretical investigation of the stability of Au microcrystallites bearing unconventional crystal lattices that exhibit enhanced stability towards Hg and aqua regia and practically no interaction with Cu during electroless plating. The unconventional gold is undoubtedly nobler.
Modulating crystal structures of noble metals can provide a library of new properties, optical, electrical, catalytic, and so on. Surprisingly, most lattice conversions occur at high temperatures and pressures. Recently, Au microcrystallites have been stabilized in body-centered orthorhombic and body-centered tetragonal lattices, together termed as bc(o,t), via chemical routes that exhibit exuberant catalytic performance. The noncubic lattices are found to be robust at pressures up to ∼40 GPa and temperature of 700 °C. Herein, we report the irreversible phase transformation to thermodynamically stable face-centered cubic (fcc) lattice induced by surfactants (such as tetrabutylammonium bromide) at high but near ambient temperatures mediated by (002)bc(o,t) → (002)fcc orientational changes involving an intermediate phase termed bct-I. The phase transformation is essentially due to oxidative etching at the nanoscale followed by redeposition of the metal. Interestingly, the conversion is governed by the binding strength of the adsorbent and thereby dependent on the alkyl chain length of the participating quaternary ammonium cation, the most effective one being the butyl chain. The study also unravels a core–shell structure of the microcrystallite, i.e., fcc capped bc(o,t).
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