[en] The fabrication of optically active inorganic nanomaterials with chiral superstructures attracts attention because of their potential applications in chemical sensing and non-linear optics. Here, we present a facile way to prepare TiO_2 nanofibres, in which the nanocrystals are helically arranged into a chiral superstructure. Notably, the chiral superstructure shows strong optical activity due to the difference of absorbing left- and right-handed circularly polarized light. This special optical activity resulted from electron transition from the valence band to the conduction band of TiO_2 through a vicinal effect of helically arranged TiO_2 nanocrystals. (focus issue paper)

[en] For miniaturized capacitive energy storage, volumetric and areal capacitances are more important metrics than gravimetric ones because of the constraints imposed by device volume and chip area. Typically used in commercial supercapacitors, porous carbons, although they provide a stable and reliable performance, lack volumetric performance because of their inherently low density and moderate capacitances. In this paper, we report a high-performing electrode based on conductive hexaaminobenzene (HAB)-derived two-dimensional metal-organic frameworks (MOFs). In addition to possessing a high packing density and hierarchical porous structure, these MOFs also exhibit excellent chemical stability in both acidic and basic aqueous solutions, which is in sharp contrast to conventional MOFs. Submillimetre-thick pellets of HAB MOFs showed high volumetric capacitances up to 760 F cm^-3 and high areal capacitances over 20 F cm^-2. Furthermore, the HAB MOF electrodes exhibited highly reversible redox behaviours and good cycling stability with a capacitance retention of 90% after 12,000 cycles. In conclusion, these promising results demonstrate the potential of using redox-active conductive MOFs in energy-storage applications.

[en] 1D materials, such as nanofibers or nanoribbons are considered as the future ultimate limit of downscaling for modern electrical and electrochemical devices. Here, for the first time, nanofibers of a solid solution transition metal trichalcogenide (TMTC), Nb${}_{1-<!--\; ???\; -->x}$Ta${}_x$S${}_3$, are successfully synthesized with outstanding electrical, thermal, and electrochemical characteristics rivaling the performance of the-state-of-the art materials for each application. This material shows nearly unchanged sheet resistance (≈740 Ω sq${}^{-<!--\; ???\; -->1}$) versus bending cycles tested up to 90 cycles, stable sheet resistance in ambient conditions tested up to 60 days, remarkably high electrical breakdown current density of ≈30 MA cm${}^{-<!--\; ???\; -->2}$, strong evidence of successive charge density wave transitions, and outstanding thermal stability up to ≈800 K. Additionally, this material demonstrates excellent activity and selectivity for CO${}_2$ conversion to CO reaching ≈350 mA cm${}^{-<!--\; ???\; -->2}$ at -0.8 V versus RHE with a turnover frequency number of 25. It also exhibits an excellent performance in a high-rate Li-air battery with the specific capacity of 3000 mAh g${}^{-<!--\; ???\; -->1}$ at a current density of 0.3 mA cm${}^{-<!--\; ???\; -->2}$. This study uncovers the multifunctionality in 1D TMTC alloys for a wide range of applications and opens a new direction for the design of the next generation low-dimensional materials. (© 2022 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)

[en] Highlights: • The formation process of novel β-Co(OH)₂/Co(OH)F hexagrams were reported. • The Co(OH)F nanorods grow along β-Co(OH)₂ hexagon edges as lateral branches. • .The lattice matching between Co(OH)F and β-Co(OH)₂ leads to the epitaxial growth. • The hybrids show high OER performance. The six-fold symmetry widely presents in both natural and artificial architectures. Understanding the growth mechanism of six-fold symmetrical materials is of fundamental interest and significance. Herein, we report the formation process of β-Co(OH)₂/Co(OH)F hierarchical hexagrams with a six-fold symmetrical arrangement. Our results demonstrate that hexagonal β-Co(OH)₂ plates are first formed under the reaction condition. These hexagonal plates then act as templates for the growth of Co(OH)F nanorods. The intermediate material is therefore composed of plate-like β-Co(OH)₂ hexagonal cores appended with six rod-like Co(OH)F branches, giving the β-Co(OH)₂/Co(OH)F hybrid. After prolonged reaction, the β-Co(OH)₂ hexagons can be completely converted, leading to authentic six-branched Co(OH)F nanorods as the final product. Consequently, for both intermediate and final materials, the Co(OH)F nanorods are arranged with a six-fold symmetry. Importantly, these Co(OH)F nanorods grow along β-Co(OH)₂ hexagon edges as lateral branches instead of perpendicular to hexagons. This uncommon epitaxial growth mechanism is considered to be a result of the matching between the b-axis of Co(OH)F crystals and the a-axis of β-Co(OH)₂ crystals, which is beneficial for the electrocatalysis. The β-Co(OH)₂/Co(OH)F hierarchical hexagrams show enhanced water oxidation activity compared to the pure β-Co(OH)₂ and Co(OH)F.

[en] Lithium-air batteries based on CO${}_2$ reactant (Li-CO${}_2$) have recently been of interest because it has been found that reversible Li/CO${}_2$ electrochemistry is feasible. In this study, a new medium-entropy cathode catalyst, (NbTa)${}_{0.5}$BiS${}_3$, that enables the reversible electrochemistry to operate at high rates is presented. This medium entropy cathode catalyst is combined with an ionic liquid-based electrolyte blend to give a Li-CO${}_2$ battery that operates at high current density of 5000 mA g${}^{-<!--\; ???\; -->1}$ and capacity of 5000 mAh g${}^{-<!--\; ???\; -->1}$ for up to 125 cycles, far exceeding reported values in the literature for this type of battery. The higher rate performance is believed to be due to the greater stability of the multi-element (NbTa)${}_{0.5}$BiS${}_3$ catalyst because of its higher entropy compared to previously used catalysts with a smaller number of elements with lower entropies. Evidence for this comes from computational studies giving very low surface energies (high surface stability) for (NbTa)${}_{0.5}$BiS${}_3$ and transmission electron microscopystudies showing the structure being retained after cycling. In addition, the calculations indicate that Nb-terminated surface promotes Li-CO${}_2$ electrochemistry resulting in Li${}_2$CO${}_3$ and carbon formation, consistent with the products found in the cell. These results open new direction to design and develop high-performance Li-CO${}_2$ batteries. (© 2023 The Authors. Advanced Functional Materials published by Wiley‐VCH GmbH)