Ultrathin Hexagonal Hybrid Nanosheets Synthesized by Graphene Oxide‐Assisted Exfoliation of β‐Co(OH)₂ Mesocrystals

Abstract

In the present study, we report the synthesis of a high-quality, single-crystal hexagonal β-Co(OH)2 nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of β-Co(OH)2 nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure-directing molecules, the β-Co(OH)2 flower-like superstructures were first grown by a nanoparticle-mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, β-Co(OH)2 nanoflowers were chemically exfoliated by surface-active GO under hydrothermal conditions into unilamellar single-crystal nanosheets. In this reaction, GO acts as a two-dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on-site conjugation of GO and Co(OH)2 promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)2 nanosheets on rGO resulted in a remarkably enhanced lithium-ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g(-1) for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO-assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics.

High Cycle Stability of Hybridized Co(OH)2 Nanomaterial Structures Synthesized by the Water Bath Method as Anodes for Lithium-Ion Batteries

“…The Coulombic efficiency increased to 94.21% in the second cycle and remained above 95% till the 150th cycle. A reversible capacity of 1050 mAh/g is obtained after 150 cycles, which is higher than the theoretical capacity (576 mAh/g) of Co(OH) 2 [33,41]. The fluctuation of the capacities could result from the difference in testing temperatures during the day and night.…”

Achieving High Lithium Storage Capacity and Long-Term Cyclability of Novel Cobalt Germanate Hydroxide/Reduced Graphene Oxide Anodes with Regulated Electrochemical Catalytic Conversion Process of Hydroxyl Groups

“…Recently, Zhou et al used positive cycled MnO nanoparticles to adjust the negative cycled Si nanospheres, and the resulting nanocomposite achieved a highly stable cycling performance . Fortunately, transition-metal hydroxides or carbonates have positive trends with increased cycling capacities because of the electrocatalytic conversion reactions of LiOH or Li 2 CO 3 triggered by in situ generated transition metals. − Therefore, transition-metal germanate hydroxides should be pretty suitable for improving the electrochemical properties of transition-metal germanates with three advantages: (i) the integration of hydroxides with germanates could compensate the negative trends of transition-metal germanates upon cycles; (ii) it is a compound rather than a composite, implying that the efficient synergistic effect between hydroxides and germanates not only promotes electrocatalytic conversion reactions of hydroxides but also boosts the electrochemical conversion of the Ge component; and (iii) transition-metal germanate hydroxides have greater potentialities for high-capacity LIBs than typical transition-metal germanates because their lithium storage mechanisms involve not only conventional conversion reactions, alloying reactions of Ge, and reversible redox reactions of the second metallic component but also further electrocatalytic conversion reactions of hydroxides. Therefore, the introduction of an electrocatalytic conversion-type component with a positive trend upon cycling is expected to effectively enhance the electrochemical performances of transition-metal germanates.…”

N-Doped Carbon Nanosheet Networks with Favorable Active Sites Triggered by Metal Nanoparticles as Bifunctional Oxygen Electrocatalysts

“…The N-CNFs exhibit a much larger surface area of 1856.30 m 2 /g due to the absence of Co. In Figure k, the intensity value ratios of the D and G bands ( I D / I G ) are 1.01 for both Co/N-CNSNs and Co/N-CNFs, revealing the formation of a highly ordered graphitic structure . The I D / I G of Ni/N-CNSNs (0.88) is lower because of nickel’s better catalytic property for carbon’s graphitization, whereas the N-CNFs present a higher I D / I G of 1.08 for less graphitization of carbon, which is in good agreement with the XRD results.…”