Xiaoyan Jin

A Direct Hybridization between Isocharged Nanosheets of Layered Metal Oxide and Graphene through a Surface‐Modification Assembly Process

An efficient and universal method to directly hybridize isocharged nanosheets of layered metal oxide and reduced graphene oxide (rGO) is developed on the basis of the surface modification and an electrostatically driven assembly process. On the basis of this synthetic method, the CoO2 -rGO nanocomposite can be synthesized with exfoliated CoO2 and rGO nanosheets, and transformed into CoO-CoO2 -rGO nanocomposites with excellent electrode performance for lithium-ion batteries. Also, this surface-modification assembly route is successfully applied for the synthesis of another mesoporous TiO2 -rGO nanocomposite. This result provides clear evidence for the usefulness of the present method as a universal way of hybridizing isocharged anionic nanosheets of inorganic solids and graphene.

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.

A 2D Metal Oxide Nanosheet as an Efficient Additive for Improving Na-Ion Electrode Activity of Graphene-Based Nanocomposites

An efficient way to improve the Na-ion electrode activity of graphene-based nanocomposite is developed by employing exfoliated metal oxide nanosheet as an additive. The titanate-nanosheet-incorporated Na-SnS2 -reduced graphene oxide (rG-O) nanocomposites can be synthesized by the electrostatically derived restacking of the colloidal mixture of SnS2 , rG-O, and titanate nanosheets with the Na+ cation. The incorporation of titanate into the Na-SnS2 -rG-O nanocomposites is effective in improving the nanoscale mixing of component nanosheets and the porosity of the composite structure. The resulting nanocomposites deliver superior discharge capacities and rate properties to the titanate-free nanocomposite. The universal applicability is further confirmed by MoS2 -rG-O nanocomposites upon the addition of titanate. This study highlights that the exfoliated metal oxide nanosheet can be used as an efficient additive for graphene-based nanocomposites to explore Na-ion electrode materials.

Heterolayered 2D nanohybrids of uniformly stacked transition metal dichalcogenide–transition metal oxide monolayers with improved energy-related functionalities

Heterolayered 2D nanohybrids of uniformly stacked transition metal dichalcogenide (TMD)–transition metal oxide (TMO) monolayers are synthesized by a self-assembly of exfoliated nanosheets (NSs) with charge-balancing cations. This is the first example of a layer-by-layer-ordered 2D nanohybrid of exfoliated TMD and TMO nanosheets. The homogeneous incorporation of MnO2 NSs into restacked MoS2 NSs is quite effective in improving the multifunctionality of MoS2 as an electrocatalyst for the hydrogen evolution reaction (HER) and electrode for Li-ion batteries, underscoring the universal merit of layer-by-layer ordering of TMD and TMO NSs. In situ spectroscopic analysis of the present TMD–TMO nanohybrid during the electrocatalytic reaction highlights the efficient interfacial charge transfer of the restacked nanosheets with enhanced porosity. The beneficial effect of incorporated TMO NSs on the performance of TMD NSs is attributable to an efficient interfacial charge transfer and increased porosity with depressed self-stacking of NSs and the stabilization of the metallic 1T TMD phase, resulting in the improvement of charge transfer kinetics, the enhancement of reactivity, and the provision of many reaction sites upon hybridization. Density functional theory (DFT) calculations further support the stabilization of the 1T TMD structure over the 2H TMD one via the interaction with neighboring TMO NSs. The present study clearly demonstrates that the restacking of the colloidal mixtures of TMO and TMD NSs can provide an effective way to explore novel multifunctional heterostructures.

A rational method to kinetically control the rate-determining step to explore efficient electrocatalysts for the oxygen evolution reaction

A novel, rational, and efficient way to explore high-performance electrocatalysts was developed by controlling the reaction kinetics of the rate-determining step (RDS). Density functional theory (DFT) calculations demonstrate that the RDS for the oxygen evolution reaction driven by transition metal hydroxides/oxides, i.e., surface adsorption of OH−/OOH• species, can be significantly promoted by increasing the electrophilicity of electrocatalysts via hybridization with electron-withdrawing inorganic nanosheets. As predicted by DFT calculation, the hybridization of Ni–Fe-layered double hydroxide (LDH)/Ni–Co-LDH, with RuO2 nanosheets (1.0u2009wt%) leads to significant lowering of the overpotentials to 207/276u2009mV at 10u2009mAu2009cm−2, i.e., one of the smallest overpotentials for LDH-based materials, with the increase in the current density. The necessity of a very small amount of RuO2 nanosheets (1.0u2009wt%) to optimize the electrocatalyst activity highlights the remarkably high efficiency of the RuO2 addition. The present study underscores the importance of kinetic control of the RDS via hybridization with electron-withdrawing species for exploring novel efficient electrocatalysts.Electrocatalysis: evolving the perfect water-splitterPlatinum and other precious metals currently used in fuel cells may ultimately be replaced by nanostructured catalysts designed with the help of computers. Catalysts are essential for speeding up the oxygen evolution reaction in fuel cells, a normally slow extraction of electrons and protons from water molecules. A team led by Hyungjun Kim from the Korea Advanced Institute of Science and Technology in Daejon and Seong-Ju Hwang from Ewha Womans University in Seoul have now used computer simulations to optimize inexpensive oxygen evolution catalysts made from transition metal hydroxides. Their calculations predicted that these normally multilayered catalysts could split water faster if exfoliated into individual sheets and attached to a ruthenium nanostructure. Fabrication of these materials revealed they had significantly higher active surface areas and improved energy efficiency compared to typical metal hydroxide catalysts.A rational way to explore economically feasible high-performance electrocatalyst for OER is developed by improving the reaction kinetics of rate-determining step via the hybridization with electron-withdrawing RuO2 nanosheet. Even with very low RuO2 content, self-assembled Ni–Fe-/Ni–Co-layered double hydroxide (LDH)–RuO2 nanohybrids show very small overpotentials of 207/276u2009mV at 10u2009mAu2009cm−2 for oxygen evolution reaction with greatly improved current densities.