Pseudocapacitive Sodium Storage by Ferroelectric Sn2 P2 S6 with Layered Nanostructure.

Sodium ion batteries (SIB) are considered promising alternative candidates for lithium ion batteries (LIB) because of the wide availability and low cost of sodium, therefore the development of alternative sodium storage materials with comparable performance to LIB is urgently desired. The sodium ions with larger sizes resist intercalation or alloying because of slow reaction kinetics. Most pseudocapacitive sodium storage materials are based on subtle nanomaterial engineering, which is difficult for large-scale production. Here, ferroelectric Sn2 P2 S6 with layered nanostructure is developed as sodium ion storage material. The ferroelectricity-enhanced pseudocapacitance of sodium ion in the interlayer spacing makes the electrochemical reaction easier and faster, endowing the Sn2 P2 S6 electrode with excellent rate capability and cycle stability. Furthermore, the facile solid state reaction synthesis and common electrode fabrication make the Sn2 P2 S6 that becomes a promising anode material of SIB.

An advanced high-rate capability sodium-ion anode: Few-layered NbSe2 with a mechanism of parallel running intercalation and conversion.

The unique superconductivity and charge density wave transition characteristics of NbSe2 make it worthy of exploring its electrochemical performance and potential applications in the field of batteries. Herein, the bulk NbSe2 was successfully exfoliated into few-layered NbSe2 nanostructures by wet grinding exfoliation approach, which solved the issues of its long activation period and poor cycle stability. The strong Nb-Se bond in the plane and weak van der Waals force between the adjacent layers could render the fast Na+ diffusion, provide abundant reaction sites and multi-directional migration paths, thus accelerate the ionic conductivity. The theoretical calculations verified the high Na+ adsorption tendency between the NbSe2 interlayers stemming from the continuous region of charge accumulation. Thanks to the unique electronic and two-dimensional few-layered structures, the exfoliated NbSe2 exhibited a high cyclic stability with a capacity of 502 mA h g-1 over 2800 cycles at 10 A/g. In addition, the reaction mechanism was studied by in-situ X-ray diffraction and other tests, indicating a reaction mechanism containing of simultaneous intercalation (NbSe2↔NaxNbSe2↔NaNbSe2↔Na1+xNbSe2) and conversion processes in NbSe2. This parallelly running mechanism not only alleviates the volume change but also ensures a high specific capacity. Additionally, different lattice planes of the NaNbSe2 intermediate in the intercalation process experience varying degrees of contraction and expanding in d-spacing due to the influence of Coulombic force.

Facile hydrothermal synthesis of layered 1T' MoTe2 nanotubes as robust hydrogen evolution electrocatalysts.

Layered transition metal dichalcogenides (TMDs), such as molybdenum ditelluride (MoTe2), have attracted much attention because of their novel structure-related physicochemical properties. In particular, semi-metallic-phase MoTe2 (1T') is considered as a competitive candidate for low-cost electrocatalysts for water splitting. However, there are few reports on the simple hydrothermal synthesis of MoTe2 nanostructures compared with other layered TMDs. In this study, a facile one-step hydrothermal process was developed for the fabrication of layered MoTe2, in which uniform nanotubes with a few layers of 1T' MoTe2 were fabricated at a lower temperature for the first time. The as-obtained MoTe2 nanotubes were fully characterized using different techniques, which revealed their structure and indicated the presence of layered 1T' nanocrystals. The efficient activity of MoTe2 nanotubes for the electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H2SO4 was demonstrated by the small Tafel slope of 54 mV/dec-1 and endurable ability, which is attributed to the abundant active sites and remarkable conductivity of 1T' MoTe2 with a few-layer feature. This provides a facile method for the design and construction of efficient layered MoTe2 based electrocatalysts.

Coatings of nanostructured pristine graphene-IrOx hybrids for neural electrodes: Layered stacking and the role of non-oxygenated graphene.

The need to enhance charge capacity in neural stimulation-electrodes is promoting the formation of new materials and coatings. Among all the possible types of graphene, pristine graphene prepared by graphite electrochemical exfoliation, is used in this work to form a new nanostructured IrOx-graphene hybrid (IrOx-eG). Graphene is stabilized in suspension by IrOx nanoparticles without surfactants. Anodic electrodeposition results in coatings with much smaller roughness than IrOx-graphene oxide. Exfoliated pristine graphene (eG), does not electrodeposit in absence of iridium, but IrOx-nanoparticle adhesion on graphene flakes drives the process. IrOx-eG has a significantly different electronic state than graphene oxide, and different coordination for carbon. Electron diffraction shows the reflection features expected for graphene. IrOx 1-2 nm cluster/nanoparticles are oxohydroxo-species and adhere to 10nm graphene platelets. eG induces charge storage capacity values five times larger than in pure IrOx, and if calculated per carbon atom, this enhancement is one order magnitude larger than the induced by graphene oxide. IrOx-eG coatings show optimal in vitro neural cell viability and function as cell culture substrates. The fully straightforward electrochemical exfoliation and electrodeposition constitutes a step towards the application of graphene in biomedical systems, expanding the knowledge of pristine graphene vs. graphene oxide, in bioelectrodes.