Gianluca Longoni

Shape-Controlled TiO2 Nanocrystals for Na-Ion Battery Electrodes: The Role of Different Exposed Crystal Facets on the Electrochemical Properties

Rechargeable sodium-ion batteries are becoming a viable alternative to lithium-based technology in energy storage strategies, due to the wide abundance of sodium raw material. In the past decade, this has generated a boom of research interest in such systems. Notwithstanding the large number of research papers concerning sodium-ion battery electrodes, the development of a low-cost, well-performing anode material remains the largest obstacle to overcome. Although the well-known anatase, one of the allotropic forms of natural TiO2, was recently proposed for such applications, the material generally suffers from reduced cyclability and limited power, due to kinetic drawbacks and to its poor charge transport properties. A systematic approach in the morphological tuning of the anatase nanocrystals is needed, to optimize its structural features toward the electrochemical properties and to promote the material interaction with the conductive network and the electrolyte. Aiming to face with these issues, we were able to obtain a fine tuning of the nanoparticle morphology and to expose the most favorable nanocrystal facets to the electrolyte and to the conductive wrapping agent (graphene), thus overcoming the intrinsic limits of anatase transport properties. The result is a TiO2-based composite electrode able to deliver an outstandingly stability over cycles (150 mA h g-1 for more than 600 cycles in the 1.5-0.1 V potential range) never achieved with such a low content of carbonaceous substrate (5%). Moreover, it has been demonstrated for the first time than these outstanding performances are not simply related to the overall surface area of the different morphologies but have to be directly related to the peculiar surface characteristics of the crystals.

The Influence of Carbonaceous Matrices and Electrocatalytic MnO2 Nanopowders on Lithium-Air Battery Performances

Here, we report new gas diffusion electrodes (GDEs) prepared by mixing two different pore size carbonaceous matrices and pure and silver-doped manganese dioxide nanopowders, used as electrode supports and electrocatalytic materials, respectively. MnO2 nanoparticles are finely characterized in terms of structural (X-ray powder diffraction (XRPD), energy dispersive X-ray (EDX)), morphological (SEM, high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM)/TEM), surface (Brunauer Emmet Teller (BET)-Barrett Joyner Halenda (BJH) method) and electrochemical properties. Two mesoporous carbons, showing diverse surface areas and pore volume distributions, have been employed. The GDE performances are evaluated by chronopotentiometric measurements to highlight the effects induced by the adopted materials. The best combination, hollow core mesoporous shell carbon (HCMSC) with 1.0% Ag-doped hydrothermal MnO2 (M_hydro_1.0%Ag) allows reaching very high specific capacity close to 1400 mAh·g−1. Considerably high charge retention through cycles is also observed, due to the presence of silver as a dopant for the electrocatalytic MnO2 nanoparticles.

WS2–Graphite Dual-Ion Batteries

A novel WS2-graphite dual-ion battery (DIB) is developed by combining a conventional graphite cathode and a high-capacity few-layer WS2-flake anode. The WS2 flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows large-scale and free-material loss production (i.e., volume up to 8 L h-1 at concentration of 10 g L-1 and exfoliation yield of 100%) of few-layer WS2 flakes in dispersion. The WS2 anodes enable DIBs, based on hexafluorophosphate (PF6-) and lithium (Li+) ions, to achieve charge-specific capacities of 457, 438, 421, 403, 295, and 169 mAh g-1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0 A g-1, respectively, outperforming conventional DIBs. The WS2-based DIBs operate in the 0 to 4 V cell voltage range, thus extending the operating voltage window of conventional WS2-based Li-ion batteries (LIBs). These results demonstrate a new route toward the exploitation of WS2, and possibly other transition-metal dichalcogenides, for the development of next-generation energy-storage devices.

An Integrated Theoretical/Experimental Study of Quinolinic–Isoquinolinic Derivatives Acting as Reversible Electrochromes

A series of compounds, featuring an ethenylic bridge and quinoline and isoquinoline end capping units possessing systematically varied substitution patterns, were prepared as molecular materials for electrochromic applications. The different structures were optimized in order to maximize the electrochromic contrast in the visible region, mostly by achieving a completely UV-absorbing oxidized state. Density functional theory (DFT) calculations are exploited in order to rationalize the correlation between the molecular structure, the functional groups’ electronic properties, and the electrochemical behavior. It is shown that the molecular planarity (i.e. ring/ring π conjugation) plays a major role in defining the mechanism of the electrochemical charge transfer reaction, while the substituent’s nature has an influence on the LUMO energy. Among the compounds here studied, the (E)-10-methyl-9-(2-(2-methylisoquinolinium-1-yl)-vinyl)-1,2,3,4-tetrahydroacri-dinium trifluoromethanesulfonate derivative shows the most interesting properties as an electrochromophore.