Nitrogen-Doped Carbon Materials as Metal-Free Catalyst for the Dechlorination of Trichloroethylene by Sulfide.

A new method for trichloroethylene (TCE) dechlorination is proposed using sulfide (HS- and S2-) as reductant under the mediation of nitrogen-doped carbon materials (NCMs). About 99% of the TCE was converted to acetylene after 200 h using this method. Dechlorination of TCE in the NCMs-sulfide system (NCSS) followed pseudo-first-order kinetics. Pyridinic N (N6) on surface of the NCMs appeared to play a critical role in NCSS as shown by the good linear relationship between the surface content of N6 and kobs. Nucleophilic substitution was suggested as the first step in TCE dechlorination, and the nucleophilic reagent was identified as a sulfur intermediate with C-S-S-H as the functional group. The generation of C-S-S-H could be ascribed to the interaction between positively charged carbon atoms in N6 and negative charged sulfide. This work is the first to demonstrate that sulfide combined with NCMs can produce active substances that are effective in TCE dechlorination and the findings will assist in the development of strategies that use natural sulfide as reductant for detoxicating organic chloroethene contaminants.

Variable-Energy Hard X-ray Photoemission Spectroscopy: A Nondestructive Tool to Analyze the Cathode-Solid-State Electrolyte Interface.

All-solid-state batteries are expected to be promising next-generation energy storage systems with increased energy density compared to the state-of-the-art Li-ion batteries. Nonetheless, the electrochemical performances of the all-solid-state batteries are currently limited by the high interfacial resistance between active electrode materials and solid-state electrolytes. In particular, elemental interdiffusion and the formation of interlayers with low ionic conductivity are known to restrict the battery performance. Herein, we apply a nondestructive variable-energy hard X-ray photoemission spectroscopy to detect the elemental chemical states at the interface between the cathode and the solid-state electrolyte, in comparison to the widely used angle-resolved (variable-angle) X-ray photoemission spectroscopy/X-ray absorption spectroscopy methods. The accuracy of variable-energy hard X-ray photoemission spectroscopy is also verified with a focused ion beam and high-resolution transmission electron microscopy. We also show the significant suppression of interdiffusion by building an artificial layer via atomic layer deposition at this interface.

Pt/TiSi x-NCNT Novel Janus Nanostructure: A New Type of High-Performance Electrocatalyst.

Novel Janus nanostructured electrocatalyst (Pt/TiSi x-NCNT) was prepared by first sputtering TiSi x on one side of N-doped carbon nanotubes (NCNTs), followed by wet chemical deposition of Pt nanoparticles (NPs) on the other side. Transmission electron microscopy (TEM) studies showed that the Pt NPs are mainly deposited on the NCNT surface where no TiSi x (i.e., between the gaps of TiSi x film). This feature could benefit the increase in the stability of the Pt NP catalyst. Indeed, compared to the state-of-the-art commercial Pt/C catalyst, this novel Pt/TiSi x-NCNT Janus structure showed ∼3 times increase in stability as well as significantly improved CO tolerance. The obvious performance enhancement could be attributed to the better corrosion resistance of TiSi x and NCNTs than the carbon black that is used in the commercial Pt/C catalyst. Pt/TiSi x-NCNT Janus nanostructures open the door for designing new type of high-performance electrocatalyst for fuel cells and other oxygen reduction reaction-related energy devices.

Atomic Layer Deposited Lithium Silicates as Solid-State Electrolytes for All-Solid-State Batteries.

Development of solid-state electrolyte (SSE) thin films is a key toward the fabrication of all-solid-state batteries (ASSBs). However, it is challenging for conventional deposition techniques to deposit uniform and conformal SSE thin films in a well-controlled fashion. In this study, atomic layer deposition (ALD) was used to fabricate lithium silicate thin films as a potential SSE for ASSBs. Lithium silicates thin films were deposited by combining ALD Li2O and SiO2 subcycles using lithium tert-butoxide, tetraethylorthosilane, and H2O as precursors. Uniform and self-limiting growth was achieved at temperatures between 225 and 300 °C. X-ray absorption spectroscopy analysis disclosed that the as-deposited lithium silicates were composed of SiO4 tetrahedron structure and lithium oxide as the network modifier. X-ray photoelectron spectroscopy confirmed the chemical states of Li in the thin films were the same with that in standard lithium silicate. With one to one subcycle of Li2O and SiO2 the thin films had a composition close to Li4SiO4 whereas one more subcycle of Li2O delivered a higher lithium content. The lithium silicate thin film prepared at 250 °C exhibited an ionic conductivity of 1.45× 10-6 S cm-1 at 373 K. The high ionic conductivity of lithium silicate was due to the higher lithium concentration and lower activation energy.

Size-dependent surface phase change of lithium iron phosphate during carbon coating.

Carbon coating is a simple, effective and common technique for improving the conductivity of active materials in lithium ion batteries. However, carbon coating provides a strong reducing atmosphere and many factors remain unclear concerning the interface nature and underlying interaction mechanism that occurs between carbon and the active materials. Here, we present a size-dependent surface phase change occurring in lithium iron phosphate during the carbon coating process. Intriguingly, nanoscale particles exhibit an extremely high stability during the carbon coating process, whereas microscale particles display a direct visualization of surface phase changes occurring at the interface at elevated temperatures. Our findings provide a comprehensive understanding of the effect of particle size during carbon coating and the interface interaction that occurs on carbon-coated battery material--allowing for further improvement in materials synthesis and manufacturing processes for advanced battery materials.