Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured δ-MnO2 cathode in association with a nonaqueous acetonitrile–Zn­(TFSI)2 electrolyte and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte–electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any side reactions or minor mechanistic pathways. Numerous factors affecting capacity fade and issues associated with the second phase formation including Mn dissolution in heavily cycled Zn/δ-MnO2 cells are presented including dramatic mechanistic differences in the storage mechanism of this couple when compared to similar aqueous electrolytes are noted.

Sponge-like composites assembled by cobalt sulfides quantum dots (Co 9 S 8 QD), mesoporous hollow carbon polyhedral (HCP) matrix, and a reduced graphene oxide (rGO) wrapping sheets are synthesized by a simultaneous thermal reduction, carbonization, and sulfidation of zeolitic imidazolate frameworks@GO precursors. Specifically, Co 9 S 8 QD with size less than 4 nm are homogenously embedded within HCP matrix, which is encapsulated in macroporous rGO, thereby leading to the double carbon-confined hierarchical composites with strong coupling effect. Experimental data combined with density functional theory calculations reveal that the presence of coupled rGO not only prevents the aggregation and excessive growth of particles, but also expands the lattice parameters of Co 9 S 8 crystals, enhancing the reactivity for sodium storage. Benefiting from the hierarchical porosity, conductive network, structural integrity, and a synergistic effect of the components, the sponge-like composites used as binder-free anodes manifest outstanding sodium-storage performance in terms of excellent stable capacity (628 mAh g −1 after 500 cycles at 300 mA g −1 ) and exceptional rate capability (529, 448, and 330 mAh g −1 at 1600, 3200, and 6400 mA g −1 ). More importantly, the synthetic method is very versatile and can be easily extended to fabricate other transition-metal-sulfides-based sponge-like composites with excellent electrochemical performances.

Fischer–Tropsch synthesis to lower olefins (FTO) opens up a compact and economical way to the production of lower olefin directly from syngas (CO and H2) derived from natural gas, coal, or renewable biomass. The present work is dedicated to a systematic study on the effect of K in the reduced graphene oxide (rGO) supported iron catalysts on the catalytic performance in FTO. It is revealed that the activity, expressed as moles of CO converted to hydrocarbons per gram Fe per second (iron time yield to hydrocarbons, termed as FTY), increased first with the content of K, passed through a maximum at 646 μmolCO gFe –1 s–1 over the FeK1/rGO catalyst, and then decreased at higher K contents. Unlike the evolution of the activity, the selectivity to lower olefins increased steadily with K, giving the highest selectivity to lower olefins of 68% and an olefin/paraffin (O/P) ratio of 11 in the C2–C4 hydrocarbons over the FeK2/rGO catalyst. The volcanic evolution of the activity is attributed to the interplay among the positive effect of K on the formation of Hägg carbide, the active phase for FTO, and the negative roles of K in increasing the size of Hägg carbide at high content and blocking the active phase by K-induced carbon deposition. The monotonic increase in the selectivity to lower olefins is ascribed to the improved chain-growth ability and surface CO/H2 ratio in the presence of K, which favorably suppressed the unwanted CH4 production and secondary hydrogenation of lower olefins.

Lithium-ion batteries (LIBs) have been demonstrated as one of the most promising energy storage devices for applications in electric vehicles, smart grids, large-scale energy storage systems, and portable electronics.