Aqueous rechargeable batteries are desirable for energy storage because of their low cost and high safety. However, low capacity and short cyclic life are significant obstacles to their practical ...applications. Here, we demonstrate a highly reversible aqueous zinc–iodine battery using encapsulated iodine in microporous carbon as the cathode material by controlling solid–liquid conversion reactions. We identified the factors influencing solid–liquid conversion reactions, e.g., the pore size, surface chemistry of carbon host, and solvent effect. Rational manipulation of the competition between the adsorption in carbon and solvation in electrolytes for iodine species is responsible for the high reversibility and cyclic stability. The zinc–iodine battery delivers a high capacity of 174.4 mAh g–1 at 1C, stable cyclic life over 3000 cycles with ∼90% capacity retention, and negligible self-discharge. We believe that the principles for stabilizing the zinc–iodine system could provide new insight for other conversion systems such as lithium–sulfur systems.
NaNO3 and other alkali nitrate salts, which are present in the molten state during use, have been described as facilitators or catalysts for CO2 absorption by both MgO and MgO-containing double ...salts. Although MgO exhibits a high capacity (exceeding 70 wt %), its regenerability in multicycle tests shows a significant loss of capacity with cycle number prior to lining out. On the other hand, the MgO–Na2CO3 double salt shows a lower (∼16 wt %) but stable capacity over multiple cycles under pressure swing operation. The purpose of this paper is to elaborate on the concept of molten salts as catalysts for CO2 absorption by MgO, and extend these observations to the MgO-containing double salt oxides. We will show that the phenomena involved with CO2 absorption by MgO and MgO-based double salts are similar and general, but with some important differences. This paper focuses on the following key concepts: (i) identification of conditions that favor or disfavor participation of isolated MgO during double salt absorption, and investigation of methods to increase the absorption capacity of double salt systems by including MgO participation; (ii) examination of the relationship between CO2 uptake and melting point of the promoter salt, leading to the recognition of the role of premelting (surface melting) in these systems; and (iii) extension of the reaction pathway model developed for the MgO–NaNO3 system to the double salt systems. This information advances our understanding of MgO-based CO2 absorption systems for application with precombustion gas streams.
The charging voltage limits of mixed-carbonate solvents for Li-ion batteries were systematically investigated from 4.9 to 5.3 V in half-cells using Cr-doped spinel cathode material ...LiNi0.45Cr0.05Mn1.5O4. The stability of conventional carbonate electrolytes is strongly related to the stability and properties of the cathode materials in the de-lithiated state. This is the first time report that the conventional electrolytes based on mixtures of EC and linear carbonate (DMC, EMC and DEC) can be cycled up to 5.2 V on LiNi0.45Cr0.05Mn1.5O4 for long-term cycling, where their performances are similar. The discharge capacity increases with the charging cutoff voltage and reaches the highest discharge capacity at 5.2 V. The capacity retention is about 87% after 500 cycles at 1C rate for all three carbonate mixtures in half-cells when cycled between 3.0 V and 5.2 V. When cycled to 5.3 V, EC-DMC still shows good cycling performance but EC-EMC and EC-DEC show faster capacity fading. EC-DMC and EC-EMC have much better rate capability than EC-DEC. The first-cycle irreversible capacity loss increases with the cutoff voltage. The “inactive” conductive carbon is also partly associated with the low first-cycle Coulombic efficiency at high voltages due to electrolyte decomposition and possible PF6- anion irreversible intercalation.
► Stability of carbonate electrolytes is strongly related to cathode materials. ► Carbonate electrolytes are stable up to 5.2 V on LiNi0.45Cr0.05Mn1.5O4 cathode. ► 87% capacity retention after 500 cycles at 1C rate is obtained in half-cells. ► EC-DMC and EC-EMC have better rate capability than EC-DEC. ► First-cycle irreversible capacity loss is partly related to conductive carbons.
The stability of various polymer binders was systematically investigated in the oxygen-rich environment required for the operation of Li–O2 batteries. Due to the coverage on air electrode surface by ...the discharge products and decomposition products of the electrolyte during the discharge process of Li–O2 batteries, the binder in the air electrode is hard to be detected making the evaluation of its stability problematic. Therefore, stability of the binder polymers against the reduced oxygen species generated during the discharge process was investigated by ball milling the polymers with KO2 and Li2O2, respectively. Most of the studied polymers are unstable under these conditions and their decomposition mechanisms are proposed according to the analyzed products. Polyethylene was found to exhibit excellent stability when exposed to superoxide and peroxide species and is suggested as a robust binder for air electrodes. In addition, the binding strength of the polymer significantly affects the discharge performance of Li–O2 batteries.
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•Various polymer binders were investigated in Li–O2 battery environment.•Discharge capacity depends on binding strength and current density.•Vinyl- and vinylidene-based polymers decompose by nucleophilic elimination.•Carbonyl-containing polymers decompose to carbonates.•Polyolefins and polytetrafluoroethylene are relatively stable.
The discontinuation of the bulk structure at the interface between metal oxide particles and water leads to altered bonding characteristics and unique facet-dependent molecular environments. Surface ...hydration and hydroxylation add further complexity to the interface, details that for metal (oxy)hydroxides are especially difficult to isolate from the background signal of bulk structural hydroxyls. Here, we probe for the first time the surface hydroxyl structures and the effect of hydration on basal surfaces of gibbsite (α-Al(OH)3) and boehmite (γ-AlOOH) nanoplates under ambient conditions, using the interface-sensitive technique vibrational sum frequency generation (VSFG) spectroscopy. VSFG spectra of the hydroxyl stretching modes at the interfaces with adsorbed water layers compared directly to Raman and infrared spectra of the bulk modes show that while gibbsite surface frequencies were sharp and nearly identical to those in the bulk, boehmite surface hydroxyls displayed a very different broad spectrum of states. Ab initio molecular dynamics simulations of both basal surfaces with and without hydration waters reveal that gibbsite surface hydroxyls interact only weakly with overlying hydration waters remaining essentially unperturbed, whereas those on boehmite can interact more strongly facilitated by higher configurational degrees of freedom at the interface and there is more extensive H-bonding on boehmite surface under ambient conditions. The findings clearly unveil substantial differences in the hydrated interfacial dynamics of these two otherwise similar materials, with implications for their interfacial chemistry, wettability, and rheology.
Dendrimer‐encapsulated ruthenium oxide nanoparticles (DEN‐RuO2) have been used as catalysts in lithium‐oxygen (Li‐O2) batteries for the first time. The results obtained from ultraviolet‐visible ...spectroscopy, electron microscopy and X‐ray photoelectron spectroscopy show that the nanoparticles synthesized by the dendrimer template method are ruthenium oxide, not metallic ruthenium as reported by other groups. The DEN‐RuO2 significantly improves the cycling stability of Li‐O2 batteries with carbon electrodes and decreases the charging potential even at ten times less catalyst loading than those reported previously. The monodispersity, porosity, and large number of surface functionalities of the dendrimer template prevent the aggregation of the RuO2 nanoparticles, making their entire surface area available for catalysis. The potential of using DEN‐RuO2 as a standalone cathode material for Li‐O2 batteries is also explored.
Dendrimer‐encapsulated ruthenium nanoparticles are readily oxidized to RuO2 when exposed to ambient conditions. These nanoparticles are used as catalysts in Li‐O2 batteries, which exhibited improved cycling thus suggesting that porous dendrimer‐encapsulated nanoparticles can be used to achieve superior performance in energy storage systems.
Warm (250–450 °C) cleanup of coal- or biomass-derived syngas requires sorbents and catalysts to protect downstream conversions. We report first a sequential ZnO bed operation in which the capacity is ...optimized for bulk desulfurization at 450 °C, while subsequent removal of sulfur to parts-per-billion levels can be accomplished at a lower temperature of approximately 300 °C. At this temperature, gaseous sulfur (H2S and COS) could be adsorbed equally well using ZnO, both with and without the presence of H2O in the feed, suggesting direct absorption of COS can occur. Following five sulfidation and regeneration cycles, the bulk desulfurization bed lost about a third of its initial sulfur capacity; however, sorbent capacity stabilized. A bench-scale process consisting of five unit operations is described for the cleanup of a several contaminants in addition to sulfur. Syngas cleanup was demonstrated through successful long-term performance of a poison-sensitive Cu-based water-gas shift catalyst placed downstream of the cleanup process train. The process removed 99+% of the sulfur; however, improvements can be made toward full regenerability of the ZnO bed and with complete elimination of sulfur slip through the guard beds. The use of a tar reformer was found to be an important and necessary operation with this particular gasification system; its inclusion provided the difference between deactivating the water-gas catalyst through carbon deposition and having a largely successful 100 h test using 1 LPM of coal-derived syngas.
Aerogels employing chalcogen-based (
i.e.
, S, Se, and/or Te) structural units and interlinking metals are termed chalcogels and have many emerging applications. Here, chalcogels are discussed in the ...context of nuclear fuel reprocessing and radioactive waste remediation. Motivated by previous work on removal of heavy metals in aqueous solution, we explored the application of germanium sulfide chalcogels as a sorbent for gas-phase I
2
based on Pearson's Hard/Soft Acid-Base (HSAB) principle. This work was driven by a significant need for high-efficiency sorbents for
129
I, a long-lived isotope evolved during irradiated UO
2
nuclear fuel reprocessing. These chalcogel compositions are shown to possess an affinity for iodine gas, I
2
(g), at various concentrations in air. This affinity is attributed to a strong chemical attraction between the chalcogen and I
2
(g), according to the HSAB principle. The high sorption efficiency is facilitated by the high porosity as well as the exceptionally large surface area of the chalcogels. This paper briefly discusses the current and alternative waste forms for
129
I, elaborates on preliminary work to evaluate a Pt-Ge-S chalcogel as a I
2
(g) sorbent, and discusses the unknown chalcogel properties related to these materials in waste form.
Here we discuss the evaluation of chalcogenide-based aerogels as a potential sorbent for
129
I evolved from nuclear fuel reprocessing.
The catalytic activity of poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated during oxygen reduction/evolution reactions in Li–O2 batteries. PEDOT was prepared by in situ chemical ...polymerization of 3,4-ethylenedioxythiophene monomer in carbon matrix. PEDOT significantly reduces the overvoltage of the charging process in a Li–O2 battery. The electrocatalytic effect of PEDOT can be attributed to its redox activity. Apparently, PEDOT acts as a mediator in electron transfer during discharge and charge processes.
► PEDOT was prepared by in situ chemical polymerization in carbon matrix. ► PEDOT has electrocatalytic effect toward oxygen reduction/evolution reactions. ► PEDOT significantly reduces the over-voltage during charging in a Li–O2 battery. ► The electrocatalytic effect of PEDOT can be attributed to its redox activity.
