58 research outputs found
Spatially Constrained Organic Diquat Anolyte for Stable Aqueous Flow Batteries
Redox-active organic materials (ROMs) are becoming increasingly attractive for use in redox flow batteries as promising alternatives to traditional inorganic counterparts. However, the reported ROMs are often accompanied by challenges, including poor solubility and stability. Herein, we demonstrate that the commonly used diquat herbicides, with solubilities of >2 M in aqueous electrolytes, can be used as stable anolyte materials in organic flow batteries. When coupled with a ferrocene-derived catholyte, the flow cells with the diquat anolyte demonstrate long galvanic cycling with high capacity retention. Notably, the mechanistic underpinnings of this remarkable stability are attributed to the improved Ď-conjugation that originated from the near-planar molecular conformations of the spatially constrained 2,2â˛-bipyridyl rings, suggesting a viable structural engineering strategy for designing stable organic materials
The lightest organic radical cation for charge storage in redox flow batteries
In advanced electrical grids of the future, electrochemically rechargeable fluids of high energy density will capture the power generated from intermittent sources like solar and wind. To meet this outstanding technological demand there is a need to understand the fundamental limits and interplay of electrochemical potential, stability, and solubility in low-weight redox-active molecules. By generating a combinatorial set of 1,4-dimethoxybenzene derivatives with different arrangements of substituents, we discovered a minimalistic structure that combines exceptional long-term stability in its oxidized form and a record-breaking intrinsic capacity of 161âmAh/g. The nonaqueous redox flow battery has been demonstrated that uses this molecule as a catholyte material and operated stably for 100 charge/discharge cycles. The observed stability trends are rationalized by mechanistic considerations of the reaction pathways.United States. Dept. of Energy. Office of Basic Energy Sciences. Chemical Sciences, Geosciences, & Biosciences Division (Contract DE-AC02-06CH11357
Annulated Dialkoxybenzenes as Catholyte Materials for Nonâaqueous Redox Flow Batteries: Achieving High Chemical Stability through Bicyclic Substitution
1,4âDimethoxybenzene derivatives are materials of choice for use as catholytes in nonâaqueous redox flow batteries, as they exhibit high openâcircuit potentials and excellent electrochemical reversibility. However, chemical stability of these materials in their oxidized form needs to be improved. Disubstitution in the arene ring is used to suppress parasitic reactions of their radical cations, but this does not fully prevent ringâaddition reactions. By incorporating bicyclic substitutions and ether chains into the dialkoxybenzenes, a novel catholyte molecule, 9,10âbis(2âmethoxyethoxy)â1,2,3,4,5,6,7,8âoctahydroâ1,4:5,8âdimethanenoanthracene (BODMA), is obtained and exhibits greater solubility and superior chemical stability in the charged state. A hybrid flow cell containing BODMA is operated for 150 chargeâdischarge cycles with a minimal loss of capacity.A novel bicyclical substituted dialkoxyâbenzene molecule, 9,10âbis(2âmethoxyâethoxy)â1,2,3,4,5,6,7,8âoctahydroâ1,4:5,8âdimethanenoanthracene (BODMA), is developed for use as catholyte materials in nonâaqueous redox flow batteries with greater solubility (in their neutral state) and improved chemical stability (in their charged state). A hybrid flow cell using BODMA demonstrates stable efficiencies and capacity over 150 cycles. The molecular design approach of BODMA can be inspirational for future development of redox active molecules.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139992/1/aenm201701272.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139992/2/aenm201701272-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139992/3/aenm201701272_am.pd
Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li^+ Solvation Structure and LiâS Battery Performance
We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the LiâS battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the LiâS battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)_2âLiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no crossover of polysulfides from the S cathode to the Li anode is observed
Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li^+ Solvation Structure and LiâS Battery Performance
We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the LiâS battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the LiâS battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)_2âLiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no crossover of polysulfides from the S cathode to the Li anode is observed
Comparison of Sugar Molecule Decomposition through Glucose and Fructose: A High-Level Quantum Chemical Study
Efficient chemical conversion of biomass is essential
to produce sustainable energy and industrial chemicals. Industrial
level conversion of glucose to useful chemicals, such as furfural,
hydroxymethylfurfural, and levulinic acid, is a major step in the
biomass conversion but is difficult because of the formation of undesired
products and side reactions. To understand the molecular level reaction
mechanisms involved in the decomposition of glucose and fructose,
we have carried out high-level quantum chemical calculations [Gaussian-4
(G4) theory]. Selective 1,2-dehydration, ketoâenol tautomerization,
isomerization, retro-aldol condensation, and hydride shifts of glucose
and fructose molecules were investigated. Detailed kinetic and thermodynamic
analyses indicate that, for acyclic glucose and fructose molecules,
the dehydration and isomerization require larger activation barriers
compared to the retro-aldol reaction at 298 K in neutral medium. The
retro-aldol reaction results in the formation of C2 and C4 species
from glucose and C3 species from fructose. The formation of the most
stable C3 species, dihydroxyacetone from fructose, is thermodynamically
downhill. The 1,3-hydride shift leads to the cleavage of the CâC
bond in the acyclic species; however, the enthalpy of activation is
significantly higher (50â55 kcal/mol) than that of the retro-aldol
reaction (38 kcal/mol) mainly because of the sterically hindered distorted
four-membered transition state compared to the hexa-membered transition
state in the retro-aldol reaction. Both tautomerization and dehydration
are catalyzed by a water molecule in aqueous medium; however, water
has little effect on the retro-aldol reaction. Isomerization of glucose
to fructose and glyceraldehyde to dihydroxyacetone proceeds through
hydride shifts that require an activation enthalpy of about 40 kcal/mol
at 298 K in water medium. This investigation maps out accurate energetics
of the decomposition of glucose and fructose molecules that is needed
to help find more efficient catalyts for the conversion of hexose
to useful chemicals
Ionic Dynamics of the Charge Carrier in Layered Solid Materials for Mg Rechargeable Batteries
Multivalent-ion batteries have attracted growing attention
due
to their high theoretical energy density that potentially outperforms
Li-ion batteries. One of the critical challenges of realizing a multivalent-ion
battery is the strong polarization that results in the sluggish intercalation
of ions in the host lattice, which motivates a fundamental understanding
of multivalent-ion dynamics in solid-state materials. In this contribution,
we investigate the diffusion mechanisms of divalent ions in a novel
Mg anode coating, BiOCl, using first-principles informed learning-on-the-fly
molecular dynamics. Based on nanosecond-scale dynamics observations,
we gained insights into the concerted diffusion mechanism of Mg cation
site-to-site hopping facilitated by synchronous anion rotational motion.
Furthermore, we compute the Mg-ion diffusion in additional candidate
host structures screened from available layered materials space. The
results suggest the co-operative divalent cationâanion motion
is likely a common phenomenon in layered oxyhalide structures. Our
findings provide a new perspective on how to enhance multivalent-ion
diffusion in layered materials
Exploring MeerweinâPonndorfâVerley Reduction Chemistry for Biomass Catalysis Using a First-Principles Approach
Liquid phase catalytic hydrogenation
of decomposition products
of sugar molecules is challenging, but essential to produce platform
chemicals and green chemicals from biomass. The MeerweinâPonndorfâVerley
(MPV) reduction chemistry is an excellent choice for the hydrogenation
of keto compounds. The energy landscapes for the liquid phase catalytic
hydrogenation of ethyl levulinate (EL) and furfural (FF) by SnÂ(IV)
and ZrÂ(IV) zeolite-like catalytic sites utilizing the hydrogen atoms
from an isopropanol (IPA) solvent are explored using quantum chemical
methods. The computed apparent activation free energy for the catalytic
hydrogenation of EL by a SnÂ(IV) zeolite-like catalyst model site is
(21.9 kcal/mol), which is close to the AlÂ(III)-isopropoxide catalyzed
(20.7 kcal/mol) EL hydrogenation indicating the similar efficiency
of the SnÂ(IV) zeolite-like catalyst compared with the AlÂ(III) catalyst
used in the traditional MPV reactions. The catalytic efficiency of
metal isopropoxides for the catalytic hydrogenation of EL is computed
to be AlÂ(III) > SnÂ(IV) > ZrÂ(IV) in IPA solution, in agreement
with
experiment. Calculations were also performed with furfuryl alcohol
as the source for hydrogen for the conversion of EL to Îł-valerolactone
using the SnÂ(IV) catalytic site. The barrier (22.7 kcal/mol) suggests
a hydrogenation using aromatic primary alcohol as a hydrogen donor
and using a SnÂ(IV) catalyst is feasible. In terms of reaction mechanisms,
an intramolecular hydride transfer through a six membered transition
state was found to be the turnover controlling transition state of
liquid phase catalytic hydrogenation of carbonyl compounds considered
in this study
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