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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Effective Storage of Electrons in Water by the Formation of Highly Reduced Polyoxometalate Clusters

Aqueous solutions of polyoxometalates (POMs) have been shown to have potential as high-capacity energy storage materials due to their potential for multi-electron redox processes, yet the mechanism of reduction and practical limits are currently unknown. Herein, we explore the mechanism of multi-electron redox processes that allow the highly reduced POM clusters of the form {MO 3 } y to absorb y electrons in aqueous solution, focusing mechanistically on the Wells-Dawson structure X 6 [P 2 W 18 O 62 ], which comprises 18 metal centers and can uptake up to 18 electrons reversibly (y = 18) per cluster in aqueous solution when the countercations are lithium. This unconventional redox activity is rationalized by density functional theory, molecular dynamics simulations, UV-vis, electron paramagnetic resonance spectroscopy, and small-angle X-ray scattering spectra. These data point to a new phenomenon showing that cluster protonation and aggregation allow the formation of highly electron-rich meta-stable systems in aqueous solution, which produce H 2 when the solution is diluted. Finally, we show that this understanding is transferrable to other salts of [P 5 W 30 O 110 ] 15- and [P 8 W 48 O 184 ] 40- anions, which can be charged to 23 and 27 electrons per cluster, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1991

Ferredoxin and ferredoxin-NADP reductase from photosynthetic and nonphotosynthetic tissues of tomato

Ferredoxin and ferredoxin-NADP+ oxidoreductase (FNR) were purified from leaves, roots, and red and green pericarp of tomato (Lycopersicon esculentum, cv VFNT and cv Momotaro). Four different ferredoxins were identified on the basis of N-terminal amino acid sequence and charge. Ferredoxins I and II were the most prevalent forms in leaves and green pericarp, and ferredoxin III was the most prevalent in roots. Red pericarp of the VFNT cv yielded variable amounts of ferredoxins II and III plus a unique form, ferredoxin IV. Red pericarp of the Momotaro cv contained ferredoxins I, II, and IV. This represents the first demonstration of ferredoxin in a chromoplast-containing tissue. There were no major differences among the tomato ferredoxins in absorption spectrum or cytochrome c reduction activity. Two forms of FNR were present in tomato as judged by anion exchange chromatography and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. FNR II had a lower apparent relative molecular weight, a slightly altered absorption spectrum, and a lower specific activity for cytochrome c reduction than FNR I. FNR II could be a partially degraded form of FNR I. The FNRs from the different tissues of tomato plants all showed diaphorase activity, with FNR II being more active than FNR I. The presence of ferredoxin and FNR in heterotrophic tissues of tomato is consistent with the existence of a nonphotosynthetic ferredoxin/FNR redox pathway to support the function of ferredoxin-dependent enzymes.

NASA Discipline Number 52-30↗
DOE OSTI2025

The influence of protein electrostatics on potential inversion in flavoproteins

Biology uses relatively few electron-transfer cofactors, tuning their potentials, electronic couplings, and reorganization energies to carry out the required chemistry. It is remarkable that the potential ordering of two-electron transfer active flavins can be normal (first oxidation at low potential and second oxidation at high potential) or inverted, and the gap between the potentials can be as large as one volt. Analysis based on structural bioinformatics and electrostatics indicates that the ordering of the flavin redox potential is influenced by protein electrostatics. In all 36 flavoproteins examined, the introduction of a negative charge near the flavin in silico increases the extent of potential inversion (by lowering the electrochemical potential of the second electron-transfer step); the introduction of a positive charge near the flavin favors normally ordered potentials. We also find that the addition of positive charges increases the electrochemical potential for the naturally occurring one-electron transition in flavodoxins (between deprotonated hydroquinone and neutral semiquinone) and also increases the second one-electron transition in bifurcating flavins (between anionic semiquinone and fully oxidized flavin). Finally, we find that proximity of a proton acceptor, notably conserved arginine, supports proton-coupled electron transfer because it may act as a proton acceptor, promoting potential inversion. This key arginine residue may enable two-electron transfer chemistry by promoting the proton-coupled electron transfer process over the pure electron transfer process, suggesting how a protein's flavin environment may influence one- or two-electron chemistry in flavoproteins.

Singh, Niven [Duke Univ., Durham, NC (United State↗
DOE OSTI2020

Effect of TiO x Substrate Interactions on the Electrocatalytic Oxygen Reduction Reaction at Au Nanoparticles

Here, we report a robust model for studying electrocatalytic reactions at metal nanoparticles (NPs) in contact with metal oxide surfaces. The metal oxide layer (TiO x ) is prepared by atomic layer deposition, and it is sufficiently thin that it does not hinder electron transfer from the underlying conductive electrode to the supported AuNP electrocatalysts. In advance of the experiments, density functional theory (DFT) predicted that direct contact between AuNPs and TiO x would lead to enhanced activity for the oxygen reduction reaction (ORR). DFT attributes the observed ORR enhancement to partial charge transfer from oxygen vacancies within the TiO x film to the supported AuNPs and hence formation of anionic Au species. The experimental findings are in near quantitative agreement with the DFT results. Specifically, compared to isolated AuNPs, decreases of ~ 100 and ~ 50 mV in the ORR onset potential are observed experimentally for AuNPs supported on TiO 1.9 and TiO 2.0 films, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Treyson Ricks - Intern Showcase Poster

Quinone-based sorbents offer a tunable, energy-efficient route to electrochemical CO2 capture, but systematic guidance for molecular design is lacking. Here, we report a high-throughput computational workflow that combines density functional theory (DFT) screening with machine-learning (ML) modeling to evaluate CO2 binding thermodynamics across several quinone derivatives, spanning benzoquinones, naphthoquinones, and anthraquinones. In addition to using solvents to stabilize the quinone anion and dianion, we studied the effect of ion-pairing on the reduction potentials and the CO2 binding energy. Automated Python scripts handled geometry optimizations and adduct-formation energies on an HPC cluster, reducing manual effort significantly. This integrated platform can uncover structure–property relationships and enables rapid in silico evaluation of untested candidates. We present one example from our workflow to showcase the capability of using quinones with ion-pairing to effectively capture CO2. Our approach paves the way for the rational selection of optimal quinone sorbents and can be extended with experimental thermochemical and kinetic data, alternative redox cycles, and stability assessments to accelerate development of next-generation electrochemical CO2 capture materials.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2023

Impact of iodide ions on the speciation of radiolytic transients in molten LiCl–KCl eutectic salt mixtures

The fate of fission-product iodine is critical for the deployment of next generation molten salt reactor technologies, owing to its volatility and biological impacts if it were to be released into the environment. To date, little is known on how ionizing radiation fields influence the redox chemistry, speciation, and transport of iodine in high temperature molten salts. Here we employ picosecond electron pulse irradiation techniques to elucidate for the first time the impact of iodide ions (I – ) on the speciation and chemical kinetics of the primary radiation-induced transient radicals generated in molten chloride salt mixtures (e S – and Cl 2 ˙– ) as a function of temperature (400–700 °C). In the presence of I – ions (≥ 1 wt% KI in LiCl–KCl eutectic), we find that the transient spectrum following the electron pulse is composed of at least three overlapping species: the e S – and the Cl 2 ˙– and ICl ˙– radical anions, for which a deconvoluted spectrum of the latter is reported here for the first time in molten salts. This new transient spectrum was consistent with gas phase density functional theory calculations. The lifetime of the e S – was unaffected by the addition of I – ions. The newly observed interhalogen radical anion, ICl˙ – , exhibited a lifetime on the order of microseconds over the investigated temperature range. The associated chemical kinetics indicate that the predominate mechanism of ICl˙ – decay is via reaction with the Cl 2 ˙– radical anion. The iodine containing product of this reaction is expected to be ICl 2 – , which will have implications for the transport of fission-product iodine in MSR technologies.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Pu(VI) Oxalate Crystal Structure and Evidence of Photoreduction to Pu(IV) Oxalate

We report the first crystal structure of a Pu(VI)-oxalate compound. This compound, [PuO 2 (C 2 O 4 )(H 2 O)]·2(H 2 O) (1), crystallizes in space group P21/c with a = 5.5993(3) Å, b = 16.8797(12) Å, c = 9.3886(6) Å, and β = 98.713(6)°. It is isostructural with the previously reported U(VI) compound, [UO 2 (C 2 O 4 )(H 2 O)]·2(H 2 O). Each plutonyl ion (PuO 2 2+ ) is coordinated in the equatorial plane by two side-on bidentate oxalates, creating an infinite chain along [001]. A coordinated water molecule and twisting of the oxalates lead to a distorted pentagonal bipyramidal geometry of the Pu. A photochemical degradation was observed for 1, which resulted in the formation of a secondary crystalline phase. The absorption spectrum of this secondary phase confirmed the presence of Pu(IV), but it did not match the spectrum of Pu(C 2 O 4 ) 2 ·6H 2 O, which is considered to be the primary product of Pu-oxalate precipitation. While compound 1 has previously been proposed to exist in solution, this is the first time it has been isolated via crystallization. Although redox interactions between Pu and oxalate have been documented in the literature, the present study is the first observation of a photochemical reduction of Pu(VI)-oxalate. Finally, this study has expanded on the limited understanding of the Pu(VI)-oxalate system, which is important for nuclear fuel cycle applications.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Kinetics of Radiation-induced Cr( II ) and Cr( III ) Redox Chemistry in Molten LiCl-KCl Eutectic

Chromium (Cr) is a frequent constituent of the metal alloys proposed for molten salt nuclear reactor (MSR) applications, and is typically the least noble metal ion present. Consequently, chromium is preferentially corroded into molten salt solutions. Here, the redox poise and redox cycling of chromium ions in the salt can greatly influence its corrosivity towards structural alloys, ultimately impacting the longevity of MSR systems. Radiation-induced chemistry is expected to play a significant role in determining the chromium oxidation state distribution during MSR operations. In the present research, electron pulse radiolysis techniques were employed to characterize the reactivity of Cr(II) and Cr(III) ions with primary radiolysis products in molten lithium chloride–potassium chloride (LiCl–KCl) eutectic over a temperature range of 400–600 °C. Both chromium oxidation states were found to rapidly react with the primary products of molten chloride salt radiolysis, i.e., the solvated electron (e S - ) and the dichlorine radical anion (Cl 2 ˙ - ). For reactions with the e S - , second-order rate coefficients (k) of k = (4.1 ± 0.2) and (6.1 ± 0.3) × 10 10 M -1 s -1 at 400 °C for Cr(II) and Cr(III), respectively, were determined. Temperature-dependent measurements allowed for the derivation of activation parameters for electron capture by Cr(II) and Cr(III). Both chromium ions also react with Cl 2 ˙ - , k = (7.2 ± 0.3) and (1.4 ± 0.1) × 10 9 M -1 s -1 at 400 °C for Cr(II) and Cr(III), respectively.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2020

Determination of the N–H Bond Dissociation Free Energy in a Pyridine(diimine)molybdenum Complex Prepared by Proton-Coupled Electron Transfer

The pyridine(diimine) molybdenum bis(imido) complex, ( iPr PDI)Mo(=NTol) 2 (Tol = 4-methylphenyl) was synthesized by addition of two equivalents of 4-methylphenylazide to a corresponding molybdenum benzene derivative, ( iPr PDI)Mo(η 6 -C 6 H 6 ) ( iPr PDI = 2,6-(2,6-iPr 2 C 6 H 3 N=CMe) 2 C 5 H 3 N). Protonation of ( iPr PDI)Mo(=NTol) 2 with 2,6-lutinidum triflate yielded a cationic molybdenum amido complex, [( iPr PDI)Mo(NHTol)(=NTol)][OTf], which was further transformed into the neutral molybdenum amido complex, ( iPr PDI)Mo(NHTol)(=NTol) by reduction with zinc powder. A series of spectroscopic, synthetic and pK a determination studies along with electrochemical measurements by the protonation-reduction pathway were used to establish an N–H bond dissociation free energy (BDFE) between 65-69 kcal/mol for the molybdenum imido-amido compound, ( iPr PDI)Mo(NHTol)(=NTol). Full molecule DFT studies provided a computed value of 61 kcal/mol. By contrast, reduction of ( iPr PDI)Mo(=NTol) 2 with KC 8 afforded the corresponding anionic molybdenum complex, K[( iPr PDI)Mo(=NTol) 2 ] that has a potassium cation intercalated with the pyridine and the tolyl groups. Protonation of K[( iPr PDI)Mo(=NTol) 2 ] with the weak amidinium acids [TBD(H)][BArF 24 ] (TBD = triazabicyclodecene, BArF 24 = B[3,5-(CF 3 ) 2 C 6 H 3 ] 4 ) also produced the neutral molybdenum amido complex, ( iPr PDI)Mo(NHTol)(=NTol). Measurement of the pKa and oxidation potential of K[( iPr PDI)Mo(=NTol) 2 ] provided a range of 69-73 kcal/mol for the N–H BDFE of ( iPr PDI)Mo(NHTol)(=NTol), in good agreement with the protonation-reduction route and completing the square scheme. The similar pK a and redox potentials obtained from each pathway demonstrate that both sequences are energetically feasible for PCET events. This study on the determination of N–H BDFE of the molybdenum amido complex renders fundamental insight into the N 2 reduction cycle by proton-coupled electron transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Regulating the Third Metal to Design and Engineer Multilayered NiFeM (M: Co, Mn, and Cu) Nanofoam Anode Catalysts for Anion-Exchange Membrane Water Electrolyzers

In this study, alkaline anion-exchange membrane water electrolyzers (AEMWEs) for green hydrogen production have received intensive attention due to their feasibility of using earth-abundant platinum group metal (PGM)-free catalysts. Herein, the third metal is incorporated into NiFe-based catalysts to regulate their electronic structures and morphologies, aiming to achieve sufficient oxygen evolution reaction (OER) activity and performance in AEMWEs. The ternary NiFeM (M: Cu, Co, or Mn) catalysts are featured with multiple layered structures and nanofoam network morphologies, consisting of highly OER-active amorphous Ni-rich oxide shells and electrically conductive metallic alloy cores. The physical and electronic perturbations to the NiFe induced by a third element lead to a fine-tuning of the redox ability of the metal sites at the reaction centers, which breaks the scaling relationship between OH* and O* intermediates at the reaction centers. Thus, the unique structural configuration and electronic regulation simultaneously benefit catalytic activity and performance improvements. These NiFeM nanofoam catalysts demonstrated promising anode performance in actual AEMWEs, comparable to the IrO 2 reference, especially at high current densities. Notably, using various electrolytes (e.g., KOH solution or pure water) for AEMWEs exhibited a different performance trend among studied NiFeM catalysts, likely due to dynamic changes of catalysts under various OER environments.

25 ENERGY STORAGE↗
DOE OSTI2023

Understanding the mechanisms of anisotropic dissolution in metal oxides by applying radiolysis simulations to liquid-phase TEM

Iron-based redox-active minerals are ubiquitous in soils, sediments, and aquatic systems. Their dissolution is of great importance for microbial impacts on carbon cycling and the biogeochemistry of the lithosphere and hydrosphere. Despite its widespread significance and extensive prior study, the atomic-to-nanoscale mechanisms of dissolution remain poorly understood, particularly the interplay between acidic and reductive processes. Here, we use in situ liquid-phase-transmission electron microscopy (LP-TEM) and simulations of radiolysis to probe and control acidic versus reductive dissolution of akaganeite (β–FeOOH) nanorods. Informed by crystal structure and surface chemistry, the balance between acidic dissolution at rod tips and reductive dissolution at rod sides was systematically varied using pH buffers, background chloride anions, and electron beam dose. We find that buffers, such as bis-tris, effectively inhibited dissolution by consuming radiolytic acidic and reducing species such as superoxides and aqueous electrons. In contrast, chloride anions simultaneously suppressed dissolution at rod tips by stabilizing structural elements while promoting dissolution at rod sides through surface complexation. Dissolution behaviors were systematically varied by shifting the balance between acidic and reductive attacks. The findings show LP-TEM combined with simulations of radiolysis effects can provide a unique and versatile platform for quantitatively investigating dissolution mechanisms, with implications for understanding metal cycling in natural environments and the development of tailored nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Oxidative Addition of Aryl Halides to a Ni(I)-Bipyridine Complex

The oxidative addition of aryl halides to bipyridine- or phenanthroline-ligated nickel(I) is a commonly proposed step in nickel catalysis. However, there is a scarcity of complexes of this type that both are well-defined and undergo oxidative addition with aryl halides, hampering organometallic studies of this process. Here, we report the synthesis of a well-defined Ni(I) complex, [( CO 2 Et bpy)Ni I Cl] 4 . Its solution-phase speciation is characterized by a significant population of monomer and a redox equilibrium that can be perturbed by π-acceptors and σ-donors. 1 reacts readily with aryl bromides, and mechanistic studies are consistent with a pathway proceeding through an initial Ni(I) → Ni(III) oxidative addition to form a Ni(III) aryl species. Such a process was demonstrated stoichiometrically for the first time, affording a structurally characterized Ni(III) aryl complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Radiation‐Induced Defects in Uranyl Trinitrate Solids

Abstract Actinides are inherently radioactive; thus, ionizing radiation is emitted by these elements can have profound effects on its surrounding chemical environment through the formation of free radical species. While previous work has noted that the presence of free radicals in the system impacts the redox state of the actinides, there is little atomistic understanding of how these metal cations interact with free radicals. Herein, we explore the effects of radiation (UV and γ) on three U(VI) trinitrate complexes, M[UO 2 (NO 3 ) 3 ] (where M=K + , Rb + , Cs + ), and their respective nitrate salts in the solid state via electron paramagnetic resonance (EPR) and Raman spectroscopy paired with Density Functional Theory (DFT) methods. We find that the alkali salts form nitrate radicals under UV and γ irradiation, but also note the presence of additional degradation products. M[UO 2 (NO 3 ) 3 ] solids also form nitrate radicals and additional DFT calculations indicate the species corresponds to a change from the bidentate bound nitrate anion into a monodentate NO 3 • radical. Computational studies also highlight the need to include the second sphere coordination environment around the [UO 2 (NO 3 ) 3 ] 0,1 species to gain agreement between the experimental and predicted EPR signatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A System Engineering Approach in the Analysis of Ionic Liquids Properties [Thesis]

Room temperature ionic liquids (RTIL) are ionic compounds, comprised of a cation and anion, in the liquid state at temperatures below 100 ⁰C. There are estimated 10 18 anion and cation combinations, which can create RTILs with unique properties. While the ionic character of RTILs made them attractive in a wide variety of electrochemical applications, their behaviors under electrochemical conditions are not well understood. In this research, we developed a RTIL testbed to investigate how RTILs differ from molecular solvents and electrolytes in electrochemical systems through the study of the effects of their morphology and chemical properties on the electron transfer processes. The test bed is composed of three modules: Electrochemistry, Material characterization, Computational. All modules have been completely developed, verified, and integrated and two of them, i.e., Electrochemistry and Material characterization have been validated in this dissertation. To evaluate the proposed system, experiments were performed on solutions of a redox active species in RTILs. It was found that it is possible to investigate the RTIL's morphology and chemical properties' impact on the electron transfer processes of the solute based on the outcomes and evaluations of tests performed by the RTIL testbed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Poly(vinylferrocene) as an Ionomer and Sulfur-Confining Additive for Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising owing to their high energy density, environmental benignity, and low cost. Most of the commonly used binders in Li-S battery cathodes are inert and have no significant effect on the challenges of sulfur as a cathode material, such as the polysulfide shuttle effect, low ionic/electronic conductivity, and a sluggish redox reaction. In this work, we demonstrate the use of poly(vinylferrocene) (PvFc) as a binder additive that can effectively increase the ionic conductivity of the cathode and act as a sulfide confining agent. Electrochemical tests performed with PvFc as part of the binder mixture used to cast the cathodes demonstrate an increase in rate capability and cycle life when compared to the baseline samples. Ionic conductivity measurements and X-ray photoelectron spectroscopy suggest that the π-cation molecular interaction between the cyclopentadienyl rings from ferrocene and Li + act like an ion couple with ferrocene acting as a static, covalently bound acceptor of Li + ions that enhances their mobility through the cathode. This coupled with the affinity between the ferrocenyl cations and the Li salt anions, which provides more distribution of counterions for Li + movement and improves accessibility to the cathode S reservoir, make PvFc a promising ionomer for Li-S batteries. In addition, the π-cation bonds between cyclopentadienyl and lithium polysulfides produce a sulfide confining effect that mitigates capacity fade through polysulfide dissolution. Furthermore, this work demonstrates an expansion in the utility of PvFc as a component in Li-ion batteries, which so far is mostly limited to use as an active material in organometallic batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

Rh → Sb Interactions Supported by Tris(8-quinolyl)antimony Ligands

The study of ambiphilic systems combining L-type and Z-type ligands within the same construct has emerged as a field of active investigation, especially in the cases of ligands containing a group 13 element as a σ-acceptor for transition metals. (1) Parallel to these developments, several groups have investigated more atypical systems in which the Z-type ligand is a group 15 element. (2) Our contributions to this area have focused on the use of phosphinostibine ligands for the generation of transition metal complexes in which the antimony moiety acts as a Z-type ligand. (1d,3) We have shown that the magnitude of the resulting M → Sb interaction can be readily modulated by the oxidation state of the antimony atom (4) as well as its charge which can be manipulated by abstraction of anionic ligands. (5) Our work has also shown that these effects can be leveraged to enhance the catalytic properties of the transition metal center. (4,5) Some of the simplest systems that we have investigated are those resulting from the reaction of platinum dichloride with the bis- or tris-phosphinostibines ClSb(o-dppp) 2 and Sb(o-dppp) 3 , respectively (o-dppp = o-(Ph 2 P)C 6 H 4 ). These reactions proceed by oxidative insertion of the stibine into a Pt- Cl bond to produce complexes A and B, (6) respectively (Chart 1). Reasoning that the properties of these complexes may also be influenced by the nature of the L-type buttresses, we have now questioned whether stibines featuring nitrogen donor ligands could also display the redox noninnocence of their phosphine counterparts and support the formation of such complexes. Following up on some of our work with ambiphilic tellurium-quinoline ligands, (7) we now report on the reaction of tris-(8-quinolyl)stibines (8) toward (MeCN) 3 RhCl 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Semiconducting Zn x Mo 3 S 13 -GO Chalcocarbogel: A High-Capacity and Stable Sulfur-Equivalent Conversion-Based Electrode for Lithium-Ion Batteries

Lithium–sulfur batteries with a sulfur electrode offer a theoretical capacity of ∼1672 mAh g –1 , but rapid capacity loss mainly constrains their practical application. This work introduces a semiconducting and amorphous Zn x Mo 3 S 13 -GO (x = 0.5) chalcocarbogel sulfur-equivalent electrode with superior capacity and stability for lithium-ion batteries (LIBs). The Zn x Mo 3 S 13 -GO is synthesized in solution under ambient conditions, and its local structure contains S–S, M-Q (M = Mo, Zn; Q = S, O), C–S, and Mo–Mo bonding motifs with Mo coordination environment closely related to Mo 3 S 13 anions, as determined by X-ray photoelectron spectroscopy, synchrotron X-ray scattering, X-ray absorption spectroscopy, and ab initio molecular dynamics simulations. The Li/Zn x Mo 3 S 13 -GO cell offers an initial discharge capacity of 1019 mAh g –1 at a rate of C/3. After the activation cycles, the Li/Zn x Mo 3 S 13 -GO cell demonstrates good cycling stability, retaining a discharge capacity of 519.4 mAh g –1 after 250 cycles with ∼99.98% Coulombic efficiency and excellent rate capabilities. Moreover, it provides an initial discharge capacity of ∼574 mAh g –1 and maintains a retention capacity of 279 mAh g –1 at 1C after 625 cycles. The Lewis acidic Zn 2+ ion enhances the Lewis basic polysulfide anchoring ability and reduces the dissolution of polysulfides produced during the redox process through Zn–S covalent interaction, while the semiconducting and amorphous structure of the chalcocarbogel increases the electrical and ionic conductivity. Furthermore, this work highlights chalcocarbogels’ potential for developing high-capacity and stable electrodes for LIBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Potential-induced wetting and dewetting in pH-responsive block copolymer membranes for mass transport control

Wetting and dewetting behavior in channel-confined hydrophobic volumes is used in biological membranes to effect selective ion/molecular transport. Artificial biomimetic hydrophobic nanopores have been devised utilizing wetting and dewetting, however, tunable mass transport control utilizing multiple transport modes is required for applications such as controllable release/transport, water separation/purification and energy conversion. Here, we investigate the potential-induced wetting and dewetting behavior in a pH-responsive membrane composed of a polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) when fabricated as a hierarchically-organized sandwich structure on a nanopore electrode array (NEA), i.e. BCP@NEA. At pH < pK a (P4VP) (pK a ~ 4.8), the BCP acts as an anion-exchange membrane due to the hydrophilic, protonated P4VP cylindrical nanodomains, but at pH > pK a (P4VP), the P4VP domains exhibit charge-neutral, hydrophobic and collapsed structures, blocking mass transport via the hydrophobic membrane. However, when originally prepared in a dewetted condition, mass transport in the BCP membrane may be switched on if sufficiently negative potentials are applied to the BCP@NEA architecture. When the hydrophobic BCP membrane is introduced on top of 2-electrode-embedded nanopore arrays, electrolyte solution in the nanopores is introduced, then isolated, by exploiting the potential-induced wetting and dewetting transitions in the BCP membrane. The potential-induced wetting/dewetting transition and the effect on cyclic voltammetry in the BCP@NEA structures is characterized as a function of the potential, pH and ionic strength. Additionally chronoamperometry and redox cycling experiments are used to further characterize the potential response. The multi-modal mass transport system proposed in this work will be useful for ultrasensitive sensing and single-molecule studies, which require long-time monitoring to explore reaction dynamics as well as molecular heterogeneity in nanoconfined volumes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗