RESUMEN
Aqueous zinc-ion batteries (ZIBs) employing zinc metal anodes are gaining traction as batteries for moderate to long duration energy storage at scale. However, corrosion of the zinc metal anode through reaction with water limits battery efficiency. Much research in the past few years has focused on additives that decrease hydrogen evolution, but the precise mechanisms by which this takes place are often understudied and remain unclear. In this work, we study the role of an acetonitrile antisolvent additive in improving the performance of aqueous ZnSO4 electrolytes using experimental and computational techniques. We demonstrate that acetonitrile actively modifies the interfacial chemistry during Zn metal plating, which results in improved performance of acetonitrile-containing electrolytes. Collectively, this work demonstrates the effectiveness of solvent additive systems in battery performance and durability and provides a new framework for future efforts to optimize ion transport and performance in ZIBs.
RESUMEN
Composite polymer electrolytes (CPEs) are attractive materials for solid-state lithium metal batteries, owing to their high ionic conductivity from ceramic ionic conductors and flexibility from polymer components. As with all lithium metal batteries, however, CPEs face the challenge of dendrite formation and propagation. Not only does this lower the critical current density (CCD) before cell shorting, but the uncontrolled growth of lithium deposits may limit Coulombic efficiency (CE) by creating dead lithium. Here, we present a fundamental study on how the ceramic components of CPEs influence these characteristics. CPE membranes based on poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (PEO-LiTFSI) with Li7La3Zr2O12 (LLZO) nanofibers were fabricated with industrially relevant roll-to-roll manufacturing techniques. Galvanostatic cycling with lithium symmetric cells shows that the CCD can be tripled by including 50 wt % LLZO, but half-cell cycling reveals that this comes at the cost of CE. Varying the LLZO loading shows that even a small amount of LLZO drastically lowers the CE, from 88% at 0 wt % LLZO to 77% at just 2 wt % LLZO. Mesoscale modeling reveals that the increase in CCD cannot be explained by an increase in the macroscopic or microscopic stiffness of the electrolyte; only the microstructure of the LLZO nanofibers in the PEO-LiTFSI matrix slows dendrite growth by presenting physical barriers that the dendrites must push or grow around. This tortuous lithium growth mechanism around the LLZO is corroborated with mass spectrometry imaging. This work highlights important elements to consider in the design of CPEs for high-efficiency lithium metal batteries.
RESUMEN
We synthesized Li and Na monocarborate salts with minimal protic impurities and reassessed their electrochemical windows. Na salts display higher efficiency for metal deposition/stripping and are more oxidatively stable than Li salts. This strong cation effect is rationalized in terms of differences in charge density between Li+ and Na+ cations.
RESUMEN
The rechargeable lithium-oxygen (Li-O2) battery has the highest theoretical specific energy density of any rechargeable batteries and could transform energy storage systems if a practical device could be attained. However, among numerous challenges, which are all interconnected, are polarization due to sluggish kinetics, low cycle life, small capacity, and slow rates. In this study, we report on use of KMnO4 to generate a colloidal electrolyte made up of MnO2 nanoparticles. The resulting electrolyte provides a redox mediator for reducing the charge potential and lithium anode protection to increase cycle life. This electrolyte in combination with a stable binary transition metal dichalcogenide alloy, Nb0.5Ta0.5S2, as the cathode enables the operation of a Li-O2 battery at a current density of 1 mA·cm-2 and specific capacity ranging from 1000 to 10â¯000 mA·h·g-1 (corresponding to 0.1-1 mA·h·cm-2) in a dry air environment with a cycle life of up to 150. This colloidal electrolyte provides a robust approach for advancing Li-air batteries.
RESUMEN
The predictive synthesis of metal nanocrystals with desired structures relies on the precise control of the crystal formation process. Using a capping ligand is an effective method to affect the reduction of metal ions and the formation of nanocrystals. However, predictively synthesizing nanostructures has been difficult to achieve using conventional capping ligands. DNA, as a class of the promising biomolecular capping ligands, has been used to generate sequence-specific morphologies in various metal nanocrystals. However, mechanistic insight into the DNA-mediated nanocrystal formation remains elusive due to the lack of quantitative experimental evidence. Herein, we quantitatively analyzed the precise control of DNA over Ag+ reduction and the structures of resulting Au-Ag core-shell nanocrystals. We derived the equilibrium binding constants between DNA and Ag+, the kinetic rate constants of sequence-specific Ag+ reduction pathways, and the percentage of active surface sites remaining on the nanocrystals after DNA passivation. These three synergistic factors influence the nucleation and growth process both thermodynamically and kinetically, which contributed to the morphological evolution of Au-Ag nanocrystals synthesized with different DNA sequences. This study demonstrates the potential of using functional DNA sequences as a versatile and tunable capping ligand system for the predictable synthesis of metal nanostructures.
RESUMEN
Atomically thin graphene electrodes enable the modulation of interfacial reactivity by means of underlying substrate effects. Here we show that plasmonic excitation of microscopic arrays composed of 50 nm Au nanoparticles situated underneath a graphene interface results in localized enhancements on the electrochemical readout. We used scanning electrochemical microscopy (SECM) in the feedback and H2O2 collection modes to identify the role of the generated plasmons on the electrochemical response. Using electrochemical imaging, supported by finite-element method simulations, we confirmed that a temperature rise of up to â¼30 K was responsible for current enhancements observed for mass transfer- limited reactions. On single-layer graphene (SLG) we observed a shift in the onset of H2O2 generation which we traced back to photothermal induced kinetic changes, raising ko' from 1.1 × 10-8 m/s to 2.2 × 10-7 m/s. Thicker 10-layer graphene electrodes displayed only a small kinetic difference with respect to SLG, suggesting that photothermal processes, in contrast to hot carriers, are the main contributor to the observed changes in interfacial reactivity upon illumination. SECM is demonstrated to be a powerful technique for elucidating thermal contributions to reactive enhancements, and presents a convenient platform for studying sublayer and temperature-dependent phenomena over individual sites on electrodes.
RESUMEN
Hematite is a promising photoanode for solar driven water splitting. Elucidating its surface chemical pathways is key to improving its performance. Here, we use redox titrations in the Surface Interrogation mode of Scanning Electrochemical Microscopy (SI-SECM) to quantitatively probe in situ the reactivity and time evolution of surface species formed on hematite during photo assisted water oxidation. Using SI-SECM, two distinct populations of oxidizing surface species were resolved with measured ksi of 316 m3/(mol·s) and 2 m3/(mol·s) for the more and less reactive species, respectively. While the surface coverage of both species was found to increase as a function of applied bias, the rate constants did not change appreciably, suggesting that the mechanism of water oxidation is independent of bias potential. In the absence of applied potential, both populations exhibit decay that is well described by second order kinetics, with kd values of 1.2 × 105 ± 0.2 × 105 and 6.3 × 103 ± 0.9 × 103 m2/(mol·s) for the fast and slow reacting adsorbates, respectively. Using transient substrate generation/tip collection mode, we detected the evolution of as much as 1.0 µmol/m2 of H2O2 during this decay process, which correlates with the coverage observed by one of the titrated species. By deconvoluting the reactivity of multiple adsorbed reactants, these experiments demonstrate how SI-SECM enables direct observation of multiple adsorbates and reaction pathways on operating photoelectrodes.
