Ternary Eutectic Electrolyte-Assisted Formation and Dynamic Breathing Effect of the Solid-Electrolyte Interphase for High-Stability Aqueous Magnesium-Ion Full Batteries.

Aqueous rechargeable magnesium batteries hold immense potential for intrinsically safe, cost-effective, and sustainable energy storage. However, their viability is constrained by a narrow voltage range and suboptimal compatibility between the electrolyte and electrodes. Herein, we introduce an innovative ternary deep eutectic Mg-ion electrolyte composed of MgCl2·6H2O, acetamide, and urea in a precisely balanced 1:1:7 molar ratio. This formulation was optimized by leveraging competitive solvation effects between Mg2+ ions and two organic components. The full batteries based on this ternary eutectic electrolyte, Mn-doped sodium vanadate (Mn-NVO) anode, and copper hexacyanoferrate cathode exhibited an elevated voltage plateau and high rate capability and showcased stable cycling performance. Ex-situ characterizations unveiled the Mg2+ storage mechanism of Mn-NVO involving initial extraction of Na+ followed by subsequent Mg2+ intercalation/deintercalation. Detailed spectroscopic analyses illuminated the formation of a pivotal solid-electrolyte interphase on the anode surface. Moreover, the solid-electrolyte interphase demonstrated a dynamic adsorption/desorption behavior, referred to as the "breathing effect", which substantially mitigated undesired dissolution and side reactions of electrode materials. These findings underscore the crucial role of rational electrolyte design in fostering the development of a favorable solid-electrolyte interphase that can significantly enhance compatibility between electrode materials and electrolytes, thus propelling advancements in aqueous multivalent-ion batteries.

Precipitated Iodine Cathode Enabled by Trifluoromethanesulfonate Oxidation for Cathode/Electrolyte Mutualistic Aqueous Zn-I Batteries.

Aqueous Zn-I batteries hold great potential for high-safety and sustainable energy storage. However, the iodide shuttling effect and the hydrogen evolution reaction that occur in the aqueous electrolyte remain the main obstacles for their further development. Herein, the design of a cathode/electrolyte mutualistic aqueous (CEMA) Zn-I battery based on the inherent oxidation ability of aqueous trifluoromethanesulfonate ((OTf)- ) electrolyte toward triiodide species is presented. This results in the formation of iodine sediment particles assembled by fine iodine nanocrystals (≈10 nm). An iodine host cathode with high areal iodine loading is realized via a spontaneous absorption process that enriched redox-active iodine and iodide species from aqueous electrolyte onto nanoporous carbon based current collector. By tuning iodide redox process and suppressing competitive hydrogen evolution reaction, the assembled CEMA Zn-I batteries demonstrate a remarkable capacity retention of 76.9% over 1000 cycles at 0.5 mA cm-2 . Moreover, they exhibit a notable rate capability, with a capacity retention of 74.6% when the current density is increased from 0.5 to 5.0 mA cm-2 . This study demonstrates the feasibility of using the oxidation effect to repel redox-active species from the electrolyte to the cathode, paving a new avenue for high-performance aqueous Zn-I batteries.

Nanocluster-agminated amorphous cobalt nanofilms for highly selective electroreduction of nitrate to ammonia.

Developing highly-efficient electrocatalysts for the nitrate reduction reaction (NITRR) is a persistent challenge. Here, we present the successful synthesis of 14 amorphous/low crystallinity metal nanofilms on three-dimensional carbon fibers (M-NFs/CP), including Al, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, Pb, Au, or Bi, using rapid thermal evaporation. Among these samples, our study identifies the amorphous Co nanofilm with fine agglomerated Co clusters as the optimal electrocatalyst for NITRR in a neutral medium. The resulting Co-NFs/CP exhibits a remarkable Faradaic efficiency (FENH3) of 91.15 % at - 0.9 V vs RHE, surpassing commercial Co foil (39 %) and Co powder (20 %), despite sharing the same metal composition. Furthermore, during the electrochemical NITRR, the key intermediates on the surface of the Co-NFs/CP catalyst were detected by in situ Fourier-transform infrared (FTIR) spectroscopy, and the possible reaction ways were probed by Density functional theory (DFT) calculations. Theoretical calculations illustrate that the abundant low-coordinate Co atoms of Co-NFs/CP could enhances the adsorption of *NO3 intermediates compared to crystalline Co. Additionally, the amorphous Co structure lowers the energy barrier for the rate-determining step (*NH2→*NH3). This work opens a new avenue for the controllable synthesis of amorphous/low crystallinity metal nano-catalysts for various electrocatalysis reaction applications.

Molecular Design Strategies for Electrochemical Behavior of Aromatic Carbonyl Compounds in Organic and Aqueous Electrolytes.

To sustainably satisfy the growing demand for energy, organic carbonyl compounds (OCCs) are being widely studied as electrode active materials for batteries owing to their high capacity, flexible structure, low cost, environmental friendliness, renewability, and universal applicability. However, their high solubility in electrolytes, limited active sites, and low conductivity are obstacles in increasing their usage. Here, the nucleophilic addition reaction of aromatic carbonyl compounds (ACCs) is first used to explain the electrochemical behavior of carbonyl compounds during charge-discharge, and the relationship of the molecular structure and electrochemical properties of ACCs are discussed. Strategies for molecular structure modifications to improve the performance of ACCs, i.e., the capacity density, cycle life, rate performance, and voltage of the discharge platform, are also elaborated. ACCs, as electrode active materials in aqueous solutions, will become a future research hotspot. ACCs will inevitably become sustainable green materials for batteries with high capacity density and high power density.