RESUMEN
Covalent modification is commonly used to tune the channel size and functionality of 2D membranes. However, common synthesis strategies used to produce such modifications are known to disrupt the structure of the membranes. Herein, we report less intrusive yet equally effective non-covalent modifications on Ti3C2Tx MXene membranes by a solvent treatment, where the channels are robustly decorated by protic solvents via hydrogen bond network. The densely functionalized (-O, -F, -OH) Ti3C2Tx channel allows multiple hydrogen bond establishment and its sub-1-nm size induces a nanoconfinement effect to greatly strengthen these interactions by maintaining solvent-MXene distance and solvent orientation. In sub-1-nm ion sieving and separation, as-decorated membranes exhibit stable ion rejection, and proton-cation (H+/Mn+) selectivity that is up to 50 times and 30 times, respectively, higher than that of pristine membranes. It demonstrates the feasibility of non-covalent methods as a broad modification alternative for nanochannels integrated in energy-, resource- and environment-related applications.
RESUMEN
Kinetics and coulombic efficiency of the electrochemical magnesium plating and stripping processes are to a significant extent defined by the composition of the electrolyte solution, optimization of which presents a pathway for improved performance. Adopting this strategy, we undertook a systematic investigation of the Mg0/2+ process in different combinations of the Mg2+-Li+-borohydride-bis(trifluoromethylsulfonyl)imide (TFSI-) electrolytes in 1,2-dimethoxyethane (DME) solvent. Results indicate that the presence of BH4- is essential for high coulombic efficiency, which coordination to Mg2+ was confirmed by Raman and NMR spectroscopic analysis. However, the high rates observed also require the presence of Li+ and a supplementary anion such as TFSI-. The Li+ + BH4- + TFSI- combination of ionic species prevents passivation of the magnesium surface and thereby enables efficient Mg0/2+ electrochemical cycling. The best Mg0/2+ performance with the stabilized coulombic efficiency of 88 ± 1% and one of the highest deposition/stripping rates at ambient temperature reported to date are demonstrated at an optimal [Mg(BH4)2]:[LiTFSI] mole ratio of 1:2.
RESUMEN
We have investigated the sodium electrochemistry and the evolution and chemistry of the solid-electrolyte interphase (SEI) upon cycling Na metal electrodes in two ionic liquid (IL) electrolytes. The effect of the IL cation chemistry was determined by examining the behavior of a phosphonium IL (P111i4FSI) in comparison to its pyrrolidinium-based counterpart (C3mpyrFSI) at near-saturated NaFSI salt concentrations (superconcentrated ILs) in their dry state and with water additive. The differences in their physical properties are reported, with the P111i4FSI system having a lower viscosity, higher conductivity, and higher ionicity in comparison to the C3mpyrFSI-based electrolyte, although the addition of 1000 ppm (0.1 wt %) of water had a more dramatic effect on these properties in the latter case. Despite these differences, there was little effect in the ability to sustain stable cycling at moderate current densities and capacities (being nearly identical at 1 mA cm-2 and 1 mAh cm-2). However, the IL based on the phosphonium cation is shown to support more demanding cycling with high stability (up to 4 mAh cm-2 at 1, 2, and 4 mA cm-2 current density), whereas C3mpyrFSI rapidly failed (at 1 mA cm-2 /4 mAh cm-2). The SEI was characterized ex situ using solid-state 23Na NMR, XPS, and SEM and showed that the presence of a Na complex, identified in our previous work on C3mpyrFSI to correlate with stable, dendrite-free Na metal cycling, was also more prominent and coexisted with a NaF-rich surface. The results here represent a significant breakthrough in the development of high-capacity Na metal anodes, clearly demonstrating the superior performance and stability of the P111i4FSI electrolyte, even after the addition of water (up to 1000 ppm (0.1 wt %)), and show great promise to enable future higher-temperature (50 °C) Na-metal-based batteries.
