Martin Eduardo Zoloff Michoff

Water plays a pivotal role in the mechanochemical degradation of S-anchored PEGylated gold interfaces.

Metallic lithium plays an important role in the development of next-generation lithium metal-based batteries. However, the uncontrolled growth of lithium dendrites limits the use of lithium metal as an anode. In this context, a stable solid electrolyte interphase (SEI) is crucial for regulating dendrite formation, stability, and cyclability of lithium metal anodes. This article proposes an artificial protective layer of P-doped carbon nitride on the lithium anode surface to address these issues. A thin film of P-doped carbon nitride (CNP) was created through a simple drop-casting method using synthesized CNP powder, forming an artificial SEI on the lithium electrode. The resulting symmetric CNP-modified Li/Li cells exhibited remarkable cyclability with low overpotentials of around 40 mV over 500 cycles at a current density of 3 mA cm⁻². Anode degradation and SEI composition were thoroughly studied for cycled electrodes to gain insight into the mechanisms underlying this modified surface. Furthermore, these CNP-modified anodes were successfully utilized in a Li–S coin cell battery, achieving high capacity and capacity retention at a high current density (1C). First-principles calculations indicate that P-doping in the carbon nitride structure significantly enhances the surface diffusion of lithium and promotes more homogeneous lithium plating.

The effect of the chain length separating sulfur atoms in bidentate thiols attached to defective gold surfaces on the rupture of the respective molecule-gold junctions has been studied computationally. Thermal desorption always yields cyclic disulfides. In contrast, mechanochemical desorption leads to cyclic gold complexes, where metal atoms are extracted from the surface and kept in tweezer-like arrangements by the sulfur atoms. This phenomenon is rationalized in terms of directional mechanical manipulation of Au-Au bonds and Au-S coordination numbers. Moreover, the flexibility of the chain is shown to crucially impact on the mechanical strength of the junction.

A detailed kinetic study has been carried out for the aminolysis of ionizable Fischer thiocarbene complexes (CO)₅MC(SR)CH₃ (M = Cr, W; R = iPr, nBu, cHex, tBu) with five primary amines and one secondary amine in aqueous acetonitrile solutions (50% MeCN–50% water (v/v)). The observed rate constants for the reaction with primary amines showed a first-order dependence on the amine concentration, while with morpholine, the rate constant has second-order dependence. The general base catalysis process was confirmed by the variation of the rate constants with the concentration of an external catalyst and the pH. The results agree with a stepwise mechanism where the nucleophilic addition to the carbene carbon to produce a tetrahedral intermediate (T^±) is the first step, followed by a rapid deprotonation of T^± to form the anion T⁻ which leads to the products by general-acid catalysed leaving group (–SR) expulsion. In general, it was found that the chromium complexes are less reactive than the tungsten analogues. The obtained Brønsted parameters for the nucleophilic addition (β_nuc) indicate that C–N bond formation has made little progress at the transition state. By using Charton's correlation, the role that the steric factor plays throughout the mechanism has been unraveled. The nucleophilic addition to the thiocarbenes is less sensitive to steric effects than the alkoxycarbenes regardless of the nature of the metal centre. Conversely, the steric effects on the general-base catalysis can be strong depending on the volume of the catalyst and the metal centre. On the basis of the structure–reactivity coefficients β and ψ and comparison with alkoxycarbene complexes, esters and thiolesters, insights into the main factors ruling the reactivity in terms of transition state imbalances are discussed.