Two-dimensional transition-metal-based carbides (or nitrides), so-called MXenes, that can be derived from the three-dimensional MAX phases, have attracted considerable attention throughout the past couple of years. The particular structure together with their hydrophilic and metallic nature make them promising candidates for a plethora of applications, such as sensors, electrodes, and catalysts. Obviously, the respective chemical and physical properties are highly dependent on the chemical composition, stoichiometry, and surface structure of the MXene. Here, we introduce a new member of the MXene family, V 4 C 3 T x (T representing the surface groups), based on the chemical exfoliation of the 413 MAX phase V 4 AlC 3 by treatment with aqueous hydrofluoric acid. X-ray powder diffraction data together with scale-bridging electron microscopy studies prove the successful removal of aluminum from the MAX phase structure. The electrocatalytic activity for the hydrogen evolution reaction of this new MXene is tested in acidic solution over the course of 100 cycles. Interestingly, we find a significant improvement of the catalytic performance over time (i.e., the overpotential required to achieve a current density of 10 mA cm −2 decreases by almost 200 mV) that we assign to the removal of an oxide species from the surface of the MXene, as shown by XPS measurements. Our study provides crucial experimental data of the electrocatalytic activity of MXenes together with the evolution of its surface structure that is also relevant for other transition-metal-based MXenes in the context of further potential applications. KEYWORDS: MAX phase, MXene, V 4 AlC 3 , V 4 C 3 T x , hydrogen evolution reaction, electrocatalysis, carbides

The data collected along a metadynamics simulation can be used to recover information about the underlying unbiased system by means of a reweighting procedure. Here, we analyze the behavior of several reweighting techniques in terms of the quality of the reconstruction of the underlying unbiased free energy landscape in the early stages of the simulation and propose a simple reweighting scheme that we relate to the other techniques. We then show that the free energy landscape reconstructed from reweighted data can be more accurate than the negative bias potential depending on the reweighting technique, the stage of the simulation, and the adoption of well-tempered or standard metadynamics. While none of the tested reweighting techniques from the literature provides the most accurate results in all the analyzed situations, the one proposed here, in addition to helping simplifying the reweighting procedure, converges quickly and precisely to the underlying free energy surface in all the considered cases, thus allowing for an efficient use of limited simulation data.

V4AlC3 belongs to the intriguing class of materials of so‐called MAX phases that are ternary carbides and nitrides crystallizing in a layered crystal structure with space group P63/mmc. They exhibit excellent mechanical properties combining characteristics of metals as well as ceramics. The synthesis of single‐phase products is far from being trivial since high temperatures are required, while most competing phases are also thermodynamically stable. Herein, we show the non‐conventional solid‐state preparation by susceptor‐assisted microwave heating within 60 min. The crystallinity of the nearly single‐phase compound is enhanced by subsequent densification using the spark plasma sintering technique. The formation mechanism of V4AlC3 is investigated by means of thermoanalysis. Intermediate as well as final products are characterized by powder X‐ray diffraction techniques.

Nanoparticles coated with hydrophilic polymers often show a reduction in unspecific interactions with the biological environment, which improves their biocompatibility. The molecular determinants of this reduction are not very well understood yet, and their knowledge may help improving nanoparticle design. Here we address, using molecular dynamics simulations, the interactions of human serum albumin, the most abundant serum protein, with two promising hydrophilic polymers used for the coating of therapeutic nanoparticles, poly(ethylene-glycol) and poly-sarcosine. By simulating the protein immersed in a polymer-water mixture, we show that the two polymers have a very similar affinity for the protein surface, both in terms of the amount of polymer adsorbed and also in terms of the type of amino acids mainly involved in the interactions. We further analyze the kinetics of adsorption and how it affects the polymer conformations. Minor differences between the polymers are observed in the thickness of the adsorption layer, that are related to the different degree of flexibility of the two molecules. In comparison poly-alanine, an isomer of poly-sarcosine known to self-aggregate and induce protein aggregation, shows a significantly larger affinity for the protein surface than PEG and PSar, which we show to be related not to a different patterns of interactions with the protein surface, but to the different way the polymer interacts with water.