Herein, we compare the bulk, 2H and 3R phases of two most prevalent TMD materials: MoS and WS. The 3R phase outperforms its 2H phase counterpart in hydrogen evolution reaction catalysis and is even comparable with the exfoliated, 1T phase in the case of MoS.
In the last few years, the development of versatile coating chemistries has become a hot topic in surface science after the discovery that catecholamines can lead to conformal coatings upon oxidation from aqueous solutions. Recently, it was found that aminomalononitrile (AMN), a molecule implicated in the appearance of life on earth, is an excellent prototype of novel material-independent surface functionalizing agents leading to conformal and biocompatible coatings in a simple and direct chemical process from aqueous solutions. So far, very little insight has been gained regarding the mechanisms underlying coating deposition. In this paper we show that the chemical evolution of AMN film deposition under slightly basic conditions is different in solution and on silica. Thereon, the coating proceeds via a nucleation process followed by further deposition of islands which evolve to produce nitrogen-rich superhydrophilic fibrillar structures. Additionally, we show that AMNbased material can form films at the air-solution interface from unshaken solutions. These 2 results open new vistas into the chemistry of HCN-derived species of potential relevance in materials science.
The development of electrocatalysts is crucial for renewable energy applications. Metal-doped graphene hybrid materials have been explored for this purpose, however, with much focus on noble metals, which are limited by their low availability and high costs. Transition metals may serve as promising alternatives. Here, transition metal-doped graphene hybrids were synthesized by a simple and scalable method. Metal-doped graphite oxide precursors were thermally exfoliated in either hydrogen or nitrogen atmosphere; by changing exfoliation atmospheres from inert to reductive, we produced materials with different degrees of oxidation. Effects of the presence of metal nanoparticles and exfoliation atmosphere on the morphology and electrocatalytic activity of the hybrid materials were investigated using electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. Doping of graphene with transition metal nanoparticles of the 4th period significantly influenced the electrocatalysis of compounds important in energy production and storage applications, with hybrid materials exfoliated in nitrogen atmosphere displaying superior performance over those exfoliated in hydrogen atmosphere. Moreover, nickel-doped graphene hybrids displayed outstanding electrocatalytic activities towards reduction of O2 when compared to bare graphenes. These findings may be exploited in the research field of renewable energy.
It is crucial to develop electrocatalysts for the oxygen reduction reaction (ORR) for renewable energy applications. Mixed‐valence transition‐metal oxides with a spinel structure have been explored for this purpose. In this work, we study the influence of the composition of the catalysts (XY2O4, X=Ni, Zn and Y=Co, Mn) on the ORR. The four different types of spinel oxide nanocrystals (NiCo2O4, NiMn2O4, ZnCo2O4, and ZnMn2O4) were synthesized by a simple and scalable method. This allowed for a systematic investigation of the transition‐metal influence on the performance of the ORR. Given the general spinel structure of XY2O4, we systematically changed X (Ni, Zn) and Y (Co, Mn). The effects of the presence of different metals in the spinel oxide on the morphology and electrocatalytic properties of the materials toward the ORR were investigated and compared by using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron microscopy, and voltammetry. In general, cobalt‐based spinel oxides displayed a significant electrocatalytic activity towards the ORR, with Ni‐substituted spinel oxides outperforming their respective Zn‐substituted congeners. These findings may have great impact in the research field of renewable energy.
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