Oxygen vacancies (O) as the active sites have significant influences on the gas sensing performance of metal oxides, and self-doping of Ce in CeO might promote the formation of oxygen vacancies. In this work, hydrothermal process is adopted to fabricate the composites of graphene and CeO nanoparticles, and the influences of oxygen vacancies as well as Ce ions on the sensing response to NO are studied. It is found that the sensitivity of the composites to NO increases gradually, as the proportion of Ce relative to all of the cerium ions is increased from 14.6% to 50.7% but decreases after that value. First-principles calculations illustrate that CeO becomes metallic at the Ce proportion of <50.7%, the chemical potential of electrons on surface decreases, and the Fermi level shifts upward due to the existence of low-electronegativity Ce ions, resulting in reduced Schottky barrier height (SBH) at the CeO/graphene interface, enhanced interfacial charge transfer, and high gas sensing performance. However, deep energy level will be induced at the Ce proportion of >50.7%, and the Fermi level is pinned at the interface. As a result, the density of free electrons is reduced, leading to increased SBH and poor gas sensing response. It demonstrates that an appropriate concentration of oxygen vacancies in CeO is needed to enhance the gas sensing performance to NO.

Ferromagnetic (FM) two-dimensional (2D) transition metal dichalcogenides (TMDs) have potential applications in modern electronics and spintronics and doping of TMDs with transition metals can enhance the magnetic characteristics. In this work, the structural stability, electronic states, and magnetic properties of Mn-doped monolayer/bilayer MoS are studied systematically by first-principles calculations. Substitutional Mn dopants at the Mo sites are energetically favorable in both monolayer and bilayer MoS under the S-rich condition which is common in the synthesis of MoS nanosheets. Two Mn dopants participate in the FM interaction in monolayer MoS and magnetic coupling of two Mn dopants via the double-exchange mechanism can be mediated by the nearest neighboring S. Magnetic coupling can be ascribed to the competition between the double-exchange, direct-exchange, and super-exchange interactions, which take place between two Mn dopants in bilayer MoS with the MnMn, MnMn and Mn-Mn configurations. Our results reveal the geometrical dependence of magnetic-exchange coupling suggesting that Mn-doped monolayer/bilayer MoS has large potential in spintronic devices.

The lithium−sulfur battery, despite having considerable advantages, is still far from its practical applications, which is primarily caused by the dissolution of polysulfide clusters of lithium (LiPSs) into the electrolyte. Entrapping these LiPSs through integration of the anchoring material with the electrode is an effective approach to overcome this problem. In this study, density functional theory and ab initio molecular dynamics have been adopted to systematically examine the anchoring behaviors of two-dimensional phosphorene-based (monovacancy/oxygen-/sulfur-doped) materials, for all the intermediates of polysulfide. The defective sites provide strong adsorption for polysulfide clusters by generating firm chemical bonds together with van der Waals interactions. As a result, the intermediate discharge products could be thermodynamically stabilized on these defective substrates, against the local environment with virtually alike to initial configurations, which cannot be achieved with pristine phosphorene. Moreover, the emerging midgap states in the electronic structures of defective phosphorene and adsorptive systems improve the electrical conductivity of the defective-phosphorene-based electrode, alleviating the low rate capability related with pristine-phosphorene based batteries. It is illustrated that the anchoring ability of pristine phosphorene can be significantly improved by the defects, among which the monovacancy structure demonstrates superior performance for achieving long cycle life.

It is difficult to generate p–n junctions in atomically thin transition metal dichalcogenides (TMDs) because of the great challenge of selective doping.

An effective approach to enhance the gas sensing performance of CeO2/graphene composites at room temperature is demonstrated and discussed.