The thermodynamic and kinetic behaviors of O atoms on/in different Al nanoparticles (ANPs) and Al crystals have been systematically studied using first-principles calculations. The O adsorption strength on clean Al...

Sodium ion batteries (SIBs) are expected to take the place of lithium ion batteries (LIBs) as next-generation electrochemical energy storage devices due to the cost advantages they offer. However, due to the larger ion radius, the reaction kinetics of Na+ in anode materials is sluggish. SnS2 is an attractive anode material for SIBs due to its large interlayer spacing and alloying reactions with high capacity. Calcination is usually employed to improve the crystallinity of SnS2, which could affect the Na+ reaction kinetics, especially the pseudo­capacitive storage. However, excessively high temperature could damage the well-designed nanostructure of SnS2. In this work, we uniformly grow SnS2 nanosheets on a Zn-, N-, and S-doped carbon skeleton (SnS2@​ZnNS). To explore the optimal calcination temperature, SnS2@​ZnNS is calcined at three typical temperatures (300, 350, and 400 °C), and the electrochemical performance and Na+ storage kinetics are investigated specifically. The results show that the sample calcined at 350 °C exhibited the best rate capacity and cycle performance, and the reaction kinetics analysis shows that the same sample exhibited a stronger pseudo­capacitive response than the other two samples. This improved Na+ storage capability can be attributed to the enhanced crystallinity and the intact nanostructure.

The interactions between NO x , N and O atoms, and aluminum (Al) surfaces including crystal planes and nanoparticles (ANPs) are systematically investigated by using density functional theory (DFT) calculations, canonical Monte Carlo (CMC) simulations, and reactive molecular dynamics (RMD) simulations. NO x has two adsorption states (molecular and dissociated) on the Al surfaces, which are separated by a low energy barrier. The adsorption of NO x in either state does not favor Al nanoparticles (ANPs), opposite to its behavior on transition metals. In addition, NO x does not show preference toward smaller ANPs or their vertices or edges; instead, it prefers threefold sites that resemble the fcc or hcp sites on a (111) surface. The big deformation energy of ANPs is found to be the reason. The N* adatoms are most stable at the tetrahedron interstitial sites between the surface and the first sublayer, where an aluminum nitride (AlN)-like structure is formed. Similar to O* adatoms on Al, the isotropic attraction between N* adatoms has a significant influence on their diffusion, both in-plane and in cross-layer. Besides, the attraction within a N−O pair as the first nearest neighbors (1NN) is roughly twice that of their respective attraction (about 0.1 eV/O−O or N−N). However, RMD simulations ignore the attraction among the N* adatoms as well as between the N* and O* adatoms, though O−O attractions are somehow incorporated. CMC simulations prove that the attraction still governs the configuration of the adatoms at 600 K with all adatoms congregating into a single polygonal island, and it is still influential even when reaching 1500 K. In addition, the fragmented products (Al x N y ) of Al combustion in NO x according to DFT feature the tetra-coordinated Al centered inside the tetrahedron of four N atoms, different from the pyramidal unit structure with Al as the vertex by RMD simulations. Our results demonstrate that the unusual behaviors of NO x including the dissociated atoms on Al are caused by both the softness (low Young's modulus) of Al and the attractions among adsorbates, which have important implications for understanding the behaviors of gas molecules on main group metals in general.

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Nanocatalysts, due to their small size and/or lattice mismatch among hetero components, are born with strain. During reaction, adsorbates alongside strain may cause the catalyst’s surface to reorganize, which can...