Heterogeneous Mercury Oxidation by HCl over CeO₂ Catalyst: Density Functional Theory Study

CeO₂-based catalysts have been regarded as potential materials for Hg removal due to high catalytic performance, nontoxicity, and low cost. Density functional theory calculations were performed to investigate the mercury oxidation mechanism by HCl over a CeO₂ catalyst. The thermodynamic stability analysis suggests that the stoichiometric CeO₂(111) is the most stable surface. The protonated CeO₂ surfaces takes place at low oxygen partial pressures, and the chlorinated CeO₂ surfaces can stably exist under low HCl concentrations. The adsorption energies and geometries show that Hg⁰ is physically adsorbed on oxygen sites of the CeO₂(111) surface and HCl is chemically adsorbed on the CeO₂(111) surface. HCl can dissociate on the CeO₂(111) surface with a low barrier. The Hg oxidation is most likely to proceed with the Eley–Rideal mechanism at the first step (Hg → HgCl), followed by the Langmuir–Hinshelwood mechanism at the second step (HgCl → HgCl₂). In the whole Hg oxidation reaction, the formation of HgCl₂ is the rate-determining step. The low energy barriers for the oxidation reaction of Hg on CeO₂ make it an attractive alternative catalyst for Hg oxidation

Few-Layer Tin Sulfide: A New Black-Phosphorus-Analogue 2D Material with a Sizeable Band Gap, Odd–Even Quantum Confinement Effect, and High Carrier Mobility

As a compound analogue of black phosphorus, a new 2D semiconductor of SnS layers is proposed. Based on state-of-the-art theoretical calculations, we confirm that such 2D SnS layers are thermally and dynamically stable and can be mechanically exoliated from α-phase SnS bulk materials. The 2D SnS layer has an indirect band gap that can be tuned from 1.96 eV for the monolayer to 1.44 eV for a six-layer structure. Interestingly, the decrease of the band gap with increasing number of layers is not monotonic but shows an odd–even quantum confinement effect, because the interplay of spin–orbit coupling and lack of inversion symmetry in odd-numbered layer structures results in anisotropic spin splitting of the energy bands. It was also found that such 2D SnS layers show high in-plane anisotropy and high carrier mobility (tens of thousands of cm² V^–1 s^–1) even superior to that of black phosphorus, which is dominated by electrons. With these intriguing electronic properties, such 2D SnS layers are expected to have great potential for application in future nanoelectronics

Excess Li-Ion Storage on Reconstructed Surfaces of Nanocrystals To Boost Battery Performance

Because of their enhanced kinetic properties, nanocrystallites have received much attention as potential electrode materials for energy storage. However, because of the large specific surface areas of nanocrystallites, they usually suffer from decreased energy density, cycling stability, and effective electrode capacity. In this work, we report a size-dependent excess capacity beyond theoretical value (170 mA h g^–1) by introducing extra lithium storage at the reconstructed surface in nanosized LiFePO₄ (LFP) cathode materials (186 and 207 mA h g^–1 in samples with mean particle sizes of 83 and 42 nm, respectively). Moreover, this LFP composite also shows excellent cycling stability and high rate performance. Our multimodal experimental characterizations and ab initio calculations reveal that the surface extra lithium storage is mainly attributed to the charge passivation of Fe by the surface C–O–Fe bonds, which can enhance binding energy for surface lithium by compensating surface Fe truncated symmetry to create two types of extra positions for Li-ion storage at the reconstructed surfaces. Such surface reconstruction nanotechnology for excess Li-ion storage makes full use of the large specific surface area of the nanocrystallites, which can maintain the fast Li-ion transport and greatly enhance the capacity. This discovery and nanotechnology can be used for the design of high-capacity and efficient lithium ion batteries