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Monolayers of metal trihalide MX3 can feasibly be exfoliated from their bulk materials and they have large band gaps.

Controlling oxygen deficiencies is essential for the development of novel chemical and physical properties such as high-T c superconductivity and low-dimensional magnetic phenomena. Among reduction methods, topochemical reactions using metal hydrides (e.g., CaH2) are known as the most powerful method to obtain highly reduced oxides including Nd0.8Sr0.2NiO2 superconductor, though there are some limitations such as competition with oxyhydrides. Here we demonstrate that electrochemical protonation combined with thermal dehydration can yield highly reduced oxides: SrCoO2.5 thin films are converted to SrCoO2 by dehydration of HSrCoO2.5 at 350 °C. SrCoO2 forms square (or four-legged) spin tubes composed of tetrahedra, in contrast to the conventional infinite-layer structure. Detailed analyses suggest the importance of the destabilization of the SrCoO2.5 precursor by electrochemical protonation that can greatly alter reaction energy landscape and its gradual dehydration (H1–x SrCoO2.5–x/2) for the SrCoO2 formation. Given the applicability of electrochemical protonation to a variety of transition metal oxides, this simple process widens possibilities to explore novel functional oxides.

Exploiting two-dimensional (2D) metallic electrodes with high energy density and fast rate performance is crucial in rechargeable ion batteries. Herein, the electronic properties of 2D monolayer Ta 2 CS 2 and its potential performance as 2D electrode candidate in Li + , Na + , K + , and Ca 2+ ion batteries have been examined by utilizing first-principles calculations. The exfoliation of metallic monolayer Ta 2 CS 2 is feasible owing to small cleavage energy of 0.64 J/m 2 and thermodynamical stability. The Ta 2 CS 2 −metal atom complexes are energetically favorable through examining adsorption energies. Furthermore, the low diffusion barriers of 0.21 eV for Li and 0.09 eV for Na and the high specific capacity of 367.23 mA h/g could be achieved. In particular, the low average opencircuit voltage of 0.45 V for Na implies 2D Ta 2 CS 2 to be a suitable anode candidate in Naion batteries. These results provide fundamental insights for 2D Ta 2 CS 2 in the field of energy conversion and storage. KEYWORDS: two-dimensional Ta 2 CS 2 , anode material, diffusion barrier, rechargeable ion batteries, first principles calculations

Two-dimensional MX3 materials with intrinsic atomic pores are proposed as ideal solid electrolytes in ultrafast ionic and energy storage devices.