Silicon-based materials are the most promising candidates to surpass the capacity limitation of conventional graphite anode for lithium ion batteries. Unfortunately, Si-based materials suffer from poor cycling performance and dimensional instability induced by the large volume changes during cycling. To resolve such problems, nanostructured silicon-based materials with delicately controlled microstructure and interfaces have been intensively investigated. Nevertheless, they still face problems related to their high synthetic cost and their limited electrochemical properties and thermal stability. To overcome these drawbacks, we demonstrate the strategic design and synthesis of a gyroid three-dimensional network in a Si@SiO x /C nanoarchitecture (3D-Si@SiO x /C) with synergetic interaction between the computational prediction and the synthetic optimization. This 3D-Si@SiO x /C exhibits not only excellent electrochemical performance due to its structural stability and superior ion/electron transport but also enhanced thermal stability due to the presence of carbon, which was formed by a cost-effective one-pot synthetic route. We believe that our rationally designed 3D-Si@SiO x /C will lead to the development of anode materials for the next-generation lithium ion batteries.

redox reactions in fuel cells and metaloxygen batteries as well as water-splitting devices. [1][2][3][4] Including the initial notable works in the 1980s, [5][6][7] many experimental and theoretical studies on the ABO 3 -type perovskite catalysts have dealt with the number of d-electrons of B-site cations, the bond strength of BOH, the position of the O 2p band center, the effect of oxygen vacancies, and the role of lattice oxygen redox in efforts to account for the crucial contributions that correlate with the high catalytic activity during the oxygen evolution reaction (OER). [6][7][8][9][10][11][12] By extensive comparison of more than ten perovskite oxides, recent studies also suggested activity descriptors on the basis of the number of e g -orbital electrons of the 3d transition metals [13] and the charge transfer energy between metal and oxygen electrons [14] to understand the OER activity differences among the perovskite family. Although various structural and electronic factors should be taken into account to precisely depict the catalytic behavior of perovskites [15][16][17] and other transitionmetal oxides, [18][19][20][21][22][23] it appears to be accepted in general that relative difference of energy level between the 3d orbitals of B-site cations and the 2p orbitals of oxygen anions play an important role in significant promotion of charge transfer between [BO 6 ] at the surface and adsorbates, resulting in much higher OER efficiency at a lower overpotential. [9,[11][12][13][14][24][25][26][27][28] In stark contrast to the [BO 6 ] octahedra in the bulk, most [BO 6 ] units at grain boundaries (GBs) in polycrystals have severely distorted geometric configurations of B and O. [29,30] Note that the atomic displacement from this distortion at GBs is usually much greater than the displacement that occurs at the crystal surface for relaxation [31] and/or is induced by the coherent strain via using the epitaxial thin-film growth. [26,32] As a result, it can be reasonably anticipated that the electronic states of transition-metal 3d and oxygen 2p orbitals at GBs considerably differ from those in the bulk. In this regard, a combination of selective analysis of the OER characteristics at GBs and observation of the grain-boundary atomic structure can provide direct and insightful information that has not been offered in previous studies to elucidate the correlation between A grain boundary forms as an internal interface when two crystalline grains with mutually different crystallographic orientations are in direct contact with each other. As a result, atomic arrangement at grain boundaries differs from that of the bulk, showing serious displacements deviating from the original symmetric positions. As these symmetry-broken configurations are difficult to achieve in the bulk crystals, grain boundaries are considered distinctive platforms that can exhibit new physical properties. By using both sintered polycrystals with various grain sizes and thin films on bicrystal substrates, it is directly verified that surfac...

Although numerous studies on oxide catalysts for an efficient oxygen evolution reaction have been carried out to compare their catalytic performance and suggest new compositions, two significant constraints have been overlooked. One is the difference in electronic conduction behavior between catalysts (metallic versus insulating) and the other is the strong crystallographic surface orientation dependence of the catalysis in a crystal. Consequently, unless a comprehensive comparison of the oxygen-evolution catalytic activity between samples is made on a crystallographically identical surface with sufficient electron conduction, misleading interpretations on the catalytic performance and mechanism may be unavoidable. To overcome these limitations, we utilize both metallic (001) LaNiO3 epitaxial thin films together with metal dopants and semiconducting (001) LaCoO3 epitaxial thin films supported with a conductive interlayer. We identify that Fe, Cr, and Al are beneficial to enhance the catalysis in LaNiO3 although their perovskite counterparts, LaFeO3, LaCrO3, and LaAlO3, with a large bandgap are inactive. Furthermore, semiconducting LaCoO3 is found to have more than one order higher activity than metallic LaNiO3, in contrast to previous reports. Showing the importance of facilitating electron conduction, our work highlights the impact of the near-Fermi-level d-orbital states on the oxygen-evolution catalysis performance in perovskite oxides.

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As chemical reactions and charge-transfer simultaneously occur on the catalyst surface during electrocatalysis, numerous studies have been carried out to attain an in-depth understanding on the correlation among the surface structure and composition, the electrical transport, and the overall catalytic activity. Compared with other catalysis reactions, a relatively larger activation barrier for oxygen evolution/reduction reactions (OER/ORR), where multiple electron transfers are involved, is noted. Many works over the past decade thus have been focused on the atomic-scale control of the surface structure and the precise identification of surface composition change in catalyst materials to achieve better conversion efficiency. In particular, recent advances in various analytical tools have enabled noteworthy findings of unexpected catalytic features at atomic resolution, providing significant insights toward reducing the activation barriers and subsequently improving the catalytic performance. In addition to summarizing important surface issues, including lattice defects, related to the OER and ORR in this Review, we present the current status and discuss future perspectives of oxide- and alloy-based catalysts in terms of atomic-scale observation and manipulation.