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We thermodynamically studied the size-dependent oxygen storage ability of nano-sized ceria by tracing the surface Ce/O ratio of octahedral particles with different diameters, from the viewpoint of lattice Ce and O in a CeO2 crystallographic structure. The high surface Ce/O ratio with small scale particle size has more excess surface Ce(4+) ions, which allows ceria to have an increasing oxygen storage ability in a crystalline lattice. For the perfect octahedron growth shape of ceria, the nonstoichiometric surfaces can produce excess Ce(4+) ions, Ce(4+) ions can be stabilized by bonding with lattice oxygen, leading to an enhanced oxygen storage ability of ceria. With the increasing particle size, the surface Ce/O ratio approaches to 0.5 owing to the decreased contributions of atoms located at the edges and corners. When the octahedron diameter D = 0.55 nm, the surface Ce/O ratio can reach 0.75. When D = 7.58 nm, the surface Ce/O ratio decreases down to 0.51. If D≥ 14.61 nm, the surface Ce/O ratios are equal to 0.5. The present study deepens the insight of the size-dependent oxygen storage ability of nano-sized ceria, focusing on the size-dependent excess Ce(4+) on nonstoichiometric surfaces of ceria in thermodynamics.

Advances in materials have preceded almost every major technological leap since the beginning of civilization. On the nanoscale and microscale, mastery over the morphology, size, and structure of a material enables control of its properties and enhancement of its usefulness for a given application, such as energy storage. In this review paper, our aim is to present a review of morphology engineering of high performance oxide electrode materials for electrochemical energy storage. We begin with the chemical bonding theory of single crystal growth to direct the growth of morphology-controllable materials. We then focus on the growth of various morphologies of binary oxides and their electrochemical performances for lithium ion batteries and supercapacitors. The morphology-performance relationships are elaborated by selecting examples in which there is already reasonable understanding for this relationship. Based on these comprehensive analyses, we proposed colloidal supercapacitor systems beyond morphology control on the basis of system- and ion-level design. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

A quantitative relationship between bond length, crystal morphology, and particle size has been established to investigate the morphology transformation of ZnO nanostructures at the nanoregime. Surface bonding conditions dominate the anisotropic growth of ZnO nanoparticles. Critical surface bond lengths at which ZnO can respectively exhibit pyramid-, truncated pencil-, pencil-, and rod-like morphologies were quantitatively calculated under different extension/shrinkage degrees of Zn−O bond length in the lattice. The size of particular ZnO nanostructures was obtained by tracking the variation of bond length in the lattice. At the nanoregime, ZnO thermodynamically prefers to exhibit nanorods with a diameter smaller than 3.60 nm, nanopyramids with size smaller than 2.94 nm, nanopencils with a diameter larger than 3.15 nm, and truncated nanopencils with a diameter larger than 3.92 nm. Our results are in agreement with experimental observations and indicate the fundamental role of surface bonding control in tailoring anisotropic growth of ZnO nanostructures.

Morphology evolution of inorganic/organic crystals during crystallization is a universal growth phenomenon. In this work, we have developed a capping agent-assisted strategy to clearly identify the whole process of morphology evolution in solution growth system. One kind of morphology evolution trend with three types of morphologies of cuprous oxide ( Cu 2 O ) was kinetically observed at varying the molar ratio of EDTA/ Cu (II) under three different pH values. Two kinds of morphology evolution trends of zinc oxide ( ZnO ) were also kinetically observed in the presence of H 2 O 2 and CH 3 COOH (HAc), respectively. Simulation results show that the morphology evolution of nano- to micro-scale crystals is strongly dependent on the bonding characteristics of a growth system. The present strategy positively explores the interesting principles of morphology evolution of functional materials, and can be widely extended to nano- to micro-scale devices research.

A proportional relationship between the specific capacitance of MnO2 and the percentage of effective Mn centers that act as active sites in the Faradaic charge storage has been established on the basis of a tunnel structure–crystallization behavior correlation. A quantitative relationship between the effective Mn centers at the surfaces and in the tunnels can distinguish the specific capacitance values that arise from the adsorption/desorption and insertion/extraction processes, respectively, of different MnO2 crystallographic forms in the Faradaic charge storage. The different specific capacitance values between the MnO2 crystallographic forms are mainly attributed to the different effective utilizations of Mn centers in the size‐limited tunnels. The present model demonstrates that increasing the percentage of effective Mn centers via decreasing the crystal size can facilitate obtaining MnO2‐based electrode materials with higher specific capacitance values.

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