Catalytic properties of nanoparticles can be significantly enhanced by controlling nanoscale alloying and its structure. In this work, by using a facet-controlled Pt@Ni core-shell octahedron nanoparticle, we show that the nanoscale phase segregation can have directionality and be geometrically controlled to produce a Ni octahedron that is penetrated by Pt atoms along three orthogonal Cartesian axes and is coated by Pt atoms along its edges. This peculiar anisotropic diffusion of Pt core atoms along the ⟨100⟩ vertex, and then toward the ⟨110⟩ edges, is explained via the minimum strain energy for Ni-Ni pair interactions. The selective removal of the Ni-rich phase by etching then results in structurally fortified Pt-rich skeletal PtNi alloy framework nanostructures. Electrochemical evaluation of this hollow nanoframe suggests that the oxygen reduction reaction (ORR) activity is greatly improved compared to conventional Pt catalysts.

as smartphones, electric vehicles, and energy storage systems depend on LIBs to provide the necessary power for optimal performance. Today, that dependency continues to grow at an exponential rate as the portfolio of electronic devices and vehicles diversifies. The common denominator for the myriad of commercialized devices is the constant demand for high power and long usage time. Accordingly, the frontrunners of today's technology are striving to optimize LIBs to meet such performance demands. While such efforts have extended the usage time of various devices, this direction has also exposed critical issues with current battery technology: safety and cost.The main cause for safety hazards with LIBs is linked to the use of organic electrolytes. In the unfortunate event of a short circuit in a battery, a sudden burst of exothermic reactions is accelerated by the presence of organic solvents, which act as fuel for ensuing fires. This problem is exacerbated in high energy density configurations where materials are densely packed. The risk of fire hazards has prompted a search for alternative battery systems, among which rechargeable aqueous batteries have garnered significant attention as viable candidates for safe batteries. Replacing the organic solvent with water as the electrolyte medium has significant implications. In addition to the benefit of heightened safety, water has a high ionic conductivity compared to conventional organic solvents (2-3 orders of magnitude higher), a useful quality for high C-rate operations. Moreover, the use of water can reduce costs incurred from moisture regulation during manufacturing.Unfortunately, despite these attractive aspects, aqueous electrolytes impose certain barriers. Most critically, the thermodynamic stability window of water is limited to 1.23 V, beyond which detrimental hydrogen and oxygen evolution reactions (HER/OER) occur. As a result, even if kinetic overpotentials are taken into account, the operating potential windows of aqueous batteries are significantly narrower than those of their organic counterparts. This motivates the search for adequate materials that provide maximum energy within such a narrow voltage window. The prevalent layered oxide/graphite system used in conventional LIBs is no longer an option in this system due to such voltage constraints. Instead, on the anode side, zinc (Zn) metal is considered to be a promising candidate. [1] Not only is Zn abundant in nature, nontoxic, and cheap, but its metallic Aqueous zinc ion batteries (AZIBs) are steadily gaining attention based on their attractive merits regarding cost and safety. However, there are many obstacles to overcome, especially in terms of finding suitable cathode materials and elucidating their reaction mechanisms. Here, a mixed-valence vanadium oxide, V 6 O 13 , that functions as a stable cathode material in mildly acidic aqueous electrolytes is reported. Paired with a zinc metal anode, this material exhibits performance metrics of 360 mAh g −1 at 0.2 A g −1 , 92% capacity retention after...

Focus Serial: Frontiers of Nonlinear Optics

A spatial confiment of polysulfides using the metal compound additives having polar surfaces has been considered to be a promising approach to address the insufficient rate capability and cyclability of lithium–sulfur batteries. Herein, we report a more effective approach outperforming this conventional one: a heterogeneous catalysis to promote polysulfide fragmentations. It was revealed using combined computational and experimental approaches that an ultrastrong adsorption of elemental sulfur on TiN surfaces resulted in a spontaenous fragmentation into shorter chains of polysulfides. This heterogeneous catalysis reaction improved the sluggish kinetics of polysulfide reduction because of the chemical disproportionation at the second plateau. A markedly enhanced rate capability was finally obtained, exhibiting a discharge capacity of 700 mAh g–1 at a scan rate of 5C.