An innovative design strategy for the structural and chemical synergistic encapsulation of polysulfides is proposed enabling the achievement of ultra stable lithium–sulfur batteries.

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Hydrogen generation from electrochemical water-splitting is an attractive technology for clean and efficient energy conversion and storage, but it requires efficient and robust non-noble electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER). Nonprecious transition metalorganic frameworks (MOFs) are one of the most promising precursors for developing advanced functional catalysts with high porosity and structural rigidity. Herein, a new transition metal-based hollow multivoid nanocuboidal catalyst synthesized from a ternary Ni-Co-Fe (NCF)-MOF precursor is rationally designed to produce dual-functionality toward OER and HER. Differing ion exchanging rates of the ternary transition metals within the prussian blue analog MOF precursor are exploited to produce interconnected internal voids, heteroatom doping, and a favorably tuned electronic structure. This design strategy significantly increases active surface area and pathways for mass transport, resulting in excellent electroactivities toward OER and HER, which are competitive with recently reported single-function nonprecious catalysts. Moreover, outstanding electrochemical durability is realized due to the unique rigid and interconnected porous structure which considerably retains initial rapid charge transfer and mass transport of active species. The MOF-based material design strategy demonstrated here exemplifies a novel and versatile approach to developing non-noble electrocatalysts with high activity and durability for advanced electrochemical water-splitting systems.

Despite the intensive studies of combining silicon (Si) and reduced graphene oxide (rGO), the architecture of Si-rGO composites still needs to be improved to maintain better electrode structure integrity and stable solid electrolyte interphase (SEI) upon extensive cycling. Herein, a conductive and protective network with rGO and CVD-implemented carbon is constructed with silicon nanoparticles (Si NPs) embedded inside for the first time. Compared with the regular Si-rGO composite with only Si NPs wrapped by rGO, Si-rGO-C composite successfully improves the electrical conductivity and structure stability. In addition to the wrapping of rGO on Si NPs, the additional carbon layer on the partially exposed Si NPs provides extra protection from fracture during volume change and helps form a stable SEI layer. Carbon rods between rGO flakes function as conductive bridges, creating an effective conductive network on a macroscopic scale. The initial capacity of Si-rGO-C composite reaches 1139 mAh g -1 and 894 mAh g -1 at 0.1 A g -1 and 1C respectively, and retains 94% of its initial capacity after 300 cycles at 1C. The electrode is stabilized at 770 mAh g -1 at 2C during rate performance testing. Introduction:The ever soaring market of portable electronic devices has triggered significant demand and unprecedented research interests for high performance batteries. Lithium ion batteries (LIBs) have been dominating the market for electronic devices due to its relatively higher working potential, higher specific power and energy densities, and better environmentally friendliness compared to previous battery technologies such as lead acid, nickel cadmium, and nickel metal hydride batteries.[1, 2] However, the development of LIB technology has fallen far behind the pace of the advancement of © 2015. This manuscript version is made available under the Elsevier user license

wileyonlinelibrary.comsulfur into the electrolyte, followed by its subsequent diffusion to the anode or more commonly known as the polysulfide (PS) shuttle effect. This causes unwanted side reactions ultimately resulting in poor cycle durability, low energy density, and low coulombic efficiency. [6b,7] A common strategy to mitigate the PS shuttle effect is to confine the PS within the cathode with host materials such as graphene foams, [8] various types of porous carbon, [6b,9] in addition to doped-carbon materials exhibiting PS adsorptive capabilities. [10] While LIS's stability and energy density is crucial, a high rate performance should be considered to be equally important and put under more scrutiny in the scientific community. In the case of electric vehicles (EV), the rate capability of the battery can influence the recharge time, acceleration, and regenerative braking efficiency. All of these parameters directly affect the final user experience of the vehicle and can cause serious damage to the reputation of EVs if poorly implemented. Often researchers have achieved LIS with impressive cycle durability, coulombic efficiency, and capacity, but do not fare well when subjected to higher rate performance tests. Indeed, a complex pore network will limit PS diffusion and provide enhanced durability, but the very same tortuous diffusion pathway out of the cathode will inevitably increase lithium ion diffusion resistance. When combined with the known electrolyte viscosity/resistance increase upon PS dissolution, [11] it is understandable as to why the rate performance is poor. Recent research into the rate performance of LIS revolves around providing efficient lithium ion and electron mass transfer pathways [12] or additional battery components such as an interlayer to provide additional surface area for faster PS reduction kinetics. [13] Interestingly, hollow structures, which have been previously used to successfully address the stability problems of LIS, commonly demonstrate excellent rate performances. [9,14] The distinct difference between hollow porous structures and regular porous carbon lies in the separation of the core electrolyte from the bulk electrolyte phases. The shell can act as a physical barrier to encapsulate PS, limiting dissolution of active sulfur material into the bulk electrolyte. More importantly, the hollow structures can serve as a electrolyte reservoir [15] to redirect PS diffusion inwards and reduce the PS concentration in the bulk electrolyte. This mitigates the effects of the PS dissolution induced viscosity increase. Accordingly, A CO 2 in water nanoparticle stabilized Pickering emulsion is used to template micrometer sized hollow porous nitrogen doped carbon particles for high rate performance lithium sulfur battery. For the first time, nanoparticles serve the dual role of an emulsion stabilizer and a pore template for the shell, directly utilizing in situ generated CO 2 bubbles as template for the core. The minimalistic nature of this method does not require expensive surfac...