No abstract

In magnetoelectric materials, magnetic and dielectric/ferroelectric properties couple to each other. This coupling could enable lower power consumption and new functionalities in devices such as sensors, memories and transducers, since voltages instead of electric currents are sensing and controlling the magnetic state. We explore a different approach to magnetoelectric coupling in which we use the magnetic spin state instead of the more traditional ferro or antiferromagnetic order to couple to electric properties. In our molecular compound, magnetic field induces a spin crossover from the S = 1 to the S = 2 state of Mn 3+ , which in turn generates molecular distortions and electric dipoles. These dipoles couple to the magnetic easy axis, and form different polar, antipolar and paraelectric phases vs magnetic field and temperature. Spin crossover compounds are a large class of materials where the spin state can modify the structure, and here we demonstrate that this is a route to magnetoelectric coupling.

Lithium‐sulfur batteries have recently attracted academic/industrial attention due to the high theoretical energy density. However, the capacity decay mainly caused by the polysulfides shuttle effect and poor conductivity of sulfur. Herein, in situ growth of ZnCo2O4 quantum dots (ZCO‐QDs) embedded into the hollow carbon‐carrier sphere (HCS) to form the ZnCo2O4 quantum dots nanocapsule (ZCO‐QDs@HCS) as the multifunctional sulfur host is rationally demonstrated. Based on density‐functional theory calculations, in situ spectroscopic techniques, and electrochemical studies, the synergistic effects on anchoring/catalyzing polysulfide of the ZCO‐QDs@HCS composite in Li‐S batteries is investigated. Interestingly, the ZCO‐QDs@HCS also allows for the controlled release of ZCO‐QDs into the Li‐S electrolyte. Subsequently, it is first discovered that these diffused ZCO‐QDs can act as self‐repairing initiators to stabilize Li metal anodes via rebuilding the damaged solid electrolyte interphase and suppressing Li dendrites growth. With this concept, quantum dots‐based catalyst delivery systems is first constructed in a Li‐S battery, which is similar to the use of nanocarrier‐based drug delivery systems in cancer therapy. The Li‐S cells with the S@ZCO‐QDs@HCS cathode display significantly superior electrochemical performances with a high specific capacity (1350.5 mAh·g−1 at 0.1 C) and excellent cycling stability (capacity decay rate of 0.057% per cycle after 1000 cycles at 3.0 C).

The advancement of a naturally rich and effective bifunctional substance for hydrogen and oxygen evolution reaction is crucial to enhance hydrogen fuel production efficiency via the electrolysis process. Herein, facile and scalable hydrothermal synthesis of bifunctional electrocatalyst of polyoxometalate anchored zinc cobalt sulfide nanowire on Ni-foam (NF) for overall water splitting is reported for the first time. The electrochemical analysis of POM@ZnCoS/NF displays significantly low HER and OER overpotentials of 170/337 and 200/300 mV to attain a current density of 10/40 and 20/50 mA cm −2 , respectively, demonstrating the notable performance of POM@ZnCoS/NF toward H 2 and O 2 evolution reaction in alkaline medium. Additionally, the electrolyzer consisting of the POM@ZnCoS/NF anode and cathode shows an appealing potential of 1.56 V to deliver 10 mA cm −2 current density for overall water splitting. The high electrocatalytic activity of the POM@ZnCoS/NF is attributed to modulation of the electronic and chemical properties, increment of the electroactive sites and electrochemically active surface area of the zinc cobalt sulfide nanowires due to the anchorage of polyoxometalate nanoparticles. These results demonstrate the advantage of the polyoxometalate incorporation strategy for the design of cost-effective and highly competent bifunctional catalysts for complete water splitting.

cathodes, fast capacity degradation, and low Coulombic efficiency. The low electrical/ionic conductivities of sulfur, shuttle effect of long-chain lithium polysulfides (Li 2 S n , 4 ≦ n ≦ 8) and large volume expansion of sulfur cathode (80%) upon lithiation during charge/discharge hinder the practical application of Li-S batteries. [6][7][8] Various strategies have been implemented to overcome these problems including a) designing novel cathodes to increase the electrode conductivity and inhibiting lithium polysulfides (LiPSs) shuttle, b) investigating new electrolyte, separator, and binder to minimize polysulfide migration, and c) protecting Li anode to avoid LiPSs passivation. [9][10][11][12] Despite much time and effort that has been devoted, the life and energy density of Li−S batteries is far from satisfactory to meet the needs of daily life so far.The insulating nature of sulfur itself and polysulfides shuttle effects become the initiator problems of Li−S batteries, therefore finding suitable cathode materials is a crucial step for the commercialization of Li-S batteries. [3,5] Initially, carbon-based materials have been extensively studied, such as micro/mesoporous carbons, hollow porous carbon spheres, carbon nanotubes/fibers, etc, but most nonpolar carbonaceous materials cannot effectively inhibit the shuttling of LiPSs. [13][14][15] The polar compounds such as metal oxides, [16,17] sulfides, [18,19] carbides, [20,21] nitrides, [22,23] metal−organic frameworks, [24] etc., as sulfur hosts have been used for LiPSs adsorption by forming chemical bonds with LiPSs. However, the low catalytic ability of oxides, [16,17] the weak affinity of carbides, [20,21] the aggregation of nitrides, [22,23] and the low conductivity of metal−organic frameworks, [24] are issues that still restrict their further application. Transition metal sulfides (TMSs) have a strong absorption with polysulfides by chemical bonding. [18,19] In particular, molybdenum disulfide (MoS 2 ) as the host cathode material is a promising candidate because of its intrinsic chemical activity and low cost. [25,26] Arava and co-workers demonstrated the preferential adsorption and conversion of LiPSs by electrocatalytic MoS 2 atomic layers. [27] Chen and co-workers also reported 3D graphene/1T MoS 2 heterostructures as highly efficient Lithium-sulfur batteries are one of the most promising next-generation energy storage systems. The efficient interconversion between sulfur/lithium polysulfides and lithium sulfide is a performance-determining factor for lithium-sulfur batteries. Herein, a novel strategy to synthesize a unique tubein-tube CNT-wired sulfur-deficient MoS 2 nanostructure embedding cobalt atom clusters as an efficient polysulfide regulator is successfully conducted in Li−S batteries. It is confirmed that encapsulating MWCNTs into hollow porous sulfur-deficient MoS 2 nanotubes embedded with metal cobalt clusters not only can accelerate electron transport and confine the dissolution of lithium polysulfide by physical/chemical adsorption, but als...