In this work, we demonstrated the enhanced oxygen evolution reaction (OER) activity of flower-shaped cobalt-nickel oxide (NiCo2O4) decorated with iridium-nickel bimetal as an electrode material. The samples were prepared by carefully depositing pre-synthesized IrNi nanoparticles on the surfaces of the NiCo2O4 nano-flowers. Compared with bare NiCo2O4, IrNi, and IrNi/Co3O4, the IrNi/NiCo2O4 exhibited significantly enhanced electrocatalytic activity in the OER, including a lower overpotential of 210 mV and a higher current density at an overpotential of 540 mV. We found that the IrNi/NiCo2O4 showed more efficient electron transport behavior and reduced polarization because of its bimetal IrNi modification by analyzing its Tafel slope and turnover frequency. Furthermore, the electrocatalytic mechanism of IrNi/NiCo2O4 in the OER was studied, and it was found that the combined active sites of the composite effectively improved the rate determining step. The synergic effect of the bimetal and metal oxide plays an important role in this reaction, enhancing the transmission efficiency of electrons and providing more active sites for the OER. The results reveal that IrNi/NiCo2O4 is an excellent electrocatalyst for OER.本文制备了一种双金属IrNi修饰的花状NiCo2O4复合材料, 并研究了其对于氧析出反应的电化学活性, 结果显示其电化学活性明显提升. NiCo2O4和IrNi分别通过水热法和热分解法制备, 再通过超声复合, 使得双金属附着在复合氧化物表面. 通过与纯NiCo2O4, IrNi以及IrNi/Co3O4相比较, 所制备的IrNi/NiCo2O4对于氧析出反应的性能最为优异. 在各个参数指标中, 拥有最低的过电势210 mV, 在540 mV的过电势下具有最高的电流密度. 电子转移数和塔菲尔斜率分析表明该复合材料由于修饰上了双金属材料, 极大地降低了极化, 具有更高效的电子转移速率. 此外本文还对电催化机理进行了研究, 发现复合材料结合反应位点有效改善了反应速率决定步骤. 其中, 协同效应起着至关重要的作用, 这一效应明显提高电子传输效率的同时提供了更多的活性位点. IrNi/NiCo2O4是一种出色的氧析出反应电催化剂.

In this context, we firstly synthesized a novel nitrogen-doped multiporous carbon material from renewable biological cells through a facile chemical activation with K2CO3. After sulfur impregnation, the carbon/sulfur composite achieved a sulfur content of about 67 wt%. The C/S composite as the cathode of lithium–sulfur batteries exhibited a discharge capacity of 1410 mAh/g and good capacity retention of 912 mAh/g at 0.1C. These outstanding results were attributed to the synergy effect of microporous carbon and natural doping nitrogen atoms. We believe that the facile approach for the synthesis of nitrogen-doped multiporous carbon from the low-cost and sustainable biological resources will not only be applied in lithium–sulfur batteries, but also in other electrode materials.A novel nitrogen-doped multiporous carbon material from renewable biological cells was synthesized through a facile chemical activation with K2CO3, and employed as sulfur stabilizers for high-performance lithium–sulfur batteries.

In this study, a facile one-pot process for the synthesis of hierarchical VS2/graphene nanosheets (VS2/GNS) composites based on the coincident interaction of VS2 and reduced graphene oxide (rGO) sheets in the presence of cetyltrimethylammonium bromide is developed for the first time. The nanocomposites possess a hierarchical structure of 50 nm VS2 sheets in thickness homogeneously anchored on graphene. The VS2/GNS nanocomposites exhibit an impressive high-rate capability and good cyclic stability as a cathode material for Li-ion batteries, which retain 89.3% of the initial capacity 180.1 mAh g–1 after 200 cycles at 0.2 C. Even at 20 C, the composites still deliver a high capacity of 114.2 mAh g–1 corresponding to 62% of the low-rate capacity. Expanded studies show that VS2/GNS, as an anode material, also has a good reversible performance with 528 mAh g–1 capacity after 100 cycles at 200 mA g–1. The excellent electrochemical performance of the composites for reversible Li+ storage should be attributed to the exceptional interaction between VS2 and GNS that enabled fast electron transport between graphene and VS2, facile Li-ion diffusion within the electrode. Moreover, GNS provides a topological and structural template for the nucleation and growth of two-dimensional VS2 nanosheets and acted as buffer matrix to relieve the volume expansion/contraction of VS2 during the electrochemical charge/discharge, facilitating improved cycling stability. The VS2/GNS composites may be promising electrode materials for the next generation of rechargeable lithium ion batteries.Keywords: cathode materials; graphene; layered-VS2; lithium ion batteries; transition metal dichalcogenides;

•UMPC synthesized with graphene as template by glucose hydrothermal carbonized self-assemble.•Stable smaller sulfur molecules were implanted in ultrathin-microporous carbon.•UMPC with excellent conductivity improves the C-rate performance of S@UMPC.•900 mAh g−1 is kept after 150 cycles charge/discharge process at 0.1 C.Ultrathin microporous carbon (UMPC) for lithium–sulfur (Li–S) cathode with uniform pore width of approximately 0.6 nm and dozens nm in thickness is synthesized with graphene oxide as template by glucose hydrothermal carbonization and surfactant-assisted assembling method. The UMPC supplies desirable S pregnancy space and the intimate contact between UMPC and S, therefore improving the conductivity of S@UMPC composite and dynamic performance. Smaller sulfur molecules limited in UMPC thoroughly prevent the formation of electrolyte-soluble polysulfides, hence excellent cycling performance with 900 mAh g−1 after 150 cycles is kept. Ultrathin three-dimensional carbon nanosheets are significant to fast electron transfer and Li+ diffusion contributing to excellent dynamic performance (710 mAh g−1 at 3 C).

•S@rGO composite was synthesized via HI reduction and surfactant assisted chemical method.•The mechanism of HI reduction of GO with high conductivity is suggested.•980 mAh g−1 capacity is kept after 200 cycles charge/discharge process.•High C-rate current activation is used to prevent the shuttle of polysulfide ions.We developed hydrogen iodide (HI) reduction of rGO and surfactant-assisted chemical reaction- deposition method to form hybrid material of sulfur (S) encapsulated in reduced graphene oxide (rGO) sheets for rechargeable lithium batteries. The surfactant-assisted chemical reaction–deposition method strategy provides intimate contact between the S and graphene oxide. Chemical reduced rGO with high conductivity as carbon coating layer prevented the dissolution of polysulfide ions and improved the electron transfer. This novel core–shell structured S@rGO composites with high S content showed high reversible capacity, good discharge capacity retention and enhanced rate capability used as cathodes in rechargeable Li/S cells. We demonstrated here that an electrode prepared from a S@rGO with up to 85 wt% S maintains a stable discharge capacity of about 980 mAh g−1 at 0.05 C and 570 mAh g−1 at 1C after 200 cycles charge/discharge. These results emphasize the importance of rGO with high electrical conductivity after HI-reduced rGO homogeneously coating on the surface of S, therefore, effectively alleviating the shuttle phenomenon of polysulfides in organic electrolyte. Our surfactant-assisted chemical reaction-HI reduction approach should offer a new technique for the design and synthesis of battery electrodes based on highly conducting carbon materials.

Lithium sulfide (Li2S), which has a high theoretical specific capacity of 1166 mA h g−1, has potential application in cathode materials because of its high safety and compatibility with lithium-free anodes for Li–S batteries. However, its low electron conductivity and lithium transfer cause significant polarization in Li2S electrodes. Here, we demonstrate the use of ultrasmall Li2S nanocrystals encapsulated in N-rich carbon (NRC) as a cathode material for Li–S batteries. By evaporating a mixture of polyacrylonitrile (PAN) and Li2S in dimethylformamide (DMF) solution and then subjecting the mixture to carbonization, a nano-Li2S@NRC composite with ultrasmall Li2S well dispersed in its carbon matrix was successfully synthesized. The obviously lower potential barriers and excellent cycling performance of nano-Li2S@NRC electrodes confirm their improved polarization because of the size effect of Li2S nanocrystals and the good electron transfer between Li2S and N-doped carbon. The nano-Li2S@NRC cathode delivers a high initial specific capacity of 1046 mA h g−1 of Li2S (∼1503 mA h g−1 of S) at 0.25C and 958 mA h g−1 of Li2S (∼1376 mA h g−1 of S) at 0.5C with a favorable cycling performance with an ∼0.041% decay rate per cycle over 1000 cycles.