Exploring noble-metal-free electrocatalysts with high efficiency for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) holds promise for advancing the production of H2 fuel through water splitting. Herein, one-pot synthesis was introduced for MoS2–Ni3S2 heteronanorods supported by Ni foam (MoS2–Ni3S2 HNRs/NF), in which the Ni3S2 nanorods were hierarchically integrated with MoS2 nanosheets. The hierarchical MoS2–Ni3S2 heteronanorods allow not only the good exposure of highly active heterointerfaces but also the facilitated charge transport along Ni3S2 nanorods anchored on conducting nickel foam, accomplishing the promoted kinetics and activity for HER, OER, and overall water splitting. The optimal MoS2–Ni3S2 HNRs/NF presents low overpotentials (η10) of 98 and 249 mV to reach a current density of 10 mA cm–2 in 1.0 M KOH for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, such heteronanorods show a quite low cell voltage of 1.50 V at 10 mA cm–2 and remarkable stability for more than 48 h, which are among the best values of current noble-metal-free electrocatalysts. This work elucidates a rational design of heterostructures as efficient electrocatalysts, shedding some light on the development of functional materials in energy chemistry.Keywords: electrocatalysis; heterointerfaces; hydrogen evolution reaction; metal sulfides; overall water splitting; oxygen evolution reaction;

•MoS2 nanosheets vertically grow on cotton-derived carbon microfibers.•The carbon fibers facilitate charge transfer and structure stabilization.•The MoS2/CDCFs exhibit enhanced cyclic performance for reversible Na+ storage.Carbon fibers derived from bio-template are low cost and environmental benign, therefore have attracted much attention in energy storage materials. In this work, we successfully fabricated MoS2/cotton-derived carbon fibers (MoS2/CDCFs) via hydrothermal route followed by carbonization process. In the composite of MoS2/CDCFs, MoS2 nanosheets vertically grow on the carbon fibers which offer fast ways for electron transfer and at the same time act as robust support to buffer the volume changes of MoS2 nanosheets during discharge/charge cycles. As anode materials for sodium-ion batteries, MoS2/CDCFs exhibit good rate performance and markedly enhanced cyclic stability due to the conductive support of CDCFs. At a current density of 0.1 A g−1, the MoS2/CDCFs-1 shows an initial reversible capacity of 504.9 mAh g−1, and maintains 444.5 mAh g−1 after 50 cycles. Even when the current density increases to 0.5 A g−1, it maintains 323.1 mAh g−1 after 150 cycles, which is much higher than the capacity retention of 149.6 mAh g−1 for the bare MoS2 nanosheets. The improved electrochemical performance verifies the effective strategy of using cotton as carbon source to construct hierarchical composites for sodium-ion batteries.Download high-res image (315KB)Download full-size image

•(SnOx-Sn)@FLG nanocomposite is prepared by oxygen plasma assisted ball milling.•SnOx-Sn nanoparticles are wrapped by in-situ exfoliated few-layered graphene.•The (SnOx-Sn)@FLG nanocomposite exhibits excellent cyclic stability for Na+ storage.The (SnOx-Sn)@few layered graphene ((SnOx-Sn)@FLG) composite has been synthesized by oxygen plasma-assisted milling. Owing to the synergistic effect of rapid plasma heating and ball mill grinding, SnOx (1 ≤ x ≤ 2) nanoparticles generated from the reaction of Sn with oxygen are tightly wrapped by FLG nanosheets which are simultaneously exfoliated from expanded graphite, forming secondary micro granules. Inside the granules, the small size of the SnOx nanoparticles enables the fast kinetics for Na+ transfer. The in-situ formed FLG and residual Sn nanoparticles improve the electrical conductivity of the composite, meanwhile alleviate the aggregation of SnOx nanoparticles and relieve the volume change during the cycling, which is beneficial for the cyclic stability for the Na+ storage. As an anode material for sodium-ion batteries, the (SnOx-Sn)@FLG composite exhibits a high reversible capacity of 448 mAh g−1 at a current density of 100 mA g−1 in the first cycle, with 82.6% capacity retention after 250 cycles. Even when the current density increases to 1000 mA g−1, this composite retains 316.5 mAh g−1 after 250 cycles. With superior Na+ storage stability, the (SnOx-Sn)@FLG composite can be a promising anode material for high performance sodium-ion batteries.Download high-res image (239KB)Download full-size image

•Carbon coating on MoS2 was achieved by CVD using ethanol vapor as carbon source.•Enhanced conductivity and stabilized nanosheets due to the coating were verified.•Carbon coated MoS2 nanosheets exhibit high rate capability and cycle stability.MoS2 nanosheets with conformal carbon coating are achieved via a facile, chemical vapor deposition process, employing ethanol vapor as carbon source. The uniform carbon layers are semi-graphitized, which facilitate kinetics for electron and ion transfer, accommodate volume variation of MoS2, and relieve dissolution of polysulfide during repeated discharge/charge cycles. As anode materials for sodium-ion batteries, the optimized carbon coated MoS2 nanosheets show stable reversible capacity of ∼500 mAh g−1 for 100 cycles at 0.1 A g−1, and maintain 351.6 mAh g−1 after 200 cycles even at 1 A g−1. Furthermore, the enhanced electron transfer, and the stabilized structure are verified through electrochemical impedance spectroscopy, cyclic voltammetry, as well as scanning electron microscopy. Our results show that the carbon coating by chemical vapor deposition is efficient and promising to improve the reversible Na+ storage performance of anode materials.Download high-res image (166KB)Download full-size image

•The biomass-derived sources are used to fabricate well-defined MoCx/CN.•Superior electrochemical HER performances are presented on MoCx/CN nanocomposites.•N-doping controlled by synthesis is important for achieving efficient MoCx/CN.Exploring noble-metal free electrocatalysts remains a great challenge for hydrogen evolution reaction (HER). Herein, we report the fabrication of molybdenum carbides supported by N-doped carbon (MoCx/CN), employing glucose and melamine as precursors to generate conducting supports. The nanosized MoCx, and its intimate contact with CN, favor the efficient HER. The optimal MoCx/CN delivers an overpotential (η) of 220 mV to produce a current density (j) of 10 mA cm−2, and a high j of 72 mA cm−2 at η=300 mV in 0.5 M H2SO4.

•Efficient Ir/H-MoOx catalysts were fabricated via one-pot strategy.•Strong electronic metal-support interactions were evidenced in Ir/H-MoOx.•Ir/H-MoOx shows highly chemoselective hydrogenation for various α,β-unsaturated aldehydes.As reducible supports, metal oxides present the varied charge effect after hydrogen doping and partial reduction, accomplishing the tunable metal-support interactions and the promoted catalytic turnover in heterogeneous catalysis. Herein, the one-pot fabrication of hydrogenated MoOx (H-MoOx) nanorods supported Ir (Ir/H-MoOx) was developed, which simultaneously combined the generation of active centers (Ir) and the hydrogen doping on supports (H-MoOx). Because of the accumulated electrons around MoO6 octahedras after hydrogen doping, the electronic perturbations arising from H-MoOx supports led to the negatively charge Irδ− species being beneficial for the selective hydrogenation of CO moiety in α,β-unsaturated aldehydes. In the hydrogenation of cinnamaldehyde to cinnamyl alcohol, Ir/H-MoOx delivered selectivity as high as ∼93%, performing among the best of current metal-based catalysts. Additionally, the efficacy for various substrates with multiple groups further verified our Ir/H-MoOx system to be competitive for chemoselective hydrogenation.H2 spillover on in-situ formed Ir was utilized to hydrogenate MoO3 on-site, accomplishing the hydrogenated MoOx supported Ir for the chemoselective hydrogenation of α,β-unsaturated aldehydes. The active Irδ- species resulting from the strong electronic metal-support interactions is responsible for the selective CO hydrogenation.

The exposure of rich active sites is crucial for MoS2 nanocatalysts in efficient hydrogen evolution reaction (HER). However, the active (010) and (100) planes tend to vanish during preparation because of their high surface energy. Employing the protection by thiourea (TU) reactant, a microwave-assisted reactant-protecting strategy is successfully introduced to fabricate active-site-rich MoS2 (AS-rich MoS2). The bifunctionality of TU, as both a reactant and a capping agent, ensures rich interactions for the effective protection and easy exposure of active sites in MoS2, avoiding the complicated control and fussy procedure related to additional surfactants and templates. The as-obtained AS-rich MoS2 presents the superior HER activity characterized by its high current density (j = 68 mA cm–2 at −300 mV vs RHE), low Tafel slope (53.5 mV dec–1) and low onset overpotential (180 mV), which stems from the rich catalytic sites and the promoted conductivity. This work elucidates a feasible way toward high performance catalysts via interface engineering, shedding some light on the development of emerging nanocatalysts.Keywords: active sites; hydrogen evolution; microwave; molybdenum disulfide; reactant-protecting

•Firstly applying Mo2C/N-C HNWs in sodium ion batteries (SIBs).•The hybrid nanostructure enables good performance of Na+ storage.•Such material will be a new promising anode material for SIBs.Herein we report Mo2C/N-doped carbon hierarchical nanowires (Mo2C/N-C HNWs) as anode materials for sodium-ion batteries. In the Mo2C/N-C HNWs, Mo2C nanocrystallites are uniformly distributed in N-doped carbon matrix. The nanocrystallites of Mo2C offer short paths for Na+ diffusion, the mesoporous structure facilitates the diffusion of electrolyte, and the N-doped carbon matrix accelerates the electron transfer. As anode materials for sodium-ion batteries, the Mo2C/N-C HNWs exhibited reversible capacities of 381 and 308 mAh g−1 at current densities of 50 and 200 mA g−1, respectively. Our results demonstrate the enhanced Na+ storage activity of Mo2C after structure tailoring, elucidating the potential of transition-metal carbides as promising anode materials for sodium-ion batteries.