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• Defective MnCo-LDH nanoflowers is obtained by simple hydrothermal method. • The MnCo-LDH shows well 3D nanostructure and bimetallic defective vacancy. • The activity of MnCo-LDH is excellent as HER and OER bifunctional catalysts. • The MnCo-LDH show high catalytic activity and stability in potential application. Manganese-cobalt layered double hydroxide (MnCo-LDH) is a kind of layered bimetallic hydroxide with good catalytic performance and stability for water decomposition. In this paper, a series of defective MnCo-LDH materials with different Mn/Co molar ratio was prepared by hydrothermal method. The results show that the MnCo-nanoflowers containing Mn and Co elements are successfully prepared, and all of them contain N, O, Mn and Co elements. The hydrogen evolution reaction (HER) catalytic performance of Co vacancy (V Co)-MnCo-LDH is better than that of commercial electrode Pt/C, and oxygen evolution reaction (OER) catalytic performance of Mn vacancy (V Mn)-MnCo-LDH is better than that of commercial electrode RuO 2. Two-electrode overall water splitting (OWS) test showed that the overpotential required by V Mn -MnCo-LDH/NF||V Co -MnCo-LDH/NF and Pt/C/NF||RuO 2 /NF were 1.56 V and 1.72 V respectively at the current density of 10 mA cm−2, and the catalytic activity of the prepared defective MnCo-LDH is excellent bifunctional electrocatalysts for both HER and OER. [ABSTRACT FROM AUTHOR]

Efficient non-noble metal catalysts for the oxygen evolution reaction (OER) are particularly important in the practical applications of electrocatalytic water splitting (ECWS). Herein, based on a simple quasi chemical vapor deposition (Q-CVD) method, we fabricate a newly Ni 3 S 2 @3-D graphene free-standing electrode for efficient OER applications. The Ni 3 S 2 @3-D graphene integrates the advantageous features of 3-D graphene and Ni 3 S 2 towards OER, such as more interfacial catalytic sites, pore-rich structure, N-doped structure and good electrical conductivity. Benefiting from the favorable features, the Ni 3 S 2 @3-D graphene (especially 900 °C sample) exhibits excellent OER performances in alkaline medium, which includes a low on-set potential (1.53 V), low overpotential of 305 mV at a current density of 10 mA cm−2, and a smaller Tafel slope (50 mV dec−1). This catalyst also shows ultrahigh stability after chronoamperometry response at 10 mA cm−2 for 48 h with 30% increase in the current density. The present work opens a new approach for the one-pot construction of hybrid materials between metal sulfide and graphene to increase the electrocatalytic activity of non-noble metal OER catalysts. • A 3D-GNs@Ni 3 S 2 free-standing electrode has been synthesized by a one-pot Q-CVD technique. • The electrode exhibits remarkable catalytic performance and stability toward OER. • It shows a low on-set potential of 1.53 V, low overpotential of 305 mV at a current density of 10 mA cm−2. • The enhancement effect of graphene acts as dominant role for the high performance and stability. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphitized carbon materials have been proposed as promising catalytic materials for oxygen evolution reaction in alkaline water-electrolysis hydrogen production. In this study, newly graphene-like graphitized carbon nanocages and nitrogen-doped graphitized carbon nanotubes are controllably prepared by using Tween-20 as molecular precursor, Ni as graphitization catalyst and urea as nitrogen source. The as-prepared materials are characterized by X-Ray Diffraction, scanning electron microscope, transmission electron microscopy and Raman spectroscopy X-ray photoelectron spectroscopy. The OER electrochemical performances are evaluated by linear sweep voltammetry and chronoamperometry. It is found that the nitrogen-doped graphitized carbon nanotubes have higher oxygen evolution activity, lower oxygen evolution overpotential and desirable electrochemical stability relative to graphitized carbon nanocages, demonstrating it is a promising catalytic material for OER in alkaline water-electrolysis hydrogen production. Nitrogen-doped graphitized carbon from molecular precursor is successfully fabricated as non-metal electrocatalyst for oxygen evolution reaction (OER). Unlabelled Image • Nitrogen-doped graphitized carbon nanotubes with controllable length are successfully prepared. • Tween-20 molecular precursor was used for rational design of nitrogen-doped graphitized carbon. • An efficient and low-cost carbon-powder-protection solid-phase synthesis strategy is proposed. • Synergistic effect between Ni-catalyzed graphitization and in-situ N doping with urea is proved. • The nitrogen-doped carbon nanotubes exhibit favorable excellent activity and stability for OER. [ABSTRACT FROM AUTHOR]

Ternary nickel cobalt iron layered double hydroxide nanosheet arrays are synthesized on nickel foam (NiCoFe-LDH/NF) and applied as an oxygen evolution reaction electrocatalyst. The oxidative etching and cation exchange caused by Fe-incorporating induce the change of morphology and the formation of Ni3+, thus increase the specific surface area and expose more active sites, finally greatly enhance the electrocatalytic OER performance. As a result, the Ni 2 CoFe 0.5 -LDH/NF electrode exhibits significantly enhanced oxygen evolution reaction performance with a small overpotential of 240 mV at the current density of 10 mA cm−2, a small Tafel slope of 65 mV dec−1 as well as an excellent durability in alkaline conditions for 72 h. Especially, the overpotential of Ni 2 CoFe 0.5 -LDH/NF is only 269 mV and 291 mV at 50 and 100 mA cm−2, respectively. This work provides a good paradigm for the design and fabrication of ternary NiCoFe-based functional electrocatalysts, and demonstrates the great practical potential of the Ni 2 CoFe 0.5 -LDH/NF electrocatalyst in oxygen evolution reaction. Image 1 [ABSTRACT FROM AUTHOR]

Efficient oxygen evolution reaction (OER) electrocatalysts with non-noble metals are very critical for the large-scale exploitation of electrocatalytic hydrogen production systems. To improve the catalytic activity of OER electrocatalysts, several design strategies, such as construction of nanostructures, porous structures and composite materials have been proposed. Herein, spinel NiCo 2 O 4 3-D nanoflowers supported on graphene nanosheets (GNs) are prepared by a simple solvothermal synthesis method as non-noble metal electrocatalysts for OER. The present NiCo 2 O 4 /GNs composite integrates multiple advantages of nanostructures, porous structures and composite materials, including high surface area, abundant catalytic sites and high stability. Benefiting from the favorable features, the NiCo 2 O 4 /GNs composite exhibits a better OER performance than NiCo 2 O 4 and RuO 2 in alkaline medium, which has a low onset potential (1.50 V), a small Tafel slope (137 mV dec−1). The present work opens a new window for the construction of the carbon-supported 3-D nanostructure of transition metal catalysts with optimizable electrocatalytic performances for electrocatalytic hydrogen production. A composite catalyst of spinel NiCo 2 O 4 3-D nanoflowers/graphene nanosheets is successfully fabricated as non-noble metal electrocatalyst for oxygen evolution reaction (OER). Image 1 • 3-D hierarchical structure of NiCo 2 O 4 nanoflowers are fabricated on graphene nanosheets. • A convenient and efficient graphene-mediated solvothermal synthesis strategy is proposed. • Hierarchical NiCo 2 O 4 nanoflowers provide short paths for fast transfer of electrolyte ions. • Graphene nanosheet makes up for the defect of poor conductivity of NiCo 2 O 4 component. • The composite exhibits favorable catalytic performance and good stability toward the OER. [ABSTRACT FROM AUTHOR]

A new nanostructure based on Ni 3 S 2 nanowires@N-doped graphene-like carbon layers supported by nickel foam (Ni 3 S 2 @NGCLs/NF) was synthesized by a conventional CVD technique for overall electrocatalytic water splitting. • N-doped graphene-like carbon layers (NGCLs) coated Ni 3 S 2 nanowires is first reported. • A conventional CVD technique is developed for the construction of Ni 3 S 2 @NGCLs/NF. • Ni 3 S 2 @NGCLs/NF shows lower overpotential and outstanding electrochemical stability. • NGCLs changes Ni 3 S 2 lattice and electron structure, leading to high catalytic activity. A new core/shell 1-D nanostructure based on Ni 3 S 2 nanowires and N-doped graphene-like carbon layers on nickel foam (i.e. Ni 3 S 2 @NGCLs/NF) has been fabricated and applied as composite electrocatalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting. The Ni 3 S 2 @NGCLs exhibit a unique architecture with a well-defined core–shell cable-like one-dimensional nanostructure in which NGCLs act as conductive shell and Ni 3 S 2 nanowire as active core. The composite has a nitrogen content of 6.39% in atomic ratio. The Ni 3 S 2 @NGCLs/NF shows low overpotentials of 271 mV and 134 mV at 10 mA cm−2 in 1.0 M KOH for OER and HER, respectively. Highly durable OER and HER performances were demonstrated by 40 h chronopotentiometry and 10,000 CV cycle tests. Excellent overall water splitting electrocatalytic activity was found in a Ni 3 S 2 @NGCLs/NF‖Ni 3 S 2 @NGCLs/NF two-electrode system. Particularly, an active-phase NiOOH, a highly active substance for OER, can be controllably formed in the reaction process due to the shell structure of multi-layer carbon that slows down the dissolution of Ni 3 S 2. Theoretical calculations suggest that Ni 3 S 2 @NGCLs/NF has a lower ΔG (H*) value of 0.51 eV for HER and lower overpotential value of 0.39 V for OER. These results suggest that the composite structure is a promising bifunctional electrocatalyst. [ABSTRACT FROM AUTHOR]

Layered double hydroxides are one of the most effective electrocatalysts owing to their compositional and structural flexibility. However, their self-stacking leads to limited active sites and low conductivity. In this work, a three-dimensional (3D) core–shell architecture with spatially separated active sites has been fabricated based on layered ternary nickel cobalt iron hydroxide (NiCoFe-LTH) nanosheets and cobalt iron Prussian blue analog (CoFe-PBA) on nickel foam (NF) (i.e., CoFe-PBA@NiCoFe-LTH/NF) with CoFe-PBA as self-sacrificial templates that are partially in situ transformed into NiCoFe-LTH nanosheets. The CoFe-PBA@NiCoFe-LTH/NF has a well-defined core–shell 3D flower-like nanostructure in which NiCoFe-LTH nanosheets create the larger shell while CoFe-PBA nanocubes form the small core. This hybrid structure is evaluated as an electrocatalyst for oxygen evolution reaction (OER) and found to exhibit a low overpotential of 228 mV at 10 mA cm−2, a low Tafel slope of 36 mV dec−1, and good catalytic stability for 72 h in 1.0 M alkaline solution. The strong performance is attributed to the unique 3D core–shell flower-like nanosheet architecture that avoids the stacking of the 2D LTH, provides abundant spatially separated active sites, and enhances electron transport and stability. Furthermore, the OER mechanism and growth process of the electrocatalysts were systematically studied. These results suggest that such electrocatalysts with unique architecture are promising for efficient and durable OER. [ABSTRACT FROM AUTHOR]