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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]