Highly-porous hierarchically microstructure of graphene-decorated nickel foam supported two-dimensional quadrilateral shapes of cobalt sulfide nanosheets as efficient electrode for methanol oxidation

In this study, unique quadrilateral shaped cobalt-based nanosheets were directly synthesized onto graphene-decorated nickel foam as a binder-free and non-noble electrocatalyst for the methanol oxidation reaction (MOR) in an alkaline solution. The graphene-decorated nickel foam was prepared via chemical vapor deposition (CVD) as the three-dimensional graphene (3DGr) substrate. The graphene-decorated nickel foam was prepared via chemical vapor deposition (CVD) as the three-dimensional graphene (3DGr) substrate. Two-dimensional quadrilateral (2DQ) Co(CO3)(0.5)center dot 0.11H(2)O nanosheets (2DQ-Co(CO3)(0.5)center dot 0.11H(2)O-NSs) were vertically synthesized onto the graphene surface of 3DGr by a hydrothermal process to form the hierarchical nanostructure of 2DQ-Co (CO3)(0.5)center dot 0.11H(2)O-NSs/3DGr. Then, Co(CO3)(0.5)center dot 0.11H(2)O-NSs was sulfurized using Na2S as the sulfur precursor to convert Co(CO3)(0.5)center dot 0.11H(2)O to Co3S4 in a second hydrothermal treatment to fabricate the 2DQ-Co3S4-NSs/3DGr electrode. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrocatalytic activity of the MOR was evaluated by cyclic voltammetry and chronoamperometry methods. Compared with the 3DGr and 2DQ-Co (CO3)(0.5)center dot 0.11H(2)O-NSs/3DGr electrodes, the 2DQ-Co3S4-NSs/3DGr electrode exhibited superior electrocatalytic activity of the MOR in the alkaline solution. The unique hierarchical microstructure of the 2DQ-Co3S4-NSs/3DGr architecture consisting of a 3D porous structure supporting 2DQ Co3S4-NSs with profuse exposed planes has many advantages. Porous 3DGr provides sufficient open space for rapid ionic transportation and provides a large surface area to load a remarkable quantity of 2DQ Co3S4-NSs. CVD-graphene decorated on nickel foam offered seamless connections at the interface of graphene and 2DQ Co3S4-NSs, and also acted as a low-inner-resistance current collector for fast electron transfer. 2DQ Co3S4-NSs directly synthesized on graphene not only provided the large surface area for the MOR, but also hindered aggregation to improve the utilization efficiency as a result of the exposed planes with plentiful catalytic active sites. The outstanding electrocatalytic activity of the hierarchical-structure, hybrid nanomaterial of the 2DQ-Co3S4-NSs/3DGr electrode is promising for the development of direct methanol fuel cells based on non-noble and low-cost catalysts.