Self-assembly of two-dimensional bimetallic nickel-cobalt phosphate nanoplates into one-dimensional porous chain-like architecture for efficient oxygen evolution reaction

The self-assembly of two-dimensional (2D) nanostructures into one-dimensional (1D) nanoarchitectures may result in materials which combine the unique physicochemical properties of 2D nanostructures with the excellent charge transport properties of 1D architectures. Herein, we report the self-stacking of 2D nickel-cobalt (Ni-Co) phosphate nanoplates into 1D chainlike architectures with the assistance of metal glycerates as self-templates. This unique self-assembly process is driven by the adsorbed ethyl glycerate on the surface of the individual nanoplates, which promotes the subsequent growth of the new nanoplate on top of the previously formed nanoplate, thereby leading to the self-stacking of these nanoplates along the vertical direction. The flexibility of the proposed method is also highlighted by the feasible preparation of nickel phosphate with the same self-assembled structure. When tested as a catalyst for oxygen evolution reaction (OER) in an alkaline medium, the bimetallic Ni-Co phosphate (derived from Ni-Co-TEP) with the nanoplate-assembled chainlike structure displays much lower overpotential (η10= 310 mV) and Tafel slope (68 mV dec-1) than its pristine counterparts. The enhanced OER activity of this bimetallic catalyst may be attributed to (i) the highly interconnected structure and the bimetallic composition which promote improved charge transport; (ii) the porous chainlike structure which provides increased number of active sites, facilitates easier electrolyte infiltration, and promotes good electrical contact with the electrolyte, and (iii) the presence of Ni3+ and Co3+ active sites (nickel-cobalt (oxy)hydroxides) which can promote the chemisorption of OH- and facilitate electron transfer from the OH- to the surface Ni/Co sites during OER.