Pore Size-Regulated Vertically Aligned CoFe-LDH on a Carbon Support for the Oxygen Evolution Reaction

Abstract

Porous carbon-supported CoFe-layered double hydroxide (LDH)-based catalysts were synthesized and utilized as excellent oxygen evolution reaction catalysts in alkaline medium. High-resolution transmission electron microscopy images and N₂-sorption experiments suggested vertical growth of LDH on the carbon support and a narrow mesoporous nature of the materials, respectively. We proposed that the surface oxygen functional groups of carbon materials provided the nucleation sites for the crystal growth of the LDH on the carbon support utilizing short-range electrostatic interactions, which led to vertical growth of LDH with a narrow mesoporous nature. Among the synthesized materials, CoFe-LDH/MMC showed a remarkable mass activity of 559.2 A g^–1, a turnover frequency of 4.22 s^–1, and a massive roughness factor value of 269. This excellent reactivity has been attributed to (a) the vertically aligned narrow mesoporous nature of the material that increased the electrolyte accessibility inside the material and thus improved active sites for catalysis, (b) the high electrical conductivity of the material that also enhanced accessibility, reduced resistance for charge transfer at the electrode/electrolyte interface, and reduced resistance for intermediate formation during water oxidation, and (c) the increased electron contribution to the 3d orbital of cobalt from carbon that weakened the Co–oxygen bond and thus further facilitated the formation of the O–O bond and O₂ desorption during water oxidation.