Carbon-supported layered double hydroxide nanodots for efficient oxygen evolution: Active site identification and activity enhancement

In this study, we developed a novel confinement-synthesis approach to layered double hydroxide nanodots (LDH-NDs) anchored on carbon nanoparticles, which formed a three-dimensional (3D) interconnected network within a porous carbon support derived from pyrolysis of metal-organic frameworks (C-MOF). The resultant LDH-NDs@C-MOF nonprecious metal catalysts were demonstrated to exhibit super-high catalytic performance for oxygen evolution reaction (OER) with excellent operation stability and low overpotential (~ 230 mV) at an exchange current density of 10 mA·cm^-2. The observed overpotential for the LDH-NDs@C-MOF is much lower than that of large-sized LDH nanosheets (321 mV), pure carbonized MOF (411 mV), and even commercial RuO₂ (281 mV). X-ray absorption measurements and density functional theory (DFT) calculations revealed partial charge transfer from Fe³⁺ through an O bridge to Ni²⁺ at the edge of LDH-NDs supported by C-MOF to produce the optimal binding energies for OER intermediates. This, coupled with a large number of exposed active sides and efficient charge and electrolyte/reactant/product transports associated with the porous 3D C-MOF support, significantly boosted the OER performance of the LDH-ND catalyst with respect to its nanosheet counterpart. Apart from the fact that this is the first active side identification for LDH-ND OER catalysts, this work provides a general strategy to enhance activities of nanosheet catalysts by converting them into edge-rich nanodots to be supported by 3D porous carbon architectures.