Amorphous nickel-cobalt bimetal-organic framework nanosheets with crystalline motifs enable efficient oxygen evolution reaction: Ligands hybridization engineering

Abstract

The proposed “ligands hybridization” strategy and the application of novel MOF-based catalysts in OER were introduced. The OER mechanism highlights the importance of Ni doping effect. Development of high-efficiency and low-cost electrocatalyst for oxygen evolution reaction (OER) is very important for use at alkaline water electrolysis. Metal-organic frameworks (MOF) provide a rich platform for designing multi-functional materials due to their controllable composition and ultra-high surface area. Herein, we report our findings in the development of amorphous nickel–cobalt bimetal-organic framework nanosheets with crystalline motifs via a simple “ligands hybridization engineering” strategy. These complexes’ ligands contain inorganic ligands (H 2 O and NO 3 − ) and organic ones, hexamethylenetetramine (HMT). Further, we investigated a series of mixed-metal with multi-ligands materials as OER catalysts to explore their possible advantages and features. It is found that the Ni doping is an effective approach for optimizing the electronic configuration, changing lattice ordering degree, and thus enhancing activities of HMT-based electrocatalysts. Also, the crystalline-amorphous boundaries of various HMT-based electrocatalyst can be easily controlled by simply changing amounts of Ni-precursor added. As a result, the optimized ultrathin (Co, 0.3Ni)-HMT nanosheets can reach a current density of 10 mA cm −2 at low overpotential of 330 mV with a small Tafel slope of 66 mV dec −1 . Our findings show that the electronic structure changes induced by Ni doping, 2D nanosheet structure, and MOF frameworks with multi-ligands compositions play critical roles in the enhancement of the kinetically sluggish electrocatalytic OER. The present study emphasizes the importance of ligands and active metals via hybridization for exploring novel efficient electrocatalysts.