Ostwald Ripening Driven Exfoliation to Ultrathin Layered Double Hydroxides Nanosheets for Enhanced Oxygen Evolution Reaction.

Abstract

As a key half-reaction in water splitting, the oxygen evolution reaction (OER) process is kinetically sluggish. Layered double hydroxides (LDHs) are regarded as the highly promising electrocatalysts to promote the OER kinetics. However, the closely stacking layered structure of pristine bulk LDHs restricts the exposure of electrocatalytically active sites, and it remains a great challenge to find an efficient strategy to exfoliate the bulk LDHs into ultrathin and stable nanosheets with increased surface area and exposed active sites. Herein, a novel Ostwald ripening driven exfoliation (ORDE) of NiFe LDHs has been achieved in situ on the electrodes by spontaneously self-etching and redepositing via a simple hydrothermal treatment without the assistance of any exfoliating reagent or surfactant. The thermodynamically driven Ostwald ripening has been expanded to the exfoliation of two-dimensional layered materials for the first time. Compared with conventional exfoliation methods, this ORDE is a time-saving and green strategy that avoids the serious adsorption of surfactant molecules. The ORDE of NiFe LDHs is accomplished in situ on a Cu mesh electrode, which not only exhibits excellent electrical contact between LDHs catalyst and electrodes but also prevents the restacking of the exfoliated LDHs. As a result, the exfoliated ultrathin, clean, and vertically aligned NiFe nanosheets with much higher surface area and numerous exposed active edges and sites demonstrated significantly enhanced OER performances with low overpotential of 292 mV at 10 mA cm-2 and long-term stability for more than 60 h, as well as remarkable flexibility. Additionally, bulk Ni(OH)2 nanosheets on Ni foams have also been exfoliated by a similar mechanism, indicating this ORDE strategy can be widely extended to other 2D layered materials for novel applications.