Ultrasound-seeded vapor-phase-transport growth of boundary-rich layered double hydroxide nanosheet arrays for highly efficient water splitting

Noble-metal-free electrodes are of significant importance for electrochemical energy storage and conversion. Transition-metal-based layered double hydroxides (TM LDHs) show great potential as advanced electrocatalysts, but low electrochemical active areas and poor electronic conductivity limit their catalytic activity. Herein, we report a novel secondary growth strategy to synthesize ultrathin NiCoFe LDH nanosheets anchored on nickel foam (NF). By coupling ultrasound-assisted oxidation (UAO) to deposit dense seeds of low-crystalline NiCoFe LDH array on semisacrificial NF, and vapor-phase-transport (VPT) of urea for kinetic control over nanosheet thickness, hierarchical self-supported electrodes with high density of exposed active sites and abundant boundaries have been facilely obtained. The NiCoFe LDH/NF electrodes show an impressive electrocatalytic performance during oxygen evolution reaction (OER) with required overpotentials of 217 and 227 mV to achieve current densities of 50 and 100 mA cm(-2) respectively, with over 150 h long-term stability, outperforming those synthesized by hydrothermal synthesis (HTT) as well as most state-of-the-art electrocatalysts. The overall water splitting device assembled using the NiCoFe LDH/NF electrode as both anode and cathode shows an ultralow cell voltage of 1.56 V to obtain 10 mA cm(-2). This strategy provides a simple and scalable methodology for synthesizing high-activity catalysts for efficient electrochemical processes.