Two-dimensional porous (Co, Ni)-based monometallic hydroxides and bimetallic layered double hydroxides thin sheets...

CoNi layered double hydroxides (LDH) and related monometallic hydroxides (Ni(OH)₂ and Co(OH)₂) were synthesized by a facile, simple and inexpensive method under mild condition (50 °C). The resulting products displayed a unique honeycomb-like nanoflakes array assembled two-dimensional (2D) thin sheets structure. Among them, CoNi-LDH thin sheets delivered higher specific capacity (394.5 C g^-1 at 1 A g^-1) with superior cyclic performance (92.3% capacity retention over 10,000 cycles) than Co/Ni monometallic hydroxides owing to the synergistic effect of cobalt and nickel. Afterward, hybrid supercapacitors (HSC) devices were fabricated using the as-obtained products (CoNi-LDH, Co(OH)₂ and Ni(OH)₂ thin sheets) and activated carbon (AC) as the positive and negative electrode, respectively. The operating voltage of the devices can be extended to 1.6 V. What's more, the assembled CoNi-LDH HSC device exhibited a maximum energy density of 20.38 Wh kg^-1 at the power density of 800 W kg^-1. Consequently, these outstanding electrochemical performances of the CoNi-LDH thin sheet endow it with great potential to be implemented in HSCs or other energy storage systems.