Two-dimensional porous cobalt-nickel tungstate thin sheets for high performance supercapattery

In order to meet the increasing demand for electric energy, it is of great significance to develop high-performance electrochemical energy storage materials. Cobalt/nickel-based tungstates (MWO4, M = Co, Ni and Co-Ni) show much higher electrical conductivity than pure oxides. However, due to their relatively low capacity and poor cycle stability, their potential as electrode materials for high-performance supercapatteries is limited to a great extent. In this paper, we reported the successful synthesis of bimetallic two-dimensional (2D) Co-Ni tungstates thin sheets assembled by nanosheets through a substrate-free hydrothermal method. The ratio of Co/Ni was optimized to 1:1 and the as-obtained Co0.5Ni0.5WO4 (CNWO) electrode exhibited a high specific capacity of 626.4 C g(-1) at 1 A g(-1) and high cyclic stability (105.3% capacity maintained over 10,000 cycles at 10 A g(-1)) in a three-electrode system, which is attributed to the synergistic effect of 2D/3D porous architecture and bimetallic composition of CNWO. An alkaline hybrid supercapattery (CNWO//activated carbon(AC)) with CNWO as the positive electrode and AC as the negative one showed the maximum specific energy of 42.2 Wh-kg(-1) at the specific power of 1047.7 W kg(-1) with a long cycle life (93.5% capacity retention after 15,000 cycles at 10 A g(-1)). The rational design of CNWO could pave the way for the preparation of bimetallic oxides with significantly improved electrochemical property.