Nickel-cobalt (oxy)hydroxide battery-type supercapacitor electrode with high mass loading.

• NiCoOOH composite was prepared by an in-situ electrochemical activation method. • The optimal electrode achieves an exceptionally high areal capacity and mass loading. • Areal capacity increases linearly by systematically tuning the pore sizes. • Volumetric capacity remain unchanged with increasing mass loading. • The electrode yields a record energy density of 19.1 mWh cm−2. Transition metal hydroxides have shown high capacity performances when at a small mass loading of active material, while it is still a great challenge to obtain a high capacity performance when the mass loading is high. To maximize the capacity at high mass loading, the microstructure of the electrode should be rationally designed. Herein, we report a nickel–cobalt (oxy)hydroxide composite with three-dimensional hierarchical porous architecture realized by an in-situ electrochemical activation method to trigger the active sites and structural rearrangement. By systematically tuning the pore sizes in the hierarchical structure, an optimal composite delivers a record high areal capacity (34.8 mAh cm−2) and energy density (19.1 mWh cm−2) at the mass loading up to 230 mg cm−2. It gives new insights for preparing high performance electrode materials by a facile method and provides a blueprint for the design of high mass-loading supercapacitors. [ABSTRACT FROM AUTHOR]