Self-Assembled Nanostructured CuCo O for Electrochemical Energy Storage and the Oxygen Evolution Reaction via Morphology Engineering.

CuCo O films with different morphologies of either mesoporous nanosheets, cubic, compact-granular, or agglomerated embossing structures are fabricated via a hydrothermal growth technique using various solvents, and their bifunctional activities, electrochemical energy storage and oxygen evolution reaction (OER) for water splitting catalysis in strong alkaline KOH media, are investigated. It is observed that the solvents play an important role in setting the surface morphology and size of the crystallites by controlling nucleation and growth rate. An optimized mesoporous CuCo O nanosheet electrode shows a high specific capacitance of 1658 F g at 1 A g with excellent restoring capability of ≈99% at 2 A g and superior energy density of 132.64 Wh kg at a power density of 0.72 kW kg . The CuCo O electrode also exhibits excellent endurance performance with capacity retention of 90% and coulombic efficiency of ≈99% after 5000 charge/discharge cycles. The best OER activity is obtained from the CuCo O nanosheet sample with the lowest overpotential of ≈290 mV at 20 mA cm and a Tafel slope of 117 mV dec . The superior bifunctional electrochemical activity of the mesoporous CuCo O nanosheet is a result of electrochemically favorable 2D morphology, which leads to the formation of a very large electrochemically active surface area.