Nanoporous CuCo ₂ O ₄ nanosheets as a highly efficient bifunctional electrode for supercapacitors and water oxidation catalysis

Efficient and low‐cost multifunctional electrodes play a key role in improving the performance of energy conversion and storage devices. In this study, ultrathin nanoporous CuCo ₂ O ₄ nanosheets are synthesized on a nickel foam substrate using electrodeposition followed by air annealing. The CuCo ₂ O ₄ nanosheet electrode exhibits a high specific capacitance of 1473 F g ^─1 at 1 A g ^─1 with a capacity retention of ∼93% after 5000 cycles in 3 M KOH solution. It also works well as an efficient oxygen evolution reaction electrocatalyst, demonstrating an overpotential of 260 mV at 20 mA cm ^─2 with a Tafel slope of ∼64 mV dec ^─1 . in 1 M KOH solution, which is the lowest reported among other copper-cobalt based transition metal oxide catalysts. The catalyst is very stable at >20 mA cm ^─2 for more than 25 h. The superior electrochemical performance of the CuCo ₂ O ₄ nanosheet electrode is due to the synergetic effect of the direct growth of 2D nanosheet structure and a large electrochemically active surface area associated with nanopores on the CuCo ₂ O ₄ nanosheet surface.