Bifunctional bamboo-like CoSe arrays for high-performance asymmetric supercapacitor and electrocatalytic oxygen evolution.

Bifunctional bamboo-like CoSe arrays are synthesized by thermal annealing of Co(CO)OH grown on carbon cloth in Se atmosphere. The CoSe arrays obtained have excellent electrical conductivity, larger electrochemical active surface areas, and can directly serve as a binder-free electrode for supercapacitors and the oxygen evolution reaction (OER). When tested as a supercapacitor electrode, the CoSe delivers a higher specific capacitance (544.6 F g at current density of 1 mA cm) compared with CoO (308.2 F g) or CoO (201.4 F g). In addition, the CoSe electrode possesses excellent cycling stability. An asymmetric supercapacitor (ASC) is also assembled based on bamboo-like CoSe as a positive electrode and active carbon as a negative electrode in a 3.0 M KOH aqueous electrolyte. Owing to the unique stucture and good electrochemical performance of bamboo-like CoSe, the as-assembled ACS can achieve a maximum operating voltage window of 1.7 V, a high energy density of 20.2 Wh kg at a power density of 144.1 W kg, and an outstanding cyclic stability. As the catalyst for the OER, the CoSe exhibits a lower potential of 1.55 V (versus RHE) at current density of 10 mA cm, a smaller Tafel slope of 62.5 mV dec and an also outstanding stability.