To further evaluate the electrochemical properties of the asprepared
Co0.85Se nanosheets for practical application, an asymmetric
supercapacitor was assembled by using Co0.85Se nanosheets
and active carbon (as shown in Fig. S6) as the positive electrode and
negative electrodes in 3 M KOH solution with one piece of cellulose
paper as the separator, respectively (Fig. 5a).