Further information about the chemical compositions and surface
electronic states of the Co0.85Se was analyzed by the XPS
technique and the obtained results are plotted in Fig. 2a and b,
which mainly exhibit the peaks of Co 2p and Se 3d, respectively. The
binding energies of ~779.0, ~780.8, ~794.0 and ~797.2 eV are Co3þ
2p3/2, Co2þ 2p3/2, Co3þ 2p1/2 and Co2þ 2p1/2, respectively, which are
in good agreement with previously reported values [35]. This result
indicates that the cobalt elements on the surface of the assynthesized
Co0.85Se sample consist of Co2þ and Co3þ. In addition,
the core level spectrum of the Se 3d region can be obviously
observed, as shown in Fig. 2b. The binding energy of 55.4 eV is close
to the reported value [36]. According to the XPS analysis, the
composition of Co0.85Se mainly contains Co3þ, Co2þ, and Se2, which
well conforms to the formula Co0.85Se.
To illustrate the morphology and microstructure of as-obtained
Co0.85Se, SEM and TEM analyses are performed. The morphologies
with different reaction times were shown in Fig. S2.