3. Results and discussion
The Raman spectra of the XC and Fe2O3/XC cathode are shown in Fig. 1a. For the both cathodes, two strong peaks at 1350 and 1580 cm1 can be assigned to the D and G bands of carbon, respectively. While in the Fe2O3/XC cathode, another three broad peaks around 350, 500, and 700 cm1 are observed, which are unique to the maghemite (g-Fe2O3) species [40], indicating that the iron oxide formed in the cathode is g-Fe2O3. The Fe2O3 formation was further confirmed through XPS analysis. The highresolution spectrum of Fe is shown in Fig. 1b. Two peaks located at 724.6 and 712.3 eV, can be assigned to the Fe 2p1/2 and Fe 2p3/2, respectively, indicating the existence of g-Fe2O3 [41]. Moreover, the Fe 2p3/2 peak is associated with a satellite situated at about 219 eV, suggesting the absent of Fe2+ [22–24]. A TEM image (Fig. 1c) shows that Fe2O3 nanoparticles with an average sizes of 3.6 0.14 nm are uniformly dispersed on the carbon surface. The measured lattice spacing of 2.09Å in Fig. 1d corresponds to the (400) crystal planes of g-Fe2O3, indicating the crystalline nature of the particles. The TEM-EDX mapping (Fig. S1) further demonstrates that the Fe2O3 nanoparticles are well distributed. Therefore, this directthermal decomposition of iron nitrate is a facile and effective approach to prepare carbon supported Fe2O3 nanocatalysts. Based on the N2-sorption measurement (see Fig. 2a), the specific surface
of pure XC and Fe2O3/XC sample is calculated to be 232.89 and 172.58 m2 g1 , respectively. The decreased specific urface area of Fe2O3/XC can be attributed to the decoration of dense Fe2O3 nanoparticles on the XC carbon. From the pore size distribution of XC and Fe2O3/XC in the inset of Fig. 2a, it is seen that the pores of the XC and Fe2O3/XC range from several nanometers to more than one hundred meters and the pore distribution does not change a lot after the introduction of Fe2O3 nanoparticles. The exact weight content of Fe2O3 in the Fe2O3/XC composite is determined by TGA
in air atmosphere to be 8.13% (see Fig. 2b), almost consistent with the designed value (10%).