The observed edge at around 520 to 570 and 600 to 640 nm could be assigned to the 6A1 → 4 T2(4G) ligand field transition of Fe3+. As revealed by Figure 6, the electronic transition
for the charge transfer in the wavelength region 380 to 450 nm dominated the optical absorption features of the NPs, while the ligand field transitions in the range of 520 to 640 nm dominated the optical absorption features of the architectures. This indicated that the absorption could be modulated by controlling the size and shape of the hematite, which was quite important for the enhancement of the photoelectrocatalytic activity. Mesoporous pod-like α-Fe2O3 check details nanoarchitectures as anode materials for lithium-ion batteries The electrochemical behavior of the hematite electrodes was evaluated by cyclic voltammetry and galvanostatic charge/discharge
cycling. As shown in Figure 7a, a spiky peak was observed at 0.65 V with a small peak appearing at 1.0 V during the cathodic polarization of the hematite NPs (presented in Figure 1b) in the first cycle. This indicated the following lithiation learn more steps [43, 64, 65]: (5) (6) Figure 7 Representative cyclic voltammograms and charge–discharge performances of the hematite electrode. (a) Representative cyclic voltammograms of the hematite nanoparticles (presented in Figure 1b) at a scan rate of 0.1 mV s−1; (b) the charge–discharge performances at various current rates (1 C = 1,006 mA g−1, corresponding to the full discharge in 1 h, a rate of n C corresponds to the full discharge GNA12 in 1/n h) of the hematite nanoparticles; (c) the rate performance and (d) the cycling performance
at a current of 1 C of an electrode fabricated with the hematite nanoparticles presented in Figure 1b; (e) the rate performance and (f) the cycling performance at a current of 1 C of an electrode fabricated with hierarchical mesoporous pod-like hematite nanoarchitectures presented in Figure 2e. With lithium ions inserted into the crystal structure of the as-prepared α-Fe2O3, the hexagonal α-Fe2O3 was transformed to cubic Li2Fe2O3. The peak at 0.65 V corresponded to the complete reduction of iron from Fe2+ to Fe0 and the decomposition of electrolyte. A broad anodic peak was recorded in the range of 1.4 to 2.2 V, corresponding to the oxidation of Fe0 to Fe2+ and further to Fe3+[66, 67]. The curve of the subsequent cycle was significantly different from that of the first cycle as only one cathodic peak appeared at about 0.8 V with decreased peak intensity, while the anodic process only showed one broad peak with a little decrease in peak intensity. The irreversible phase transformation during the process of lithium insertion and extraction in the initial cycle was the reason for the difference between the first and second cathodic curves . After the first discharge process, α-Fe2O3 was completely reduced to iron NPs and was dispersed in a Li2O matrix.