Partially Reduced TiO₂ Aerogel as a Catalyst of Oxygen Reduction Reaction in Alkaline Solution

General Approach to the Synthesis of Metal Hybrid Carbon/Titania Aerogel for the Oxygen Reduction Reaction

“…The results showed an increase of electron density for the Ti atom in CTA-M, which may be attributed to the formation of oxygen vacancies. 12,23 Although no XRDdetectable crystalline phase has been formed, this valence state existed in the system. This is due to the fact that these two peaks originated from oxygen vacancies in the anatase crystalline form, and the appearance of oxygen vacancies leads to the transformation of Ti 4+ to Ti 3+ to fit the electrostatic equilibrium in the system, thereby leading to a transformation in the electronic structure around Ti and the emergence of peaks.…”

“…The first stage occurred at 400 °C and was due to the oxidation of free carbon. 12,23,28 The second stage of weight loss occurred after 478 °C, and the rate of weight loss decreased as a result of the oxidation of titanium oxide reductants and iron-containing materials. The weight loss of the other catalysts was primarily caused by the oxidation of free carbon.…”

“…In an Ar atmosphere, all samples exhibited micro−meso−macroporous-graded structures, except CTA-La-A and CTA-Zr-A with micro−mesoporous-graded structures, while in a N 2 atmosphere (panels c and d of Figure 4), except for CTA-La-N and CTA-Cu-N with micro−mesopo-rous-graded structures, all of the samples were micro−meso− macroporous-graded structures. 23,25,27,29,35,38 The FESEM images of the metal-doped aerogel electrocatalysts are shown in Figure 5. After heat treatment under an Ar atmosphere, the morphological structures of CTA-La-A (Figure 5a), CTA-Sm-A (Figure 5b), CTA-Zr-A (Figure 5c), and CTA-Cu-A (Figure 5f) aerogel catalysts appeared relatively dense, which corresponded to the low pore volume.…”

“…It can be observed that the Tafel slopes of CTA-Fe-A/N are superior to those of other metal-doped samples. 12,23 The number of transferred electrons (n) and hydrogen peroxide yield (HO 2 − ) are important performance indicators to evaluate the oxygen reduction electrocatalysts, as shown in Figure 12. The number of electrons transferred was 3.93 and 3.97 for CTA-Fe-A and CTA-Fe-N, corresponding to the HO 2 − yields of 3.6 and 1.39% when the potential was 0.6 V versus RHE.…”

Fe Ions-Doped TiO2 Aerogels as Catalysts of Oxygen Reduction Reactions in Alkaline Solutions

“…Fe-doped titanium oxide-based aerogel catalysts had better electrical conductivity and ORR catalytic activity due to the impurity levels of oxygen vacancies and Fe ions. In addition, the ORR catalytic performance of the TA/Fe3 were better than those of the undoped materials (initial potential (0.80 V), half wave potential (0.71 V), highest limiting current density (4.84 mA·cm −2 ), stability of electrochemistry (1.2 mV), and Tafel slope (70 mV·dec −1 )) [ 32 ]. The formation of oxygen vacancies, which was proved by the XPS characterization, would serve as donors.…”