4.2.1.5 Electrochemical Reduction
Electrochemical reduction was reported to be an easy and simple method to introduce Ti
3+ species into TiO 2 photocatalysts. Compared with the high requirement of
traditional approaches, electrochemical reduction method is easy to achieve, and it
avoids expensive facilities, harsh experimental conditions, or polluting by-products
[52]. Zhang et al. reported the TiO 2–x nanotube arrays induced by electrochemical
reduction process [53]. Unlike the direct synthesis of TiO 2–x via anodization,
Swaminathan et al. reported the cathodic reduction of the anodized TiO 2 sample.
Firstly, TiO 2 was obtained by the anodization of Ti, then neutral oxygen atoms were
removed in the cathodization process, and oxygen vacancies were formed (Fig. 4.5).
The formation of oxygen vacancies in TiO 2–x nanomaterial was influenced by the
duration of anodization and the post-annealing treatment [54].
Mo et al. demonstrated that during electrochemical reduction process, atomic H
was generated on the Ag electrode and then diffused into TiO 2 as interstitial
hydrogen (H i ), while in the gas hydrogenation process, the hydrogen was like to
occupy the position of oxygen vacancies and became negatively charged (H o ), based
on the results of DFT calculations (Fig. 4.6) [56]. However, the weak bonding
between H i and the closet oxygen atoms facilitates to break, making the obtained
TiO 2–x samples sensitive to aging at room temperature. Therefore, a combination of
electrochemical reduction and post-heating treatment was employed to further
stabilize the Ti
3+ in TiO 2–x [54]. In addition, Liu et al. demonstrated that cathodic
reduction led to the activation of Ti
3+ species in TiO 2 , and a combination of cathodic
reduction and H 2 -gas heating treatment resulted into a synergistic effect in
Fig. 4.5 Schematic illustration of TiO 2–x photocatalyst through cathodic reduction of the anodized
TiO 2 samples. (Reprinted with permission from Ref. [55], copyright 2016 American Chemical
Society)
4.2 Synthesis of TiO 2–x Photocatalysts
81
Electrochemical reduction was reported to be an easy and simple method to introduce Ti
3+ species into TiO 2 photocatalysts. Compared with the high requirement of
traditional approaches, electrochemical reduction method is easy to achieve, and it
avoids expensive facilities, harsh experimental conditions, or polluting by-products
[52]. Zhang et al. reported the TiO 2–x nanotube arrays induced by electrochemical
reduction process [53]. Unlike the direct synthesis of TiO 2–x via anodization,
Swaminathan et al. reported the cathodic reduction of the anodized TiO 2 sample.
Firstly, TiO 2 was obtained by the anodization of Ti, then neutral oxygen atoms were
removed in the cathodization process, and oxygen vacancies were formed (Fig. 4.5).
The formation of oxygen vacancies in TiO 2–x nanomaterial was influenced by the
duration of anodization and the post-annealing treatment [54].
Mo et al. demonstrated that during electrochemical reduction process, atomic H
was generated on the Ag electrode and then diffused into TiO 2 as interstitial
hydrogen (H i ), while in the gas hydrogenation process, the hydrogen was like to
occupy the position of oxygen vacancies and became negatively charged (H o ), based
on the results of DFT calculations (Fig. 4.6) [56]. However, the weak bonding
between H i and the closet oxygen atoms facilitates to break, making the obtained
TiO 2–x samples sensitive to aging at room temperature. Therefore, a combination of
electrochemical reduction and post-heating treatment was employed to further
stabilize the Ti
3+ in TiO 2–x [54]. In addition, Liu et al. demonstrated that cathodic
reduction led to the activation of Ti
3+ species in TiO 2 , and a combination of cathodic
reduction and H 2 -gas heating treatment resulted into a synergistic effect in
Fig. 4.5 Schematic illustration of TiO 2–x photocatalyst through cathodic reduction of the anodized
TiO 2 samples. (Reprinted with permission from Ref. [55], copyright 2016 American Chemical
Society)
4.2 Synthesis of TiO 2–x Photocatalysts
81