Lithium ion-inserted TiO2 nanotube array photoelectrocatalysts

• Published in: Applied catalysis. B, Environmental Environmental, 2013-08, Vol.140-141, p.233-240
• Main Authors: Kang, Unseock, Park, Hyunwoong
• Format: Article
• Language: English
• Subjects: Catalysis; Charge separation; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; IPCE; Photoelectrocatalytic; Photoelectrochemical; Photoelectrochemistry. Electrochemiluminescence; Solar fuels; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2013.04.003

•Li+ is quickly inserted into TiO2 nanotube arrays (TNTs) by electrochemical methods.•Li+ insertion enhances photocurrent generation and IPCE by ∼70% and 250%, respectively.•Photoelectrocatalytic performance is enhanced by 2.5 times with Li+ insertion for 3s.•Li+ prevents charge recombination, enhancing the generation of e− and OH. A quick electrochemical Li ion insertion into TiO2 nanotube arrays (TNTs) markedly enhances the photoelectrochemical and photoelectrocatalytic performance. Potential pulses (−1.0∼−1.7VSCE for 1–11s in 1M LiClO4) to pre-annealed TNTs effectively insert Li ions (pre-annealed Li-TNTs) into the mouth/wall and bottom TiO2 depending on the insertion condition. Pre-annealed Li-TNTs prepared under an optimal Li ion insertion condition (−1.4VSCE for 3s) exhibit ∼70%-enhanced photocurrent generation, ∼2.5 fold-higher incident photon-to-current efficiency, and an improved photoelectrocatalytic activity for the degradation of phenolic compounds in 1M KOH electrolyte. A change in photoluminescence (PL) emission spectra and decrease in charge transfer resistance by Li ion insertion suggest that the inserted Li ions play a role in inhibiting charge recombination by compensating for the photogenerated Ti3+ charges (Li+-Ti3+-OH). However, as KOH concentration is diluted such enhanced Li+ effects gradually vanish primarily due to liberation of reversibly inserted Li ions. To insert Li ions irreversibly, the potential pulses were applied to non-annealed TNTs followed by annealing (post-annealed Li-TNTs). Comparison between pre-annealed and post-annealed Li-TNTs in circum-neutral pH (0.1M Na2SO4 at pH ∼6) indicates that the former exhibits a similar performance to bare TNTs (absence of Li ion effect), whereas the latter shows a superior performance with ca. 2.5-fold higher photoelectrochemical and photoelectrocatalytic activities. Detailed surface analyses (XPS, XRD, PL, SEM, ICP-MS, etc.) and Li+-induced reaction mechanism were discussed.