Interfacial Electron Transfer Dynamics for [Ru(bpy)2((4,4鈥?PO3H2)2bpy)]2+ Sensitized TiO2 in a Dye-Sensitized Photoelectrosynthesis Ce

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• 作者：Wenjing Song ; M. Kyle Brennaman ; Javier J. Concepcion ; Jonah W. Jurss ; Paul G. Hoertz ; Hanlin Luo ; Chuncheng Chen ; Kenneth Hanson ; Thomas J. Meyer
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 14, 2011
• 年：2011
• 卷：115
• 期：14
• 页码：7081-7091
• 全文大小：1069K
• 年卷期：v.115,no.14(April 14, 2011)
• ISSN：1932-7455

文摘

Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy)₂(4,4鈥?(PO₃H₂)₂bpy)]²⁺ attached to TiO₂ nanoparticle films, TiO₂鈭扲u^II, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H₂ production. In these experiments, laser flash excitation of TiO₂鈭扲u^II and rapid injection lead to TiO₂(e^{鈭?/sup>)鈭扲uIII with subsequent TiO₂(e鈭?/sup>)鈭扲uIII 鈫?TiO₂鈭扲uII back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA4鈭?/sup>) as irreversible electron transfer donors. With added TEOA or EDTA4鈭?/sup>, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H₂ production in the photoelectrosynthesis cell. Reduction of TiO₂(e鈭?/sup>)鈭扲uIII by both TEOA and EDTA4鈭?/sup> occurs with k_D 106 M鈭? s鈭?. EDTA4鈭?/sup> is a more efficient scavenger by a factor of 3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (畏_coll), and in photocurrent measurements with H₂ production. Evaluation of electron collection efficiencies by transient current measurements gave 畏_coll 24% for TEOA and 70% for EDTA4鈭?/sup>. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I鈭扸 measurements. A pH dependent plateau is reached at 0 V at pH = 4.5 (EDTA4鈭?/sup>) and at 鈭?.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO₂鈭扲uII with IPCE values 3 times higher for EDTA4鈭?/sup> than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H₂ production is minimizing back electron transfer. Application of a sufficiently positive potential relative to E_CB for TiO₂ accelerates loss of electrons from the film in competition with back electron transfer allowing for H₂ production with efficiencies approaching 14.7% under steady-state irradiation.}