Photocatalytic Water Splitting with Suspended Calcium Niobium Oxides: Why Nanoscale is Better than Bulk 鈥?A Kinetic Analysis

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• 作者：Erwin M. Sabio ; Rachel L. Chamousis ; Nigel D. Browning ; Frank E. Osterloh
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：February 2, 2012
• 年：2012
• 卷：116
• 期：4
• 页码：3161-3170
• 全文大小：644K
• 年卷期：v.116,no.4(February 2, 2012)
• ISSN：1932-7455

文摘

The layered Dion鈥揓acobson phase KCa₂Nb₃O₁₀ is known to catalyze photochemical water reduction and oxidation under UV light in the presence of sacrificial agents. The same reactions are catalyzed by tetrabutylammonium hydroxide-supported HCa₂Nb₃O₁₀ nanosheets obtained by chemical exfoliation of the parent phase. Here we describe a factorial study into the effects of nanoscaling, sacrificial charge donors, cocatalysts, and cocatalyst deposition conditions on the activity of these catalysts. In water, nanoscaling leads to a 16-fold increase in H₂ evolution and an 8-fold increase in O₂ evolution over the bulk phase under the same conditions. The sacrificial electron donor methanol improves H₂ production by 2鈥? orders of magnitude to 20鈥?0 mmol of H₂/h/g, while the electron acceptor AgNO₃ increases O₂ production to 400 渭mol of O₂/h/g. Rates for H₂ and O₂ evolution further depend on the presence of cocatalysts (Pt or IrO_x) and, in the case of H₂, inversely on their particle size. To rationalize these findings and the increased activity of the nanoscale particles, we propose a kinetic model for photocatalysis with semiconductor particles. The model calculates the electronic rate of the catalysts as a product of terms for charge generation, charge and mass transport, chemical conversion, and charge recombination. The analysis shows that the activity of the catalysts is limited mainly by the kinetics of the redox reactions and by the rate of charge transport to the water鈥揷atalyst interface. Mass transport in the solution phase does not play a major role, and neither does surface charge recombination.