The use of TiO2 photoanodes sensitized with ruthenium(II) polypyridine complexes bearing phosphonic acid anchoring groups has been investigated in the context of photoinduced hydrogen generation. The photoanodes sustained 240 h of irradiation without undergoing appreciable hydrolysis and decomposition in an aqueous environment at pH 3. While the use of organic sacrificial donors, like ascorbic acid, considerably enhanced the photoanodic response, the exploitation of iodide was more problematic because the adsorption of photogenerated I3 - from aqueous media favored charge recombination with conduction band electrons, thus limiting the efficiency of the photoelectrosynthetic device. However, experiments performed in a three-compartment cell, where the photolectrode was in contact with an organic solvent, showed a remarkable photocurrent, with an electrolysis yield close to 87%. Introduction The use of sunlight to drive thermodynamically unfavorable reactions is the primary goal of any artificial photochemical system aimed to produce electricity or valuable materials such as fuels. The growing demand of a sustainable and renewable alternative to fossil fuels has aroused interest in photodriven hydrogen production on semiconductor substrates. A semiconductor with a band gap higher than 1.23 eV would be required to photogenerate electron-hole pairswith sufficient driving force to carry out the two redox reactions for water splitting: 4H2Oþ4e- f 2H2 þ4OH- 4OH- f O2 þ4e- þ2H2O These reactions are multi-electron-transfer processes that can efficiently occur on the surface of a semiconductor provided that (a) the band edges match the redox potentials for water reduction and oxidation, (b) the charge-transfer processes at the interface are fast, and (c) the stability requirements under irradiation are met. The simplest method to use sunlight to produce hydrogen and oxygen fromwater consists of the direct electrolysis of an aqueous solution by means of a solid-state photovoltaic device (e.g., silicon solar cells appropriately connected in series to reach the required overpotential for water
Photoelectrochemical behaviour of sensitized tiO2 photoanodes in aqueous solutions: application to hydrogen production
CARAMORI, Stefano;V. Cristino;ARGAZZI, Roberto;BIGNOZZI, Carlo Alberto
2010
Abstract
The use of TiO2 photoanodes sensitized with ruthenium(II) polypyridine complexes bearing phosphonic acid anchoring groups has been investigated in the context of photoinduced hydrogen generation. The photoanodes sustained 240 h of irradiation without undergoing appreciable hydrolysis and decomposition in an aqueous environment at pH 3. While the use of organic sacrificial donors, like ascorbic acid, considerably enhanced the photoanodic response, the exploitation of iodide was more problematic because the adsorption of photogenerated I3 - from aqueous media favored charge recombination with conduction band electrons, thus limiting the efficiency of the photoelectrosynthetic device. However, experiments performed in a three-compartment cell, where the photolectrode was in contact with an organic solvent, showed a remarkable photocurrent, with an electrolysis yield close to 87%. Introduction The use of sunlight to drive thermodynamically unfavorable reactions is the primary goal of any artificial photochemical system aimed to produce electricity or valuable materials such as fuels. The growing demand of a sustainable and renewable alternative to fossil fuels has aroused interest in photodriven hydrogen production on semiconductor substrates. A semiconductor with a band gap higher than 1.23 eV would be required to photogenerate electron-hole pairswith sufficient driving force to carry out the two redox reactions for water splitting: 4H2Oþ4e- f 2H2 þ4OH- 4OH- f O2 þ4e- þ2H2O These reactions are multi-electron-transfer processes that can efficiently occur on the surface of a semiconductor provided that (a) the band edges match the redox potentials for water reduction and oxidation, (b) the charge-transfer processes at the interface are fast, and (c) the stability requirements under irradiation are met. The simplest method to use sunlight to produce hydrogen and oxygen fromwater consists of the direct electrolysis of an aqueous solution by means of a solid-state photovoltaic device (e.g., silicon solar cells appropriately connected in series to reach the required overpotential for waterI documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
