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Redox-Active Monolayers in Mesoporous Silicon

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journal contribution
posted on 02.08.2012 by Simone Ciampi, Bin Guan, Nadim Darwish, Peter J. Reece, J. Justin Gooding
Herein, redox reactions at chemically derivatized porous silicon (PSi) films are investigated. Passivation of the PSi matrix, by replacing metastable Si–H termini with nonpolar SiCCR linkages, allows the electrochemical PSi device to operate in aqueous environments under oxidizing conditions (i.e., electron hole accumulation regime). Cu­(I)-catalyzed alkyne–azide cycloaddition reactions are used to anchor ferrocene derivatives and probe electrochemical reactions at the exceedingly large surface area-to-volume ratio of mesoporous PSi. The forward-biased p-type PSi/electrolyte interface retains a quasi-metallic behavior throughout its entire contour, and it does so for prolonged times even when the electrode is poised at potentials at which a bare silicon electrode would rapidly oxidize. The interfacial capacitance of the PSi matrix is, however, unexpectedly low. An explanation is proposed where PSi morphology and the semiconductor space-charge layer capacitance play a significant role in determining the charging properties of the electrode. These results are important for the application of porous semiconductor electrodes in sensing, electrocatalytic, and energy-conversion devices.