Abstract
Abstract Scanning tunneling microscopy (STM) and tunneling spectroscopy investigations of α 2 -K 8 P 2 W 17 (M·OH 2 )O 61 (M = Mn II , Zn II , Fe II , Co II , and Ni II ) Wells–Dawson heteropolyacids (HPAs) were conducted. HPAs formed self-assembled and well-ordered arrays on graphite surface. Negative differential resistance (NDR) phenomena were observed in the tunneling spectra of the HPAs. NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential and with decreasing UV–visible absorption edge energy. HPAs were then applied to the electro-oxidation of methanol as a redox mediator. The oxidation activity for residual intermediates in the reaction increased as NDR peak voltage of HPA appeared at less negative voltage.
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