Flat Band Potential Measurements of Naked and Viologen-Modified n-WS2 Electrodes in Aqueous Iodide and Triiodide Solutions

Abstract

The flat band potentials, E[sub FB], of naked n-WS[sub 2] electrodes and cationic viologen polymer-modified n-WS[sub 2] electrodes have been determined in KI and KI[sub 3] solutions by differential capacitance measurements. The E[sub FB] values for naked n-WS[sub 2] electrodes are shifted negatively in electrolyte media containing I[sup [minus]] or I[sub 3][sup [minus]]. This negative shift is much larger in the I[sub 3][sup [minus]] solution than in the I[sup [minus]] solution. The magnitude of the shift depends on the concentration of I[sup [minus]] or I[sub 3][sup [minus]] in the solution, and this dependence can be modeled by Langmuir adsorption isotherms. The polymer-modified electrodes are formed by deposition of the polymer via hydrolysis of N,N[prime]-(bis(p-trimethoxysilyl)-benzyl)-4,4[prime]-bipyridinium. Because of the high concentration of anions in the cationic viologen polymer due to electrostatic forces, the polymer-modified n-WS[sub 2] surface is in contact with a high concentration of I[sup [minus]] or I[sub 3][sup [minus]] even in dilute I[sup [minus]] or I[sub 3][sup [minus]] solution. However, the E[sub FB] shifts are about the same for both naked and polymer-modified electrodes in a wide range of concentrations of I[sup [minus]] or I[sub 3][sup [minus]] solution, as expected form a thermodynamic analysis. 11 refs., 7 figs., 1 tab.