Effect of composition on the point of zero charge of RuO 2 + TiO 2 mixed oxides

Abstract

RuO 2 + TiO 2 mixed oxides have been prepared by thermal decomposition of RuCl 3 + TiCl 4 at 450°C. The structural features have been investigated by X-ray diffraction, while the Braunauer-Emmett-Teller method has been used to determine the surface area of the powders. The point of zero charge (pzc) has been measured by potentiometric titration of oxide suspensions in KNO 3 solution. The charge-pH curves have been transformed into capacitance values which have been used at the pzc to estimate in-situ the real surface area and the inner layer capacitance. In the absence of RuO 2, Tio 2 is mainly in the anatase form. The rutile form of TiO 2 has a pzc close to that of RuO 2 which results in a pzc varying very little between 40 and 100% RuO 2. The same is the case with the real surface area. This is in accord with the performances of electrodes showing RuO 2-like properties down to 30–40% RuO 2. The behaviour of RuO 2 + TiO 2 oxides is structurally, electronically and chemically dominated by that of the RuO 2 component.