Dissolution kinetics of WO3 in acidic solutions

Abstract

Potentiostatic polarization and rotating disk electrode techniques were used to obtain the rate constant for the dissolution of electrochemically-formed (at 1 V) WO 3 on tungsten (W) in acidic solutions. The corresponding rate constant for the chemical dissolution of WO 3 (s) powder was found by measuring the dissolved tungsten concentration as a function of time and pH. The chemical dissolution experiments supported the view that the ratedetermining step in the anodic reaction of W in acidic solution is the chemical dissolution of WO 3 (s) formed on the metal surface. Zeta potential measurements gave the isoelectric point (iep) of the WO 3 (s) powder as pH 1.5, a value that was somewhat smaller than the point of zero charge (pzc) of WO 3 (s) formed on W metal (pH 2.5). This difference was attributed to the highly hydrated nature of the oxide film formed on W metal in aqueous systems.

Probing the activities of UV and visible-light absorbing photocatalyst powders using a resazurin-based photocatalyst activity indicator ink (Rz Paii )

“…Bandgap (Ebg) [26], band position (i.e. of the conduction and valence band, ECB and EVB) [26] and point of zero charge values [26][27][28][29][30][31] were gleaned from the literature. Table 1 lists these key characteristics of the tested semiconductor powders.…”

Improving O2 production of WO3 photoanodes with IrO2 in acidic aqueous electrolyte

“…At higher pH, OH À ions induce chemical dissolution by the reaction WO 3 (s) + OH À -WO 4 2À + H + . 30,31 Even in acidic conditions, some photocorrosion of WO 3 has been observed due to the formation of peroxo-species as intermediates during water oxidation. [22][23][24]32 Although peroxide formation and the oxidation of most acid counterion species are reactions that are thermodynamically less feasible than water oxidation, the kinetics of these reactions are often more favorable than oxygen evolution.…”

WO3/TiO2 composite coatings: Structural, optical and photocatalytic properties

“…7a, both TiO 2 and WO 3 /TiO 2 coatings adsorbed the dye in the equilibrium period of 60 min before the exposure to visible light. It is known from the literature that the zero point charge (pH zpc ) of TiO 2 lies between 6 and 6.8 [46][47][48], whereas the isoelectric point of WO 3 is even lower and lies in the range 1.5-2.5 [49]. At higher pH values than these WO 3 and TiO 2 surfaces should be negatively charged.…”