Kinetics and Faradaic Efficiency of Oxygen Evolution on Reduced H_xWO₃ Photoelectrodes

Abstract

Tungsten oxide (WO 3 ) electrodes were synthesized by spin-coating an ammonium metatungstate sol. Instability in photocurrent during water oxidation applications has previously been attributed to formation of destructive peroxide intermediates. Under constant illumination, repeated cycles of poising WO 3 electrodes at 0.98 V vs Ag/AgCl in pH 1 sulfate solution followed by measuring the open-circuit potential for several hours show reversibility in the photocurrent decay. This behavior is attributed to photochromic H x WO 3 generated at low concentration within the electrode, which serves to increase the donor density. The Mott−Schottky analysis of electrochemical impedance spectroscopy measurements on WO 3 electrodes before and after performing the oxygen-evolution reaction (OER) exhibits a decrease in donor density from 2.8 × 10 22 to 6.0 × 10 21 cm −3 with a corresponding 110 mV positive shift in the flat-band potential, indicative of tungsten oxidation during the OER. Tungsten oxidation is corroborated by a decrease in W 5+ signal in the X-ray photoelectron spectroscopy data. Measuring the OER rate by gas chromatography during water oxidation shows concurrent recovery of catalytic activity after resting at open circuit under illumination, illustrating the key role of H x WO 3 during photoelectrocatalysis.

Revisiting cyclic voltammetry and electrochemical impedance spectroscopy analysis for capacitance measurements

“…4 and 5) for each EIS scan and reported as a function of the applied potential as shown in Figure 2. The results clearly reveal a significant variation (about 30 %) of the capacitance as a function of the frequency when the system is considered as an ideal capacitor, as previously reported by several authors [22][23][24]. The difference in C dl value at two different frequencies when the system is considered as an ideal capacitor clearly emphasise the error made with this assumption.…”

Photocatalytic primary alcohol oxidation on WO3 nanoplatelets

“…Such an occurrence is not uncommon, as seen in our previous report, among others, on the reduction of tungsten in the synthesis of WO 3 . 29 This minimal W 5+ content is also observed in the commercially available WO 3 powder with 2.6% W 5+ , calculated from the deconvoluted W 4f XPS spectra (Fig. S7 †).…”

Oxidizing Ethanol and 2-Propanol by Hypochlorous Acid Generated from Chloride Ions on HxWO3 Photoelectrodes

“…In 1 M NaCl, both ethanol and 2-propanol oxidation by HClO generated on H x WO 3 proceeds with 90% of the charge passed contributing to an oxidized product. Previous work by our group has shown that the oxygen evolution reaction is the dominant reaction on H x WO 3 in the sulfate electrolyte, which should result in a lower yield for alcohol oxidation in the sulfate electrolyte. Indeed, in a control experiment containing 1 M Na 2 SO 4 , we observe significantly lower conversion.…”