Comparison between the Quantum Yields of Compact and Porous WO₃ Photoanodes

Ordered structures offer the potential for producing photoanodes with enhanced minority-carrier collection. To evaluate this approach to visible-light-driven oxidation in aqueous electrolytes, porous WO 3 structures were synthesized by the potentiostatic anodization of W foil. The photoelectrochemical behavior of the porous WO 3 photoanodes was compared to that of compact WO 3 films. Relative to planar electrodes, the porous WO 3 electrodes exhibited a 6-fold increase in photocurrent density, from 0.12 to 0.75 mA cm –2, under 100 mW cm –2 of simulated solar illumination. Spectral response measurements indicated that the porous electrodes exhibited internal quantum yields of ∼0.5 throughout most of the region of WO 3 absorption. The external quantum yield of the porous WO 3 films was a function of the angle of incidence of the light, increasing from 0.25 at normal incidence to 0.50 at 65° off normal. The porous WO 3 films showed excellent stability against photodegradation. This work demonstrates that morphological control can improve the internal quantum yield of photoanodes in contact with aqueous electrolytes.