Comparison between the Quantum Yields of Compact and Porous WO_3 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