Influence of the morphology of ZnO nanowires on the photoelectrochemical water splitting efficiency

Abstract

Defect-free ZnO nanowire arrays were synthesized and assessed as photoanodes in photoelectrochemical cells. Several tens of samples classified into five different average diameters in the range 40–260 nm were prepared to explore the role of morphology and polar surfaces. The photoelectrochemical performance of the NWs was studied in basic aqueous electrolytes (pH 12.7). A non-monotonic behavior of the performance was demonstrated, which maximizes for nanowires with diameter ∼120 nm. The maximum applied bias photoconversion efficiency is ∼6.3% upon irradiation with 11.5 mW at 365 nm. The photoanodes exhibit a rather stable performance for ∼10 h, while they stabilize at ∼60% of the initial photocurrent after 20 h of continuous bias illumination. The degradation of their performance was attributed to partial detachment of the NWs from the supporting conductive film. The enhanced stability is attributed to the decrease of the pH at the electrochemical interface to values that inhibit the dissolution of ZnO.