Effects of electrochemical synthetic conditions on surface property and photocatalytic performance of copper and iron-mixed p-type oxide electrodes

Abstract

Earth-abundant copper and iron-mixed oxide (CuO/CuFeO2; CFO) film electrodes are synthesized using an electrochemical deposition (ED) technique at two different ED potentials (−0.36 and −0.66V vs saturated calomel electrode (SCE); denoted as ED-1 and ED-2, respectively). Then, their surface morphologies are compared, and the photo(electro)catalytic activities for the reduction of Cr(VI) are examined in aqueous solutions at pH 7 under simulated sunlight (AM 1.5G; 100mWcm−2). The degree of the electrical potential applied to the ED process significantly affects the thickness of the synthesized electrode film and the intensity ratio of the diffraction peaks of CuO (111) and CuFeO2 (012). A 200μm thick ED-2 sample with a distinct stacking of CuO on CuFeO2 exhibits a larger broadband absorption spectrum than the 50-μm thick ED-1 with less separate stacking. Furthermore, the ED-2 sample has a higher intensity ratio of the diffraction peaks of CuO (111) and CuFeO2 (012) than ED-1. As-synthesized ED-2 samples produce larger photocurrents, leading to faster Cr(VI) reduction on the surface under given potential bias (−0.5V vs SCE) or bias-free conditions. The energy levels (i.e., flatband potential) for the two samples are almost the same (only 10mV difference), presumably supposing that the enhanced photoactivity of the ED-2 sample for Cr(VI) reduction is due to the facilitated charge transfer. The time-resolved photoluminescence emission spectra analysis reveal that the lifetime (τ) of the charge carriers in the ED-1 sample is 0.103ns, which decreases to 0.0876ns in the ED-2. The ED-2 sample synthesized at a high negative potential is expected to contribute greatly to the application of other solar-to-fuel energy conversion fields as a highly efficient electrode material.