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 -0.66 V 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; 100 mW cm^-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 200 μm 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 (-0.5 V vs SCE) or bias-free conditions. The energy levels (i.e., flatband potential) for the two samples are almost the same (only 10 mV 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 0.103 ns, which decreases to 0.0876 ns 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.

Key words: Artificial photosynthesis, Solar fuel, Delafossites, Morphology, Charge transfer