Riza Ariyani Nur Khasanah, Chi-Hung Lee, Hsi-Lien Hsiao, Tsong-Shin Lim, Po-Ya Chang, Hwo-Shuenn Sheu, Rike Yudianti, Forest Shih-Sen Chien
This study investigates the physicochemical responses of cuprous oxide (Cu2O)/electrolyte interface to electrostatic potential (optical bias, VOB) and electrochemical potential (quasi-Fermi level separation, eΔVF) using electrochemical impedance spectroscopy. VOB and ΔVF were determined from open-circuit photopotential and constant-current photopotential measurements, respectively. Electrochemical impedance was measured while modulating the photocharge density in Cu2O by varying oxygen vacancy (OV) density and light intensity. Cu2O films prepared from 0.01 M and 0.04 M Cu(CH3COO)2 solutions exhibited oxygen deficiencies of 2 % and 8 %, respectively, as characterized by X-ray diffraction. The short-circuit photocurrents of these films under 455 nm light irradiation (5 mW cm‒2) were 90 μA and 28 μA, indicating that lower OV density led to higher photoanodic currents due to a reduced number of recombination centers, increasing photocharge density. The photocatalytic oxidation rate was dominated by the apparent shift in hole quasi-Fermi level, e(ΔVF – VOB), where the lower OV density yielded a shift of 0.5 eV, whereas the higher OV density resulted in a shift of only 0.05 eV. Under low electron injection, the rates of water oxidation in the electrical double layer (EDL) and hole generation in the space charge layer (SCL) at the Cu2O/electrolyte interface showed a linear dependence on light intensity. Increasing light intensity led to a decrease in EDL capacitance and an increase in SCL capacitance, attributed to the rise in VOB. The physicochemical mechanism at the Cu2O/electrolyte interface was governed by photogenerated holes, which enhanced the interfacial oxidation reaction and thereby improved the photocatalytic performance. © 2025
Department of Physics Education, Universitas Negeri Yogyakarta, Yogyakarta, 55281, Indonesia; Department of Applied Physics, Tunghai University, Taichung, 407224, Taiwan; Research Center for Advanced Materials, National Research and Innovation Agency (BRIN), South Tangerang, Banten, 15314, Indonesia; National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
