Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe₂O₃Heterojunction Devices for Hydrogen Production

Abstract

p-CuSCN/n-Fe 2 O 3 heterojunctions were electrochemically prepared by sequentially depositing α-Fe 2 O 3 and CuSCN films on FTO (SnO 2 :F) substrates. The α-Fe 2 O 3 and CuSCN films and the α-Fe 2 O 3 /CuSCN heterojunctions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), and X-Ray Diffraction (XRD). Pure crystalline CuSCN films were electrochemically deposited on α-Fe 2 O 3 films by fixing the SCN/Cu molar ratio in the electrolytic bath to 1:1.5 at 60 °C and at a potential of-0.4 V. The photocurrent measurements showed an increase of the intrinsic surface states or defects at the α-Fe 2 O 3 /CuSCN interface. The photoelectrochemical performance of the α-Fe 2 O 3 /CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. It was found that the α-Fe 2 O 3 /CuSCN structure exhibits a higher photoelectrochemical activity when compared to α-Fe 2 O 3 thin films. The highest photocurrent density was obtained for α-Fe 2 O 3 /CuSCN films in 1 M NaOH electrolyte. This high photoactivity was attributed to the high active surface area and to the external applied bias;, which favors the transfer and the separation of the photogenerated charge carriers in α-Fe 2 O 3 /CuSCN heterojunction devices. The flat band potential and the donor density were found to be maximal for the heterojunction. These results suggest a substantial potential to achieve heterojunction thin films in photoelectrochemical water splitting applications.

Electrochemical Characterization of CuSCN Hole-Extracting Thin Films for Perovskite Photovoltaics

“…Figure B shows the Mott–Schottky plot of CuSCN@FTO, which was obtained by electrochemical impedance spectroscopy (EIS, eq ). The plot has a negative slope as is expected for the p-doped semiconductor: ,− where e is the electron charge, ε 0 is the permittivity of free space, ε r is the dielectric constant (for CuSCN ε r ≈ 5.1), E is the applied voltage, E FB is the flatband potential, k B is Boltzmann’s constant, and T is the temperature. The capacitances are referenced to the geometric area of the electrode which neglects any surface roughness.…”

“…Furthermore, the literature N A values for CuSCN, estimated from eq , exhibit large spread from ca. 10 16 to 10 20 cm –3 ,, or even more. ,, This highlights the fact that solely Hall measurements using high-resistivity substrates provide correct carrier concentrations in these cases.…”

“…10 16 to 10 20 cm −3 15,26,27 or even more. 24,25,29 This highlights the fact that solely Hall measurements using high-resistivity substrates provide correct carrier concentrations in these cases.…”

“…A more exact procedure, based on fitting of complete impedance spectra, was employed only rarely. 29 The use of FTO or ITO substrates is problematic not only for their n-semiconducting nature (Figure 2) 4,12,13,30,31 but also for the misalignment of their conduction band minimum (−4.7 to −4.8 eV for ITO 9,33 or −4.5 to −4.6 eV for FTO) 4,31,34−36 with the VBM of CuSCN, the latter occurring at considerably lower energy levels (−5.3 to −5.5 eV). 3,8,9,33 In the electrochemical scale, the average position of VBM of CuSCN is ca.…”

“…−0.3 to 0.2 V vs Ag/AgCl) should be considered with care. 22,29 3.3. Electrochemical Tests of Blocking Function.…”