Fabrication of WO3 /Fe2O3 heterostructure photoanode by PVD for photoelectrochemical applications

The bottleneck of cost-effective green hydrogen production through the photoelectrochemical (PEC) water splitting process is lack of suitable materials. To address the material challenge, we have fabricated a heterostructure nanorod of WO3/ Fe2O3 utilizing a high-throughput radio frequency (RF) sputtering Physical vapor deposition (PVD) technique. With optimized parameters, such as as-deposited Fe of 70 nm, a deposition angle of 70°, and an annealing temperature of 500 °C, WO3/ Fe2O3 photoanodes with a morphology of vertically aligned nanorods were fabricated. A rod-like morphology with WO3 nanoparticles was synthesized by the addition of 15 nm of tungsten oxide (WO3) to the Fe2O3 nanorods. To study the optical behavior and morphology, the pristine and WO3 /Fe2O3 heterostructure thin films were characterized by ultraviolet photoelectron spectroscopy (UPS), ultraviolet UV, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). This has led to a 5-fold improvement in PEC performance (0.588 mA/cm2 at 1.23 V vs. RHE for the mixture compared to 0.122 mA/cm2 at 1.23 V vs. RHE for the pristine). As a co-catalyst, WO3 successfully suppressed recombination and assisted in the hole transfer, which immediately increased the photocurrent density of fabricated photoanodes. This was illustrated via the electrochemical impedance spectra including both Nyquist and Mott-Schottky plots with or without illumination. When sustained in steady illumination for 900 s, this photoanode displayed highly stable behavior under PEC conditions.