Synthesis of WO3/MnO2 Heterojunction Thin Film by AACVD for Photoelectrochemical Water Splitting

Aerosol-assisted chemical vapor deposition (AACVD) was used to prepare a thin film of the heterojunction MnO2/WO3 onto an FTO glass substrate. The WO3/MnO2 heterojunction thin film exhibited a monoclinic WO3 structure characterized by a nanorod-like shape and substantial interfacial bonding. The detected surface area of the WO3/MnO2 thin film is 32.58 ± 0.79 μm2, while the values of Ra and Rq are 23.20 ± 2.26 nm and 29.60 ± 2.40 nm, respectively, which are higher than pure MnO2 (Ra =13.40 ± 0.99 nm), while lower than pure WO3 (Ra = 69.75 ± 1.34 nm) thin films. The UV–Vis spectra demonstrated extensive absorption in the visible to near-infrared range. The absorption spectrum of UV–Vis (200–900 nm) displayed a distinct absorption edge under 400 nm. The band gap of the pure WO3 thin film equals 2.79 eV, whereas an effective band gap of WO3/MnO2 was observed to equal 1.51 eV, which is significantly smaller than that of the individual oxides (MnO2 = 4.47 eV and WO3 = 2.79 eV). Photoluminescence (PL) verified the robust interfacial electronic interaction. The investigation of the PEC performance exhibited the best performance and the greatest photocurrent under illumination than either pure component. Additionally, there was a good enhancement and improvement in the charge separation due to combining the catalytic MnO2 thin film with a photoactive WO3, owing to its effective charge transfer and decreased recombination.