Abstract
The photoelectrochemical (PEC) method has potential for harvesting solar energy to eventually resolve the fossil fuel crisis owing to its green and renewable characteristics and inherently low conversion efficiency. Herein, we introduce a controlled ZnO decoration layer on a WO3/BiVO4 type II heterojunction array using a facile spin-coating method to enhance the PEC performance of photoelectrodes. The ZnO decoration layer plays a crucial role in attaining superior charge transfer, reduced charge recombination, and stable photoactivity in the composite WO3/BiVO4/ZnO systems. An optimally decorated ZnO layer with oxygen vacancies in the WO3/BiVO4/ZnO photoanode allows extended light absorbance in the UV and visible wavelength regions with a narrow band gap and passivates the underlying WO3/BiVO4 type II heterojunction surfaces by covering the defect sites. Thus, the optimized WO3/BiVO4/ZnO-3 photoanode exhibits the highest photocurrent density (190 μA cm−2 at 1.23 VRHE) with the lowest onset potential (0.41 VRHE), reproducible photo-reaction under chopped light, the smallest charge transfer resistance in the Nyquist plot (1755 Ω), the highest quantum efficiencies for ABPE, IPCE, and APCE (0.036% at 0.92 VRHE, 6% at 380 nm at 1.23 VRHE and 11% at 380 nm, respectively), the highest reliability (30% decay after 1500 s), and high charge injection (63%) and charge separation (7.3%) efficiencies. These findings demonstrate that the component optimization in WO3/BiVO4/ZnO-x composite photoelectrodes is crucial in achieving high PEC performance by improving charge separation and reducing charge recombination.
Published Version
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