Sol−Gel Concentration-Mediated WO3(002) Photoanodes: Synthesis and Photoelectrochemical Properties

Abstract

Photoelectrochemical (PEC) water splitting is a promising technology for producing clean hydrogen, but the slow rate of the oxygen evolution reaction (OER) severely limits its overall efficiency. WO3 is a competitive n-type semiconductor for OER photoanodes owing to its low cost, good electron mobility, and suitable band structure. In this study, we successfully fabricated WO3 photoanodes with preferred (002) crystal orientation via a simple sol−gel concentration strategy, without introducing any dopants or crystal-directing agents. The influence of calcination temperature and film thickness on PEC performance was systematically explored, and 500 °C was verified as the optimal calcination temperature for a well-crystallized structure and fast charge transfer. Under AM 1.5G simulated solar light and an applied potential of 1.57 V vs. RHE, the single-layer WO3(002) photoanode achieves a photocurrent density of 0.40 mA cm−2. Further thickness regulation via multi-layer spin-coating greatly improves light absorption and charge separation, and the optimized sample delivers a high photocurrent density of 2.11 mA cm−2. Characterizations confirm that the concentrated precursor effectively induces selective growth of active (002) facets. This work proposes a low-cost, scalable approach to tailoring WO3 crystal facets, providing valuable guidance for designing high-performance photoanodes for efficient PEC water splitting.