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.