Optimizing Surface Composition and Structure of FeWO4 Photoanodes for Enhanced Water Photooxidation

Abstract

AbstractPhotoelectrochemical water splitting is a promising approach to produce green hydrogen using solar energy. A primary bottleneck remains the lack of efficient photoanodes to catalyze the sluggish water photooxidation reaction. Engineering photoabsorbers with a narrow bandgap and suitable band edge can boost the photoelectrochemical performance. Herein, nanostructured iron tungstate (FeWO4) photoanodes are engineered directly on a fluorine doped tin oxide glass substrate via a scalable and ultra‐fast flame synthesis route in 13 seconds. Physiochemical, optoelectronic, and electrochemical properties of these photoanodes are systematically investigated. The key roles of charge transport, transfer, and dissolution of W and Fe ions from the FeWO4 matrix within long‐term performance are revealed. Optimal FeWO4 photoanode with a bandgap of 1.82 eV and a FeOOH/NiOOH co‐catalyst coating shows an improved water photooxidation performance, reaching a photocurrent density of 0.23 mA cm−2 at 1.4 V versus reversible hydrogen electrode in 1 m potassium hydroxide. It further demonstrates relatively good photostability, maintaining ≈96% of photocurrent density after 1‐hour continuous photooxidation, albeit some trace of Fe, W and Ni elements dissolution. Insights on the photooxidation performance of nanostructured FeWO4 provide promising directions for the engineering of small band‐gap catalysts for a variety of photoelectrochemical applications.