Optimizing Surface Composition and Structure of FeWO<sub>4</sub> Photoanodes for Enhanced Water Photooxidation
Xuan Minh Chau Ta, Thi Kim Anh Nguyen, Anh Dinh Bui, Hieu T. Nguyen, Rahman Daiyan, Rose Amal, Thành Trần‐Phú, Antonio Tricoli
Abstract
Abstract Photoelectrochemical 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 (FeWO 4 ) 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 FeWO 4 matrix within long‐term performance are revealed. Optimal FeWO 4 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 FeWO 4 provide promising directions for the engineering of small band‐gap catalysts for a variety of photoelectrochemical applications.