Hexagonal Boron Nitride Quantum Dots as a Superior Hole Extractor for Efficient Charge Separation in WO₃-Based Photoelectrochemical Water Oxidation

Photoelectrochemical (PEC) water splitting is one of the most desirable techniques to harvest clean chemical energy from abundant solar energy. However, the anodic half reaction, i.e., water oxidation, is complicated due to the involvement of multiple electrons in this process. Herein, stable WO3 nanoblocks with the monoclinic phase have been modified by the incorporation of hexagonal boron nitride quantum dots (h-BNQDs) to improve the photogenerated electron–hole separation and additionally to hinder the charge recombination process. The photocurrent density (J) value for the modified WO3 photoanode by incorporation of BNQDs has been found to be 1.63 mA/cm2 at the potential of 1.23 VRHE, which is approximately 2.4-fold higher than the bare WO3 photoanode. The enhancement in photocurrent density is mainly due to the hole extraction property of BNQDs on the surface of the WO3 nanoblocks. A 2-fold increment in photogenerated charge carrier density (ND) value has been achieved due to better charge separation of electron–hole pairs in the modified system, confirmed by the Mott–Schottky (MS) plot. The present work demonstrates a unique, low-cost strategy for enhancement of PEC water oxidation by modification of the photoanode with hole extracting agents.