Boosting H₂O₂ generation by shortening the charge migration distance in BiPO₄ nanocrystals

The photocatalytic production of H₂O₂ has gained recognition as an economical and eco-friendly technology, but it suffers from limitations such as low production rates and difficulty in achieving high concentrations. This study was designed to overcome these limitations by preparing BiPO₄ nanocrystals (BIP NCs) via high-temperature hydrolysis, and X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that BIP NCs with particle sizes of 8.5 ± 3 nm were synthesized. In a photocatalytic performance test, only H₂O and O₂ were used to produce H₂O₂, resulting in an accumulation of H₂O₂ of up to 30.44 mM·g^-1, as measured with the potassium titanium oxalate method; this value was 3.13 times greater than that of bulk BiPO₄ (BIP-B). The resulting nanocrystals demonstrated superior electron-hole transport and separation efficiency compared to those of BIP-B, and H₂O₂ was formed in a one-step two-electron process. Furthermore, a film composed of a gas diffusion layer (GDL) and BIP NCs provided continuous accumulation of H₂O₂; a concentration of 7.23 mM was achieved after 96 h of reaction, and the stability of the film was confirmed by comparing scanning electron microscopy (SEM) images obtained before and after the reaction. Construction of a nanocrystalline structure to enhance the activities of photocatalysts and films and achieve continuous accumulation of H₂O₂ will provide insights into the photocatalytic production of highly concentrated H₂O₂.