High-Performance Photoelectrochemical Water Oxidation with Phosphorus-Doped and Metal Phosphide Cocatalyst-Modified g-C₃ N₄ Formation Through Gas Treatment

Graphitic carbon nitride (g-C₃ N₄ ) has been widely explored as a photocatalyst for water splitting. The anodic water oxidation reaction (WOR) remains a major obstacle for such processes, with issues such as low surface area of g-C₃ N₄ , poor light absorption, and low charge-transfer efficiency. In this work, such longtime concerns have been partially addressed with band gap and surface engineering of nanostructured graphitic carbon nitride (g-C₃ N₄ ). Specifically, surface area and charge-transfer efficiency are significantly enhanced through architecting g-C₃ N₄ on nanorod TiO₂ to avoid aggregation of layered g-C₃ N₄ . Moreover, a simple phosphide gas treatment of TiO₂ /g-C₃ N₄ configuration not only narrows the band gap of g-C₃ N₄ by 0.57 eV shifting it into visible range but also generates in situ a metal phosphide (M=Fe, Cu) water oxidation cocatalyst. This TiO₂ /g-C₃ N₄ /FeP configuration significantly improves charge separation and transfer capability. As a result, our non-noble-metal photoelectrochemical system yields outstanding visible light (>420 nm) photocurrent: approximately 0.3 mA cm^-2 at 1.23 V and 1.1 mA cm^-2 at 2.0 V versus RHE, which is the highest for a g-C₃ N₄ -based photoanode. It is expected that the TiO₂ /g-C₃ N₄ /FeP configuration synthesized by a simple phosphide gas treatment will provide new insight for producing robust g-C₃ N₄ for water oxidation.