High‐Performance Photoelectrochemical Water Oxidation with Phosphorus‐Doped and Metal Phosphide Cocatalyst‐Modified g‐C₃N₄ Formation Through Gas Treatment

Graphitic carbon nitride (g‐C 3 N 4 ) 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‐C 3 N 4 , 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‐C 3 N 4 ). Specifically, surface area and charge‐transfer efficiency are significantly enhanced through architecting g‐C 3 N 4 on nanorod TiO 2 to avoid aggregation of layered g‐C 3 N 4 . Moreover, a simple phosphide gas treatment of TiO 2 /g‐C 3 N 4 configuration not only narrows the band gap of g‐C 3 N 4 by 0.57 eV shifting it into visible range but also generates in situ a metal phosphide (M=Fe, Cu) water oxidation cocatalyst. This TiO 2 /g‐C 3 N 4 /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‐C 3 N 4 ‐based photoanode. It is expected that the TiO 2 /g‐C 3 N 4 /FeP configuration synthesized by a simple phosphide gas treatment will provide new insight for producing robust g‐C 3 N 4 for water oxidation.