Abstract Cocatalysts have been extensively used to promote water oxidation efficiency in solar‐to‐chemical energy conversion, but the influence of interface compatibility between semiconductor and cocatalyst has been rarely addressed. Here we demonstrate a feasible strategy of interface wettability modification to enhance water oxidation efficiency of the state‐of‐the‐art CoO x /Ta 3 N 5 system. When the hydrophobic feature of a Ta 3 N 5 semiconductor was modulated to a hydrophilic one by in situ or ex situ surface coating with a magnesia nanolayer (2–5 nm), the interfacial contact between the hydrophilic CoO x cocatalyst and the modified hydrophilic Ta 3 N 5 semiconductor was greatly improved. Consequently, the visible‐light‐driven photocatalytic oxygen evolution rate of the resulting CoO x /MgO(in)–Ta 3 N 5 photocatalyst is ca. 23 times that of the pristine Ta 3 N 5 sample, with a new record (11.3 %) of apparent quantum efficiency (AQE) under 500–600 nm illumination.

Interface Engineering of a CoOx/Ta3N5 Photocatalyst for Unprecedented Water Oxidation Performance under Visible‐Light‐Irradiation