Graphitic carbon nitride (g-CN) has been widely studied as a metal-free photocatalyst, leading to some excellent results; however, the rapid recombination of photogenerated charge carriers substantially limits its performance. Here, we establish two types of g-CN-based heterojunction (type II and nonmediator assisted Z-scheme) photoanodes on a transparent conducting substrate via coupling with rod-like and nanoparticulate WO, respectively. In these composites, g-CN film grown by electrophoretic deposition of exfoliated g-CN serves as the host or guest material. The optimized type II WO/g-CN composite exhibits an enhanced photocurrent of 0.82 mA cm at 1.23 V vs. RHE and an incident photo-to-current conversion efficiency (IPCE) of 33% as compared with pure WO nanorods (0.22 mA cm for photocurrent and 15% for IPCE). Relative to pure g-CN film (with a photocurrent of several microampere and an IPCE of 2%), a largely improved photocurrent of 0.22 mA cm and an IPCE of 20% were acquired for the Z-scheme g-CN/WO composite. The enhancement can be attributed to accelerated charge separation in the heterointerface because of the suitably aligned band gap between WO and g-CN, as confirmed by optical spectroscopy and ultraviolet photoelectron spectroscopy (UPS) analysis. The photocatalytic process and mechanism of the g-CN-based heterojunctions are proposed herein, which potentially explain the origin of the enhanced photoelectrochemical performance. This achievement and the fundamental information supplied here indicate the importance of rationally designing heterojunction photoelectrodes to improve the performance of semiconductors. This is particularly important for materials such as pure g-CN and WO, as their photoactivities are strongly restricted by high recombination rates.

Zinc oxide is regarded as a promising candidate for application in photoelectrochemical water oxidation due to its higher electron mobility. However, its instability under alkaline conditions limits its application in a practical setting. Herein, we demonstrate an easily achieved wet-chemical route to chemically stabilize ZnO nanowires (NWs) by protecting them with a thin layer Fe O shell. This shell, in which the thickness can be tuned by varying reaction times, forms an intact interface with ZnO NWs, thus protecting ZnO from corrosion in a basic solution. The reverse energetic heterojunction nanowires are subsequently activated by introducing an amorphous iron phosphate, which substantially suppressed surface recombination as a passivation layer and improved photoelectrochemical performance as a potential catalyst. Compared with pure ZnO NWs (0.4 mA cm ), a maximal photocurrent of 1.0 mA cm is achieved with ZnO/Fe O core-shell NWs and 2.3 mA cm was achieved for the PH -treated NWs at 1.23 V versus RHE. The PH low-temperature treatment creates a dual function, passivation and catalyst layer (Fe PO ), examined by X-ray photoelectron spectroscopy, TEM, photoelectrochemical characterization, and impedance measurements. Such a nano-composition design offers great promise to improve the overall performance of the photoanode material.

Graphitic carbon nitride (g‐C3N4) 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‐C3N4, 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‐C3N4). Specifically, surface area and charge‐transfer efficiency are significantly enhanced through architecting g‐C3N4 on nanorod TiO2 to avoid aggregation of layered g‐C3N4. Moreover, a simple phosphide gas treatment of TiO2/g‐C3N4 configuration not only narrows the band gap of g‐C3N4 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‐C3N4/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‐C3N4‐based photoanode. It is expected that the TiO2/g‐C3N4/FeP configuration synthesized by a simple phosphide gas treatment will provide new insight for producing robust g‐C3N4 for water oxidation.