Conducting oxide surface engineering enables the growth of a low-defect carbon nitride film for unbiased photoelectrochemical water splitting

Favorable crystal surface exposure of the substrate enables the growth of semiconductor films with strong adhesion and fast charge transfer at the interface. Herein, the exposure of (211) of SnO₂ : F (FTO) via surface etching led to the uniform synthesis of a crystalline carbon nitride (CN) film. The as-synthesized CN film showed preferable electron transfer from CN to FTO, low structural defects, and excellent charge separation and transport. It produced a state-of-the-art photovoltage of 0.64 V. Photoelectrochemical (PEC) water splitting investigation demonstrated excellent performance with low water oxidation onset potential of 0.22 V vs. RHE and an impressive unbiased photocurrent of 12.4 μA cm⁻². The use of an NiCo-LDH cocatalyst led to a high photocurrent of 440 μA cm⁻² in a triethanolamine containing electrolyte, with a H₂ yield of 40.9 mmol m⁻² h⁻¹ and IPCE (400 nm) of 26.7%. This work demonstrates a good example for the growth of high-quality CN films with high PEC performance via substrate surface engineering, which could also expand other applications of CN films.