Localized Phosphorization Manipulating Internal Electric Field Orientation in Carbon Nitride Homojunction for Efficient Photocatalytic Hydrogen Evolution

Abstract

Internal electric fields (IEF) have been recognized as an efficacious driving force to improve the reactivity of photocatalysis. However, the manageable modulation of IEF in homojunction remains a great challenge. Herein, a local phosphorization strategy by precisely controlling phosphorus (P) atom doping location is presented to modulate the IEF orientation smartly in high-low crystalline carbon nitride (g-C₃N₄) homojunction. Different orientation of IEF is found to guide different photocatalytic reaction paths. By incorporating P in low-crystalline g-C₃N₄ (P-LCN), IEF is modulated by directing from P-LCN to high-crystalline g-C₃N₄ (HCN), which contributes to S-scheme mechanism over the P-LCN/HCN homojunction. Conversely, P doping in HCN (P-HCN) modulates the IEF in LCN/P-HCN reversing from P-HCN to low-crystalline g-C₃N₄ (LCN), and the photocatalytic reaction follows type-II mechanism. Profiting from the effective photocarriers transfer and separation dynamics, especially the favored electrons reducing capacity, P-LCN/HCN performs a superior H₂ evolution (12.09 mmol·g⁻¹·h⁻¹) than LCN/P-HCN (4.53 mmol·g⁻¹·h⁻¹). Even in 3% NaCl solution and real seawater, the P-LCN/HCN still exhibits incredible H₂ production rates of 8.45 and 4.61 mmol·g⁻¹·h⁻¹, respectively. This study unravels the modulating principle of local phosphorization-dependent IEF orientation for the first time and opens a potential strategy for enhancing the photocatalytic efficiency of g-C₃N₄ homojunction.