A Metal-Free Boron Carbon Nitride (BCN) Photocatalyst for Enhanced CO₂-to-CH₄ Conversion by Surface Electronic Tuning

Graphitic carbon nitride (g-C₃N₄) has emerged as an attractive metal-free photocatalyst due to its numerous advantages like tunable surface chemistry, Earth abundance, and nontoxicity. Unfortunately, its photocatalytic efficiency has been seriously limited by charge carrier recombination and low reaction dynamics. Here, we report a metal-free BCN photocatalyst achieving highly selective CO₂-to-CH₄ conversion under visible light without requiring any metal cocatalyst. The exfoliated CN nanosheets can enrich the reaction interface with protons to accelerate the protonation of CO intermediate to further produce CH₄. Moreover, B doping not only introduces more reactive defects but also tunes its electronic structure with a more negative conduction band for rapid electron extraction and enhance CO₂-to-CH₄ conversion. Photocatalytic measurements show that CH₄ production rate and CH₄/CO ratio are 24 and 13 times higher than those of bulk CN, respectively. The CH₄ production rate can also reach 130 and 31 times higher than that of few-layer g-C₃N₄ (FL-CN) and Cu/FL-CN, respectively. The electron selectivity toward CH₄ generation on BCN photocatalysts can reach ≈90%. Furthermore, sunlight driving CO₂-to-CH₄ conversion on such BCN photocatalysts has also been demonstrated. This work offers new insights for the design of customized multifunctional 2D materials for solar-driven CO₂ conversion to CH₄.