Self-assembled lead-free double perovskite-MXene heterostructure with efficient charge separation for photocatalytic CO₂ reduction

Lead-free double perovskites with superior stability have been considered as promising non-toxic substitutes to their lead-contained counterparts in photocatalysis. However, the severe charge recombination greatly restricts their potential as high-performance photocatalysts. Herein, for the first time, we present a self-assembled heterostructure of lead-free double perovskite Cs₂AgBiBr₆ nanocrystals (NCs) on the surface of MXene nanosheets via mutual electrostatic attraction. The presence of MXene nanosheets effectively promotes the formation of free charge carriers in Cs₂AgBiBr₆ NCs via reducing the exciton binding energy. Additionally, the ultrafast photogenerated electron transfer from Cs₂AgBiBr₆ to MXene with a timescale of 1.1 ps largely prolongs the charge carrier lifetime by two times. As a result of the efficient charge separation and electron extraction, the Cs₂AgBiBr₆/MXene heterostructures achieve a high photoelectron consumption yield of 50.6 µmol g⁻¹ h⁻¹ for photocatalytic CO₂ reduction, which surpasses most previously reported lead-free perovskite-based catalysts.