Plasmon-induced charge separation and accumulation in Ag2S/Cu2−xS S-scheme junction for broad-spectrum photothermal-assisted photocatalysis

Abstract

Step-scheme junctions have demonstrated great potential in photocatalysis owing to their unique charge separation mechanism. However, the further acceleration of charge separation and extension of the light response remain challenging. Herein, a plasmon-mediated S-scheme junction is demonstrated in Ag₂S/Cu_2−xS nanotubes, which show efficient photocatalytic hydrogen generation driven by enhanced light absorption, notable photothermal conversion, and ultrafast charge separation. Due to the plasmonic excitation and hollow tubular architecture, the hybrid can efficiently harvest light over a wide wavelength range. Meanwhile, the well-matched band alignment of Ag₂S and Cu_2−xS confers upon the hybrid a built-in electric field and a plasmon-mediated S-scheme charge-transfer pathway for charge separation. The transient absorption tests indicate that the ultrafast plasmon-induced hot electron injection from Cu_2−xS to Ag₂S effectively promotes the recombination of electrons in Cu_2−xS with holes in Ag₂S within the S-scheme junction. As a result, the lifetimes of the hot holes in the trap states of Cu_2−xS and the electrons of the conduction band of Ag₂S are prolonged, leading to the accumulation of holes and electrons at high oxidation and reduction potentials, respectively. Under light irradiation (>420 nm), Ag₂S/Cu_2−xS nanotubes achieve a highly enhanced photothermal-assisted photocatalytic hydrogen evolution rate, which is much higher than that of Ag₂S and Cu_2−xS. This study provides valuable insights for the design of efficient photocatalysts based on S-scheme heterojunctions for energy conversion.