Efficient hot carrier injection in plasmonic semiconductor heterojunction for artificial photosynthesis of ammonia

Abstract Plasmonic semiconductors are arising as potential photocatalysts for the artificial synthesis of green ammonia. However, plasmon excitation-generated hot carriers on a single nanoparticle are easily recombined, leading to low photoconversion efficiency, and energetic defects make plasmonic semiconductors subject to unexpected changes, limiting post-engineering. Here, we developed a plasmonic semiconductor p-n junction by in situ growing p-type Cu3BiS3 in n-type Bi2S3 nanorods by an ion exchange method. The formation of plasmonic semiconductor heterojunctions was verified through high-resolution transmission electron microscopy, Mott-Schottky tests, valence band spectroscopy, and X-ray diffraction (XRD). Additionally, the rapid transfer of hot carriers between the heterojunctions was investigated using transient absorption spectroscopy. The plasmonic p-n junction shows strong localized surface plasmon resonance absorption in the near-infrared range and delivers a 61 times enhancement of the ammonia production rate under full spectrum irradiation in pure water. It can achieve an apparent quantum efficiency of 0.45% at 400 nm and 0.16% at 1000 nm. In situ Fourier-transform infrared (FTIR) reveal that the plasmonic semiconductor heterojunction promotes the nitrogen chemisorption and activation. Using ultrafast transient absorption spectroscopy, we found that localized surface plasmon resonance (LSPR) induced hot carriers can be efficiently injected from plasmonic Cu3BiS3 to non-plasmonic Bi2S3, with sufficient energy to drive water oxidation. We further confirmed that photothermal effects have little contribution to the photocatalytic performance in the water-particle suspension system. The present study shows a potential strategy utilizing plasmonic semiconductors made of earth-abundant elements for green ammonia synthesis.