Plasmonic Au nanoparticle sandwiched CuBi2O4/Sb2S3 photocathode with multi-mediated electron transfer for efficient solar water splitting

Abstract

Developing efficient photocathodes with novel design is essential for enhancing the functioning of photoelectrodes in photoelectrochemical (PEC) water splitting. The efficiency of solar-to-fuel conversion has been proven to be improved by using a suitable structural composition to create heterostructures. Apart from surface reactions, charge transfer between heterojunction interfaces is critically important. We report the first-ever novel and rational design of a hybrid photocathode using a CuBi₂O₄ based absorber material with a Sb₂S₃ heterojunction and evenly dispersed plasmonic Au nanoparticles (NPs) sandwiched between CuBi₂O₄ and Sb₂S₃. The heterostructure comprising CuBi₂O₄/Sb₂S₃ revealed an enhanced photoactivity due to ameliorated light absorption and charge separation showing a photocurrent density of −2.25 mA cm⁻² at 0 V vs. RHE at pH 6.65. The crucial dual role of sandwiched Au NPs, as an electron relay mediator, facilitates the electron transfer at the heterojunction interface. Secondly, a plasmonic sensitizer enhances light absorption and charge carrier concentration via charge injection in CuBi₂O₄/Au/Sb₂S₃. The CuBi₂O₄/Au/Sb₂S₃ photocathode displayed a remarkable photocurrent density of −3.2 mA cm⁻² at 0 V vs. RHE (0.85% HC-STH at 0.45 V vs. RHE) at pH 6.65, two-fold enhancement compared to CuBi₂O₄ (−1.5 mA cm⁻² at 0 V vs. RHE, 0.27% HC-STH at 0.3 V vs. RHE). The high-performance CuBi₂O₄/Au/Sb₂S₃ photocathode achieves the highest photocurrent and HC-STH efficiency for a heterojunction to the best of our knowledge. Our findings will pave the way for developing new photoelectrodes with metal NPs sandwiched between semiconductor heterostructures and increasing PEC performance for solar-driven PEC water splitting.