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

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.