Photoanode/electrolyte interface modification in solar PEC cells sensitized with Cd0.8Zn0.2S quantum dots for efficient dye degradation

Abstract

Quantum dot (QD) sensitized solar photoelectrochemical (PEC) cells can be used to degrade organic dyes efficiently with the advantages of no secondary pollution and energy conservation. Ternary TiO₂/Cd_0.8Zn_0.2S/ZnS photoanodes in heterojunction structure were designed in PEC cells for degradation of several organic dyes. The molar ratio of Cd to Zn in alloy CdZnS colloid QDs as solar sensitizer was optimized through the computation based on modified DFT to meet carrier transfer thermodynamic requirement in ternary TiO₂/CdZnS/ZnS photoanode. ZnS QDs as passivation layer can inhibit reverse photocurrent and improve the wettability in electrolytes simultaneously. The TiO₂/CdZnS/6ZnS photoanode cell device exhibited the current density maximum of 0.3235 mA/cm² under one sun (AM 1.5, 100 mw/cm²) and achieved 89 % decoloration rate for methylene blue (MB) after 3-hour degradation at 0.8 V applied bias, comparing with 0.059 mA/cm² and 78 % decolorization rate of TiO₂/CdZnS photoanode cell. Furthermore, the device showed high PEC stability that decolorization rate decreased from 89 % to 84 % after five cycles of 3-hour degradation. The effects of applied bias, ZnS content and dye type on PEC performance and decoloration rate were investigated systematically for clarifying degradation mechanism of organic dyes in PEC cells.