A review of CdS-based S-scheme for photocatalytic water splitting: Synthetic strategy and identification techniques

Solar energy is considered a sustainable energy resource for various electrochemical reactions, but its conversion efficacy is controlled by excitons transference and isolation. To increase the conversion efficacy, it is vital to restrict the recombination rate of photocarriers and boost their redox potentials. For this, S-scheme-based photocatalysts offer an effective charge migration mechanism. Herein, we have highlighted the basics of the electronic and optical properties of CdS as a potential photocatalyst using DFT simulation. Afterward, an overview of the thermodynamic kinetics for PWS has been defined. The high point of the review is the CdS-based S-scheme charge transferal route comprising of a reductive and oxidative photocatalyst having staggered band alignment with a difference in Fermi energy level for H2 evolution. Also, the factors determining the S-scheme charge transferal route with respective validating techniques, like in/ex-situ XPS analysis, EPR, AFM, and DFT theoretical simulations, have been discussed. These characterization techniques successfully validated the S-scheme mechanism. Lastly, shortcomings of CdS-based S-scheme heterostructures that further need to be examined in this promising research arena have been outlined.