Theoretical investigation to explore PdSnSe2-n/PdPSe (n = 0, 1, 2) heterostructures as advanced photocatalysts for water splitting applications

Abstract

The photocatalytic water-splitting reaction through semiconductors is a promising approach to converting solar energy into hydrogen, addressing global energy and environmental challenges. This study systematically investigates the photocatalytic properties of two-dimensional (2D) PdS_nSe_2-n/PdPSe (n = 0, 1, 2) heterostructures using density functional theory (DFT) calculations. Among, PdS₂/PdPSe and PdSe₂/PdPSe exhibit type-II band alignment with band gaps of 1.24 eV and 1.45 eV, respectively, while PdSSe/PdPSe is unsuitable for photocatalyst due to a type-I band structure. Optical analysis reveals that PdS₂/PdPSe and PdSe₂/PdPSe demonstrate strong visible-light absorption in the 400 to 600 nm region. Free energy calculations show that the PdPSe monolayer drives the oxygen evolution reaction (OER) with an additional external potential of 1.10 V. In contrast, PdSe₂ monolayer is more efficient for the hydrogen evolution reaction (HER), with a free energy change of 0.09 eV. Band edge alignment analysis further confirms that only PdSe₂/PdPSe possesses the necessary oxidation and reduction potentials for water splitting. PdSe₂/PdPSe exhibits high electron carrier mobility of 683.71 cm²V⁻¹s⁻¹ in the x-direction. The calculated solar-to-hydrogen (STH) efficiency of PdSe₂/PdPSe reaches 31.4 %, higher than the isolated monolayers’ counterparts. Therefore, the PdSe₂/PdPSe heterostructure represents the best combination for photocatalytic water splitting among the studied structures.