P5W30/g-C3N4 heterojunction thin film with improved photoelectrochemical performance for solar water splitting

Abstract

New photocatalysts have been synthesized with inorganic clusters of polyoxometalates (POMs) and graphitic carbon nitride (g-C₃N₄) under hydrothermal conditions. In this research, for the first time, a Preyssler-type polyoxometalate (Na₁₄[NaP₅W₃₀O₁₁₀]·xH₂O) with g-C₃N₄ was applied to design P₅W₃₀/g-C₃N₄, and photoelectrocatalytic water splitting with a g-C₃N₄/P₅W₃₀ photoanode was investigated. All of applied characterization methods verified the preparation of g-C₃N₄ nanorods and the successful compositing of POMs with g-C₃N₄. The photoelectrocatalytic results reveal that the photocurrent density of P₅W₃₀/g-C₃N₄ (0.3 : 1), of around 44 μA cm⁻², is greater than those of g-C₃N₄, P₅W₃₀/g-C₃N₄ (0.1 : 1), or P₅W₃₀/g-C₃N₄ (0.5 : 1). The lower slope of the transient open circuit potential decay for P₅W₃₀/g-C₃N₄ (0.3 : 1) in comparison with other photocatalysts demonstrates more efficient separation and lower recombination rate of photo-induced charge carriers. Also, the constant photocurrent density in chronoamperometry analysis confirms a stable photoelectrocatalytic performance during three cycles under light irradiation for all of the prepared photoanodes. Mott–Schottky plots displayed a deeper band bending for P₅W₃₀/g-C₃N₄ (0.3 : 1) compared to that of g-C₃N₄, implying a greater charge carrier density, which leads to greater electron accumulation on its surface and simplifies electron transfer at the photoelectrode/electrolyte interface.