Preparation of type-Ⅱ heterojunction of Ta₃N₅/CdS for enhanced photocathodic protection

Constructing type-II heterojunctions is an effective way to enhance the photoelectrochemical (PEC) performance of semiconductor-based materials. In this study, in order to increase the specific surface area, a novel coral-like 3D porous Ta₃N₅ nanostructure was first synthesized via a hydrothermal method. Subsequently, CdS quantum dots were deposited on the coral-like Ta₃N₅ substrate by a successive ionic layer adsorption and reaction (SILAR) method with 40, 80, and 120 cycles (named Ta₃N₅/CdS-40, Ta₃N₅/CdS-80, and Ta₃N₅/CdS-120) to modulate the band structures and optical absorption properties of the composites. The results show that Ta₃N₅/CdS-80 exhibits a continuous and dense CdS overlayer with effectively passivated surface states, delivering the optimal PEC performance (3625 μA·cm⁻² at +1 V about 39 times that of the pure Ta₃N₅). This is because the Type-II heterojunction between CdS and Ta₃N₅ facilitates the separation of photogenerated carriers, and the high-quality CdS coating reduces the capture of photogenerated carriers by defects. When coupled with 304 stainless steel, Ta₃N₅/CdS-80 yields a photovoltage drop of 0.39 V and a net photocurrent density of 99.39 μA·cm⁻², significantly outperforming the Ta₃N₅/CdS-40 and Ta₃N₅/CdS-120 samples. This work provides experimental evidence for the development of superior Ta₃N₅-based photogenerated cathodic protection materials.