Tailoring Mo/W ratio in Mo/WO3@ZnIn2S4 for regulating the round-the-clock photocathodic protection

Abstract

The low sustainable current density in darkness restricts the advancement of photocathodic protection (PCP) for steels in marine environments. A combination of MoO₃/WO₃ (Mo/WO₃) was proposed as an electron storage system to enhance capacitance and charge/discharge rates. Subsequently, incorporating ZnIn₂S₄ (ZIS) extended light harvesting and improved photocarrier separation efficiency, resulting in efficient round-the-clock PCP performance. Under illumination, the open circuit potential (OCP) of 10Mo/WO₃@ZIS coupled with 304SS reaches −0.97 V vs. Ag/AgCl, approximately 600 mV and 140 mV more negative than corrosion potential (E_corr) of 304SS and WO₃@ZIS coupled 304SS, whth photocurrent density of 134 μA/cm². The excellent PCP performance is attributed to superior photocarrier separation and enhanced light-harvesting capability. Notably, in the dark, the OCP of the coupled system remains ca. 0.4 V below the E_corr of 304SS, with an average current density of 30 μA/cm², demonstrating the regulated electron storage capabilities of Mo/WO₃. Furthermore, capacity and charge/discharge rates correlate with Mo/W ratio and electrolyte species. 10Mo/WO₃@ZIS exhibits a charge capacity of 2.93 mC, nearly 3 times higher than that of WO₃@ZIS. The innovative application of MoO₃ and WO₃ proves the potential to regulate the electron storage performance, revealing the factors for photoelectron storage/release.