Enhanced electron storage capacity achieved by coupling NiO with WO3/BiVO4 for persistent photocathodic protection of 316 stainless steel

Employing a photoanode with energy self-storage capability is crucial to provide continuous photocathodic protection (PCP) for metal under intermittent irradiation. In this work, NiO, a hole collector, was coupled with WO 3 /BiVO 4 to improve photoelectrochemical properties and photocathodic protection ability for stainless steel (316 SS). The optimal WO 3 /BiVO 4 /NiO photoanode (WB2N2) exhibited 35.1% and 26.6% increase in energy storage capacity compared with WO 3 and WO 3 /BiVO 4 under illumination, respectively. The open-circuit potential (OCP) of 316SS coupled with irradiated WB2N2 was reduced from −143 mV (uncoupled OCP) to −726 mV, and the electrode potential can maintain at −540 mV after light was turned off. It was calculated that electrons of about 1.286×10 −2 C was transferred from WB2N2 to 316 SS after 50 s illumination, which was 11.7 and 5.1 times of that WO 3 and WB2 passed to 316SS, respectively, confirming the best persistent PCP performance of WB2N2 in the absence of light. The positive role of NiO on the PCP and persistent PCP performance was analyzed. The long-term OCP test and XRD analysis proved the stability of WO 3 /BiVO 4 /NiO in PCP performance and chemical composition .