Anode-to-cathode area ratio governs corrosion behavior and microbial community structure on steel surfaces

To address the challenges of microbiologically influenced corrosion on Q355 steel in marine environments and the bottleneck in regulating the protection efficiency of Cathodic Protection (CP) with sacrificial anodes, this study constructed a CP system using Al-Zn-In-Cd sacrificial anodes in natural seawater. This study investigated the influence mechanisms by which different cathode-to-anode exposed area ratios (1:1, 40:1, 80:1) affect the corrosion behavior, evolution of corrosion product layers, and the succession of microbial communities of Q355 steel, with a specific focus on revealing the mechanisms of early biomineralization and community succession. The unprotected Q355 steel exhibited a corrosion rate of 246.43 μm/y, with a loose rust layer dominated by β-FeOOH and green rust formed on its surface. The microbial community of the unprotected steel exhibited high diversity, with 111 unique Operational Taxonomic Units (OTUs) identified, and was enriched with iron-oxidizing bacteria such as Mariprofundus . After applying CP, the corrosion rate decreased significantly. In the CP-treated Q355 system with a cathode-to-anode area ratio of 1:1, the corrosion rate decreased to 1.93 μm/y corresponding to a protection efficiency of up to 99.21%. The microbial community structure was distinctly different from that of the unprotected Q355 system and other CP systems, with Thiomicrohabdus accounting for 90.53%. As the area ratio increased to 40:1 and 80:1, the protection efficiency decreased sequentially to 62.98% and 43.00%, respectively. Notably, the CP Q355-80 system with an area ratio of 80:1 had a maximum pitting depth of 36.51 μm.