Understanding voltage variation in interface corrosion reactions: A theoretical approach based on PDM and DFT

The hydrothermal method is an effective and sustainable approach for biomass utilization, yet electrochemical corrosion poses significant risks to equipment safety. This study theoretically investigates interface electrochemical reactions and their voltage changes, which are challenging to measure experimentally. Employing the Point Defect Model (PDM), we constructed a bi-layer model to represent the metal/barrier (m/bl) and barrier/environment (bl/e) interfaces in carbon steel, utilizing density functional theory (DFT) to explore atomic-scale corrosion processes. Voltage changes for key reactions were calculated across varying barrier layer thicknesses. Results indicated that voltages for reactions (2), (3), and (7) initially increase before decreasing with greater barrier thickness, while reaction (1) shows continuous decline and reaction (5) a steady rise. Reaction pairs (2) and (5) were found to be more favorable than pairs (1) and (4). Using the Interaction Region Indicator (IRI), we visualized chemical bonds, van der Waals interactions, and steric hindrance effects, further supporting the preferential occurrence of reactions (2) and (5). Additionally, environmental H⁺ ion concentration emerged as a critical factor influencing reactions (3) and (7). These findings enhance understanding of atomic-scale corrosion mechanisms and provide a theoretical basis for refining PDM analytical models, contributing to improved corrosion prevention strategies in hydrothermal systems.