Engineering tannin@biochar bio-composites for synergistic enhancement of anticorrosion performance in zinc-rich epoxy coatings

• Tannin@biochar biocomposites are synthesized for steel corrosion protection. • Biocomposites exhibit electrical conductivity and pH-responsive inhibitor release. • Biocomposites enhances long-term anticorrosion performance of ZRE coating. In this study, spruce wood-derived biochar particles are innovatively used as both conductive additives and carriers to load the green corrosion inhibitor, tannin biopolymer. The microstructure, composition, electrical conductivity, and tannin-releasing behavior are thoroughly investigated. Subsequently, the prepared tannin@biochar (TA@BC) bio-composites serve as environmentally friendly fillers for zinc-rich epoxy (ZRE) coating with long-term anti-corrosion properties. The corrosion resistance behaviour and mechanism are emphatically tested and analyzed through salt spray exposure test, electrochemical impedance spectroscopy, and potential-time measurements. Results show that an optimal tannin concentration enables the preparation of (TA@BC) bio-composites with a more controllable on-demand release, leading to improved anticorrosion performance when incorporated into ZRE coating. This enhancement is attributed to the synergistic effect of prolonged cathodic protection and improved barrier property, resulting from the electrical conductivity of BC and the smart inhibition action of TA.