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phys.org:Cheap, sustainable battery made from tree bark tannins

"The greatest benefit of using a renewable polymer tannin is that Nature produces a huge amount of tannin, which can be extracted from underused bark with minimal cost and efforts," Zhu told Phys.org. "The redox-active phenolic hydroxyl groups of tannins are more than 5000 times higher than lignin, which was previously considered to be the most promising biopolymer for electrochemical energy storage. Due to tannin's significant low molecular weight and extremely high phenolic hydroxyl content, the interpenetrating network of tannins and polypyrrole shows an outstanding electrochemical performance. We think tannin is the new champion of naturally occurring redox-active biopolymers."