Electrochemical Commodity Polymer Up- and Re-Cycling: Toward Sustainable and Circular Plastic Treatment

Abstract

The demand for commodity plastics reaches unprecedented dimensions. In contrast to the well-developed plethora of methods for polymer synthesis, sustainable strategies for the end-of-life management of plastics continue to be scarce. While mechanical re-cycling often results in downgraded materials, chemical re-cycling or up-cycling offers tremendous potential for an efficient and green approach, thereby addressing the precarious treatment of post-use plastics within a circular carbon economy. Recently, electrochemistry surfaced as a uniquely powerful tool for polymer up-cycling via polymer functionalization or degradation obtaining either novel polymers with valorized properties or high-value recycled small molecules, respectively. While discussing recent progress in that domain, future perspectives of electrochemical polymer modifications until January 2025 are outlined herein.

Keywords: electrocatalysis; electrochemistry; plastic recycling; polymer degradation; polymer functionalization.

Scheme 1

A) Simplified life‐cycle of plastic from production to post‐use strategies. B) Methods for chemical polymer waste treatment through re‐cycling. C) Comparison of costs for common chemical oxidants and reductants versus electricity in € per mol. [a] Average prices for the largest units obtained from ABCR, Fisher Scientific, Sigma‐Aldrich, and Nippon Gases (for H₂ and O₂). FG = functional group.

Scheme 2

Transition metal‐free electrochemical dearomatization of polystyrene. CCE = constant current electrolysis.

Scheme 3

Electrochemical approaches for polymer modification employing transition metal catalysts. A. Hydroazidation of alkene‐containing polymers. B. Cobalt‐catalyzed electrochemical grafting of PVC.

Scheme 4

Manganaelectro‐catalyzed azidation of commodity polymers via C─H functionalization.

Scheme 5

Examples for electrochemical depolymerization by direct electron‐transfer. A) Degradation of olefins‐containing polymers. B) Depolymerization of polylactic acid. C) Electrochemical cleavage of halogen containing polymers. D) Chlorination of arenes with PVDC.

Scheme 6

Examples for redox‐mediator induced electrochemical degradation of polymers. A) Degradation of polystyrene. B) Degradation of ether‐containing polymers. C) Depolymerization of polyethylene terephthalate. D) Chlorination of arenes with PVC.

Scheme 7

Iron‐catalyzed electrodegradation of polystyrene.

Scheme 8

Mechanistic proposal for the iron‐electrodegradation of polystyrene.