Redox-Active Organometallic Polymers for Environmental and Energy Applications

Redox metallopolymers have been explored extensively for catalysis, energy storage and molecular recognition.¹ When properly designed, these charged polymers can become powerful vehicles to tune the redox-properties at an electrode interface, due to their fast Faradaic reaction and electron-transfer properties. Here, we present nanostructured electrodes functionalized with poly(vinyl)ferrocene/carbon nanotubes (PVF-CNT) as a attractive platform for the selective separation of organic micropollutants under competitive binding, with separation factors >150 based on specific functional group recognition for harmful carboxylates, sulfonates and phosphonates, and ion-capacity >200 mg/g.² The mechanism for this selectivity is explored through both spectroscopic, electrochemical and computational methods. In tandem, cobaltocenium-based polymer counter-electrodes (PMMAECoCp-CNT) were designed as efficient cathodes to increase pseudocapacitive charge and suppress side-reactions, especially the water reduction reaction, thus both enhancing energy storage capabilities (specific capacitance of 498 F/g) as well as increasing ion-selective behavior of the anode (98% current efficiency towards ion-selective process). The non-covalent functionalization of these organometallic polymers onto the electrodes grants cycling stability for over two days and >5000 cycles. Finally, further cathode design through ligand exchange has enabled us to develop cation-selective electrodes for both heavy-metal removal as well as aromatic organic cations – and in tandem, these asymmetric systems become highly energy-efficient systems for wastewater treatment, chemical purification and even bio-separations. This work highlights the potential of asymmetric polymer-functionalized redox-systems for electrochemical separations and energy storage, and the importance of organometallic design for selectively targeting molecular-level pollutants.

References

¹   G. R. Whittell and I. Manners, Advanced Materials, 2007, 19, 3439-3468.

² Su, X.; Kulik, H; Jamison, T.F.; Hatton, T. A. 2016. Anion-selective redox electrodes: electrochemically-mediated separation with organometallic interfaces. Advanced Functional Materials. Advance Article Online. DOI: 10.1002/adfm.201600079