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Operando NMR electrochemical gating studies of ion dynamics in PEDOT:PSS.

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Lyu, Dongxun 
Jin, Yanting 
Magusin, Pieter CMM  ORCID logo
Sturniolo, Simone 


Although organic mixed ionic-electronic conductors are widely proposed for use in bioelectronics, energy generation/storage and neuromorphic computing, our fundamental understanding of the charge-compensating interactions between the ionic and electronic carriers and the dynamics of ions remains poor, particularly for hydrated devices and on electrochemical cycling. Here we show that operando 23Na and 1H nuclear magnetic resonance (NMR) spectroscopy can quantify cation and water movement during the doping/dedoping of films comprising the widely used mixed conductor poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT:PSS). A distinct 23Na quadrupolar splitting is observed due to the partial ordering of the PSS chains within the PEDOT:PSS-rich domains, with respect to the substrate. Operando 23Na NMR studies reveal a close-to-linear correlation between the quadrupolar splitting and the charge stored, which is quantitatively explained by a model in which the holes on the PEDOT backbone are bound to the PSS SO3- groups; an increase in hole concentration during doping inversely correlates with the number of Na+ ions bound to the PSS chains within the PEDOT-rich ordered domains, leading to a decrease in ions within the ordered regions and a decrease in quadrupolar splitting. The Na+-to-electron coupling efficiency, measured via 23Na NMR intensity changes, is close to 100% when using a 1 M NaCl electrolyte. Operando 1H NMR spectroscopy confirms that the Na+ ions injected into/extracted from the wet films are hydrated. These findings shed light on the working principles of organic mixed conductors and demonstrate the utility of operando NMR spectroscopy in revealing structure-property relationships in electroactive polymers.



3403 Macromolecular and Materials Chemistry, 34 Chemical Sciences, 3406 Physical Chemistry, 40 Engineering, 4016 Materials Engineering, 7 Affordable and Clean Energy

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Nat Mater

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Springer Science and Business Media LLC
Engineering and Physical Sciences Research Council (EP/M009521/1)
European Commission Horizon 2020 (H2020) Marie Sk?odowska-Curie actions (101022365)
European Commission Horizon 2020 (H2020) ERC (835073)
EPSRC (EP/W017091/1)
We acknowledge the Cambridge Trust and the China Scholarship Council for funding (D.L.) and thank Dr. Zuozhen Liu, Prof. Yong Yang, Dr. Pedro Braga Groszewicz, Dr. David M. Halat and Yuning Zhou for helpful discussions and Drs. Chris M. Proctor and Anastasios Polyravas for advice concerning the PEDOT:PSS film preparation. D.L., Y.J. and C.P.G. acknowledge funding support from EPSRC under grant number EP/M009521/1. We thank Dr. Oliver Pecher for assistance with the NMR hardware. S.S. acknowledges support from the CCP for NMR Crystallography and EPSRC grant EP/M022501/1.