Summary
The study demonstrates the use of operando nuclear magnetic resonance (NMR) spectroscopy in shedding light on the charge-compensating interactions and ion dynamics in organic mixed conductors, particularly in hydrated devices and on electrochemical cycling. The researchers used a widely used mixed conductor, poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), and conducted 23Na and 1H NMR spectroscopy to quantify cation and water movement during the doping/dedoping of the films.
One of the significant findings of the study is the observation of a distinct 23Na quadrupolar splitting due to the partial ordering of the PSS chains within the PEDOT:PSS-rich domains, with respect to the substrate. The researchers correlated this quadrupolar splitting with the charge stored, and they found a close-to-linear correlation between the two. They proposed a model in which the holes on the PEDOT backbone are bound to the PSS SO3− groups, and an increase in hole concentration during doping leads to a decrease in ions within the ordered regions and a decrease in quadrupolar splitting. This finding provides fundamental insights into the working principles of organic mixed conductors and could lead to the development of more efficient and effective devices.
Another significant finding is the Na+-to-electron coupling efficiency, which was measured to be close to 100% when using a 1 M NaCl electrolyte. This high coupling efficiency suggests that the Na+ ions injected into/extracted from the wet films are tightly coupled to the electronic carriers, which is crucial for the efficient operation of mixed conductors in various applications.
The study also confirmed that the Na+ ions injected into/extracted from the wet films are hydrated, as observed using operando 1H NMR spectroscopy. This finding is particularly relevant for applications in bioelectronics, where hydrated devices are commonly used.
Overall, the study highlights the utility of operando NMR spectroscopy in revealing structure-property relationships in electroactive polymers. It provides fundamental insights into the charge-compensating interactions and ion dynamics in mixed conductors, which are crucial for the development of more efficient and effective devices. The findings could pave the way for the design and optimization of mixed conductors for various applications, including energy generation/storage and neuromorphic computing. The use of operando NMR spectroscopy in this study could also inspire future studies using other advanced characterization techniques to further elucidate the working principles of organic mixed conductors.
The paper is published in Nature Materials “Operando NMR electrochemical gating studies of ion dynamics in PEDOT:PSS“
