TY - JOUR

T1 - Spins at work: probing charging and discharging of organic radical batteries by electron paramagnetic resonance spectroscopy

AU - Kulikov, Ilia

AU - Panjwani, Naitik A.

AU - Vereshchagin, Anatoliy A.

AU - Spallek, Domenik

AU - Lukianov, Daniil A.

AU - Alekseeva, Elena V.

AU - Levin, Oleg V.

AU - Behrends, Jan

N1 - Publisher Copyright: © 2022 The Royal Society of Chemistry

PY - 2022/6/23

Y1 - 2022/6/23

N2 - Organic radical batteries (ORBs) are a promising class of electrochemical power sources employing organic radicals as redox-active groups. This article reports on the development of a versatile on-substrate electrode setup for spectroelectrochemical Electron Paramagnetic Resonance (EPR) measurements on redox conductive polymers for ORBs. Quantitative in operando EPR experiments performed on electrochemical cells with a di-TEMPO Ni-Salen polymer as active electrode material demonstrate a strong decrease in the number of paramagnetic centers upon oxidizing the film. The distinct EPR signatures of the TEMPO-containing polymer and its fragments in different molecular environments are used to study its degradation upon repeated cycling. A comparison between the number of EPR-active sites and the number of electrochemically active charges, as measured by cyclic voltammetry, provides information on the nature of the degradation process. Low-temperature ex situ pulse EPR measurements on the oxidized polymer film reveal the spectrum of dilute nitroxide species, which may be associated with electrochemically inactive islands. These experiments pave the way for advanced EPR techniques for accurately determining distances between adjacent paramagnetic centers and thus for identifying performance-limiting loss mechanisms, which can eventually help develop strategies for making ORBs powerful contenders on the path towards sustainable electrochemical power sources.

AB - Organic radical batteries (ORBs) are a promising class of electrochemical power sources employing organic radicals as redox-active groups. This article reports on the development of a versatile on-substrate electrode setup for spectroelectrochemical Electron Paramagnetic Resonance (EPR) measurements on redox conductive polymers for ORBs. Quantitative in operando EPR experiments performed on electrochemical cells with a di-TEMPO Ni-Salen polymer as active electrode material demonstrate a strong decrease in the number of paramagnetic centers upon oxidizing the film. The distinct EPR signatures of the TEMPO-containing polymer and its fragments in different molecular environments are used to study its degradation upon repeated cycling. A comparison between the number of EPR-active sites and the number of electrochemically active charges, as measured by cyclic voltammetry, provides information on the nature of the degradation process. Low-temperature ex situ pulse EPR measurements on the oxidized polymer film reveal the spectrum of dilute nitroxide species, which may be associated with electrochemically inactive islands. These experiments pave the way for advanced EPR techniques for accurately determining distances between adjacent paramagnetic centers and thus for identifying performance-limiting loss mechanisms, which can eventually help develop strategies for making ORBs powerful contenders on the path towards sustainable electrochemical power sources.

UR - http://www.scopus.com/inward/record.url?scp=85133626060&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/eda2de1f-7ce0-3f2f-af2e-4c409bd14ff5/

U2 - 10.1039/d2ee01149b

DO - 10.1039/d2ee01149b

M3 - Article

VL - 15

SP - 3275

EP - 3290

JO - Energy and Environmental Science

JF - Energy and Environmental Science

SN - 1754-5692

IS - 8

ER -