Carbon Nanotube Electrodes as a Versatile Platform for Operando Film-Electrochemical EPR Spectroscopy

Spectroelectrochemical platforms that integrate electron paramagnetic resonance (EPR) with electrochemistry offer unprecedented insight into electron transfer and catalytic mechanisms, yet their potential has been constrained by electrode materials that compromise sensitivity and stability. There is a fundamental challenge to provide high electrochemical electrode conductivity whilst minimising microwave losses in the EPR cavity. We use reductive ‘nanotubide’ processing to prepare high-quality buckypapers from long, undamaged single-walled carbon nanotubes. The resulting electrodes provide a unique combination of high conductivity, low microwave loss, and low EPR background. With their excellent mechanical robustness and high accessible surface area, these free-standing electrodes enable film-electrochemical EPR (FE-EPR) spectroelectrochemistry under operando conditions across a 2V potential window and broad pH range. Redox active species can be readily attached to the electrode surface, as illustrated by diazonium-mediated TEMPO-grafting. This model system demonstrates exceptionally stable spectroelectrochemical performance, providing a Pourbaix diagram of all three redox states (TEMPO+, TEMPO•, TEMPOH). The application to redox catalysis is illustrated using TEMPO-mediated alcohol oxidation; we track radical intermediates in real time and extract kinetic parameters, revealing how surface properties govern electron transfer and catalytic turnover. By providing a stable platform for operando spectroelectrochemistry, carbon nanotube buckypapers enable mechanistic insight into electron-transfer reactions.