The design and application of a cost-effective, customisable electrochemical cell suitable for in situ X-band (9–10 GHz) Electron Paramagnetic Resonance (EPR) experiments is demonstrated. The cell is optimized for investigating electrochemical parameters of redox-active polymer films at room temperature using polar organic electrolytes. The polymer film to be studied is directly deposited onto the surface of a platinum wire acting as the working electrode. The three-electrode cylindrical cell design with mutual arrangement of the electrodes, inspired by the “ultramicroelectrode concept”, provides enhanced electrochemical response by minimizing ohmic drop while maintaining flexibility for a wide range of experimental setups. The cell performance is demonstrated using a redox conducting polymeric cathode material for organic radical batteries, namely poly[N,N″-bis(3-(4-oxy(2,2,6,6-tetramethylpiperidin-1-oxyl)butoxy)salicylidene)ethylenediiminato nickel(II)], as a test material. Continuous-wave EPR experiments using a portable benchtop spectrometer at a fixed magnetic field allow detecting the material's state of charge, initialisation of oxidation and reduction processes, as well as estimating electrochemical properties. The cell design presented here enables potentiostatic, galvanostatic, and potentiodynamic measurement modes, while offering the possibility of customisation through 3D printing and the use of various electrode materials.
