Fig. 4: Operando imaging of the active species transport in the NEUTRA beamline with the neutron attenuating BF₄⁻ supporting ion.

a Schematic representation of the non-aqueous cell designs during charge and discharge mode, where the counter electrode (CE) corresponds to 0.5 M TEMPO and the working electrode (WE) to 0.5 M TEMPO⁺BF₄⁻. b Electrochemical sequence over time showing the applied potential steps and measured averaged current output at two inlet flow rates of 15.1 mL min^-1 and 5.6 mL min^-1. c–e Cumulative active species (TEMPO/TEMPO⁺) and BF₄⁻ supporting ion concentration profiles over the reactor area. The averaged snapshots over the whole period of each individual potential step of the cell after image processing and the concentration profiles are shown for various applied potential steps and show the influence of various operation parameters: c applied potential magnitude (OCV, −0.3 V and −0.6 V at 15.1 mL min⁻¹), d flow rate (−0.3 V at 15.1 mL min^-1 and 5.6 mL min^-1) and e polarization sign (−0.6 V and +0.6 V at 5.6 mL min^-1).