  Generator-collector experiments offer insights into the mechanisms of
electrochemical reactions by correlating the product and generator currents.
Most commonly, these experiments are performed using a rotating ring-disk
electrode (RRDE). We developed a double electrode flow cell (DEFC) with
exchangeable generator and detector electrodes where the electrode width equals
the channel width. Commonalities and differences between the RRDE and DEFC are
discussed based on analytical solutions, numerical simulations and measurements
of the ferri-/ferrocyanide redox couple on Pt electrodes in a potassium
chloride electrolyte. The analytical solutions agree with the measurements
using electrode widths of 5 and 2 mm. Yet, we find an unexpected dependence on
the exponent of the width so that wider electrodes cannot be analysed using the
conventional analytical solution. In contrast, all the investigated electrodes
show a collection efficiency of close to 35.4% above a minimum rotation speed
or flow rate, where the narrowest electrode is most accurate at the cost of
precision and the widest electrode the least accurate but most precise. Our
DEFC with exchangeable electrodes is an attractive alternative to commercial
RRDEs due to the flexibility to optimize the electrode materials and geometry
for the desired reaction.
