This work describes the development and characterisation of an electrochemical cell which can be used to give high reactant conversion without the need for a membrane. The undivided cell uses two high porosity flow-through graphite felt electrodes, with the products flowing through the back of each electrode. A series of tests have been conducted using an equimolar mixture of potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III) to characterise the cell design and identify suitable operating conditions. It has been shown that high reactant conversion (in excess of 90%) can be achieved for high concentrations of redox species at low flow rates (superficial velocities of around 0.1 mm s−1). However, the cell voltage required to achieve high conversions increased with increasing concentration.