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 flowthrough 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. Keywords Undivided cell Á Flow-through electrodes Á Redox species Á Potassium hexacyanoferrate (II) Á Potassium hexacyanoferrate (III) Nomenclature a Specific surface area (m 2 m -3 ) C 0 Feed concentration (mol dm -3 ) C 0 Outlet concentration (mol dm -3 ) E cell Cell potential (V) F Faraday constant (96,487 C mol -1 ) I Cell current (A) k m Mass transport coefficient (m s -1 ) L Porous electrode thickness (m) L a Active electrode thickness (m) n Number of electrons transferred per mole of reactants Q Volumetric flow rate of electrolyte (cm 3 s -1 ) Re Reynolds number u Mean flow velocity (m s -1 ) V Total volume of electrolyte reacted (m 3 ) W.E Working electrode X Reactant conversionGreek symbols a = k m a/u (m -1 ) / Current efficiency j Electrolyte conductivity (S m -1 )