A novel Rotating Electrolyte Disc (RED) apparatus has been developed to determine parameters controlling mass transport of dissolved oxygen (and other gases) and oxidised species including metal oxide in liquid metal anode SOFCs. The validity of the concept and design for high temperature studies was first demonstrated by testing the setup in an aqueous system at ambient temperature (equimolar solution of ferrous and ferric chloride in KCl as supporting electrolyte). The diffusion coefficients have been determined for Fe 2+ and Fe3+ by measuring the limiting oxidation and reduction diffusion-controlled currents. The obtained data have been compared with appropriate literature data. Preliminary testing of RED in molten tin electrodes is discussed.