A new device and method is described for enhancing the power output and thermodynamic efficiency of batteries and fuel cells. In addition to the anode and cathode, the new device introduces a third electrode together with an auxiliary circuit which is run in the electrolytic mode and permits battery or fuel cell operation under previously inaccessible anode-cathode potential differences. The new device and method introduces a new controllable variable in fuel cell and battery operation. It significantly reduces overpotential and causes up to 700% enhancement in solid oxide fuel cell power output and also an enhancement in overall thermodynamic efficiency. (C) 2004 The Electrochemical Society.