By applying a DC electrical bias to a central graphene gate electrode, which separated the anode and the cathode in an electrochemical cell, we controlled the external cell's current, I-cell, electrically. By irradiating the cell with modulated light intensity, we obtained an AC open-circuit response. The optically induced open-circuit AC voltage could be tuned by the DC electrical bias. Such findings suggest novel methods to control and monitor ion currents in electrochemical cells. (c) 2013 Elsevier Ltd. All rights reserved.