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.