An electrochemical cell behaves like an electrolytic cell when

If an external opposite potential is applied on the electrochemical cell, the reaction continues to take place till the opposite voltage reaches the value 1.1 V. At this stage, no current flow through the cell and if there is any further increase in the external potential (E_external), then reaction starts functioning in opposite direction i.e. an electrochemical cell behaves like an electrolytic cell.

${\mathrm{E}}_{\text{external }}>{\mathrm{E}}_{\text{cell }}$