Residual H2 and O2 may also explain the differences observed when the cells were switched to OCP. For the ME-cell, Ecell,iR corr. decreased to near zero within a few minutes of the current hold ending while for the LE-cell Ecell,iR corr. remained above 1 V at OCP throughout the stability test as shown in Figure . It is possible that the larger LE-cell retained gas in the catalyst layers for longer due to its larger active area and lower area specific flow rate of 8 mL min -1 cm -2 resulting in a higher OCP. Meanwhile the smaller ME-cell was easily cleared of gas because of a considerably higher area specific flow rate of 56 mL min -1 cm -2 . These reversible performance losses are, however, separate from the long-term degradation of the Fumasep® based CCM revealed by the overall voltage increase observed in both cells over each 20 h stability test, where Ecell,iR corr. increased at a similar rates of 6 and 9 mV h⁻¹ for the ME and LE-cell respectively.