ICP-MS -The EFC was coupled with an ICP-MS detector, namely Agilent 7900ce ICP-MS instrument (Agilent Technologies, Palo Alto, CA), equipped with a MicroMist glass concentric nebulizer and a Peltier cooled Scott-type double-pass quartz spray chamber. A forward radiofrequency power of 1500 W was used with Ar gas flows: carrier 0.85 L min -1 ; makeup 0.28 L min -1 ; plasma 1 L min -1 ; and cooling 15 L min -1 . The signals were recorded for Cu started; in order to check for the effect of the lower potential limit, the electrocatalysts were cycled for 3 cycles between 0.925-0.X VRHE (X = 0.7, 0.65 and 0.6) with 9 cycles in total (scan rate of 5 mV s -1 ). In another set of experiments, ''memory effect'' was checked by omitting X = 0.7 and 0.65 and only performing 3 cycles between 0.925-0.6 VRHE. In both cases, the experiment was followed with two cycles between 0.05-1.4 VRHE (scan rate of 5 mV s -1 ). After each experiment, a sequence of potential pulses (see SI, Figure ) was performed in order to synchronise the electrochemical experiment with the ICP-MS signal. Briefly, at the end of the experiment, the system is left at OCP for 200 seconds for the MS signal to reach background levels. This is followed by applying the first potential (oxidative) 'pulse' (for 0.5 s) till 1.4 VRHE. After additional 150 seconds of waiting at OCP, a second potential (reductive) 'pulse' (for 0.5 s) of 0.05 VRHE is applied. Both pulses result in significant dissolution in the ICP-MS data and enabling one to observe the time difference between the electrochemical pulse and the detection of the metal dissolution on the MS.