I tried four trials of the same Copper Phosphides sample in Alkaline medium ( 0.5M KOH) with Hg/HgO reference electrode and Pt as counter electrode. I used 0.001 V/s scan rate for first three trials. Then I noticed that the current is dropping after it was exceed 1.75 V. But if I used a higer scan rate (0.1 V/s), there was no peak. Please can anybody explain what should I do to avoid this current drop? Please note that I did this without rotate the solution. I repeated a same experiment under magnetic stirrer rotating solution. But the results ramains same. I used Glassy Carbon Electrode (GCE) as working electrode and I dropcasted Cu3P sample onto GCE.