The continuous decrease in redox peak intensity observed during cyclic voltammetry of Co foil in 0.1 M KOH may be attributed to several factors, including surface passivation, Co dissolution, or formation of an insulating layer such as Co(OH)₂ or Co₃O₄, which can hinder electron transfer. In alkaline media, cobalt can undergo oxidative dissolution or form stable oxide/hydroxide layers that reduce electrochemical activity over time. The issue may be exacerbated in unpurified KOH due to impurities that accelerate surface degradation or passivation. To mitigate this, strategies such as using high-purity KOH, limiting the upper potential to avoid over-oxidation, applying mild activation steps (e.g., pre-cycling or galvanostatic conditioning), or modifying the surface with conductive or protective coatings may help maintain redox activity.

Why do you prepare your cobalt foil in 1 M HCl and then use KOH as the electrolyte? Have you tried preparing your foil in KOH instead of HCl? Also, 1 M is a very high concentration — try using 0.1 M instead. To observe redox behavior, a redox couple such as K₄[Fe(CN)₆]/K₃[Fe(CN)₆] is typically used at a concentration of 5 mmol L⁻¹ in a 1 mol L⁻¹ KCl solution. That way, you could observe what happens to your signal in cyclic voltammetry — whether there is signal enhancement, reversibility, etc. Good luck... Greetings from Ecuador.