Here we investigated the dynamics of OER activity of NiFe (90/10) catalysts over 1000 potential sweep cycles as a function of their mass loading. Over twenty different films with mass loading in the 10 ng/cm2-30 μg/cm2 range were deposited by Supersonic Cluster Beam Deposition (SCBD), allowing to study the progress of OER in sub-monolayer, monolayer and multilayer regimes. Upon prolonged potential sweeps the electrocatalytic performances of multilayers decreased, while those of monolayers were significantly improved. The best balance in terms of catalytic efficiency and stability in working conditions is found for mass loadings corresponding to a NiFe monolayer, corresponding to a mass loading around 1 μg/cm2 and a thickness of about 3 nm.