The study of hydrogen permeation behavior in Armco-Fe showed that 0.1 M H 2SO 4 was a more effective medium for cathodic polarization compared to 0.1 M NaOH. When both electrolytes were "poisoned" with 1.00 g/L Na 2HAsO 4 • 7H 2O, as hydrogen recombination inhibitor, the corresponding hydrogen permeation levels were 3.5 × 10 -5 A/cm 2 in 0.1 M H 2SO 4 while 0.75 × 10 -5A/cm 2 in 0.1 M NaOH. The breakthrough times were less than 30 s in 0.1 M H 2SO 4, while about 100 s in the NaOH. With varying amounts of "poisons", peak permeation of hydrogen (1.75 × 10 -5 A/cm 2) was achieved with 10 g/L Na 2HAsO 4 • 7H 2O in 0.1 M H 2SO 4, while the least permeation resulted with 10 g/L (NH 2CSH 2) Thiourea addition for same level of 1.00 mA/cm 2 cathodic polarization. © 2007 ASM International.