(A) The original catalyst (O-catalyst) was immersed for a time t (x-axis) in a pH 1 H2SO4-solution, then filtered, rinsed with deionized water and dried overnight in an oven at 80°C. Then, an ink was made with the acid-washed catalyst, an aliquot of the ink was deposited on the glassy carbon and the activity measured by RDE in a pH 1 H2SO4-electrolyte. The normalized activity is based on that of the original catalyst, which was 2.8 ± 0.6 Ag-1.
(B) The bulk iron content was measured by neutron activation analysis and the error is 5 %.