The behavior of Fe-based non-precious metal catalysts (NPMCs) in different electrolytes and the repercussion for the oxygen reduction reaction (ORR) has been studied. For this matter, a series of Febased NPMC electrocatalysts have been prepared from different carbon sources, carbon black and multiwalled carbon nanotubes. The catalysts have been subjected to chemical treatments in 0.5 M H2SO4 and thoroughly characterized. Their performance for the ORR in different electrolytes e.g. HCIO4, H2SO4, CF3SO3H, KOH and NaOH has been.studied. Higher ORR rates have been recorded in the alkaline electrolytes as compared to the acid ones. Remarkably, the effect of the electrolyte is almost negligible when measured at a given pH value; i.e., the ORR performance is not affected by the nature of the anion when measured in acid electrolytes or the cation when measured in alkaline electrolytes. On the other hand, the activity of NPMCs for the ORR decreases remarkably after treatment of the catalysts in 0.5 M H2SO4. This effect accounts to both the removal of active sites for the ORR during acid treatment and to the blockage of active sites due to the presence of adsorbed sulfates. (C) 2014 Elsevier B.V. All rights reserved.