Figure 3: Protocol to determine catalyst site density through reversible nitrite poisoning.

(a) Flow diagram showing steps required to assess the performance of a catalyst and determine the catalyst site density; (b) measurement protocol used to measure the electrochemical performance of the ORR and assess the charge associated with reductive stripping of the adsorbed nitrite; (c) protocol used to poison the electrode using a nitrite containing solution; (d) ORR performance of catalyst layer before, during and after nitrite adsorption; (e) wide range baseline scan (avoiding nitrite reduction area) for the catalyst layer before, during and after nitrite adsorption; (f) narrow baseline scan in the nitrite reductive stripping region before, during and after nitrite adsorption; (g) expansion of the region associated with nitrite stripping. All experiments were performed in a 0.5 M acetate buffer at pH 5.2 for Fe–N/C catalyst using a rotating disk electrode setup; loading 0.27 mg cm⁻².