Analysis of Adsorption Effects on a Metal-Nitrogen-Carbon Catalyst Using a Rotating Ring-Disk Study

Abstract

A steady-state, rotating ring disk study of the oxygen reduction reaction (ORR) was conducted in acid environment using a pyrolyzed metal/nitrogen/carbon (MNC) electrocatalyst. Analysis of peroxide generation indicates that ORR proceeds both via a direct fourelectron pathway to water at high potentials and an indirect peroxide pathway at low potentials. Above 0.6 V vs RHE, the direct four-electron pathway to water without a desorbing intermediate dominates oxygen reduction because peroxide generation is inhibited due to site availability. In contrast, at potentials below 0.6 V, oxygen reduction begins to shift to the indirect peroxide pathway due to fast kinetics and higher site availability. The net peroxide generation remains relatively low over the entire range due to reduction of peroxide to water.

Influence of the Structure-Forming Agent on the Performance of Fe-N-C Catalysts

“…Second, it is well known for Me-N-C catalysts that the observable diffusion limiting current density is depending on the loading. This might be due to a 2 × 2 electron mechanism, where the probability of re-adsorbing and further reducing any of the formed hydrogen peroxide increases with catalyst film thickness on the electrode [27,28]. Also here, RRDE experiments at different loadings would assist in answering this question.…”

Effect of pyrolysis pressure on activity of Fe–N–C catalysts for oxygen reduction

“…Based on our previous experience, the ratios of iron acetate, Ketjenblack and melamine are kept constant. 15,16,17,18,24 Nitrogen and iron content is thereby fixed at ~ 24 and 1 % wt, respectively. Pyrolysis at 700-1000 °C usually enhances the activity and durability of a MNC catalyst and a proper temperature will result in higher activity.…”

“…Pyrolysis at 700-1000 °C usually enhances the activity and durability of a MNC catalyst and a proper temperature will result in higher activity. Based on our previous work, 15,16,18,24 800 °C is chosen as the optimum pyrolysis temperature for HPP synthesis of Fe-N-C. The dried precursor mixture is placed in a quartz reaction tube followed by the insertion of a quartz rod (Fig.…”

Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions

“…Due to the possibility of a 2 Â 2 electron reduction with peroxide as the intermediate, measurements at high loading underestimate the true peroxide formation. [49][50][51][52][53] As peroxide formation can lead to a further oxidation of the carbon support or might attack the active sites, 54 peroxide formation was tracked during activity This journal is © The Royal Society of Chemistry 2022 measurements and between the ASTs (see below). The peroxide formation was largest for the FeNC reference catalyst Ref with approx.…”