Observation of Active Sites for Oxygen Reduction Reaction on Nitrogen-Doped Multilayer Graphene

Abstract

Active sites and the catalytic mechanism of nitrogen-doped graphene in an oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads), which should chemically attach to the active sites, remains on the carbon atoms neighboring pyridinic nitrogen after ORR. In addition, a high amount of the OH(ads) attachment after ORR corresponds to a high catalytic efficiency and vice versa. These pinpoint that the carbon atoms close to pyridinic nitrogen are the main active sites among the different nitrogen doping configurations.

Cobalt Oxide and Cobalt‐Graphitic Carbon Core–Shell Based Catalysts with Remarkably High Oxygen Reduction Reaction Activity

“…We attribute this to the chelation of Co (III) by EDTA in aqueous solution forming essentially six‐coordination complexes of Co center with two nitrogens and four oxygens from EDTA which have unpaired electrons 19. N 1s XPS spectra provide an additional hint into the possibility of ORR activity contribution from nitrogen‐doped carbon as reported in several works 5, 6, 7. Comparison between the spectra of CoO x /Co@GC‐NC and CoO x /Co@GC‐NC‐0 (Figure 2c; Figure S7c, Supporting Information; the results of which are summarized in Table S2, Supporting Information) establishes the dominant presence of pyridinic nitrogen in the most active catalyst.…”

“…[[qv: 5h,l]] Notably, the nature of the interfacial contact and dispersion between the metal cores and the carbon shells plays a key role toward optimizing the ORR activity. Nitrogen‐doped carbon also favors enhanced ORR activity which was attributed to the activity of the pyridinic nitrogen sites by most studies 5, 6. Distinct N active sites were reported to have distinct role where typically pyridinic N contributes to improved onset potential whereas graphitic N facilitates enhanced current density 7.…”

Rational Design and Synthesis of Low-Temperature Fuel Cell Electrocatalysts

“…11b). The carbon neighbouring pyridinic N (α-C) has been proposed to be an active atom in alkaline electrolytes by Qiao et al [121]. The same phenomenon in acid electrolyte was also observed by Guo et al [113] As shown in Fig.…”

Carbon catalysts for electrochemical hydrogen peroxide production in acidic media

“…From Figure 4A we can see that carbons containing similar amounts of N can have very different selectivities for the ORR. This could be due to the fact that different nitrogen containing functionalities can have different influences on the selectivity for the ORR, as the nature of the active sites for ORR in CN-type catalysts is still controversial (compare for instance refs [75,[77][78][79]). This is in line with these findings of Biddinger and Ozkan [80] and Zhao et al [75], that indicate that the overall nitrogen content is a poor indicator of ORR activity, and only certain types of nitrogen, e.g., on the edges of graphitic sheets promotes the 4-electron process [81,82].…”