Effect of metal species on the stability of Me-N-C catalysts during accelerated stress tests mimicking the start-up and shut-down conditions

Martinaiou, Ioanna; Shahraei, Ali; Grimm, Fabian; Zhang, Hongbin; Wittich, Carolin; Klemenz, Sebastian; Dolique, Stephanie; Kleebe, Hans‐Joachim; Stark, Robert W.; Kramm, Ulrike I.

doi:10.1016/j.electacta.2017.04.134

Cited by 72 publications

(89 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We also notice in Figure f, the emergence of three different bands, located at 2710, 2920, and 3240 cm −1 , in the second‐order Raman spectrum after the O 2 ‐LC protocol. These three bands are attributed to a combination of D 1 and G bands overtone, and suggest preferential corrosion of the structurally disordered carbon domains present in the Fe 0.5 RP catalyst during O 2 ‐LC, leaving behind the more graphitic domains, in agreement with former findings . Note also that the Raman spectra after the O 2 ‐LC and the O 2 ‐ST/ST protocols are similar, thus supporting our hypothesis that carbon corrosion was intense during the O 2 ‐LC protocol.…”

Section: Resultssupporting

confidence: 90%

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

Kumar,

Dubau,

Mermoux

et al. 2020

Angew Chem Int Ed

180

170

View full text Add to dashboard Cite

Fe‐N‐C catalysts containing atomic FeNx sites are promising candidates as precious‐metal‐free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The durability of Fe‐N‐C catalysts in fuel cells has been extensively studied using accelerated stress tests (AST). Herein we reveal stronger degradation of the Fe‐N‐C structure and four‐times higher ORR activity loss when performing load cycling AST in O2‐ vs. Ar‐saturated pH 1 electrolyte. Raman spectroscopy results show carbon corrosion after AST in O2, even when cycling at low potentials, while no corrosion occurred after any load cycling AST in Ar. The load‐cycling AST in O2 leads to loss of a significant fraction of FeNx sites, as shown by energy dispersive X‐ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O2 is due to reactive oxygen species produced between H2O2 and Fe sites via Fenton reactions.

show abstract

Section: Resultssupporting

confidence: 90%

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

Kumar,

Dubau,

Mermoux

et al. 2020

Angew Chem Int Ed

180

170

View full text Add to dashboard Cite

show abstract

“…As this loss in activity was also correlating with the displacement of metal out of the N 4 plane, we attributed a contribution of MeN 4 related vibrations to be located in the D 3 band region [37]. As given in Figure 7d, up to a ratio of 40% oxalic acid in the SFA the D 3 /G band ratio is increasing and then does not change significantly (It should be noted that the worst performing catalyst reached a value of 0.7).…”

Section: Resultsmentioning

confidence: 74%

“…In a previous work, we were able to show by analyzing the Raman spectra of a group of Me-N-C catalysts before and after accelerated stress tests (AST), that a decrease in the D 3 /G ratio correlated with the decrease in ORR activity observed during AST [37]. As this loss in activity was also correlating with the displacement of metal out of the N 4 plane, we attributed a contribution of MeN 4 related vibrations to be located in the D 3 band region [37].…”

Section: Resultsmentioning

confidence: 98%

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

et al. 2018

Self Cite

View full text Add to dashboard Cite

Abstract:In this work, the influence of the structure-forming agent on the composition, morphology and oxygen reduction reaction (ORR) activity of Fe-N-C catalysts was investigated. As structure-forming agents (SFAs), dicyandiamide (DCDA) (nitrogen source) or oxalic acid (oxygen source) or mixtures thereof were used. For characterization, cyclic voltammetry and rotating disc electrode (RDE) experiments were performed in 0.1 M H 2 SO 4 . In addition to this, N 2 sorption measurements and Raman spectroscopy were performed for the structural, and elemental analysis for chemical characterization. The role of metal, nitrogen and carbon sources within the synthesis of Fe-N-C catalysts has been pointed out before. Here, we show that the optimum in terms of ORR activity is achieved if both N-and O-containing SFAs are used in almost similar fractions. All catalysts display a redox couple, where its position depends on the fractions of SFAs. The SFA has also a strong impact on the morphology: Catalysts that were prepared with a larger fraction of N-containing SFA revealed a higher order in graphitization, indicated by bands in the 2nd order range of the Raman spectra. Nevertheless, the optimum in terms of ORR activity is obtained for the catalyst with highest D/G band ratio. Therefore, the results indicate that the presence of an additional oxygen-containing SFA is beneficial within the preparation.

show abstract

“…There is also a strong relation between the capacity and the BET surface area (not shown) underlining that in most of the cases indeed edges of graphene layers might contribute to the D-band intensity (rather than curvatures). In a previous work, we were able to show by analyzing the Raman spectra of a group of Me-N-C catalysts before and after accelerated stress tests (AST), that a decrease in the D3/G ratio correlated with the decrease in ORR activity observed during AST [33]. As this loss in activity was also correlating with the out-of-plane displacement of metal out of the N4 plane, we attributed a contribution of MeN4 related vibrations to be located in the D3 band region [33].…”

Section: Preprints (Wwwpreprintsorg) | Not Peer-reviewed | Postedmentioning

confidence: 98%

“…In a previous work, we were able to show by analyzing the Raman spectra of a group of Me-N-C catalysts before and after accelerated stress tests (AST), that a decrease in the D3/G ratio correlated with the decrease in ORR activity observed during AST [33]. As this loss in activity was also correlating with the out-of-plane displacement of metal out of the N4 plane, we attributed a contribution of MeN4 related vibrations to be located in the D3 band region [33]. As given in Figure 5d, up to a ratio of 40 % oxalic acid in the SFA the D3/G band ratio is increasing and then does not change significantly.…”

Section: Preprints (Wwwpreprintsorg) | Not Peer-reviewed | Postedmentioning

confidence: 98%

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

Schardt¹,

Weidler²,

Wallace³

et al. 2018

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract:In this work the influence of the structure forming agent on the composition, morphology and oxygen reduction reaction (ORR) activity of Fe-N-C catalysts was investigated. As structure forming agent (SFA), dicyandiamide (DCDA) (nitrogen source) or oxalic acid (oxygen source) or mixtures thereof were used. For characterization, cyclic voltammetry and rotating disc electrode (RDE) experiments were performed in 0.1 M H2SO4. In addition to this, N2 sorption measurements and Raman spectroscopy were performed for the structural characterization. The role of metal, nitrogen and carbon sources within the synthesis of Fe-N-C catalysts has been pointed out before. Here, we show that the optimum in terms of ORR activity is achieved if both N-and O-containing SFAs are used in almost similar fractions. All catalysts display a redox couple, whereat its position depends on the fractions of SFAs. The SFA has also a strong impact on the morphology: Catalysts that were prepared with a larger fraction of N-containing SFA revealed a higher order in graphitization, indicated by bands in the 2 nd order range of the Raman spectra. Nevertheless, the optimum in terms of ORR activity is obtained for the catalyst with highest D/G band ratio. Therefore, the results indicate that the presence of an additional oxygen-containing SFA is beneficial within the preparation.

show abstract

Effect of metal species on the stability of Me-N-C catalysts during accelerated stress tests mimicking the start-up and shut-down conditions

Cited by 72 publications

References 63 publications

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

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

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

Contact Info

Product

Resources

About

Effect of metal species on the stability of Me-N-C catalysts during accelerated stress tests mimicking the start-up and shut-down conditions

Cited by 72 publications

References 63 publications

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

On the Influence of Oxygen on the Degradation of Fe‐N‐C Catalysts

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

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

Contact Info

Product

Resources

About

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