Limits...
Effects of cobalt precursor on pyrolyzed carbon-supported cobalt-polypyrrole as electrocatalyst toward oxygen reduction reaction.

Yuan X, Hu XX, Ding XL, Kong HC, Sha HD, Lin H, Wen W, Shen G, Guo Z, Ma ZF, Yang Y - Nanoscale Res Lett (2013)

Bottom Line: The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure.The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR.Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. yuanxx519@163.com.

ABSTRACT
A series of non-precious metal electrocatalysts, namely pyrolyzed carbon-supported cobalt-polypyrrole, Co-PPy-TsOH/C, are synthesized with various cobalt precursors, including cobalt acetate, cobalt nitrate, cobalt oxalate, and cobalt chloride. The catalytic performance towards oxygen reduction reaction (ORR) is comparatively investigated with electrochemical techniques of cyclic voltammogram, rotating disk electrode and rotating ring-disk electrode. The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure. It shows that the cobalt precursor plays an essential role on the synthesis process as well as microstructure and performance of the Co-PPy-TsOH/C catalysts towards ORR. Among the studied Co-PPy-TsOH/C catalysts, that prepared with cobalt acetate exhibits the best ORR performance. The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR. Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too.

No MeSH data available.


Calculated values of n and Y(H2O2) during ORR catalyzed by Co-PPy-TsOH/C catalysts prepared from various cobalt precursors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3842826&req=5

Figure 3: Calculated values of n and Y(H2O2) during ORR catalyzed by Co-PPy-TsOH/C catalysts prepared from various cobalt precursors.

Mentions: where ID is the disk current, IR is the ring current, and N is the collection efficiency of RRDE. In the present work, the value of N is 0.22. During the actual calculation, the valid potential range is usually chosen from 0.1 to 0.6 V since the values of ID and IR are too small when the potential is larger than 0.6 V leading to a huge error [26]. The calculated values of Y(H2O2) and n from the RRDE data are presented in Figure 3 as function of the potential. It is revealed that the hydrogen peroxide yield and the transferred-electron number are strongly potential dependent, the former decreases with decrease in the disk potential, while the later decreases with increase in the disk potential. However, the relativity remains the same in the whole potential range lower than 0.55 V, the trend for n, with respect to cobalt precursor, is cobalt acetate > cobalt nitrate > cobalt chloride > cobalt oxalate, while that for Y(H2O2) is just the opposite. This discloses different ORR mechanism by the Co-PPy-TsOH/C catalysts prepared with different cobalt precursors. The ORR catalyzed by the catalyst with cobalt acetate as precursor proceeds radically through four-electron-transfer reaction, since its calculated electron-transfer number reaches 3.99 in the whole studied potential range. However, it could be obviously acquired that the electron-transfer number of the catalysts prepared from the other salts are evidently lower than 4, indicating that the catalyzed ORR progresses through both two-electron-transfer reduction and four-electron-transfer reduction, while the latter is dominant. Therefore, it could be concluded that cobalt precursors have significant influence on ORR mechanism of the synthesized catalyst Co-PPy-TsOH/C, the selectivity to four-electron-transfer reaction to produce H2O follows the order that cobalt acetate > cobalt nitrate > cobalt chloride > cobalt oxalate. This agrees well with the order of catalytic activities discussed above.


Effects of cobalt precursor on pyrolyzed carbon-supported cobalt-polypyrrole as electrocatalyst toward oxygen reduction reaction.

Yuan X, Hu XX, Ding XL, Kong HC, Sha HD, Lin H, Wen W, Shen G, Guo Z, Ma ZF, Yang Y - Nanoscale Res Lett (2013)

Calculated values of n and Y(H2O2) during ORR catalyzed by Co-PPy-TsOH/C catalysts prepared from various cobalt precursors.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842826&req=5

Figure 3: Calculated values of n and Y(H2O2) during ORR catalyzed by Co-PPy-TsOH/C catalysts prepared from various cobalt precursors.
Mentions: where ID is the disk current, IR is the ring current, and N is the collection efficiency of RRDE. In the present work, the value of N is 0.22. During the actual calculation, the valid potential range is usually chosen from 0.1 to 0.6 V since the values of ID and IR are too small when the potential is larger than 0.6 V leading to a huge error [26]. The calculated values of Y(H2O2) and n from the RRDE data are presented in Figure 3 as function of the potential. It is revealed that the hydrogen peroxide yield and the transferred-electron number are strongly potential dependent, the former decreases with decrease in the disk potential, while the later decreases with increase in the disk potential. However, the relativity remains the same in the whole potential range lower than 0.55 V, the trend for n, with respect to cobalt precursor, is cobalt acetate > cobalt nitrate > cobalt chloride > cobalt oxalate, while that for Y(H2O2) is just the opposite. This discloses different ORR mechanism by the Co-PPy-TsOH/C catalysts prepared with different cobalt precursors. The ORR catalyzed by the catalyst with cobalt acetate as precursor proceeds radically through four-electron-transfer reaction, since its calculated electron-transfer number reaches 3.99 in the whole studied potential range. However, it could be obviously acquired that the electron-transfer number of the catalysts prepared from the other salts are evidently lower than 4, indicating that the catalyzed ORR progresses through both two-electron-transfer reduction and four-electron-transfer reduction, while the latter is dominant. Therefore, it could be concluded that cobalt precursors have significant influence on ORR mechanism of the synthesized catalyst Co-PPy-TsOH/C, the selectivity to four-electron-transfer reaction to produce H2O follows the order that cobalt acetate > cobalt nitrate > cobalt chloride > cobalt oxalate. This agrees well with the order of catalytic activities discussed above.

Bottom Line: The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure.The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR.Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. yuanxx519@163.com.

ABSTRACT
A series of non-precious metal electrocatalysts, namely pyrolyzed carbon-supported cobalt-polypyrrole, Co-PPy-TsOH/C, are synthesized with various cobalt precursors, including cobalt acetate, cobalt nitrate, cobalt oxalate, and cobalt chloride. The catalytic performance towards oxygen reduction reaction (ORR) is comparatively investigated with electrochemical techniques of cyclic voltammogram, rotating disk electrode and rotating ring-disk electrode. The results are analyzed and discussed employing physiochemical techniques of X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, elemental analysis, and extended X-ray absorption fine structure. It shows that the cobalt precursor plays an essential role on the synthesis process as well as microstructure and performance of the Co-PPy-TsOH/C catalysts towards ORR. Among the studied Co-PPy-TsOH/C catalysts, that prepared with cobalt acetate exhibits the best ORR performance. The crystallite/particle size of cobalt and its distribution as well as the graphitization degree of carbon in the catalyst greatly affects the catalytic performance of Co-PPy-TsOH/C towards ORR. Metallic cobalt is the main component in the active site in Co-PPy-TsOH/C for catalyzing ORR, but some other elements such as nitrogen are probably involved, too.

No MeSH data available.