Limits...
N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction

View Article: PubMed Central - PubMed

ABSTRACT

Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m2 g−1, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of −0.045 V and a half-wave potential of −0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ∼5% as compared to ∼14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.

No MeSH data available.


Related in: MedlinePlus

(a) TGA plot of a glycine chunk in an Ar atmosphere. (b) EDAX spectrum of char pyrolyzed at 300 °C showing the presence of O, N, S and P. SEM images of (c) a glycine chunk, (d) char and (e), (f) NaOH activated carbon, SC-600.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC5036483&req=5

Figure 3: (a) TGA plot of a glycine chunk in an Ar atmosphere. (b) EDAX spectrum of char pyrolyzed at 300 °C showing the presence of O, N, S and P. SEM images of (c) a glycine chunk, (d) char and (e), (f) NaOH activated carbon, SC-600.

Mentions: During the pyrolysis of the soya chunk at 300 °C, the oil content of the soya first evaporated and was deposited as reddish-yellow slurry on the furnace tube, leaving behind primarily the protein and carbohydrate part. Thermogravimetric analysis (TGA, figure 3(a)) of the soya chunks exhibited a continuous weight loss of ∼68% with a sharp drop around 300 °C, which can be attributed to the removal of oils and other small molecules. The char obtained at 300 °C maintained a chunk-like morphology almost without any noticeable features such as surface-porosity (figures 3(c) and (d)). In order to instill pore-like features to increase the surface area, activation of this char was carried out at a high temperature (at 600 °C) by NaOH etching. During etching, the NaOH reacts with the carbon precursors, leading to the development of functional groups such as –ONa. Due to the formation of such –ONa bonds in char, oxidation of the cross-linking carbon atoms in the adjoining lamella takes place, resulting in the rupture of cross-linking between neighbouring lamella. As the lamellae are disturbed from their usual configuration into a slightly wrinkled form, they are unable to regain their original nonporous state upon cooling, leading to interlayer voids and producing porosity and high surface area carbon [34, 35]. In figures 3(e) and (f), we show SEM images of the etched materials, clearly demonstrating porous material and the effect of chemical etching. However, no transparent sheet-like features observed for graphene-based materials were observed at this stage of treatment.


N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction
(a) TGA plot of a glycine chunk in an Ar atmosphere. (b) EDAX spectrum of char pyrolyzed at 300 °C showing the presence of O, N, S and P. SEM images of (c) a glycine chunk, (d) char and (e), (f) NaOH activated carbon, SC-600.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036483&req=5

Figure 3: (a) TGA plot of a glycine chunk in an Ar atmosphere. (b) EDAX spectrum of char pyrolyzed at 300 °C showing the presence of O, N, S and P. SEM images of (c) a glycine chunk, (d) char and (e), (f) NaOH activated carbon, SC-600.
Mentions: During the pyrolysis of the soya chunk at 300 °C, the oil content of the soya first evaporated and was deposited as reddish-yellow slurry on the furnace tube, leaving behind primarily the protein and carbohydrate part. Thermogravimetric analysis (TGA, figure 3(a)) of the soya chunks exhibited a continuous weight loss of ∼68% with a sharp drop around 300 °C, which can be attributed to the removal of oils and other small molecules. The char obtained at 300 °C maintained a chunk-like morphology almost without any noticeable features such as surface-porosity (figures 3(c) and (d)). In order to instill pore-like features to increase the surface area, activation of this char was carried out at a high temperature (at 600 °C) by NaOH etching. During etching, the NaOH reacts with the carbon precursors, leading to the development of functional groups such as –ONa. Due to the formation of such –ONa bonds in char, oxidation of the cross-linking carbon atoms in the adjoining lamella takes place, resulting in the rupture of cross-linking between neighbouring lamella. As the lamellae are disturbed from their usual configuration into a slightly wrinkled form, they are unable to regain their original nonporous state upon cooling, leading to interlayer voids and producing porosity and high surface area carbon [34, 35]. In figures 3(e) and (f), we show SEM images of the etched materials, clearly demonstrating porous material and the effect of chemical etching. However, no transparent sheet-like features observed for graphene-based materials were observed at this stage of treatment.

View Article: PubMed Central - PubMed

ABSTRACT

Highly stable, cost-effective electrocatalysts facilitating oxygen reduction are crucial for the commercialization of membrane-based fuel cell and battery technologies. Herein, we demonstrate that protein-rich soya chunks with a high content of N, S and P atoms are an excellent precursor for heteroatom-doped highly graphitized carbon materials. The materials are nanoporous, with a surface area exceeding 1000 m2 g−1, and they are tunable in doping quantities. These materials exhibit highly efficient catalytic performance toward oxygen reduction reaction (ORR) with an onset potential of −0.045 V and a half-wave potential of −0.211 V (versus a saturated calomel electrode) in a basic medium, which is comparable to commercial Pt catalysts and is better than other recently developed metal-free carbon-based catalysts. These exhibit complete methanol tolerance and a performance degradation of merely ∼5% as compared to ∼14% for a commercial Pt/C catalyst after continuous use for 3000 s at the highest reduction current. We found that the fraction of graphitic N increases at a higher graphitization temperature, leading to the near complete reduction of oxygen. It is believed that due to the easy availability of the precursor and the possibility of genetic engineering to homogeneously control the heteroatom distribution, the synthetic strategy is easily scalable, with further improvement in performance.

No MeSH data available.


Related in: MedlinePlus