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

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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.

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(a), (b), (d) TEM images of SC-1000 showing the formation of a transparent sheet-like morphology. (c) TEM image of an edge showing graphene-like features. (e) SAED on doped carbon showing the diffused ring patterns generated from a graphene-like region. (f) N2 adsorption and desorption profile of char, SC-900 and SC-1000. (g) NLDFT pore size distribution of SC-900 and SC-1000. The narrow peaks centred at ∼1.2 nm correspond to uniform nanopores present in both samples. (h) PXRD pattern of SC-1000.
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Figure 5: (a), (b), (d) TEM images of SC-1000 showing the formation of a transparent sheet-like morphology. (c) TEM image of an edge showing graphene-like features. (e) SAED on doped carbon showing the diffused ring patterns generated from a graphene-like region. (f) N2 adsorption and desorption profile of char, SC-900 and SC-1000. (g) NLDFT pore size distribution of SC-900 and SC-1000. The narrow peaks centred at ∼1.2 nm correspond to uniform nanopores present in both samples. (h) PXRD pattern of SC-1000.

Mentions: The SC-600 was further graphitized at higher temperatures (700–1000 °C) to obtain heteroatom high surface area doped carbon-based materials. Depending on the temperature of the graphitization, the yield of the material was found to vary between 55–70 weight %. The microscopic features of the graphitized samples are shown in figure 4, which contained porous wrinkled structures that resemble the porous features of the etched materials. However, careful observation of the images infers that an increase in the graphitization degree leads to an increase in the surface roughness and porosity of the material. The sample obtained at 1000 °C is highly wrinkled and contains sheet-like structures too. TEM investigations on the SC-1000 (figures 5(a)–(d)) showed a transparent wrinkled sheet throughout the sample. Figure 5(c) shows few-layer-graphene-like features, usually observed for this sample at the pore edges. We also recorded selected area diffraction patterns (SAED) at various portions of the sample, which confirmed the formation of a graphitized region across the sample (figure 5(e)). The uneven, wrinkled surface structure of these materials compared to the SC-600 is generated by the evaporation of small molecules (including oxides and sulphides of carbon, as we observed a reduction of the O and S content after graphitization) at a high graphitization temperature. In addition, since the decrease of O, S and P content is higher (supported by XPS and Raman data, as described later) with the increasing process temperatures, we speculate that a higher temperature leads to more evaporation around the heteroatoms. This also possibly leads to higher surface area of the material.


N- and S-doped high surface area carbon derived from soya chunks as scalable and efficient electrocatalysts for oxygen reduction
(a), (b), (d) TEM images of SC-1000 showing the formation of a transparent sheet-like morphology. (c) TEM image of an edge showing graphene-like features. (e) SAED on doped carbon showing the diffused ring patterns generated from a graphene-like region. (f) N2 adsorption and desorption profile of char, SC-900 and SC-1000. (g) NLDFT pore size distribution of SC-900 and SC-1000. The narrow peaks centred at ∼1.2 nm correspond to uniform nanopores present in both samples. (h) PXRD pattern of SC-1000.
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Related In: Results  -  Collection

License 1 - License 2
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Figure 5: (a), (b), (d) TEM images of SC-1000 showing the formation of a transparent sheet-like morphology. (c) TEM image of an edge showing graphene-like features. (e) SAED on doped carbon showing the diffused ring patterns generated from a graphene-like region. (f) N2 adsorption and desorption profile of char, SC-900 and SC-1000. (g) NLDFT pore size distribution of SC-900 and SC-1000. The narrow peaks centred at ∼1.2 nm correspond to uniform nanopores present in both samples. (h) PXRD pattern of SC-1000.
Mentions: The SC-600 was further graphitized at higher temperatures (700–1000 °C) to obtain heteroatom high surface area doped carbon-based materials. Depending on the temperature of the graphitization, the yield of the material was found to vary between 55–70 weight %. The microscopic features of the graphitized samples are shown in figure 4, which contained porous wrinkled structures that resemble the porous features of the etched materials. However, careful observation of the images infers that an increase in the graphitization degree leads to an increase in the surface roughness and porosity of the material. The sample obtained at 1000 °C is highly wrinkled and contains sheet-like structures too. TEM investigations on the SC-1000 (figures 5(a)–(d)) showed a transparent wrinkled sheet throughout the sample. Figure 5(c) shows few-layer-graphene-like features, usually observed for this sample at the pore edges. We also recorded selected area diffraction patterns (SAED) at various portions of the sample, which confirmed the formation of a graphitized region across the sample (figure 5(e)). The uneven, wrinkled surface structure of these materials compared to the SC-600 is generated by the evaporation of small molecules (including oxides and sulphides of carbon, as we observed a reduction of the O and S content after graphitization) at a high graphitization temperature. In addition, since the decrease of O, S and P content is higher (supported by XPS and Raman data, as described later) with the increasing process temperatures, we speculate that a higher temperature leads to more evaporation around the heteroatoms. This also possibly leads to higher surface area of the material.

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