Superior pore network retention of carbon derived from naturally dried ginkgo leaves and its enhanced oxygen reduction performance

Razmjooei, F.,Singh, K.P.,Yu, J.S. Elsevier Science Publishers 2016 CATALYSIS TODAY - Vol.260 No.-

<P>Obtaining a highly porous carbon has always been considered as an essential issue in many electrochemical applications. Ginkgo leaves have not only unique shape and color, but also interesting chemical and medical properties, which have inspired us to investigate them. In present approach, the naturally dried yellow ginkgo leaves, collected in autumn season, are directly used to prepare the porous carbon with simple two-step template-free procedure of pyrolysis at different temperatures followed by acid treatment for removal of inherent mineral salts. Interestingly, it is found that inherent salts present in the resulting carbon backbone can play as porogen to create high amount of pores in the carbon framework when the salts are removed by acid treatment. Effect of alternations in ginkgo leaves structure during the climate change, from spring to autumn, on ORR activity is examined for the first time on the carbons obtained by carbonizing different color, greenish and yellowish, ginkgo leaves at 1000 degrees C. Yellow leaves can maintain their original tissue structure during the gradual drying in cold weather of late fall, which results in formation of more stable structure, leading to development of much more pores and larger surface area in the resulting carbon. The unforeseen results exhibit surprisingly higher ORR activity for carbon catalyst obtained from yellow leaves (LY-1000) compared with one prepared from green leaves collected in summer, (LG-1000). Higher surface area of LY-1000 is found to be the most important key factor for its enhanced ORR activity. Furthermore, electrocatalytic property of the carbon greatly depends on the carbonization temperature, which is a crucial factor to make a balance between electrical conductivity, heteroatom doping and surface area. As the temperature increases, the heteroatom doping decreases, which is not favorable for ORR, but at the same time, the conductivity and surface area increase, which is beneficial for ORR, indicating intriguing trade-off between them as a function of temperature, which needs to be optimized for best ORR performance. Moreover, present work enables a large-scale production of efficient heteroatom-doped porous carbon from ginkgo leaf waste without using any activation and templating agents. (C) 2015 Elsevier B.V. All rights reserved.</P>

A new class of electroactive Fe- and P-functionalized graphene for oxygen reduction

Razmjooei, Fatemeh,Singh, Kiran Pal,Bae, Eun Jin,Yu, Jong-Sung The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.20

<▼1><P>A new class of electroactive Fe- and P-functionalized reduced graphene oxide is prepared, which illustrates high ORR activity both in alkaline and acidic conditions due to its high surface area and formation of active Fe–P complex.</P></▼1><▼2><P>While metal and electronegative N-containing carbon has aroused great interest as an efficient catalyst towards the oxygen reduction reaction (ORR), no combination of metal with other heteroatom-containing carbon has received considerable attention. This has motivated us to explore the performance of carbon functionalized with metal and electropositive phosphorous. Herein, we present the first report on the synthesis of a new class of electroactive Fe- and P-functionalized graphene (GPFe) and its electrocatalytic properties in alkaline and acidic media. The introduction of Fe causes remarkable synergistic effects on P-doped reduced graphene oxide by increasing surface area, enhancing the P doping level due to the interaction between Fe and P and generating electrochemically active Fe–P species. N-oxides are known to be in-active for ORR in Fe–N systems, whereas in present Fe–P systems, oxides of Fe and P are found to be beneficial for ORR. Interestingly, after the introduction of Fe, mostly inactive P-doped carbon becomes active in acidic medium. We propose that this study will surely provide renewed insights into active sites for ORR in metal and heteroatom-doped carbon systems.</P></▼2>

Enhanced electrocatalytic activity due to additional phosphorous doping in nitrogen and sulfur-doped graphene: A comprehensive study

Razmjooei, F.,Singh, K.P.,Song, M.Y.,Yu, J.S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.78 No.-

Effect on oxygen reduction reaction (ORR) of ternary-doped reduced graphene oxide (RGO) as an electrocatalyst is evaluated by employing thiourea as a single source of nitrogen (N) and sulfur (S), and triphenylphosphine for phosphorous (P) as precursors for heteroatom doping. The topographical studies show that by doping the RGO, disruption in surface charge and spin asymmetry is introduced into the carbon matrix due to the difference in the bond length and electronegativity between carbon and heteroatoms, which makes carbon lattice ORR active. Ternary (N, S and P)-doped RGO shows excellent ORR activity, which is ~2 times better than that of binary (N and S)-doped RGO, and ~5 times better than that of single (P)-doped RGO. The catalytic activity of the ternary-doped carbon even exceeds the commercial Pt in alkaline medium. Additional P doping causes remarkable synergistic effect on binary N and S-doped RGO by generating active P-N species, improving graphitic order and increasing surface area as well as mesopore volume, which in turn enhances the ORR activity.

Active sites and factors influencing them for efficient oxygen reduction reaction in metal-N coordinated pyrolyzed and non-pyrolyzed catalysts: a review

Singh, Kiranpal,Razmjooei, Fatemeh,Yu, Jong-Sung Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.38

<P>With increasing demand for clean energy and approaching commercialization of polymer electrolyte membrane fuel cells (PEMFCs), replacing expensive Pt-based cathode catalysts with much cheaper non-precious metal (NPM) catalysts has become absolutely essential. This review highlights the parameters that have been considered vital to improving the overall performance of the NPM-based catalysts for oxygen reduction reaction (ORR). In the present review, we focus on well-known catalytic systems in three categories of NPM catalysts,<I>i.e.</I>biomimetic heme-copper oxidase enzymes, non-pyrolyzed/polymeric systems, and pyrolyzed NPM-nitrogen-doped carbon (M-N/C) (M = Fe, Ni, Co,<I>etc.</I>) catalysts. The ORR mechanism on the reported active sites and the effect of varying their local environments are considered and discussed in detail. Among all the catalysts, only pyrolyzed M-N/C catalysts have shown activity and stability much closer to that of the state-of-the-art commercial carbon-supported platinum (Pt/C) catalyst. Although great heights have been climbed in pyrolyzed M-N/C-based catalysts, still general consensuses need to be established regarding the active sites in the NMP-based M-N/C catalysts to help enhance the activity and stability of the catalytic system. By comparing the ORR mechanisms of the three studied systems, various similarities between the active sites are identified and reported comprehensively. On the basis of the information amassed, some future directions for improving the activity, selectivity, and durability of the NPM-based catalysts are also discussed.</P>

Silicon core-mesoporous shell carbon spheres as high stability lithium-ion battery anode

Prakash, Sengodu,Zhang, Chunfei,Park, Jong-Deok,Razmjooei, Fatemeh,Yu, Jong-Sung Elsevier 2019 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.534 No.-

<P><B>Abstract</B></P> <P>An innovative and simple synthesis strategy of silicon nanoparticle (Si NP) core covered by mesoporous shell carbon (MSC) structure is demonstrated. The Si core@MSC (SCMSC) composite is developed for addressing the issues for Si anode material in lithium ion batteries (LIBs) such as high volume expansion and low electrical conductivity. Significant improvement in the electrochemical performance for the SCMSC anode is observed compared with bare Si anode. The SCMSC composite delivers an initial specific capacity of 2450 mAh g<SUP>−1</SUP> at 0.166 A g<SUP>−1</SUP> with Coulombic efficiency of 99.2% for 100 cycles. Compared to bare Si anode, the SCMSC anode exhibits much higher Li storage capacity, superior cyclability, and good rate capability, highlighting the advantages of hierarchical MSC in the SCMSC structure.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Nitrogen-Doped Ordered Mesoporous Carbon with Different Morphologies for the Oxygen Reduction Reaction: Effect of Iron Species and Synergy of Textural Properties

Yang, Dae-Soo,Bhattacharjya, Dhrubajyoti,Song, Min Young,Razmjooei, Fatemeh,Ko, Jaejung,Yang, Quan-Hong,Yu, Jong-Sung Wiley Blackwell (John Wiley Sons) 2015 ChemCatChem Vol.7 No.18