Min Young Song

Transforming Hair into Heteroatom‐Doped Carbon with High Surface Area

Herein, a unique approach to dispose of human hair by pyrolizing it in a regulated environment is presented, yielding highly porous, conductive hair carbons with heteroatoms and high surface area. α-keratin in the protein network of hair serves as a precursor for the heteroatoms and carbon. The carbon framework is ingrained with heteroatoms such as nitrogen and sulfur, which otherwise are incorporated externally through energy-intensive, hazardous, chemical reactions using proper organic precursors. This judicious transformation of organic-rich waste not only addresses the disposal issue, but also generates valuable functional carbon materials from the discard. This unique synthesis strategy involving moderate activation and further graphitization enhances the electrical conductivity, while still maintaining the precious heteroatoms. The effect of temperature on the structural and functional properties is studied, and all the as-obtained carbons are applied as metal-free catalysts for the oxygen reduction reaction (ORR). Carbon graphitized at 900 °C emerges as a superior ORR electrocatalyst with excellent electrocatalytic performance, high selectivity, and long durability, demonstrating that hair carbon can be a promising alternative for costly Pt-based electrocatalysts in fuel cells. The ORR performance can be discussed in terms of heteroatom doping, surface properties, and electrical conductivity of the resulting porous hair carbon materials.

Heteroatom-doped highly porous carbon from human urine

Human urine, otherwise potentially polluting waste, is an universal unused resource in organic form disposed by the human body. We present for the first time “proof of concept” of a convenient, perhaps economically beneficial, and innovative template-free route to synthesize highly porous carbon containing heteroatoms such as N, S, Si, and P from human urine waste as a single precursor for carbon and multiple heteroatoms. High porosity is created through removal of inherently-present salt particles in as-prepared “Urine Carbon” (URC), and multiple heteroatoms are naturally doped into the carbon, making it unnecessary to employ troublesome expensive pore-generating templates as well as extra costly heteroatom-containing organic precursors. Additionally, isolation of rock salts is an extra bonus of present work. The technique is simple, but successful, offering naturally doped conductive hierarchical porous URC, which leads to superior electrocatalytic ORR activity comparable to state of the art Pt/C catalyst along with much improved durability and methanol tolerance, demonstrating that the URC can be a promising alternative to costly Pt-based electrocatalyst for ORR. The ORR activity can be addressed in terms of heteroatom doping, surface properties and electrical conductivity of the carbon framework.

High Pt loading on functionalized multiwall carbon nanotubes as a highly efficient cathode electrocatalyst for proton exchange membrane fuel cells

A very efficient, reproducible approach has been developed to fabricate a multiwall carbon nanotube (MWCNT)-supported, high Pt loading electrocatalyst. In this strategy, MWCNT was first functionalized with an anionic surfactant, sodium dodecylsulfate (SDS), to enhance the hydrophilicity of the MWCNTs for high Pt loading. The SDS-modified MWCNTs were further used to support high loading of Pt nanoparticles (NPs) through a urea-assisted homogeneous deposition (HD) strategy, followed by reduction using ethylene glycol (EG) as the precursor of a reducing agent. Through the input of SDS on the MWCNTs, Pt complex species can be readily anchored on the outer surface of the MWCNTs, while in situ pH adjustment of the solution with urea and reduction by EG enable the Pt NPs to disperse very uniformly on the SDS–MWCNT support with small particles size. Due to its unique structural characteristics, such as high electronic conductivity, the one-dimensional nanotube structure favouring fast electron transfer and more uniform Pt NP dispersion on the support with smaller particle size, the SDS-MWCNT-supported Pt (60 wt%) catalyst considerably outperformed a commercially available Johnson Matthey catalyst with the same Pt loading supported on Vulcan carbon black, when they were each employed as a cathode catalyst in proton exchange membrane fuel cells.

Iodine-treated heteroatom-doped carbon: conductivity driven electrocatalytic activity

A high conductivity and surface area are the most highly desired properties of an electrocatalyst. Herein, we report a novel technique to synthesize highly conductive and microporous N and S-doped carbon from polyaniline (PANI) via a simple, template-free hydrothermal method followed by carbonization in the presence of iodine. The iodine treatment removes a large amount of the attached oxygen atoms and other heteroatoms and, as a consequence, increases the carbon content. Thus, the iodine treatment decreases the doping of catalytically active heteroatoms, which is unfavourable for the ORR, but at the same time, significantly increases the electrical conductivity, which is beneficial for the ORR. In particular, iodine-treated carbonized PANI (CPANI) shows an exceptionally high conductivity i.e., about 3 times that of untreated CPANI. Iodine treatment is also found to enhance the micropore surface area of the PANI during carbonization without using a harmful activating agent or a hard template. An electrocatalytic study indicates that the activity of the iodine-treated sample is considerably higher than that of an untreated sample. This remarkable upsurge in activity is mainly attributed to the large increase in the conductivity and surface area of the iodine-treated sample. The ORR activity is discussed in terms of the heteroatom content, surface area and conductivity of the carbon. This convenient, innovative approach can offer new possibilities for the design of future highly efficient fuel cell electrocatalysts.

Iron–polypyrrole electrocatalyst with remarkable activity and stability for ORR in both alkaline and acidic conditions: a comprehensive assessment of catalyst preparation sequence

A new facile template-free method is presented to synthesize Fe-treated N-doped carbon (Fe/N–C) catalysts for oxygen reduction reaction (ORR) by employing a synthesis protocol of pyrolysis–leaching–stabilization (PLS) sequence of polypyrrole in the presence of ferric source, which serves dual purposes of an oxidant for pyrrole polymerization and an iron source. Each step in the PLS sequence is assessed in detail in terms of the related structural properties of the resulting carbon catalysts, and their effects on ORR activities are elaborated to confirm the validity of the current synthesis protocol. It is found that the as-prepared carbon catalyst exhibits outstanding high catalytic activity in both alkaline and acidic conditions. The carbon catalyst prepared at a pyrolysis temperature of 900 °C (FePPyC-900) shows remarkably high ORR activity with onset potential of 0.96 V (vs. RHE), which is similar to that of Pt/C, whereas the half-wave potential (E1/2) of FePPyC-900 is 0.877 V, more positive than that of Pt/C at the same catalyst loading amount under alkaline conditions. Furthermore, the FePPyC-900 catalyst also illustrates exceptionally high activity under acidic conditions with onset and half-wave potentials of 0.814 and 0.740 V, respectively, which are almost comparable to those (0.817 and 0.709 V) of the state-of-the-art Pt/C catalyst, which is rarely observed for non-Pt-based carbon catalysts. In addition, the FePPyC-900 catalyst displays much better stability and methanol tolerance than the Pt/C and exhibits a four electron transfer pathway under both alkaline and acidic conditions. Such extraordinary high ORR activity and stability of the FePPyC-samples can be attributed to the implementation of extra stabilization step in addition to conventional sample preparation steps of pyrolysis and subsequent leaching in current PLS synthesis protocol as well as to the use of highly conducting PPy as a single precursor of carbon and nitrogen in the presence of Fe.

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

Nitrogen‐doped ordered mesoporous carbons (N‐OMCs) with different morphologies are prepared as oxygen reduction reaction (ORR) catalysts through pyrolysis of iron phthalocyanine‐infiltrated SBA‐15 silica with different mesochannel lengths. Excellent ORR activity with a nearly four‐electron transfer process is observed in both alkaline and acidic media. In particular, the difference in half‐wave potential for ORR relative to commercial Pt/C catalyst is only 50 mV negative in acidic medium, whereas it is 50 mV more positive in alkaline medium. Interestingly, it is found that although the use of iron is necessary for the preparation of highly active nitrogen‐doped ORR carbon catalysts, its presence is not necessary for N‐OMC to be active in the ORR in either alkaline or acidic media. In addition, the ORR activity increases gradually with decreasing mesopore channel length, with maximum activity in N‐OMC with short channels, demonstrating the high synergistic influence of structural morphology on ORR in heteroatom‐doped carbon.