A comparative study of activated carbon aerogel and commercial activated carbons as electrode materials for organic electric double-layer capacitors

Yang, Inchan,Kwon, Dahye,Kim, Myung-Soo,Jung, Ji Chul Elsevier 2018 Carbon Vol.132 No.-

<P><B>Abstract</B></P> <P>In this study, we thoroughly compared the electrochemical performances of activated carbon aerogel (ACA) and commercial activated carbons (CACs) as electrode materials for organic electric double-layer capacitors (EDLCs) to investigate the feasibility of ACA for commercial applications. The capacitive behavior of carbon materials as EDLC electrodes is strongly influenced by their specific surface areas and electronic resistances, which are determined by several preparation factors, including raw materials and activation methods. Unlike CACs, which have only micropores, ACA has both abundant micropores and mesopores, leading to a high surface area and low density. ACA also shows relatively low electronic resistance because of its three-dimensional structural features. Accordingly, ACA exhibits considerable capacitance at a low charge–discharge rate and excellent performance even at a high charge–discharge rate, indicating that ACA is a promising carbon material for organic EDLC electrodes. Furthermore, this comparison study clearly demonstrates that newly developed carbon materials for commercially advanced EDLC electrodes should exhibit both high specific surface area and low electronic resistance.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of the Mixing of an Active Material and a Conductive Additive on the Electric Double Layer Capacitor Performance in Organic Electrolyte

Yang, Inchan,Kwon, Soon Hyung,Kim, Bum-Soo,Kim, Sang-Gil,Lee, Byung-Jun,Kim, Myung-Soo,Jung, Ji Chul Materials Research Society of Korea 2015 한국재료학회지 Vol.25 No.3

The effects of the mixing of an active material and a conductive additive on the electrochemical performance of an electric double layer capacitor (EDLC) electrode were investigated. Coin-type EDLC cells with an organic electrolyte were fabricated using the electrode samples with different ball-milling times for the mixing of an active material and a conductive additive. The ball-milling time had a strong influence on the electrochemical performance of the EDLC electrode. The homogeneous mixing of the active material and the conductive additive by ball-milling was very important to obtain an efficient EDLC electrode. However, an EDLC electrode with an excessive ball-milling time displayed low electrical conductivity due to the characteristic change of a conductive additive, leading to poor electrochemical performance. The mixing of an active material and a conductive additive played a crucial role in determining the electrochemical performance of EDLC electrode. The optimal ball-milling time contributed to a homogeneous mixing of an active material and a conductive additive, leading to good electrochemical performance of the EDLC electrode.

Relationships between pore size and charge transfer resistance of carbon aerogels for organic electric double-layer capacitor electrodes

Yang, Inchan,Kim, Sang-Gil,Kwon, Soon Hyung,Kim, Myung-Soo,Jung, Ji Chul Elsevier 2017 ELECTROCHIMICA ACTA Vol.223 No.-

<P><B>Abstract</B></P> <P>Carbon aerogels are prepared from polycondensation of resorcinol and formaldehyde using sodium carbonate as a base catalyst while controlling the ratio of resorcinol to catalyst (R/C). Pore size of the carbon aerogel shows a tendency to increase with the R/C ratio because of the low addition reaction rate between two starting materials with a small amount of catalyst. In addition, the pore size of the carbon aerogels strongly affects their charge transfer resistance and their potential use as organic electric double-layer capacitor electrodes. Ionic resistance to facile mobility of electrolyte ions decreases with increasing pore size of the carbon aerogels, while their electronic resistance exhibited the opposite trend with respect to pore size. These compensation effects between ionic resistance and electronic resistance lead to a different optimum pore size of carbon aerogels for EDLC electrodes depending on the applied charge-discharge rate. A carbon aerogel with large pore size is favorable for use in a low-rate charge-discharge process, while one with small pore size have good performance in a high-rate charge-discharge process. Therefore, we suggest that designing an efficient mesoporous carbon material for an EDLC electrode should include significant consideration of its end use, especially the rate employed for the charge-discharge process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Carbon aerogels with different mesopore sizes were successfully prepared. </LI> <LI> Carbon aerogels were applied to active materials for organic EDLC electrodes. </LI> <LI> The effect of pore size of carbon aerogels was investigated. </LI> <LI> The pore size of carbon aerogels affected their charge transfer resistance. </LI> <LI> The optimum pore size was different depending on the charge-discharge rate. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Comparative studies of the serum half-life extension of a protein <i>via</i> site-specific conjugation to a species-matched or -mismatched albumin

Yang, Byungseop,Kim, Jong Chul,Seong, Jihyoun,Tae, Giyoong,Kwon, Inchan The Royal Society of Chemistry 2018 Biomaterials Science Vol.6 No.8

<P>Human serum albumin (HSA) has been investigated as a serum half-life extender of therapeutic proteins thanks to its unusually long serum half-life. However, in mice, the serum half-life of a HSA-conjugated protein was much shorter than that of HSA in humans, likely due to the species-dependent nature of albumin-FcRn interactions. Herein, we investigated species-dependent albumin-FcRn interactions using species-matched albumin (mouse serum albumin) and species-mismatched albumin (HSA) in non-transgenic mice. We site-specifically introduced a clickable non-natural amino acid to a target protein followed by conjugation to an albumin species <I>via</I> a hetero-bifunctional linker. Using <I>in vitro</I> binding assays, we showed that both HSA- and MSA-conjugated proteins bound mouse FcRns. Conjugation of HSA led to very limited extension of the serum half-life of sfGFP in mice (16.3 h), compared to that of HSA in transgenic mice harboring an allele of mouse FcRn knock-out and expressing humn FcRn (67 h) reported previously. These results suggest that the FcRn-mediated recycling of HSA is not effective in mice. However, conjugation of mouse serum albumin (MSA) resulted in a serum half-life of sfGFP (27.7 h) comparable to that of MSA in mice (28.8 h). Altogether, our study supported that albumin-FcRn interactions are species dependent <I>in vivo</I>.</P>

Site-Specific Albumination as an Alternative to PEGylation for the Enhanced Serum Half-Life in Vivo

Yang, Byungseop,Lim, Sung In,Kim, Jong Chul,Tae, Giyoong,Kwon, Inchan American Chemical Society 2016 Biomacromolecules Vol.17 No.5

<P>Polyethylene glycol (PEG) has been widely used as a serum half-life extender of therapeutic proteins. However, due to immune responses and low degradability of PEG, developing serum half-life extender alternatives to PEG is required. Human serum albumin (HSA) has several beneficial features as a serum half-life extender, including a very long serum half-life, good degradability, and low immune responses. In order to further evaluate the efficacy of HSA, we compared the extent of serum half-life extension of a target protein, superfolder green fluorescent protein (sfGFP), upon HSA conjugation with PEG conjugation side-by-side. Combination of site-specific incorporation of p-azido-L-phenylalanine into sfGFP and copper-free click chemistry achieved the site-specific conjugation of a single HSA, 20 kDa PEG, or 30 kDa PEG to sfGFP. These sfGFP conjugates exhibited the fluorescence comparable to or even greater than that of wild-type sfGFP (sfGFP-WT). In mice, HSA-conjugation to sfGFP extended the serum half-life 9.0 times compared to that of unmodified sfGFP, which is comparable to those of PEG-conjugated sfGFPs (7.3 times for 20 kDa PEG and 9.5 times for 30 kDa PEG). These results clearly demonstrated that HSA was as effective as PEG in extending the serum half-life of a target protein. Therefore, with the additional favorable features, HSA is a good serum half-life extender of a (therapeutic) protein as an alternative to PEG.</P>

Site-Specific PEGylation vs. Site-Specific Albumination for the Prolonged Serum Half-life of a Therapeutic Protein In Vivo

Inchan KWON,Byeongsup YANG 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Comparison of Serum Half-life Extension between PEGylated and Albuminated Proteins in Animal Studies

Byungseop YANG,Inchan KWON 한국생물공학회 2015 한국생물공학회 학술대회 Vol.2015 No.10

Comparision of Serum Half-life Extension Between PEGylated and Albuminated Proteins in Animal Studies

Byungseop YANG,Inchan KWON 한국생물공학회 2016 한국생물공학회 학술대회 Vol.2016 No.4

Bioconjugation and Active Site Design of Enzymes Using Non-natural Amino Acids

Kwon, Inchan,Yang, Byungseop American Chemical Society 2017 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.56 No.23

<P>Enzymes are biocatalysts that play key roles in diverse chemical reactions in living organisms and industrial conversion processes generating value-added products. Since wild-type enzymes obtained from nature are normally not optimal for various applications, enzyme engineering is usually required for enhanced or new properties. Site-specific incorporation of a non-natural amino acid became a powerful protein-engineering tool. In this short review, we briefly summarize our contribution to enzyme complex formation and active site design of enzymes using the technique of site-specific incorporation of a non-natural amino acid. First, site-specific incorporation of a non-natural amino acid at a permissive site of an enzyme led to bioconjugation to other molecules without compromising critical properties. Murine dihydrofolate reductase (mDHFR) was site-specifically conjugated to a biotin via click chemistry to achieve site-specific immobilization. Similarly, formate dehydrogenase (FDH) was site-specifically conjugated to an organometallic catalyst for cofactor regeneration. Furthermore, successive applications of two different click chemistries allowed site-specific coupling of FDH and mannitol dehydrogenase for the enhanced overall reaction efficiencies via substrate channeling effects and active site-orientation control. Besides enzyme bioconjugation, precise control of non-natural amino acid incorporation also allows for active site modification with a non-natural amino acid. Introduction of a bulky non-natural amino acid into the mDHFR active site lowered binding affinity to its inhibitor methotrexate without compromising binding affinity to its substrate dihydrofolate. Similarly, introduction of a bulky non-natural amino acid into the mDHFR active site led to the alteration of substrate specificity toward a poor substrate folate over a good substrate dihydrofolate.</P>

A K₂NiF₄-type La₂Li_0.5Al_0.5O₄ catalyst for the oxidative coupling of methane (OCM)

Kwon, Dahye,Yang, Inchan,Sim, Yujin,Ha, Jeong-Myeong,Jung, Ji Chul Elsevier 2019 CATALYSIS COMMUNICATIONS - Vol.128 No.-

<P><B>Abstract</B></P> <P>In this study, the significant activity and noticeable C<SUB>2</SUB>-selectivity of a La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> catalyst with a K<SUB>2</SUB>NiF<SUB>4</SUB>-type structure in the oxidative coupling of methane (OCM) was reported for the first time. The high C<SUB>2</SUB>-selectivity of the La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> catalyst originated from its abundance of electrophilic lattice oxygen species, which facilitated the selective formation of C<SUB>2</SUB>-hydrocarbons from methane. Although the activity of the La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> catalyst changed slightly owing to its gradual structural change into LaAlO<SUB>3</SUB> perovskite during OCM, it is highly significant that this catalyst, with a K<SUB>2</SUB>NiF<SUB>4</SUB>-type structure, appears as a potentially promising catalyst for the OCM reaction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> catalyst with a K<SUB>2</SUB>NiF<SUB>4</SUB>-type structure was prepared. </LI> <LI> A La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> shows significant activities in the oxidative coupling of methane. </LI> <LI> A La<SUB>2</SUB>Li<SUB>0.5</SUB>Al<SUB>0.5</SUB>O<SUB>4</SUB> has abundant electrophilic lattice oxygen species. </LI> <LI> Electrophilic oxygen species are responsible for the formation of C<SUB>2</SUB>-hydrocarbons. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>