Chemically controlled <i>in-situ</i> growth of cobalt oxide microspheres on N,S-co-doped reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Khandelwal, Mahima,Chandrasekaran, Sundaram,Hur, Seung Hyun,Chung, Jin Suk Elsevier 2018 Journal of Power Sources Vol.407 No.-

<P><B>Abstract</B></P> <P>A chemically controlled facile approach is developed for the <I>in-situ</I> growth of Co<SUB>3</SUB>O<SUB>4</SUB> microspheres on N,S-co-doped rGO sheets (Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO) employing thiamine hydrochloride (THCl) (7.41 mM) as the N and S co-doping agent under mild experimental conditions. The THCl concentration plays a vital role in controlling the growth of cobalt crystals anchored on the surface of N,S-rGO. The change in concentration of THCl from 7.41 to 22.20 mM alters the deposition of cobalt crystal on the N,S-rGO surface from Co<SUB>3</SUB>O<SUB>4</SUB> to Co<SUB>9</SUB>S<SUB>8</SUB> (Co<SUB>9</SUB>S<SUB>8</SUB>/N,S-rGO). This change is understood due to the formation of different intermediate complex structure driven by supramolecular interactions. The altered cobalt crystal phase leads to tuned morphologies, surface areas and catalytically active centers which are investigated by various characterization techniques. Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO exhibits superior electrocatalytic activity for oxygen reduction reaction (ORR) compared to Co<SUB>9</SUB>S<SUB>8</SUB>/N,S-rGO. Moreover, Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO shows more positive onset potential (0.90 V vs. RHE), half-wave potential (0.74 V vs. RHE), relatively high limiting current density and smaller Tafel slope (52 mV per decade) compared to its separate components owing to synergistic effects. Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO hybrid also outperforms the electrocatalytic activity of commercial Pt/C in terms of durability and methanol tolerance under alkaline conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A facile synthesis of Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO was achieved by using thiamine hydrochloride. </LI> <LI> Thiamine hydrochloride controlled the growth and phase of cobalt crystal on N,S-rGO. </LI> <LI> ORR activity of Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO hybrid was enhanced due to synergistic effect. </LI> <LI> Active sites and electroactive surface area were found to be vital for improved ORR. </LI> <LI> Co<SUB>3</SUB>O<SUB>4</SUB>/N,S-rGO hybrid showed better durability and methanol tolerance than Pt/C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Single precursor mediated one-step synthesis of ternary-doped and functionalized reduced graphene oxide by pH tuning for energy storage applications

Khandelwal, Mahima,Li, Yuanyuan,Molla, Aniruddha,Hyun Hur, Seung,Suk Chung, Jin Elsevier 2017 Chemical engineering journal Vol.330 No.-

<P><B>Abstract</B></P> <P>The present work reports for the first time a one-step hydrothermal synthesis of ternary-doped (N, S, and P) reduced graphene oxide (rGO) under acidic pH conditions (NSPrGO2-12) using thiamine pyrophosphate (TPP) as both a reducing agent and a single source N, S, and P doping agent under mild experimental conditions. The change in pH of the reaction mixture from acidic (∼2.2) to basic (∼8.5) creates a change in the surface chemistry of rGO, resulting in TPP-functionalized rGO with modified morphology, structure, surface area and electrochemical performance. This change has been analyzed in terms of the different interactions between the graphene oxide functional groups and various functionalities of TPP at different pH conditions. Under acidic pH conditions, the sample had a crumpled sheet morphology with wrinkles on its surface having interconnected network and possessing a relatively large surface area. Meanwhile, under basic pH conditions, the sample exhibited stacked layer-by-layer sheets that formed an aggregated network-like structure with a smaller surface area. NSPrGO2-12 delivers a high specific capacitance (C<SUB>s</SUB>) value of 269F/g at 20A/g with long cyclic stability (93% retention after 5000 cycles at 20A/g), high coulombic efficiency (100%) and high energy/power density (23.55Wh/kg/7923.4W/kg) in an aqueous electrolyte. Moreover, the C<SUB>s</SUB> value of the ternary-doped rGO is significantly higher than its mono- and co-doped counterparts under similar experimental conditions. These features clearly demonstrate the tremendous potential of NSPrGO2-12 as an electrode material for energy storage applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A one-step synthesis of ternary (N, S and P) – doped rGO is demonstrated. </LI> <LI> Thiamine pyrophosphate act as single source precursor for N, S and P dopants. </LI> <LI> Change in pH from acidic (∼2.2) to basic (∼8.5) results in functionalized rGO. </LI> <LI> The resulted tri-doped rGO showed high capacitance of 269F/g at 20A/g. </LI> <LI> Tri-doped rGO shows excellent cycling stability and high energy/power density. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Surface modification of co-doped reduced graphene oxide through alkanolamine functionalization for enhanced electrochemical performance

Khandelwal, Mahima,Li, Yuanyuan,Hur, Seung Hyun,Chung, Jin Suk The Royal Society of Chemistry 2018 NEW JOURNAL OF CHEMISTRY Vol.42 No.2

<P>This manuscript presents the facile synthesis of alkanolamine functionalized N,S co-doped reduced graphene oxide (NSrGO) using thiamine hydrochloride as a reducing and co-doping agent for N and S, and triethanolamine (TEA) as a functionalizing agent. The functionalization of TEA molecules on N,S co-doped rGO (TEA-NSrGO) was confirmed by FTIR and XPS analyses. Chemical functionalization of TEA on the surface of NSrGO minimizes restacking of the co-doped sheets and results in an enhanced surface area, as was evidenced by FESEM, TEM, and BET measurements. Moreover, the formation of oxygen-containing groups on NSrGO <I>via</I> covalent functionalization of TEA molecules effectively tunes the surface chemistry of NSrGO, making the electrode material accessible to electrolyte ions. Interestingly, the synergistic effect of TEA functionalization and co-doping in rGO results in impressive electrochemical performance, with a high specific capacitance value of 363 F g<SUP>−1</SUP> at 20 A g<SUP>−1</SUP>, outstanding cycling stability (91% retention after 10 000 cycles at 20 A g<SUP>−1</SUP>), high coulombic efficiency (99.5-100%), and high energy/power density (31.86 W h kg<SUP>−1</SUP>/7646 W kg<SUP>−1</SUP>). These electrochemical features suggest the potential of this electrode material for energy storage applications.</P>

Anion-controlled sulfidation for decoration of graphene oxide with iron cobalt sulfide for rapid sonochemical dyes removal in the absence of light

Molla, Aniruddha,Li, Yuanyuan,Khandelwal, Mahima,Hur, Seung Hyun,Chung, Jin Suk Elsevier 2018 Applied Catalysis A Vol.561 No.-

<P><B>Abstract</B></P> <P>Anion-controlled sulfidation was used to decorate graphene oxide with iron cobalt sulfide via a simple hydrothermal reaction. Anion exchange was carried out using sodium sulfide as an exchanger without any templates or backbone architecture, and in an easy and economical way. Interchange of oxalate, chloride, and hydroxide anions with sulfide anions was performed to tune the morphology of the materials, which subsequently affected their surface area (48.64–83.52 m<SUP>2</SUP>/g) and band gap (2.45–2.91 eV). Ultrasonically-cavity-induced degradation activity without light was rapid (1–3 min) for both positive dyes (rhodamine B and methylene blue), a negative dye (methyl orange), and their mixture. Degradation of the dyes and their mixture in the presence of the prepared samples was a pseudo first-order reaction with rate constant value from 0.780 to 1.702 min<SUP>−1</SUP> that followed the sequence <B>FCS@GO-2 </B>> <B>FCS@GO-1</B> ∼ <B>FCS@GO-3</B> and MB > RhB > MO for catalyst and dyes, respectively. By using terephthalic acid, it was found that the sono-Fenton process quickly generated reactive oxygen species (ROS) even in absence of light. The ROS production was greater for <B>FCS@GO-2</B> than <B>FCS@GO-1</B> or <B>FCS@GO-3</B>, consistent with the catalytic activities of the different catalysts. The prompt production of ROS resulted in a very active process, and the presence of mixed valance states of iron and cobalt resulted in an effective and stable process. It is the synergistic effect of the catalyst that allowed effective breakdown of dyes even in absence of light. The auto-cleaning effect of sonication allowed reuse of the decorated graphene oxide for at least five cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Iron cobalt sulfide@GO was obtained via anion-controlled hydrothermal reaction. </LI> <LI> The band gap, morphology and surface area were tuned via anion exchange. </LI> <LI> The cavity induced sonochemical dyes degradation without light was rapid (1–3 min). </LI> <LI> Generation of ROS by sono-Fenton process was identified using terephthalic acid. </LI> <LI> Dyes degradation was quantitative and repetitive even after five cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Using anion-controlled sulfidation, the morphology, surface area, and band gap (2.45–2.91 eV) of iron cobalt sulfide-decorated graphene oxide was tuned via a simple hydrothermal reaction and allowed for ultrasonic cavity-induced catalytic removal of organic dyes via a sono-Fenton process in the absence of light.</P> <P>[DISPLAY OMISSION]</P>

정밀 마이크로 슈퍼커패시터 전극 제작을 위한 퓨란 페턴 임프린팅과 레이저 탄화 공정

장진아(Jina Jang),Phuong Thi Nguyen,Chau Van Tran,Hao Yu Zhou,Mahima Khandelwal,인정빈(JungBin In) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12