Synthesis of Co₃O₄ macrocubes catalyst using novel chitosan/urea template for hydrogen generation from sodium borohydride

Tomboc, Gracita Raquel M.,Tamboli, Ashif H.,Kim, Hern Elsevier 2017 ENERGY Vol.121 No.-

<P><B>Abstract</B></P> <P>Co<SUB>3</SUB>O<SUB>4</SUB> catalyst with porous macrocubes structure were one pot formulated by hydrothermal treatment of chitosan/urea/Co(NO<SUB>3</SUB>)<SUB>2</SUB>·6H<SUB>2</SUB>O mixtures at 180 °C for 8 h and then calcined at different temperatures for 4 h. Chitosan and urea are both compounds containing amino group, which made them different from the previous supporting materials. In this study, chitosan was the major template in the solution and determined the shape of the Co<SUB>3</SUB>O<SUB>4</SUB> catalyst while urea played a major support to cobalt (II) nitrate hexahydrate during crystal growth of the catalyst. The prepared materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), UV–vis Absorption Spectrum and BET technique. A remarkably high hydrogen generation rate of 1497.55 ml<SUB>H2</SUB> min<SUP>−1</SUP> g<SUB>cat</SUB> <SUP>−1</SUP> was obtained from the hydrolysis of 2 wt % NaBH<SUB>4</SUB> solution with 0.02 g catalyst at 25 °C. The catalytic activity of the as-prepared sample was examined for hydrolysis reaction of sodium borohydride (NaBH<SUB>4</SUB>) at different temperatures, catalyst amount and NaBH<SUB>4</SUB> concentration. The results reveal that the average crystallite size, macrocubes thickness, surface properties and catalytic activity of Co<SUB>3</SUB>O<SUB>4</SUB> macrocubes could be controlled by varying the mass ratio of chitosan/urea to cobalt concentration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesized Co<SUB>3</SUB>O<SUB>4</SUB> catalyst thru hydrothermal treatment using chitosan/urea. </LI> <LI> Optimal ratio of Co(NO<SUB>3</SUB>)<SUB>2</SUB>·6H<SUB>2</SUB>O to urea is 1:10 and calcination temperature at 700 °C. </LI> <LI> Co<SUB>3</SUB>O<SUB>4</SUB> catalyst has macrocubes structure w/sponge surface & crystal size is 42.35 nm. </LI> <LI> A remarkably high HGR of 1497.55 ml<SUB>H2</SUB> min<SUP>−1</SUP> g<SUB>cat</SUB> <SUP>−1</SUP> was obtained. </LI> <LI> Activation energy was calculated using the Arrhenius eq'n & result was 47.97 KJ/mol. </LI> </UL> </P>

Derivation of both EDLC and pseudocapacitance characteristics based on synergistic mixture of NiCo₂O₄ and hollow carbon nanofiber: An efficient electrode towards high energy density supercapacitor

Tomboc, Gracita M.,Kim, Hern Elsevier 2019 ELECTROCHIMICA ACTA Vol.318 No.-

<P><B>Abstract</B></P> <P>In this study we fabricated a hollow carbon nanofiber (CNF) via a facile dual nozzle electrospinning process and directly used as low-cost and environmental friendly carbon source material, which were incorporated to NiCo<SUB>2</SUB>O<SUB>4</SUB> (NCO). We designed a hybrid nanocomposite based on synergistic mixture of hollow structure CNF and spinel NCO, with 3D dandelion like morphology, hierarchical mesoporous surface, high specific surface area, and directly grown onto the surface of nickel foam substrate. We modified the structural properties of hybrid NCO–CNF nanocomposite in aim to improve its overall electrochemical performance towards supercapacitor application. In here, we fabricated our hollow CNF using dual concentric nozzle electrospinning method, comprising of poly (vinyl pyrrolidone) (PVP) as soluble core and polyacrylonitrile (PAN) as shell. It was essential in our study to fully leach out the PVP to obtain a hollow structure: this hollow structure of CNF provided a conductive network that guaranteed the high speed movement of electron/electrolyte. Furthermore, the overall specific capacitance and energy density of the hybrid NCO–CNF electrode were remarkably boost up due to the derivation of both electric double layer capacitance and pseudocapacitance characteristics based on the synergistic mixture of graphitic carbon and transition metal oxides. The fabricated binder-free hybrid NCO–CNF electrode displayed efficient charge transfer and achieved outstanding specific capacitance and energy density as high as 1188.19 F g<SUP>−1</SUP> and 37.23 W h kg<SUP>−1</SUP>, respectively, even at high current density of 50 A g<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of hollow CNF via dual nozzle electrospinning. </LI> <LI> Synergistic mixture of NiCo<SUB>2</SUB>O<SUB>4</SUB> and hollow CNF that facilitates both EDLC and pseudocapacitance characteristics. </LI> <LI> Assembly of binder-free hybrid NCO–CNF electrode towards supercapacitor. </LI> <LI> Outstanding specific capacitance and energy density of 2991.96 F g<SUP>−1</SUP> and 93.76 W h kg<SUP>−1</SUP> at 5 A g<SUP>−1</SUP> </LI> <LI> Remarkable capacity retention of 97.02% after 3000 GCD cycles at 30 A g<SUP>−1</SUP> </LI> </UL> </P>

Improved electrocatalytic oxygen evolution reaction properties using PVP modified direct growth Co-based metal oxides electrocatalysts on nickel foam

Tomboc, Gracita M.,Agyemang, Frank Ofori,Kim, Hern Elsevier 2018 ELECTROCHIMICA ACTA Vol.263 No.-

<P><B>Abstract</B></P> <P>Polyvinyl pyrrolidone supported ZnCo<SUB>2</SUB>O<SUB>4</SUB> and NiCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles with 3D nanocactus and nanoflower-like morphology, respectively, directly grown on the surface of nickel foam through a one-step hydrothermal process followed by calcination treatment were used as improved electrocatalyst for oxygen evolution reaction. This study is continuation of our previous objective about the use of polyvinyl pyrrolidone as surface stabilizer and growth modifier during nanoparticles synthesis. The resulting products were analyzed by using X-ray diffraction (XRD), field emission scanning electron micrographs (FE-SEM) equipped with energy dispersive X-ray spectrometer (EDX), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). The calculated overpotential for ZnCo<SUB>2</SUB>O<SUB>4</SUB> NPs is as low as 0.282 V while for NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs is 0.298 V. Additionally, ZnCo<SUB>2</SUB>O<SUB>4</SUB> NPs had obtained a low Tafel slope of 79.90 mv dec<SUP>−1</SUP> while 92.28 mV dec<SUP>−1</SUP> Tafel slope for NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs. Lastly, the current density was almost retained during 24 h electrochemical running and obtained 97.74% and 96.18% efficiency, for ZnCo<SUB>2</SUB>O<SUB>4</SUB> and NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> PVP supported synthesized ZnCo<SUB>2</SUB>O<SUB>4</SUB> and NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs as improved OER electrocatalysts. </LI> <LI> ZnCo<SUB>2</SUB>O<SUB>4</SUB> and NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs electrocatalysts obtained improved OER activities. </LI> <LI> Calculated overpotential for ZnCo<SUB>2</SUB>O<SUB>4</SUB> NPs is 0.282 V and 0.298 V for NiCo<SUB>2</SUB>O<SUB>4</SUB>. </LI> <LI> Tafel slope of 79.90 mv dec<SUP>−1</SUP> for ZnCo<SUB>2</SUB>O<SUB>4</SUB> NPs and 92.28 mV dec<SUP>−1</SUP> for NiCo<SUB>2</SUB>O<SUB>4</SUB>. </LI> <LI> 97.74% and 96.18% efficiency after 24 h test for ZnCo<SUB>2</SUB>O<SUB>4</SUB> and NiCo<SUB>2</SUB>O<SUB>4</SUB> NPs, respectively. </LI> </UL> </P>

Synthesis of porous hollow cobalt microspheres using novel chitosan/urea template for hydrogen generation from sodium borohydride

( Gracita Tomboc ),김헌 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.0

Co2O4 hollow microspheres with porous crystalline structure were one pot formulated by hydrothermal treatment of Chitosan/Urea/ Co(NO3)2 mixtures at 180°C for 12 h and then calcined at different temperatures for 4 h. The prepared materials were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and BET technique. The catalytic activity of the as-prepared sample was examined for hydrolysis reaction of sodium borohydride (NaBH4) at different temperature, catalyst amount and (NaBH4) amount. The results reveal that the average crystallite size, microsphere thickness, surface properties and catalytic activity of Co2O4 hollow microspheres could be controlled by varying the molar ratio of chitosan/urea to cobalt concentration. Further results indicate that hollow microspheres can be separated from the reaction mixture by simple filtration or centrifugation after catalytic reaction and reused for several runs.

Highly porous-3D architecture NiMoO₄ tailored onto amine functionalized CNT as advanced nanocomposite electrocatalyst for supercapacitor application

( Gracita Raquel Tomboc ),김헌 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.1

Electrospun carbon nanofiber-carbon nanotubes coated polyaniline composites with improved electrochemical properties for supercapacitors

Agyemang, Frank Ofori,Tomboc, Gracita M.,Kwofie, Samuel,Kim, Hern Elsevier 2018 ELECTROCHIMICA ACTA Vol.259 No.-

<P><B>Abstract</B></P> <P>The carbon nanofiber-carbon nanotube (CNF-CNT) composites were fabricated by simple electrospinning and carbonization of polyacrylonitrile (PAN)-CNT solution prepared by first sonicating and stirring the CNT in N, N-dimethylformamide (DMF) as solvent. Aniline monomer was then coated on the composite materials via in situ chemical polymerization to form CNF-CNT-PANI composite. The as-prepared samples were then characterized. Importantly, the dispersed CNTs in the CNF-CNT composites were crucial for the CNF-CNTs acting as supports for the CNF-CNT-PANI composites to attain high electrochemical properties. The composite electrode material is found to be used as effective electrode material for supercapacitors with specific capacitance as high as 1119 F g<SUP>−1</SUP>at 1 A g<SUP>−1</SUP> compared to the bare CNF film with a specific capacitance of 278 F g<SUP>−1</SUP>. The composite electrode displaced excellent cyclic stability with retention of 98% even after 2000 cycles at a current density of 10 A g<SUP>−1</SUP>.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Galvanic replacement reaction to prepare catalytic materials

홍용주,VENKATESHALU SANDHYA,정상연,Gracita M. Tomboc,조진형,박종식,이광렬 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.1

Galvanic replacement reaction (GRR) has gained considerable interest as a fac- ile and versatile synthetic method for modulating compositions, morphologies, and corresponding physicochemical properties of metallic nanoparticles. Thus far, extensive knowledge of GRR on monometallic templates has been accumu- lated, backed with ample experimental data and computational modeling and validation. The GRR templates have recently been extended to other materials such as alloys, oxides, sulfides, and liquid metals. These new materials have demonstrated potential applications in electrochemical energy conversion sys- tems, which have been relatively unexplored for GRR-originated materials. In this review, the recent findings in GRR on these new template materials are introduced, pointing to the incredible versatility of the GRR methodology in diversifying the catalytic materials classes. We further discuss the remaining critical issues and future research directions of GRRs to fully exploit the poten- tial of GRR in spearheading future advances in electrocatalytic energy conver- sion and other important applications.