Browsing by Author "Konkena, Bharathi"

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    Co3O4@Co/NCNT Nanostructure Derived from a Dicyanamide Based Metal-Organic Framework as Efficient Bi-functional Electrocatalyst for Oxygen Reduction and Evolution Reactions
    (Chemistry–A European Journal, 2017) Sikdar, Nivedita; Konkena, Bharathi; Masa, Justus; Schuhmann, Wolfgang
    There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)2(N(CN)2)]⋅(N(CN)2)⋅(5 H2O)}n [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN)2−=dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H2/Ar atmosphere (at 800 °C) and further mild calcination yielded Co3O4@Co core–shell nanoparticle-encapsulated N-doped carbon nanotubes (Co3O4@Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core–shell Co3O4@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of −1 mA cm−2 and the OER with a potential of 1.61 V at 10 mA cm−2, which is competitive with the most active bi-functional catalysts reported previously.
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    Metallic NiPS3@NiOOH Core-shell Heterostructures as Highly Efficient and Stable Electrocatalyst for the Oxygen Evolution Reaction
    (Acs Catalysis, 2017) Konkena, Bharathi; Masa, Justus; Botz, Alexander J.R.
    We report metallic NiPS3@NiOOH core–shell heterostructures as an efficient and durable electrocatalyst for the oxygen evolution reaction, exhibiting a low onset potential of 1.48 V (vs RHE) and stable performance for over 160 h. The atomically thin NiPS3 nanosheets are obtained by exfoliation of bulk NiPS3 in the presence of an ionic surfactant. The OER mechanism was studied by a combination of SECM, in situ Raman spectroscopy, SEM, and XPS measurements, which enabled direct observation of the formation of a NiPS3@NiOOH core–shell heterostructure at the electrode interface. Hence, the active form of the catalyst is represented as NiPS3@NiOOH core–shell structure. Moreover, DFT calculations indicate an intrinsic metallic character of the NiPS3 nanosheets with densities of states (DOS) similar to the bulk material. The high OER activity of the NiPS3 nanosheets is attributed to a high density of accessible active metallic-edge and defect sites due to structural disorder, a unique NiPS3@NiOOH core–shell heterostructure, where the presence of P and S modulates the surface electronic structure of Ni in NiPS3, thus providing excellent conductive pathway for efficient electron-transport to the NiOOH shell. These findings suggest that good size control during liquid exfoliation may be advantageously used for the formation of electrically conductive NiPS3@NiOOH core–shell electrode materials for the electrochemical water oxidation.
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    MoSSe@reduced Graphene Oxide Nanocomposite Heterostructures as Efficient and Stable Electrocatalysts for the Hydrogen Evolution Reaction
    (Nano Energy, 2016) Konkena, Bharathi; Masa, Justus; Xia, Wei; Muhler, Martin; Schuhmann, Wolfgang
    Non-noble metal based materials efficiently catalyzing the hydrogen evolution reaction (HER) are reported based on a novel strategy where electrocatalytically active ultrathin molybdenum sulphoselenide sheets are incorporated into electrically conducting reduced graphene oxide sheets via a self-assembly approach. By taking advantage of the electrostatic attraction between the two oppositely charged nanosheets, MoSSe@rGO composite materials are obtained exhibiting superior electrocatalytic activity and stability for the HER allowing a current density of 5mAcm−2 at a low overpotential of only 135mV. These findings pave the way to novel electrocatalysts based on composites of MoSSe and reduced graphene oxide towards the design of ultra-light, mechanically robust and electrically conductive electrode materials for electrocatalytic water splitting.