Browsing by Author "Lahtinen, Jouko"

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    Dumbbell-Shaped Ternary Transition-Metal (Cu, Ni, Co) Phosphate Bundles: A Promising Catalyst for the Oxygen Evolution Reaction
    (American Chemical Society, 2022-01-27T00:00:00) Singh, Harjinder; Biswas, Rathindranath; Ahmed, Imtiaz; Thakur, Pooja; Kundu, Avinava; Panigrahi, Abhishek Ramachandra; Banerjee, Biplab; Halder, Krishna Kamal; Lahtinen, Jouko; Mondal, Krishnakanta; Haldar, Krishna Kanta
    Development of economical and high-performance electrocatalysts for the oxygen evolution reaction (OER) is of tremendous interest for future applications as sustainable energy materials. Here, a unique member of efficient OER electrocatalysts has been developed based upon structurally versatile dumbbell-shaped ternary transition-metal (Cu, Ni, Co) phosphates with a three-dimensional (3D) (Cu2(OH)(PO4)/Ni3(PO4)2�8H2O/Co3(PO4)2�8H2O) (CNCP) structure. This structure is prepared using a simple aqueous stepwise addition of metal ion source approach. Various structural investigations demonstrate highly crystalline nature of the composite structure. Apart from the unique structural aspect, it is important that the CNCP composite structure has proved to be an excellent electrocatalyst for OER performance in comparison with its binary or constituent phosphate under alkaline and neutral conditions. Notably, the CNCP electrocatalyst displays a much lower overpotential of 224 mV at a current density of 10 mA cm-2 and a lower Tafel slope of 53 mV dec-1 with high stability in alkaline medium. In addition, X-ray photoelectron spectroscopy analysis suggested that the activity and long-term durability for the OER of the ternary 3D metal phosphate are due to the presence of electrochemically dynamic constituents such as Ni and Co and their resulting synergistic effects, which was further supported by theoretical studies. Theoretical calculations also reveal that the incredible OER execution was ascribed to the electron redistribution set off in the presence of Ni and Cu and the most favorable interaction between the *OOH intermediate and the active sites of CNCP. This work may attract the attention of researchers to construct efficient 3D ternary metal phosphate catalysts for various applications in the field of electrochemistry. � 2022 American Chemical Society.
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    Facile Fabrication of Ni9S8/Ag2S Intertwined Structures for Oxygen and Hydrogen Evolution Reactions
    (John Wiley and Sons Inc, 2022-12-21T00:00:00) Biswas, Rathindranath; Ahmed, Imtiaz; Manna, Priyanka; Mahata, Partha; Dhayal, Rajendra S.; Singh, Amol; Lahtinen, Jouko; Haldar, Krishna Kanta
    Here, we report the fabrication of the unique intertwined Ni9S8/Ag2S composite structure with hexagonal shape from their molecular precursors by one-pot thermal decomposition. Various spectroscopic and microscopic techniques were utilized to confirm the Ni9S8/Ag2S intertwined structure. Powder X-ray Powder Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggest that there is an enrichment of Ni9S8 phase in Ni9S8/Ag2S. The presence of Ag2S in Ni9S8/Ag2S improves the conductivity by reducing the interfacial energy and charge transfer resistance. When Ni9S8/Ag2S is employed as an electrocatalyst for electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity, it requires a low overpotential of 152 mV for HER and 277 mV for OER to obtain the geometrical current density of 10 mA cm?2, which is definitely superior to that of its components Ni9S8 and Ag2S. This work provides a simple design route to develop an efficient and durable electrocatalyst with outstanding OER and HER performance and the present catalyst (Ni9S8/Ag2S) deserves as a potential candidate in the field of energy conversion systems. � 2022 Wiley-VCH GmbH.