Browsing by Author "Anand P. Tiwari"

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Activation of Ternary Transition Metal Chalcogenide Basal Planes through Chemical Strain for the Hydrogen Evolution Reaction
(Wiley-VCH Verlag, 2017) Yongshin Kim; Anand P. Tiwari; Om Prakash; Hyoyoung Lee
Catalytically inactive basal planes pose challenges for the efficient hydrogen evolution reaction (HER) in two-dimensional (2 D) transition metal chalcogenide (TMC) nanosheets. Herein, a new hybrid structure is reported in which zero-dimensional TMC nanodots (NDs) are decorated on the basal planes of 2 D nanosheets of TMCs to enhance their catalytic activity towards the HER process. A novel process is developed to fabricate a hybrid Cu2MoS4 (2 D ternary transition metal chalcogenide Cu2MoS4 nanosheets)/MoSe2 (0 D binary transition metal chalcogenide MoSe2 ND) nanostructure by controlling the size of the MoSe2 NDs to enhance the HER activity. In acidic media, this optimal hybrid Cu2MoS4/MoSe2 nanostructure achieves excellent catalytic activity for HER, which exhibits a low overpotential of 166 mV at a current density of 10 mA cm−2, which corresponds to a Tafel slope of 74.7 mV dec−1. In addition, the synthesized hybrid nanostructure shows excellent stability when under acidic medium for 16 h of continuous electrolysis. Therefore, it is suggested that our strategy may open a new path for the design of hybrid nanostructures by using ternary transition metal chalcogenides (TTMCs) with binary transition metal chalcogenides (BTMCs) for alternative non-noble metal catalysts towards HER. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Activation of Ternary Transition Metal Chalcogenide Basal Planes through Chemical Strain for the Hydrogen Evolution Reaction
(Wiley-VCH Verlag, 2017) Yongshin Kim; Anand P. Tiwari; Om Prakash; Hyoyoung Lee
Invited for this month's cover are collaborators from the Institute for Basic Science (South Korea), Sungkyunkwan University (South Korea), and Banaras Hindu University (India). The cover picture shows the two-dimensional layered transition metal chalcogenide for efficient hydrogen evolution. Read the full text of the article at 10.1002/cplu.201700164. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Highly active and stable layered ternary transition metal chalcogenide for hydrogen evolution reaction
(Elsevier Ltd, 2016) Anand P. Tiwari; Doyoung Kim; Yongshin Kim; Om Prakash; Hyoyoung Lee
Layered ternary transition metal chalcogenides (TTMCs) material has great potentials that can overcome to the limitation of active sites which is challenging in binary transition metal chalcogenides (BTMC), such as MoS2, towards electrochemical hydrogen production. Here, we demonstrate TTMC material which contains two transition metals Cu and Mo with chalcogen S. The TTMC, Cu2MoS4 has been successfully synthesized by a facile solution-processed method. Moreover, by anion doping such as Se in as the synthesized Cu2MoS4, it has been found that TTMC can be exfoliated into single layer nanosheets. Furthermore, by controlling the number of layers, single layers TTMC exhibit the highest electrocatalytic activity towards hydrogen evolution reaction (HER) because the single layers can provide more catalytic active sites than multilayers and bulk. The onset potential for hydrogen generation is −96 mV for single layer TTMC electrode material with corresponding Tafel slope 52 mV/decade. After 1000 cycles with continuous electrolysis in acid electrolyte for 15 h, the electrode material preserves its structure and robust catalytic activity perfectly. Our new TTMC materials show highly active electrocatalytic performance and high stability which overcome the intrinsic limitation of BTMC. As a result, our work can guide new strategy for the developments of real applications of TMCs in HER. © 2016
Studies on de/rehydrogenation characteristics of nanocrystalline MgH 2 co-catalyzed with Ti, Fe and Ni
(2013) Rohit R. Shahi; Anand P. Tiwari; M.A. Shaz; O.N. Srivastava
In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH2. Mechanical milling of MgH2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H2 pressure lead to the formation of nano MgH2-Ti5Fe5Ni5. The decomposition temperature of nano MgH2-Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH2 alone. It is also found that the nano MgH 2-Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg 2NiH4 and Mg2FeH6 respectively. On the other hand, when MgH2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH 2. Moreover the activation energy for dehydrogenation of nano MgH2 co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH2 catalyzed through transition metal elements. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.