Browsing by Author "Baghendra Singh"

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Axial ligand-induced high electrocatalytic hydrogen evolution activity of molecular cobaloximes in homo- and heterogeneous medium
(Royal Society of Chemistry, 2024) Jitendra Kumar Yadav; Baghendra Singh; Anjali Mishra; Sarvesh Kumar Pal; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Three new molecular cobaloxime complexes with the general formula [ClCo(dpgH)2L] (1-3), where L1 = N-(4-pyridylmethyl)-1,8-naphthalimide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalimide, L3 = 4-piperidin-N-(4-pyridylmethyl)-1,8-naphthalimide, have been synthesized and characterized by UV-Vis, multinuclear NMR, FT-IR and PXRD spectroscopic techniques. The crystal structures of all complexes have also been reported. The electrocatalytic activity of complexes is investigated under two catalysis conditions: (i) homogeneous conditions in acetonitrile using acetic acid (AcOH) as a proton source and (ii) heterogeneous conditions upon immobilization onto the surface of activated carbon cloth (CC). Complex 3 exhibited high electrocatalytic HER activity under both homogeneous and heterogeneous conditions. It catalyses proton reduction to molecular hydrogen in acetonitrile solution at a lower overpotential (640 mV) with a high turnover frequency (TOF) of 524.57 s−1 and demonstrates good stability in acidic conditions. Furthermore, catalytic (working) electrodes are prepared by immobilizing the complexes onto the surface of activated carbon cloth (CC) for electrocatalytic HER under heterogeneous conditions. An impressive HER performance was again obtained with catalytic electrode 3@CC in 1.0 M KOH, achieving a current density of −10 mA cm−2 at an overpotential of 262 mV. Chronoamperometric (CA) studies showed no significant decay of the initial current density for 10 h, indicating the excellent stability of 3@CC. Additionally, UV-Vis and NMR spectral studies of the recovered catalyst after electrocatalysis revealed no structural changes, demonstrating its robustness under reaction conditions. © 2024 The Royal Society of Chemistry.
Chlorocobaloxime containing N-(4-pyridylmethyl)-1,8-naphthalamide peripheral ligands: synthesis, characterization and enhanced electrochemical hydrogen evolution in alkaline medium
(Royal Society of Chemistry, 2022) Jitendra Kumar Yadav; Baghendra Singh; Sarvesh Kumar Pal; Nanhai Singh; Prem Lama; Arindam Indra; Kamlesh Kumar
Two new discrete cobaloxime based complexes with the general formula [ClCo(dioxime)2L] (1 and 2), L1 = N-(4-pyridylmethyl)-1,8-naphthalamide, L2 = 4-bromo-N-(4-pyridylmethyl)-1,8-naphthalamide have been synthesized and characterized by various spectroscopic techniques such as FT-IR, 1H, 13C{1H} NMR and PXRD. The molecular structures of both complexes have also been determined using single crystal X-ray crystallography. The solid state molecular structures revealed distorted octahedral geometry around the Co(iii) central metal ion with two dioximes in the equatorial plane and axial positions are occupied by chloro and pyridine nitrogen of N-(4-pyridylmethyl)-1,8-naphthalamide ligands. Both complexes exhibit weaker non-covalent interactions (C-H⋯O, C-H⋯Cl and C-H⋯π(Centroid) in complex 1 whereas C-H⋯O and C-H⋯Br in complex 2) resulting in the formation of dimeric and 1D supramolecular structures. Furthermore, these complexes are immobilized onto the surface of activated carbon cloth (CC) and their electrocatalytic performance for the hydrogen evolution reaction (HER) has been investigated in alkaline and acidic media as well as buffer solution. In alkaline medium, we found that complex 2 exhibited impressive electrocatalytic HER activity and produced a current density of −10 mA cm−2 at an overpotential of 260 mV, whereas complex 1 produced the same current density at an overpotential of 334 mV. An electrochemical impedance spectroscopy (EIS) spectral study revealed the faster charge transfer kinetics of complex 2 than that of complex 1. Similarly, the low Tafel slope (100 mV dec−1) for the HER with complex 2 indicates faster HER kinetics compared to complex 1. The chronoamperometric study showed that complex 2 is stable under electrocatalytic HER conditions for 5 h without losing the initial current density and it has also been established that the complex structure is retained after electrocatalysis. © 2023 The Royal Society of Chemistry.
Homoleptic Ni(ii) dithiocarbamate complexes as pre-catalysts for the electrocatalytic oxygen evolution reaction
(Royal Society of Chemistry, 2022) Sarvesh Kumar Pal; Baghendra Singh; Jitendra Kumar Yadav; Chote Lal Yadav; Michael G. B. Drew; Nanhai Singh; Arindam Indra; Kamlesh Kumar
Four new functionalized Ni(ii) dithiocarbamate complexes of the formula [Ni(Lx)2] (1-4) (L1 = N-methylthiophene-N-3-pyridylmethyl dithiocarbamate, L2 = N-methylthiophene-N-4-pyridylmethyl dithiocarbamate, L3 = N-benzyl-N-3-pyridylmethyl dithiocarbamate, and L4 = N-benzyl-N-4-pyridylmethyl dithiocarbamate) have been synthesized and characterized by IR, UV-vis, and 1H and 13C{1H} NMR spectroscopic techniques. The solid-state structure of complex 1 has also been determined by single crystal X-ray crystallography. Single crystal X-ray analysis revealed a monomeric centrosymmetric structure for complex 1 in which two dithiocarbamate ligands are bonded to the Ni(ii) metal ion in a S^S chelating mode resulting in a square planar geometry around the nickel center. These complexes are immobilized on activated carbon cloth (CC) and their electrocatalytic performances for the oxygen evolution reaction (OER) have been investigated in aqueous alkaline solution. All the complexes act as pre-catalysts for the OER and undergo electrochemical anodic activation to form Ni(O)OH active catalysts. Spectroscopic and electrochemical characterization revealed the existence of the interface of molecular complex/Ni(O)OH, which acts as the real catalyst for the OER. The active catalyst obtained from complex 2 showed the best OER activity achieving 10 mA cm−2 current density at an overpotential of 330 mV in 1.0 M aqueous KOH solution. © 2022 The Royal Society of Chemistry.