Synthesis of nonprecious metal-based efficient electrocatalysts for the development of water electrolyzers is of significant interest. Herein, we describe the synthesis of a defectrich electrocatalytically active Co 9 S 8 -CoSe 2 heterostructure and its electrochemical water splitting performance for the development of a water electrolyzer. The Co 9 S 8 -CoSe 2 heterostructure is synthesized in a single step by a solvothermal approach, and it has a defect-rich nanoflake-like morphology. The in situ grown Co 9 S 8 and CoSe 2 are chemically coupled. The heterostructure is electrocatalytically active toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It delivers the benchmark current density of 10 mA/cm 2 for HER at an overpotential of 61 and 150 mV in acidic and alkaline pH, respectively. It is also highly active toward OER and requires 340 mV to attain 10 mA/cm 2 . The superior electrocatalytic performance of the Co 9 S 8 -CoSe 2 heterostructure is ascribed to geometrical and electronic effects. Defect-rich Co 9 S 8 -CoSe 2 nanoflakes have abundant catalytically active sites that promote electrolyte contact and favor facile electron transfer kinetics. Electronic interaction and chemical coupling between Co 9 S 8 and CoSe 2 modulate chemisorption energies of hydrogen-and oxygencontaining intermediates for better electrocatalytic performance. Post-OER analysis reveals that the Co 9 S 8 -CoSe 2 heterostructure serves as a precatalyst and transforms to electrocatalytically active CoOOH during OER. As a proof-of-concept demonstration, a labmade water electrolyzer is fabricated using the Co 9 S 8 -CoSe 2 heterostructure-based anode and cathode. The device delivers 10 mA/ cm 2 current density at a cell voltage of 1.66 V and retains 85% of its initial current density even after 20 h of continuous electrolysis.

A general strategy for the synthesis of the core-shell nanostructure of nitrogen-doped carbon encapsulated MoP and WP (MoP@NC and WP@NC) and the electrochemical hydrogen evolution reaction (HER) are demonstrated. The synthetic procedure involves the self-assembling of polyoxometalate (M = Mo/W) and phytic acid on a polyetheleneimine backbone and the subsequent pyrolysis of the self-assembled supramolecular aggregates in an inert atmosphere without a traditional phosphidating agent. MoP@NC has a quasi-spherical shape with a MoP core (57 nm) and nitrogen doped porous carbon shell, whereas WP@ NC has a nitrogen-doped carbon coated rodlike nanostructure. MoP@NC has a large amount of pyridinic (∼59%) and Mo-bonded (∼33%) nitrogen. MoP@NC is highly active toward hydrogen evolution reaction (HER) and delivers the benchmark current density 10 mA/cm 2 at an overpotential of 52, 106, and 171 mV in acidic, alkaline and neutral pH, respectively. It shows a Tafel slope of 49 mV/dec, high turnover frequency (0.28 s −1 at η = 100 mV), and faradaic efficiency (96%) in acidic electrolyte. MoP@NC has remarkable durability in acidic and alkaline pH with a negligible increase in overpotential after 1000 extensive repeated potential cycles. The encapsulating nitrogen-doped carbon shell protects the active catalyst from corrosion and the catalyst retains its phase purity and structural integrity even after 10 h of long-time hydrogen evolution at constant potential. The outstanding HER activity of MoP@NC is accounted for by the small particle size, large surface area, and strong chemical coupling between MoP and nitrogendoped carbon.

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Synthesis of a high performance pH universal electrochemical hydrogen evolution catalyst based on OsP2.

Isothiocyanato and azido coordination induced structural diversity in zinc(II) complexes with Schiff base containing tetrahydrofuran group: synthesis, characterization, crystal structure and fluorescence study † Haridas Mandal, Sukanta Chakrabartty and Debashis Ray * Three new structurally diverse zinc(II) complexes of formula [H 3 O][ZnL 2 ]ClO 4 (1), [Zn 2 (m-L) 2 (NCS) 2 ] (2) and [Zn 3 (m-L) 2 (m-N 3 ) 4 ] n (3) have been synthesized using the same furan-based tridentate ONO-donor Schiff base ligand HL (2-hydroxybenzyl-2-tetrahydrofurylmethyl)imine and characterized by X-ray structural analysis. Complex 1 is mononuclear, whereas 2 is a double phenoxido-bridged dinuclear compound. The novel polymeric compound 3 from azido coordination driven aggregation possesses a very rare 1D structure in which the dinuclear ligand-bound Zn 2 L 2 fragments are bridged by four ligand-free m 1,1 -azido bridging Zn(N 3 ) 4 2À units resulting in a zigzag arrangement of repeating triangular Zn 3 motifs with structural similarity to the P1 nuclease. Solid state mixing and grinding processes were applied for the ligand exchange reaction and core conversion. In mechanochemical solvent free synthetic routes 1 reacts with isothiocyanato and azido ions to provide 2 and 3 in pure form. The ligand HL serves as sensitive fluorescent probe for Zn 2+ , and complex 1 for SCN À and N 3 À ions in MeOH medium. Coordination induced fluorescence enhancement due to intraligand p / p* transition in the presence of Zn 2+ of HL and quenching of emission intensities of 1 with SCN À and N 3 À anions are accounted for by the formation of hitherto unknown complexes [Zn(L)(X)] (where X ¼ ClO 4 À , SCN À and N 3 À ). HL shows chelation-enhanced fluorescence response from strong metal ion coordination and binding of isothiocyanato and azido anions with an appreciable lifetime of the fluorophore signals. Excitation at 380 nm of MeOH solutions of all three complexes in air exhibit excited state life-time spanning from 2.5-4.8 ns.