Nickel sulfide is regarded as a material with tremendous potential for energy storage and conversion applications. However, it exists in a variety of stable compositions and obtaining a pure phase is a challenge. this study demonstrates a potentially scalable, solvent free and phase selective synthesis of uncapped α-niS, β-niS and α-β-niS composites using nickel alkyl (ethyl, octyl) xanthate precursors. Phase transformation and morphology were observed by powder-X-ray diffraction (p-XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The comparative efficiency of the synthesized samples was investigated for energy storage and generation applications, in which superior performance was observed for the niS synthesized from the short chain xanthate complex. A high specific capacitance of 1,940 F/g, 2,150 F/g and 2,250 F/g was observed at 2 mV/s for bare α-niS, β-niS and α-β-NiS composite respectively. At high current density of 1 A/g, α-niS showed the highest capacitance of 1,287 F/g, with 100% of Coulombic efficiency and 79% of capacitance retention. In the case of the oxygen evolution reaction (oeR), β-NiS showed an overpotential of 139 mV at a current density of 10 mA/cm 2 , with a Tafel slope of only 32 mV/dec, showing a fast and efficient process. It was observed that the increase in carbon chain of the synthesized self-capped nickel sulfide nanoparticles decreased the overall efficiency, both for energy storage and energy generation applications. As a step towards the implementation of sustainable energy development strategies, research on the design of high-performance energy storage and conversion systems is gathering renewed momentum 1-3. Sodium ion batteries (SIBs), lithium-ion batteries (LIBs), and supercapacitors (SCs) are examples of the most studied energy storage devices 4,5. Energy conversion systems on the other hand, constitute a series of electrochemical reactions occurring in an electrolytic cell or in a hydrogen-oxygen fuel cell 3. Hydrogen is a clean and sustainable energy carrier, currently regarded as the best alternative fuel of the future 6,7. Its generation via the electrocatalytic splitting of water is a commonly investigated energy conversion technology 8. The performance of both energy storage devices and energy conversion systems is largely influenced by the type of electroactive material employed. Generally, for energy conversion systems the goal is to develop low cost, earth-abundant and efficient electrocatalysts that will replace Pt-, Ir-and Ru-based compounds 9 , while for energy storage devices, the goal is to develop advanced electrode materials that can deliver high energy and power densities 10. Carbon-based materials 11 , conductive polymers 12 , transition metal oxides 13 , nitrides 14 , carbides 14 , phosphides 15 , and sulfides 5 are among the materials investigated for both energy storage and generation applications. Owing to their low cost, high electrochemical activity as well as mechanical and thermal stability, transition

The development of cost-effective and easily accessible bifunctional materials, which can be effectively used for energy storage and energy generation, is highly desirable. Herein, a new molecular precursor [tris(morpholinodithiocarbamato)Co (III)] has been synthesized and the X-ray crystal structure of the complex determined. The precursor was used to prepare oleylamine (OLA)-capped cobalt sulfide nanoplatelets, using a facile hot injection method at two different temperatures (200°C and 260°C). The characterization of the samples shows that CoS synthesized at 200°C is slightly sulfur rich, whereas CoS synthesized at 260°C is slightly cobalt rich. The effect of off-stoichiometry of CoS nanoplatelets on the energy gener-ation and storage applications was studied. The oxygen evolution reaction catalytic performance of both samples indicate overpotentials of 307 and 276 mV as well as Tafel slopes of 96 and 82 mV/dec, respectively. Similarly, overpotentials of 132 and 153 mV were observed for the hydrogen evolution reaction, with Tafel slopes of 159 and 154 mV/dec, respectively. The capacitive behavior of the samples was also examined, and specific capacitance values of 298 and 440 F/g were obtained with cycling stabilities of 73 and 97 %, after 5000 cycles, respectively. The results indicate that sulfur-deficient CoS can show superior performance for efficient energy generation and storage devices.[a] C.

Herein, the synthesis of three nickel(II) dithiophosphonate complexes of the type [Ni{S2P(OR)(4‐C6H4OMe)}2] [R=H (1), C3H7 (2)] and [Ni{S2P(OR)(4‐C6H4OEt}2] [R=(C6H5)2CH (3)] is described; their structures were confirmed by single‐crystal X‐ray studies. These complexes were subjected to surfactant/solvent reactions at 300 °C for one hour as flexible molecular precursors to prepare either nickel sulfide or nickel phosphide particles. The decomposition of complex 2 in tri‐octylphosphine oxide/1‐octadecene (TOPO/ODE), TOPO/tri‐n‐octylphosphine (TOP), hexadecylamine (HDA)/TOP, and HDA/ODE yielded hexagonal NiS, Ni2P, Ni5P4, and rhombohedral NiS, respectively. Similarly, the decomposition of complex 1 in TOPO/TOP and HDA/TOP yielded hexagonal Ni2P and Ni5P4, respectively, and that of complex 3 in similar solvents led to hexagonal Ni5P4, with TOP as the likely phosphorus provider. Hexagonal NiS was prepared from the solvent‐less decomposition of complexes 1 and 2 at 400 °C. NiS (rhom) had the best specific supercapacitance of 2304 F g−1 at a scan rate of 2 mV s−1 followed by 1672 F g−1 of Ni2P (hex). Similarly, NiS (rhom) and Ni2P (hex) showed the highest power and energy densities of 7.4 kW kg−1 and 54.16 W kg−1 as well as 6.3 kW kg−1 and 44.7 W kg−1, respectively. Ni5P4 (hex) had the lowest recorded overpotential of 350 mV at a current density of 50 mA cm−2 among the samples tested for the oxygen evolution reaction (OER). NiS (hex) and Ni5P4 (hex) had the lowest overpotentials of 231 and 235 mV to achieve a current density of 50 mA cm−2, respectively, in hydrogen evolution reaction (HER) examinations.

The development of cost-effective, functional materials that can be efficiently used for sustainable energy generation is highly desirable. Herein, a new molecular precursor of bismuth (tris(selenobenzoato)bismuth(III), [Bi(SeOCPh) 3 ]), has been used to prepare selectively Bi or Bi 2 Se 3 nanosheets via a colloidal route by the judicious control of the reaction parameters. The Bi formation mechanism was investigated, and it was observed that the trioctylphosphine (TOP) plays a crucial role in the formation of Bi. Employing the vapor deposition method resulted in the formation of exclusively Bi 2 Se 3 films at different temperatures. The synthesized nanomaterials and films were characterized by p-XRD, TEM, Raman, SEM, EDX, AFM, XPS, and UV–vis spectroscopy. A minimum sheet thickness of 3.6 nm (i.e., a thickness of 8–9 layers) was observed for bismuth, whereas a thickness of 4 nm (i.e., a thickness of 4 layers) was observed for Bi 2 Se 3 nanosheets. XPS showed surface oxidation of both materials and indicated an uncapped surface of Bi, whereas Bi 2 Se 3 had a capping layer of oleylamine, resulting in reduced surface oxidation. The potential of Bi and Bi 2 Se 3 nanosheets was tested for overall water-splitting application. The OER and HER catalytic performances of Bi 2 Se 3 indicate overpotentials of 385 mV at 10 mA cm –2 and 220 mV, with Tafel slopes of 122 and 178 mV dec –1 , respectively. In comparison, Bi showed a much lower OER activity (506 mV at 10 mA cm –2 ) but a slightly better HER (214 mV at 10 mA cm –2 ) performance. Similarly, Bi 2 Se 3 nanosheets were observed to exhibit cathodic photocurrent in photoelectrocatalytic activity, which indicated their p-type behavior.