Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

A new catalyst based on a nickel(II) complex of diiminodiphosphine for hydrogen evolution and oxidation

Based on that hydrogen energy is widely used in fuel cells, we focus our interests on the design and research of new complexes that catalyze the reaction in both directions, such as hydrogen evolution reactions (HERs) and hydrogen oxidation reactions (HORs). A highly efficient catalyst for both hydrogen evolution and oxidation, based on a nickel(II) complex, [Ni-en-P₂](ClO₄)₂, has been designed and provided by the reaction of Ni(ClO₄)₂ with N,N′-bis[o-(diphenylphosphino)benzylidene]ethylenediamine (en-P₂) in our group. Its structure has been determined by X-ray diffraction. [Ni-en-P₂](ClO₄)₂ can electro-catalyze hydrogen evolution both from acetic acid and a neutral buffer (pH 7.0) with a turnover frequency (TOF) of 204 and 1327 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) under an overpotential (OP) of 914.6 mV and 836.6 mV, respectively. [Ni-en-P₂](ClO₄)₂ also can electro-catalyze hydrogen oxidation with a TOF of 111.7 s⁻¹ under an OP of 330 mV. The results can be attributed to that [Ni^II-en-P₂](ClO₄)₂ has three good reversible redox waves at 1.01 (Ni^III/II), −0.79 (Ni^II/I) and −1.38 V (Ni^I/0) versus Fc^+/0, respectively. We hope these findings can afford a new method for the design of electrocatalysts for both H₂ evolution and H₂ oxidation.     

Heteroleptic thiolate diamine nickel complexes: Noble-free-metal catalysts in electrocatalytic and light-driven hydrogen evolution reaction

Three mononuclear heteroleptic nickel complexes bearing the non-innocent o-aminobenzenethiolate (2-amnt) ligand and different diamine ligands, namely, [Ni(2-amnt)(o-phen)] (o-phen = o-phenylenediamine) (1), [Ni(2-amnt)(3,4-daba)] (3,4-daba = 3, 4-diamino benzoic acid) (2) and [Ni(2-amnt)(dmnt)] (dmnt = diaminomaleonitrile) (3), were synthesized and characterized. Complexes 1–3 are active homogeneous proton reduction electrocatalysts in dimethylformamide with trifluoroacetic acid as a proton source. All the three complexes are tested in light-driven hydrogen evolution reaction, indicating different catalytic efficiencies. Thus, although complex 3 indicates no catalytic action, both complexes 1 and 2 catalyze H₂ evolution in water-dimethylformamide solutions using fluorescein (Fl) as a photosensitizer. Complex 2 acts as a homogeneous catalyst reached 834 turnovers (TON); whereas 1, despite being active in hydrogen evolution reaction (HER), decomposes to form nanomaterials. DFT calculations combined with electrochemical and spectroscopic data were employed to investigate the catalytic mechanism for H₂ formation as well as to unravel the key factors that influence the relative catalytic efficiencies. The proposed catalytic pathway involves ligand-based reduction and protonation steps followed by the formation of a nickel-hydride intermediate that reacts with a solution proton to generate H₂ via a very low energy transition state.     

Electro- and photocatalytic hydrogen generation in acetonitrile and aqueous solutions by a cobalt macrocyclic Schiff-base complex

The cobalt(III) macrocyclic Schiff-base complex, [Co^III(CR)Cl]ClO₄ (CR = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene), is an active catalyst for the electrocatalytic proton reduction to generate dihydrogen in both acetonitrile and 100% aqueous solution (at −0.57 and −0.85 V vs SCE, respectively), using p-cyanoanilinium tetrafluoroborate and acetic acid as proton sources, respectively. Bulk electrolysis confirmed that dihydrogen is produced with >90% Faradaic yields and >50 TON in both solvents. [Co^III(CR)Cl₂]ClO₄ also catalyzes photo-driven (λ > 390 nm) hydrogen production in aqueous acetonitrile at TON of 180 (not optimized), using [Ir^III(ppy)₂(bpy)]PF₆ as the photosensitizer, triethanolamine (TEOA) as the sacrificial donor and acetic acid as the proton source.     

Hydrogen generation from the hydrolysis of sodium borohydride with new pyridinium dicationic salts containing transition metal complexes

Pyridinium based dicationic ionic salts [C₆(mpy)₂] containing transition metal halide anions [NiCl₄]²⁻ and [CoCl₄]²⁻ were synthesized and characterized by ¹H NMR, ¹³C NMR, LRMS-MS & TGA. The catalytic activities of dicationic ionic liquids were studied for the first time in the hydrolysis reaction of sodium borohydride. The reported work includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (Ea = 56.36 kJ/mol) and effects of the amount of catalyst, amount of substrate and temperature on the rate for the catalytic hydrolysis of NaBH₄. The activation energy of the catalyst dicationic tetrachloronickelate (II) anion for hydrogen production is comparable to that of other metal halide catalysts.     

Proton reduction by a Ni(II) catalyst and foot-of-the wave analysis for H2 evolution

A nickel based molecular catalyst [Ni(QCl-tpy)₂]Cl₂·7H₂O (where QCl-tpy = 2-choloro-3-(2,6-di (pyridin-2yl)pyridine-4-yl) quinoline) has been synthesized, characterized by single crystal XRD and other spectroscopic techniques. The complex [Ni^II(QCl-tpy)₂]²⁺ has also been employed for the electrocatalytic proton reduction in DMF/H₂O (95:5 v/v) using trifluoro acetic acid (TFA) as the proton source. It exhibits a reasonably efficient catalytic ability towards proton reduction under organic media. Compared to the parent [Ni^II(tpy)₂]²⁺ during the electro-catalysis, the complex [Ni^II(QCl-tpy)₂]²⁺ behaves as a better catalyst in terms of higher catalytic current and 180 mV of lower overpotential as well. It is expected due to the presence of 2-chloroqinoline moiety in the terpyridine framework. The rate of H₂ evolution was analysed with the use of Foot-of-the Wave Analysis (FOWA) method. The complex shows a TOF of 3.68 s⁻¹ as obtained from Foot-of-the Wave Analysis (FOWA) at the scan rate 100 mVs⁻¹ for 1.0 mM [Ni^II(QCl-tpy)₂]²⁺ complex. The acid base equilibria reveals the dechelation followed by protonation at one of the coordinated pyridine rings of the QCl-tpy ligand. There could be a pendant base effect towards hydrogen evolution due to dechelated pyridine ring of the coordinated QCl-tpy ligand, which acts as a proton relay. Based on the spectroscopic evidence and electrochemical studies a plausible mechanism for the reduction of proton to H₂ has been proposed.     

Reversible dehydrogenation of Mg(BH4)2–LiH composite under moderate conditions

The Mg(BH₄)₂-xLiH (0.1 ≤ x ≤ 0.8) composites which exhibit favorable dehydrogenation and encouraging reversibility are experimentally investigated. LiH additive reduces the onset temperature for dehydrogenation to 150 °C. And hydrogen release exceeds 10 wt.% from the new binary material below 250 °C. Furthermore, rehydrogenation results show that 3.6 wt.% hydrogen can still be recharged after twenty cycles at 180 °C. It should be emphasized that the long-term reversibility of borohydride under 200 °C is long overdue. TPD, PCT, and high-pressure DSC measurements are used to characterize the improvements in thermodynamic and kinetic ways. In addition, FT-IR and NMR studies indicate that the composite has a significant synergistic effect during (de)hydrogenation processes. This work suggests that controlled cation stoichiometry combined with doping by metal Li⁺ subvalent to Mg²⁺ facilitate the formation of polyborane intermediates [B₃H₈]⁻ and [B₂H₆]²⁻. They improve the dehydrogenation properties and make the material reversible under mild conditions.     

An infinite chain, {[Ni(tn)2]3[Fe(CN)4(μ-CN)2]2}n,a new catalyst for electrochemical-driven water splitting and photochemical-driven hydrogen evolution from water under blue light

A new catalyst for both water reduction and oxidation, based on an infinite chain, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n, is formed by the reaction of NiCl₂, 1,3-propanediamine (tn) and K₃ [Fe(CN)₆]. {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can electro-catalyze hydrogen evolution from a neutral aqueous buffer (pH 7.0) with a turnover frequency (TOF) of 1561 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) at an overpotential (OP) of 837 mV {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n also can electro-catalyze O₂ production from water with a TOF of ～45 mol O₂ (mol cat)^?1s^?1 at an OP of 591 mV. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H₂A) as a sacrificial electron donor, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can photo-catalyze hydrogen generation from an aqueous buffer (pH 4.0) with a turnover number (TON) of 11,450 mol H₂ per mole of catalyst (mol of H₂ (mol of cat)^?1) during 10 h irradiation. The average of apparent quantum yield (AQY) is as high as 40.96% during 10 h irradiation. Studies indicate that {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n exists in two forms: a cyano-bridged chain ({[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n) in solid, and a salt ([Ni(tn)₂]₃ [Fe(CN)₆]₂) in aqueous media; Catalytic reaction occurs on the nickel center of [Ni(tn)₂]²⁺, and the introduction of [Fe(CN)₆]^3- can improve the catalytic efficiency of [Ni(tn)₂]²⁺ for H₂ or O₂ generation. We hope these findings can afford a new method for the design of catalysts for both water reduction and oxidation.     

The effects of micellar media on the photocatalytic H2 production from water

The photocatalytic H₂ production efficiency of a multi-component system, containing [Ir(ppy)₂(bpy)]⁺ as photosensitizer, [Co(bpy)₃]²⁺ as H₂-evolving catalyst, and triethanolamine (TEOA) as sacrificial electron donor, was investigated in water/acetonitrile (8:2, v/v) solution in the presence of different kinds of surfactants, such as cetyl trimethyl ammonium bromide (CTAB), Triton X-100, and sodium lauryl sulfonate (NaLS). The H₂ evolution rate is found to follow the order of cationic micellar media > nonionic micellar media > anionic micellar media > water/acetonitrile solution. The underlying mechanism was discussed.     

Design of high-efficiency solid-state dye-sensitized solar cells using coupled dye mixtures

A solid-state dye-sensitized solar cell comprising dye mixtures of [Ru(2,2-bpy-4,4′-dicarboxylic acid)(NCS)₂] and [Ru(4,4′,4″-tricarboxy-2,2;6,2″-terpy)(NCS)₃] on TiO₂ thin film was fabricated. The different optical properties of dyes results in increased photocurrent and incident photon to photocurrent efficiency (IPCE). The multiple dye system showed the short circuit current (I_sc) of 10.2 mA/cm² and a cell efficiency (η) of 2.8 while broadening the spectral sensitivity of the cell. When a single dye is used, I_sc of 6 and 5 mA/cm² and cell efficiency of 1.7 and 1.2 were observed for [Ru(4,4-bis(carboxy)-bpy)₂(NCS)₂] (dye 1) and [Ru(2,2′,2″-(COOH)₃-terpy)(NCS)₃] (dye 2), respectively. Additionally, the resulting IPCE for the solar cell consisting of dye mixture was 50% at wide wavelength range from 530 to 650 nm while for the dye 1, 32% IPCE was observed at 535 nm while for the dye 2, highest IPCE value observed was 20% at 620 nm.     

Intermediate hydroxide enforced electrodeposited platinum film for hydrogen evolution reaction

Competitive catalytic activity of platinum (Pt) makes it as a promising cathode material for hydrogen evolution reaction. But cost of Pt makes it impractical for its use in commercial applications. Unlike literature known methods, our study entails on a methodology of ambient temperature electrodeposition of Pt films, without the use of a complexing agent or pH adjustments or both. Pt films are deposited in an electrochemical bath, which is prepared by adding platinum chloride complex [H₂PtCl₆.x H₂O] in triple-distilled water. Pt films deposited at different potentials are analyzed for their morphological (SEM), structural (XRD), electrochemical study (Cyclic Voltammetry and Linear sweep measurements). The growth and catalytic activity of Pt film show strong dependence on applied deposition potential (−0.25 V to −0.40 V) and reduction kinetics of [PtCl₆]²⁻ or [Pt(OH)Cl₅]²⁻ intermediate hydroxide ions, that occurs during the process. Binding energy (BE) of Pt(4f_7/2) peak in a film increases to 72.4 eV (until −0.30 V), which slightly decreases at a deposition potential of −0.40 V. XRD data show changes along (111) and (200) planes, to which [PtCl₆]²⁻ and [Pt(OH)Cl₅]²⁻ intermediate hydroxide ions are found to be responsible. The average particle size with respect to applied potential, obtained from SEM data is found to be 25–40 nm. The catalytic activity (Peak current density in cyclic voltammetry) versus deposition potential data is correlated with Pt film formation by reduction of intermediate hydroxide ions.     

Kinetics of NaBH4 hydrolysis on carbon-supported ruthenium catalysts

In this work, different shapes (powder and spherical) of ruthenium-active carbon catalysts (Ru/C) were prepared by impregnation reduction method for hydrogen generation (HG) from the hydrolysis reaction of the alkaline NaBH₄ solution. The effects of temperature, amount of catalysts, and concentration of NaOH and NaBH₄ on the hydrolysis of NaBH₄ solution were investigated with different shapes of Ru/C catalysts. The results show that the HG kinetics of NaBH₄ solution with the powder Ru/C catalysts is completely different from that with the spherical Ru/C catalysts. The main reason is that both mass and heat transfer play important roles during the reaction with Ru/C catalysts. The HG overall kinetic rate equations for NaBH₄ hydrolysis using the powder Ru/C catalysts and the spherical catalysts are described as r = A exp (−50740/RT) [catalyst]^1.05 [NaOH]^−0.13 [NaBH₄]^−0.25 and r = A exp (−52,120/RT) [catalyst]^1.00 [NaOH]^−0.21 [NaBH₄]^0.27 respectively.     

Highly efficient thiomolybdate [Mo2S12]2- nanocluster cocatalyst decorated on TiO2 to boost photocatalytic hydrogen evolution

The exploitation of noble-metal-free photocatalysts with high solar-to-H₂ conversion efficiency is a hot topic in the photocatalysis field. Molybdenum sulfide materials, which have good physicochemical properties and excellent hydrogen evolution activity, have become an effective noble metal cocatalyst substitute and attracted widespread attention. In this work, a highly efficient photocatalyst constructed by decorating thiomolybdate [Mo₂S₁₂]^2- nanoclusters on TiO₂ is reported for the first time. The resultant [Mo₂S₁₂]^2-/TiO₂ photocatalyst shows a remarkable enhanced hydrogen evolution rate under the Xenon light irradiation. At the optimal loading amount of [Mo₂S₁₂]^2-, the photocatalyst exhibits a photocatalytic hydrogen evolution rate of 213.1 μmol h^?1 g^?1, which is about 51 times that of the pure TiO₂. Characterization results show that the intimate contact between [Mo₂S₁₂]^2- and TiO₂ promotes the separation of hole-electron pairs, prolongs the lifetime of carriers, and thereby increases the photocatalytic activity. Furthermore, abundant bridging S in the [Mo₂S₁₂]^2- acts as active sites for hydrogen evolution, which also contributes to the enhanced hydrogen production rate. This work demonstrates an efficient way for the construction of noble-metal-free hydrogen evolution photocatalyst and provides a useful reference for the development of low cost photocatalysts in the future.     

Facile synthesis of Co3O4 nanoparticles from a novel tetranuclear cobalt(III) complex. Application as efficient electrocatalyst for oxygen evolution reaction in alkaline media

A tetranuclear cobalt complex [Co₄^III(L′)₆] was synthesized by the direct reaction of cobalt(II) acetate with a N₂S₂ Schiff base ligand H₂L containing a disulfide bond under aerobic conditions {H₂L = 2,2′-bis(2-hydroxynaphthyliminobenzyl)disulfide}. The X-ray crystal structure of [Co₄^III(L′)₆] indicates reductive disulfide bond scission of H₂L upon reaction with Co²⁺ to give [L^′]^2–. Furthermore, cobalt oxide nanoparticles of about 30 nm size were synthesized by thermal decomposition of [Co₄^III(L′)₆] as a precursor. The Co₃O₄ nanoparticles were characterized by XRD, FE-SEM, TEM, and FT-IR spectroscopy. The electrocatalytic activity of the resulting oxide was examined in oxygen evolution reaction (OER) by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in 1.0 mol L^?1 KOH. The NPs displays efficient electrocatalytic activity for oxygen evolution reaction with a current density of 10.0 mA cm^?2 at 1.65 V, good onset potential of 1.52 V vs. RHE and small Tafel slope of 44 mV dec^?1.     

Enhanced hydrogen storage capacity of NiAl-layered double hydroxide modified with Tb3Fe5O12 nanostructures

Under ultrasonic irradiation, the porous Tb₃Fe₅O₁₂ (TFO) and Nickel Aluminum layer double hydroxide (NiAl-LDH) were synthesized by investigation the effect of sonication time. Synthesis of TFO was conducted in the presence of tetradentate Schiff-base ligand H₂salophen, [N,N′-bis(salicylidene)-1,2-phenylenediamine] as complexing agent to size controlling and further growth prevention of crystals. The resultant nanocomposites of TFO/NiAl-LDH used as novel active compounds for applying in hydrogen storage strategies. Comprehensively, the hydrogen capacitance after 15 cycles was displayed on the pure NiAl-LDH and TFO materials about 115 and 334 mAhg⁻¹ respectively. It demanded the maximum capacitance for Tb₃Fe₅O₁₂/NiAl-LDH nanocomposites was 451 mAhg⁻¹, which was higher than the initial NiAl-LDH structure. It was exposed from the spillover effect that; the endorsed electrochemical hydrogen storage (EHS) performance is ascribed to the reaction of the redox pair of Fe³⁺/Fe²⁺ at the active sites throughout the EHS procedure. This work delivers a novel plan and potential sorption electrode materials to progress the intrinsic action of layered compounds.     

Fabrication of highly dispersed palladium/graphene oxide nanocomposites and their catalytic properties for efficient hydrogenation of p-nitrophenol and hydrogen generation

In this report, graphene oxide (GO) nanosheets decorated with ultrafine Pd nanoparticles (Pd NPs) have been successfully fabricated through a reaction between [Pd₂(μ-CO)₂Cl₄]²⁻ and water in the presence of GO nanosheets without any surfactant or other reductant. The as-synthesized small Pd NPs with average diameter of about 4.4 nm were well-dispersed on the surface of GO nanosheets. The Pd/GO nanocomposites show remarkable catalytic activity toward the hydrogenation of p-nitrophenol at room temperature. The kinetic apparent rate constant (k_app) could reach about 34.3 × 10⁻³ s⁻¹. Furthermore, the as-prepared Pd/GO nanocomposites could also be used as an efficient and stable catalyst for hydrogen production from hydrolytic dehydrogenation of ammonia borane (AB). The catalytic activity is much higher than the conventional Pd/C catalysts.     

Oleylamine-stabilized ruthenium(0) nanoparticles catalyst in dehydrogenation of dimethylamine-borane

Oleylamine-stabilized ruthenium(0) nanoparticles were in situ generated from the reduction of ruthenium(III) chloride by dimethylamine-borane during its dehydrogenation at room temperature. Nearly monodispersed ruthenium(0) nanoparticles of 1.8 ± 0.7 nm size were reproducibly isolated from the reaction solution by filtration and characterized by TEM, XRD, HRTEM, ¹¹B NMR, ATR-IR and UV–visible spectroscopy. Oleylamine-stabilized ruthenium(0) nanoparticles are highly active catalyst in hydrogen generation from dimethylamine-borane providing a release of 1.0 equivalent H₂ per mole of dimethylamine-borane and an initial turnover frequency of 137 (mol H₂) (mol Ru)⁻¹ (h)⁻¹ at 25.0 ± 0.5 °C. By considering the activity and stability of ruthenium(0) nanoparticles, the optimum ratio of stabilizer to the catalyst was found to be 3.0. Oleylamine-stabilized ruthenium(0) nanoparticles with a stabilizer to ruthenium ratio of 3.0 are stable and reusable catalyst providing 20,660 turnovers in hydrogen generation from dimethylamine-borane at 25.0 ± 0.5 °C. They preserve 75% of their initial catalytic activity even after the fifth run of dehydrogenation of dimethylamine-borane with the complete conversion of Me₂NHBH₃ to [Me₂NBH₂]₂ plus 1 equivalent of H₂ at room temperature. The report also includes the detailed kinetic study of the dehydrogenation of dimethylamine-borane catalyzed by oleylamine-stabilized ruthenium(0) nanoparticles depending on the catalyst concentration, substrate concentration, and temperature as well as the activation parameters of catalytic reaction calculated from the kinetic data. The poisoning experiments showed that the dehydrogenation of dimethylamine-borane catalyzed by ruthenium(0) nanoparticles is heterogeneous catalysis.     

Lithium clusters on graphene surface and their ability to adsorb hydrogen molecules

This research describes the theoretical study of the adsorption of lithium clusters on graphene and the ability to capture hydrogen molecules. The results of the studied structures showed that the [Li₁C₅₄H₁₈]⁺ system is capable of accepting three hydrogen molecules showing adsorption energies of 0.12 eV. On the other hand, it is important to note that in [Li_nC₅₄H₁₈] n = 2–6 systems, the lithium atoms that do not interact with the graphene surface, they can adsorb up to four hydrogen molecules. The [Li₆C₅₄H₁₈]4H₂ system presented a higher adsorption energy value of 0.31 eV. Finally, the Li–H₂ interactions were characterized by a NBO analysis, which showed that hydrogen atoms are the donors and lithium atoms are the acceptors.     

A phenylcarbazole functionalized ruthenium dye for efficient dye-sensitized solar cells

A new heteroleptic Ru(II) complex of [Ru(Hcpip)(Hdcbpy)(NCS)₂]⁻·[N(C₄H₉)₄]⁺·H₂O {where Hcpip = 2-(4-(9H-carbazol-9-yl)phenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline, Hdcbpy = 4-carboxylic acid-4′-carboxylate-2,2′-bipyridine} has been synthesized and demonstrated to function as an efficient sensitizer for nanocrystalline TiO₂-based dye-sensitized solar cell (DSSC). The DSSC based on this Ru(II) complex showed a short-circuit photocurrent density of 19.2 mA cm⁻², an open-circuit photovoltage of 630 mV, a fill factor of 57.7%, corresponding to an overall light to electricity conversion efficiency of 6.98% under simulated solar light irradiation at 100 mW cm⁻². This efficiency value is 2.81- and 1.08-fold efficiency values of 2.48% and 6.47% observed for carbazole-free parent complex [Ru(Hpip)(Hdcbpy)(NCS)₂]⁻·[N(C₄H₉)₄]⁺·H₂O {where Hpip = 2-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline}- and cis-bis(isothiocyanato)bis(4,4′-dicarboxylic acid-2,2′-bipyridine)ruthenium(II) N3-based solar cells respectively, under identical experimental conditions. The molecular structures and electronic properties of the Ru(II) complexes were also investigated by means of density functional theory calculations in an effort to understand the device performance observed.     

Metal and phosphonium-based ionic liquid: A new Co and P dual-source for synthesis of cobalt phosphide toward hydrogen evolution reaction

Phosphonium-based ionic liquid, containing cobalt ion, was applied as novel phosphorus and metal dual-source for fabrication of cobalt phosphide. Trihexyl(tetradecyl)phosphonium tetrachlorocobaltate(II) ([P_6,6,6,14]₂[CoCl₄]) with carbon nanotubes (CNTs) was utilized to obtain the Co₂P/CNTs via one step phosphidation. This material exhibits a good catalytic activity toward hydrogen evolution reaction (HER) including an onset overpotential of 85 mV, a Tafel slope of 47 mV dec⁻¹, current densities of 10 and 20 mA cm⁻² at overpotentials of 150 and 178 mV, and it has a good stability to keep the HER activity. All experimental results confirmed that [P_6,6,6,14]₂[CoCl₄] can form Co₂P without adding other reagent and CNTs can improve the electrical conductivity and contribute to the formation of cobalt phosphide.