Mol H2 Research Articles

Photoreforming of model carbohydrate mixtures from pulping industry wastewaters

The photoreforming of organic molecules is a growingly interesting technology to achieve faster hydrogen production than with water splitting, while simultaneously mineralising organic pollutants in water. This paper investigates the possibility to produce hydrogen or gaseous fuel mixtures by using simulated wastewaters of the pulping industry. Glucose was first used as model molecule for carbohydrate-containing wastewaters, while tartaric acid was the model for those rich of carboxylic acids. Different titania catalysts were prepared starting form the P25 commercial material and monometallic Pt or Au, or bi-metallic AuxPty formulations were prepared in form of surface-decorated nanomaterials.The effect of pH and co-catalysts addition was explored, achieving after 5 h of irradiation the highest glucose conversion (15.2%) and H2 productivity (4.1 mol H2 kgcat−1 hirr−1) with sample 1.0 wt%Au6Pt4/P25. This result competes with the best ones reported in the literature. Testing of tartaric acid showed much faster conversion of the substrate, but limited hydrogen productivity, ethane and CO2 being the main products, anyway leading to a valorisable gaseous fuel mixture.The best performing materials were also tested for the photoreforming of simulated wastewaters representative of pulping industry effluents, according to the two pulp processing technologies, the Kraft and sulphite ones. Similar results than tartaric acid were obtained when testing the Kraft spent liquor, mainly composed of hydroxycarboxylic acids. By contrast, the Sulphite spent liquor was mainly composed of carbohydrates, acetic and gluconic acids and led to methane as main product, possibly coming from the decarboxylation of acetic acid.The results overall testify the interest of photoreforming to valorise wastewaters into gaseous fuels in a circular economy concept.

Novel Dithiolene Nickel Complex Catalysts for Electrochemical Hydrogen Evolution Reaction for Hydrogen Production in Nonaqueous and Aqueous Solutions

Three molecular catalysts based on mononuclear nickel(II) complexes with square planar geometries, [BzPy]2[Ni(mnt)2] (1), [BzPy]2[Ni(i-mnt)2] (2), and [BzPy]2[Ni(tdas)2] (3) (BzPy = benzyl pyridinium) are synthesized by the reaction of NiCl2∙6H2O, [BzPy]Br, and Na2(mnt)/Na2(i-mnt)/Na2(tdas) (mnt = 1,2-dicyanoethylene-1,2-dithiolate for (1), i-mnt = 2,2-dicyanoethylene-1,1-dithiolate for (2), and tdas = 1,2,5-thiadiazole-3,4-dithiolate for (3)), respectively. The structures and compositions of these three catalysts are characterized by XRD, elemental analysis, FT-IR, and ESI-MS. The electrochemical properties and the corresponding catalytic activities of these three catalysts are studied by cyclic voltammetry. The controlled-potential electrolysis with gas chromatography analysis confirms the hydrogen production with a turnover frequency (TOF) of 116.89, 165.51, and 189.16 moles of H2 per mole of catalyst per hour at a potential of − 0.99 V (versus SHE) in acetonitrile solutions containing the catalysts, respectively. In a neutral buffer solution, these three molecular catalysts exhibit a TOF of 411.85, 488.76, and 555.06 mol of H2 per mole of catalyst per hour at a potential of − 0.49 V (versus SHE), respectively, indicating that Complex 3 constitutes the better active catalyst than Complexes 1 and 2. For fundamental understanding, a catalytic HER mechanism is also proposed.Graphical abstract

Analysis of Intermediates and Products from the Dehydrogenation of Mg(BH4)2.

The thermodynamic properties of key compounds Mg(B3H8)2, MgB2H6, MgB10H10, Mg(B11H14)2, Mg3(B3H6)2, and MgB12H12, proposed to be formed in the release of hydrogen from magnesium borohydride Mg(BH4)2 and the uptake of hydrogen by MgB2, have been investigated using solid-state density functional theory (DFT) calculations. More accurate tretment of the cell-size effects with respect to the entropies was also investigated in order to improve the accuracy of the thermodynamic properties of complex borohydrides. We find that the zero-point energy corrections can lower the electronic energies of reaction by 20-30 kJ/(mol H2) for these intermediates, while adding the thermal and entropy contibutions results in a total decrease of up to ∼50 kJ/(mol H2). Although our treatment lowers the calculated formation energy of Mg(B3H8)2, it is still too high to explain the experimental observation of B3H8-. We discuss possible reasons for this disparity and propose that the formation of B3H8- and H- in a disordered amorphous phase has a large energy difference compared to the phase-separated Mg(B3H8)2 and MgH2 considered in calculations. A comparison of the experimental and NMR chemical shifts calculated within a DFT approach for known species Mg(BH4)2, Mg(B3H8)2, Mg(B11H14)2, MgB10H10, and MgB12H12 provides validation for predicting the chemical shifts of the other compounds which are yet to be confirmed experimentally. These include MgB2H6 and the proposed trianion species Mg3(B3H6)2 that both have favorable thermodynamics for reversible hydrogen storage in Mg(BH4)2 without the formation of MgH2 as a coproduct which could phase separate and inhibit rehydrogenation.

A bis(thiosemicarbazonato)‐zinc complex, an electrocatalyst for hydrogen evolution and oxidation via ligand‐assisted metal‐centered reactivity

AbstractBased on that hydrogen energy is widely used in fuel cells, the design and research of new catalysts for both hydrogen evolution reactions (HERs) and hydrogen oxidation reactions (HORs) are becoming increasingly important. A new catalyst for both hydrogen evolution and oxidation, based on a zinc complex, [Zn‐ATSE]2, is designed and provided by the reaction of Zn (CH3CO2)2 with diacetyl‐2‐(4‐N‐ethyl‐3‐thiosemicarbazone)‐3‐(4‐N‐amino‐3‐thiosemicarbazone) (H2ATSE) in our group. Electrochemical investigations show that [Zn‐ATSE]2 can electro‐catalyze hydrogen evolution from acetic acid with a turnover frequency (TOF) of 64 mol H2 mol catalyst−1 h−1 under an overpotential of 914.6 mV. Moreover, [Zn‐ATSE]2 also can electro‐catalyze hydrogen oxidation with a TOF of 13.52 s−1. The results can be attributed to the hydrazine group of [Zn‐ATSE]2 that can form a ligand‐based radical species. Possible electrocatalytic cycles for H2 production and oxidation by [Zn‐ATSE]2 are afforded. We hope these findings can afford a new method for the design of electrocatalysts for both H2 evolution and H2 oxidation.

Design of Nb-Ti-Fe hydrogen permeable alloys based on the ductile-to-brittle transition-hydrogen concentration region

Nb-based dual-phase alloys are one of the most promising candidates for hydrogen purification. To solve their brittle fracture in hydrogen-containing atmospheres, the ductile-to-brittle transition-hydrogen concentration (DBTC) is a significant reference index, and the dissolved hydrogen concentration should be controlled below the lower limit of the DBTC, i.e., 0.72 H/M (atomic hydrogen to metal ratio). In this study, hydrogen permeable Nb-Ti-Fe alloys were designed and developed by using the above DBTC concept. Four hyper-eutectic Nb-Ti-Fe alloy membranes were prepared, and their hydrogen solubility was systematically analyzed by corresponding pressure-composition isotherms (PCT curves). The results show that all these samples had a linear relationship between the hydrogen concentration and square root of the hydrogen pressure between 0.1 and 0.4 MPa, which is in accordance with the Sieverts’ law. The hydrogen solubility of the specimens containing the primary TiFe phase was lower than 0.72 H/M, but the alloys with the primary Nb phase had a value that was much higher. The latter was completely broken during the test, even if the feed hydrogen pressure was reduced to 0.15 MPa. Based on the above results and DBTC concept, novel insights into the design of Nb-Ti-Fe hydrogen permeable alloys were elucidated; that is, an improvement in both the hydrogen permeability and hydrogen embrittlement resistance can be attained by controlling the hydrogen solubility. Following this concept, a Nb5Ti58Fe35Cu2 alloy was successfully developed that exhibited a high permeability of 4.32 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 673 K, which is 2.7 times than that of a pure Pd membrane under the same test conditions. The present work demonstrated the feasibility and applicability of the DBTC concept in the design of dual-phase Nb-Ti-Fe hydrogen permeable alloy membranes.

Structure and properties of niobium carbide coated vanadium composite membranes for high temperature hydrogen separation

Niobium carbide (NbC) catalytic films were deposited on vanadium (V) foils by magnetron sputtering to prepare the NbC/V composite membranes for high temperature hydrogen separation. It is found that the sputtering power and substrate bias largely affect the structure and catalytic activity of the NbC films, and thus the hydrogen permeability of the NbC/V composite membranes. Optimized conditions for membrane preparation were obtained, which generated a pronounced high hydrogen permeability, particularly ~5.85 × 10−8 mol H2 m−1 s−1 Pa−0.5 at 650 °C. This is 1.9 times that of pure palladium (Pd). The high hydrogen permeability of the NbC/V membranes can be attributed to the high catalytic activity of the NbC films towards hydrogen dissociation, as the cubic NbC phase in the films exhibits preferential growth along the catalytically dominated crystalline plane and a relatively high percentage. This work demonstrates that the NbC/V system shows high potential as a new non-precious metal membrane for hydrogen separation and purification at high temperatures.

Biohydrogen production from diluted-acid hydrolysate of rice straw in a continuous anaerobic packed bed biofilm reactor

Bio-hydrogen production in a continuously operated anaerobic packed bed biofilm reactor (APBR) using acid-hydrolysate of rice straw as feedstock and inoculated with an anaerobic mesophilic sludge from a municipal wastewater treatment plant was investigated at three different HRTs (17, 8.2 and 2 h). Fermentable sugars solution achieved from a two-stage diluted acid hydrolysis of rice straw was used as the feedstock. First, rice straw was treated with 1% w v−1 sulfuric acid at 120 °C for 30 min with a yield of 58.5% xylose. Higher temperature of 180 °C for 10 min at 0.5% w v−1 sulfuric acid was applied in the second stage in which cellulosic crystalline structure was partially depolymerized to glucose with a yield of 19.3% glucose. Hydrogen production rate and yield were enhanced as the hydraulic retention time was decreased with a maximum production rate of 252 mL L−1 h−1 and yield of 1 mol H2 mol−1 sugar consumed at 2 h HRT. Experimental results illustrated the increase of COD conversion from 44% to 47% by shortening the HRT from 17 to 2 h. Furthermore, acetic acid and butyric acid production were reduced slower than other soluble metabolites like ethanol.

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 °C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2·molCo-1·min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2·gCo-1·min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

Cu/Ni-NiOx Nanoparticles Distributed on Graphene as Catalysts for the Methanolysis of Ammonia Borane to Produce Hydrogen

Ultrasmall Cu/Ni-NiOx nanoparticles (NPs) had been successfully prepared by attaching and growing Ni-NiOx NPs on the surface of Cu NPs and then uniformly dispersed onto graphene (G) surface. High-angle annular dark-field–scanning transmission electron microscopy (HAADF-STEM) characterization confirmed that Ni-NiOx NPs were uniformly distributed on the surface of Cu NPs. The catalytic methanolysis of ammonia borane (AB) proved that Cu/Ni-NiOx NPs possessed high catalytic hydrogen (H2) evolution activity, and the highest turnover frequency (TOF) was 17.72 mol H2·mol–1 Cu·min–1. Comparative experiments revealed that the high catalytic activity originated from the abundant catalytic active sites of Cu/Ni-NiOx NPs. The attachment of Ni-NiOx on the surface of Cu NPs that dispersed on G (G-Cu/Ni-NiOx) can not only effectively improve the antioxidative performance of Cu NPs under ambient conditions but also promote the methanolysis of AB to produce H2.

Syngas Components Recovery during Membrane Gas Separation

Membrane operations are a promising way of improving and adjusting the composition of the biomass gasification product – syngas – before it can be further transformed into fuels and energy. The presented study focuses on the recovery of individual components (H2, CO, CO2) during membrane separation under varying conditions – pressure difference and the feed composition. Model syngas mixtures with four different compositions containing between 12-24 %mol H2, 34-39 %mol CO and 43-49 %mol CO2 were tested under different pressure differences ranging from 1 to 8 bar (retentate pressure ranging from 2 to 10 bar, permeate pressure from 1 to 4 bar), at temperature 22 °C. Results of the study indicate exponential dependency existence between total pressure drop and the components recovery. The data were approximated with fixed parameter for minimal pressure difference for each component (p0 = 0.5 bar for H2 and p0 = 0.7 bar for CO2) and with variable exponent coefficients. The coefficients in exponent are strongly dependant on permeate pressure (ranging from 0.33 to 0.88 bar-1 for different permeate pressures for CO2 recovery) and vary with feed composition as well (from 0.75 to 0.83 bar-1 across different mixtures for CO2 at fixed permeate pressure).

Experimental comparison of performance and emissions of a direct-injection engine fed with alternative gaseous fuels

Performance and emissions of a direct-injection (DI) spark-ignition engine with high compression-ratio (15.5:1) fed with hydrogen, hydrogen-rich reformate, and methane are discussed. Differences in the particle formation with hydrogen and the reformate containing 75% mol H2 and 25% mol CO2 are investigated for the first time and compared with methane. The total particle number (PN) concentration with the reformate was the highest at all loads because of its significantly longer injection duration. This new finding explains why the elevated PN emission was measured in a DI engine fed with the reformate in contrast to the previously published data for hydrogen and the reformate PFI engines. Hydrogen combustion resulted in higher particle formation compared to methane under high engine loads. The combined effect of the flame quenching distance, fuel carbon content, and injection duration defines the PN formation in a DI ICE fed with gaseous fuel. The study findings demonstrated the appearance of an optimal hydrogen injection strategy enabling the minimization of PN emission. Hydrogen combustion results in the highest engine thermal efficiency. However, when the exhaust waste heat utilization in the engine with the reformate combustion is considered, the overall system thermal efficiency above that of the hydrogen engine is achieved. Negligible and the lowest, in comparison to hydrogen and methane, NOx emissions are found with the reformate-fed engine. CO2 contained in the reformate acts as an inherent EGR enabling almost full mitigation of NOx formation even at the highest engine loads.

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 influence of surface corrosion on microstructure and hydrogen permeability of Nb-Hf-Co dual-phase alloys

Nb-HfCo quasi-binary alloys are prospective hydrogen separation membrane materials due to their price advantage and excellent hydrogen permeation performance. However, a small amount of acidic gas (e.g. CO2 and H2S) is often mixed in the feed gas, which corrodes the surface of the alloy membrane in the process of their application. Up to now, the corrosion behaviours and the corresponding influencing factors have not been studied yet, and the relationship between the microstructure and corrosion resistance has yet to be established. To this end, NbxHf(100−x)/2Co(100−x)/2 (x = 40.60) dual-phase alloys were prepared by arc melting and then corroded using an electrochemical workstation, and their microstructure, corrosion resistance and hydrogen permeability before and after corrosion were systematically studied. The results show that an oxide layer (Nb2O5, HfO2, CoO) is formed around the alloy surface after corrosion, and the order of corrosion resistance of these alloys is as follows: Nb60Hf20Co20 < Nb40Hf30Co30 < Nb50Hf25Co25 < Nb45Hf27.5Co27.5. The Nb45Hf27.5Co27.5 alloy, with the strongest corrosion resistance, exhibits a high hydrogen permeability of 6.70 × 10−8 mol H2 m−1 s−1 Pa−1/2 at 673 K after corrosion, which is the highest value reported in this alloy system up to now. In addition, the hydrogen permeation mechanism for Nb-based alloy membranes in a corrosive environment, is proposed for the first time. The present work demonstrates that Nb45Hf27.5Co27.5 alloy is an attractive candidate for hydrogen separation in an acidic corrosive environment.

Effect of metal centers of complexes bearing bipyridine ligand for electrochemical‐ and photochemical‐driven hydrogen evolution

In this work, two complexes with bipyridine ligand, [Co (bpy)2(SCN)2] 1 and [Ni (bpy)2(SCN)2] 2 have been prepared and well determined by single crystal X‐crystallography, power X‐ray diffraction (XRD), IR spectra, and so forth. Both exhibit good catalytic activity for electrochemical‐ and photochemical driven‐hydrogen evolution. Complexes 1 and 2 can electro‐catalyze H2 evolution from a neutral buffer (pH 7.0) with a turnover frequency (TOF) of 699.6 and 1469 mol H2/mol catalyst/h at an overpotential (OP) of 837.6 mV, respectively. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid as a sacrificial electron donor, complexes 1 and 2 also can photo‐catalyze H2 evolution from water. Under an optimal condition, the turnover numbers (TONs) reach 10,600 (complex 1) and 15,180 (complex 2) mol of H2 per mol of catalyst during 48‐h irradiation, respectively. The average apparent quantum yields (AQYs) of complex 1 and complex 2 are 15.07% and 22.7%, respectively. Electrochemical and photochemical investigations show that the nickel complex has a higher activity for hydrogen evolution than that of the cobalt complex. These results can provide a new insight into design and manufacture of new H2‐production catalyst.

Amine-functionalized carbon nanotubes supported NiAuPd nanoparticles as an efficient in-situ prepared catalyst for formic acid dehydrogenation

Hydrogen (H2) generation from formic acid (FA) decomposition is a promising route in practical application of hydrogen energy. As a promising H2 supplier, besides the advantage of high H2 content and excellent stability, FA can also be used as a mild reducing agent. Herein, an in-situ prepared NiAuPd nanoparticles (NPs) supported on amine-functionalized carbon nanotubes (NiAuPd/NH2-CNTs) with FA as the reducing agent is successfully developed at room temperature. The as-prepared NiAuPd/NH2-CNTs are directly used for the catalytic decomposition of FA, exhibiting excellent activity and 100% H2 selectivity with the initial turnover frequency (TOFinitial) value of 699.1 and 3006.1 mol H2 mol Pd-1 h-1 at 303 and 333 K, respectively. Moreover, the additive sodium formate (SF) can further facilitate the reduction process and enhance the catalytic performance, with the TOFinitial value of 4391.1 mol H2 mol Pd-1 h-1 at 333 K, which are comparable to most of the reported heterogeneous catalysts with the complicated post-treatment. The excellent catalytic performance of NiAuPd/NH2-CNTs is mainly attributed to the high dispersion of NPs and the boost effect of -NH2 group on O–H cleavage. This work provides a feasible strategy to design in-situ prepared catalysts for the efficient high-quality H2 generation from FA for fuel cells application.

Synthesis, structure, characterization, EPR investigation and catalytic behavior for hydrogen evolution of a bis(thiosemicarbazonato)-palladium complex

The reaction of H2ATSE with Pd(CH3CN)2Cl2 affords a new palladium complex, Pd-ATSE, which has been characterized by physico-chemical and spectroscopic methods. EPR investigations show that there are the couplings of 105Pd with the neighboring 14N and 33S nuclei from the ATSE2- ligand. Under an overpotential of 837.6 mV, Pd-ATSE can afford 666 mol of hydrogen per mole of catalyst per hour. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) and ascorbic acid (H2A), Pd-ATSE can catalyze hydrogen generation with a turnover number (TON) of 3520 mol H2 per mol of catalyst (mol of cat−1) during 28 h irradiation.

Insights into the Mechanism of Methanol Steam Reforming Tandem Reaction over CeO2 Supported Single-Site Catalysts.

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2gRu-1s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

Modeling the kinetic behavior of the Li-RHC system for energy-hydrogen storage: (I) absorption

The Lithium–Boron Reactive Hydride Composite System (Li-RHC) (2 LiH + MgB2/2 LiBH4 + MgH2) is a high-temperature hydrogen storage material suitable for energy storage applications. Herein, a comprehensive gas-solid kinetic model for hydrogenation is developed. Based on thermodynamic measurements under absorption conditions, the system's enthalpy ΔH and entropy ΔS are determined to amount to −34 ± 2 kJ∙mol H2−1 and −70 ± 3 J∙K−1∙mol H2−1, respectively. Based on the thermodynamic behavior assessment, the kinetic measurements' conditions are set in the range between 325 °C and 412 °C, as well as between 15 bar and 50 bar. The kinetic analysis shows that the hydrogenation rate-limiting-step is related to a one-dimensional interface-controlled reaction with a driving-force-corrected apparent activation energy of 146 ± 3 kJ∙mol H2−1. Applying the kinetic model, the dependence of the reaction rate constant as a function of pressure and temperature is calculated, allowing the design of optimized hydrogen/energy storage vessels via finite element method (FEM) simulations.

Catalytic performance of a square planar nickel complex for electrochemical‐ and photochemical‐driven hydrogen evolution from water

A square planar nickel complex bearing salicylketoxime (SAO), Ni-SAO has been synthesized and well characterized by ESI-MS and single-crystal X-ray diffraction, etc. Ni-SAO exhibits good activity in both electrocatalytic and photocatalytic hydrogen evolution reaction (HER). Under an overpotential (OP) of 837.6 mV, Ni-SAO can electrocatalyze hydrogen evolution from a neutral aqueous buffer with a turnover frequency (TOF) of 1428 mol of hydrogen per mole of catalyst per hour (mol H2 /mol catalyst/h). Moreover, under blue light (λ = 469 nm), a three-component system containing Ni-SAO as a catalyst, CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor also can afford hydrogen with a turnover number (TON) of 8138 mol H2 per mol of catalyst (mol of cat−1) during 48 h irradiation. The highest apparent quantum yield (AQY) is about 16.5% at 469 nm.

Synthesis, structure, characterization and catalytic behavior of a bis(thiosemicarbazonato)-nickel complex

4-Phenyl-3-thiosemicarbazide reacts with 2,3-butanedione to provide a new compound, diacetyl-bis(N4-phenyl-3-thiosemicarbazonato) (H2ATSP). In the presence of triethylamine (Et3N), the reaction of H2ATSP with NiCl2 affords a new nickel complex, diacetyl-bis(N4-phenyl-3-thiosemicarbazonato)nickle(II) (NiII-ATSP), a diamagnetic material, which has been characterized by physicochemical and spectroscopic methods. Studies exhibit that Ni-ATSP has good catalytic activities for both electrochemical and photochemical driven hydrogen evolution. Under an overpotential (OP) of 837.6 mV, 188.7 moles of hydrogen per mole of catalyst per hour (mol H2/mol catalyst/h) are afforded from an electrolysis of neutral water with Ni-ATSP. With blue light (λ = 469 nm) irradiation, together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor, Ni-ATSP can catalyze hydrogen generation with a turnover number (TON) of 9554 moles H2 per mol of catalyst (mol of cat−1) during 50 h irradiation in a heterogeneous environment.