Mechanism Of Hydrogen Production Research Articles

Study on the mechanism of hydrogen production from bamboo gasification in supercritical water by ReaxFF molecular dynamics simulation

Study on the mechanism of hydrogen production from bamboo gasification in supercritical water by ReaxFF molecular dynamics simulation

Direct Hydrogen Production Promoted by Laser-Induced Water Plasma.

Hydrogen, as a clean energy carrier, plays an important role in addressing the current energy and environmental crisis. However, conventional hydrogen production technologies require extreme reaction conditions, such as high temperature, high pressure, and catalysts. Herein, we study the microscopic mechanism of laser-induced water plasma and subsequent H2 production with real-time time-dependent density functional theory simulations and ab initio molecular dynamics simulations. The results demonstrate that intense laser excites liquid water to generate nonequilibrium plasma in a warm-dense state, which constitutes a superior reaction environment. Subsequent annealing leads to the recombination of energetic reactive particles to generate H2, O2, and H2O2 molecules. Annealing rate and laser wavelength are shown to modulate the product ratio, and the energy conversion efficiency can reach ∼9.2% with an annealing rate of 1.0 K/fs. This work reveals the nonequilibrium atomistic mechanisms of hydrogen production from laser-induced water plasma and shows far-reaching implications for the design of optically controllable hydrogen technology.

Preparation of C-doped g-C3N4 by Co-polycondensation of melamine and sucrose for improved photocatalytic H2 evolution

g-C3N4, a well-known semiconductor is widely used for photocatalysis because of its renowned and special properties. It is a nonmetallic polymeric material that is abundant in sources and easy to prepare, making it an attractive choice for photocatalysis that responds to visible light. However, due to various intrinsic structural and chemical drawbacks, it is very far from further applications. Herein, we used sucrose to modify the physicochemical characteristics of ordinary g-C3N4 to prepare a carbon self-doped g-C3N4 (Cn-MA) material through co-polycondensation with melamine and applied it for hydrogen production. The characterization showed that the addition of sucrose resulted in a narrowed band gap, widened absorption range, enhanced photoresponse, and photogenerated charge carrier separation. Furthermore, the prepared material was applied for hydrogen production activity, which revealed that it has higher photocatalytic performance than pristine g-C3N4. The H2 production rate of the optimized material (C7.5-MA) was recorded as 7.3 times greater than that of pure g-C3N4. Through cycling tests, the stability of C7.5-MA was examined. The results showed that, even after four consecutive cycles, no apparent drop in its performance was observed. Additionally, here the mechanism of hydrogen production is also discussed.

Hydrogen production mechanism and catalytic productivity of Ni-X@g-C3N4 (X = precious and non-precious promoter metals) catalysts from KBH4 hydrolysis under stress loading and atmospheric pressure: Experimental analysis and molecular dynamics approach

In this study, the pressure effect of Ni-based catalysts added a second promoter metal to increase of catalyst performance supported a graphite carbon nitride (g-C3N4) monolayer on hydrogen release mechanisms from potassium boron hydride (KBH4) hydrolysis was investigated using molecular dynamics (MD) method based on tight-binding density functional theory (DFT). The use of the various promoters, such as transition metals (X = Cu, Ta and W) and noble metals (X = Pd, Pt and Rh) with applying a high external pressure was investigated to understand the role on catalytic performance of the Ni-based catalysts under stress loading. The g-C3N4 monolayer doped with Ni-X nano-catalysts was used for efficient H2 release from KBH4 hydrolysis. The computational results show that the number of H2 shows more increment with MD time for NiW and NiRh catalysts than other NiTa and NiCu (transition metals) and NiPd and NiPt (noble metals) under 0 GPa pressure. On the other hand, a notable increase in H2 amount is seen only NiCu and NiRh catalysts under 50 GPa. Also, the mechanism of the H2 production reaction from KBH4 hydrolysis of g-C3N4 doped NiCo catalysts was clarified. High-performance cost metal catalysts such as NiCo was investigated as both experimentally and modeling under atmospheric pressure to enhance its commercial application value. Some experimental applications and analyzes were also performed to measure the accuracy of the modeling for the relevant molecular groups in the system.

Pyrolysis characteristics and hydrogen production mechanism of biomass impregnated with transition metals

The application of metal impregnation pretreatment to improve the quality of biomass pyrolysis gas production is considered as a promising upgrading technology. Transition metals have been well developed for the unique structural characteristics. After impregnation pretreatment, the product distribution of biomass pyrolysis was changed, and the transfer path of H atoms and the formation mechanism of H2 can be revealed through analysis. The effects of impregnation pretreatment with three different transition metals (iron, cobalt, and nickel) on the pyrolysis characteristics of corn straw were evaluated in this work. Three transition metal solutions with concentrations of 0.5 M, 1 M, and 2 M were used to explore the influence of impregnation concentration on the yield and composition of the pyrolysis products. The results showed that iron promoted the formation of liquid products, whose proportion increased by 37.29% upon increasing the impregnation solution concentration. The addition of cobalt and nickel led to more pyrolysis gas generation. When the impregnation solution concentration was greater than 0.5 M, the gas production rate exceeded 45 wt%. Nickel simultaneously promoted the generation of H2 and CH4 in pyrolysis gas, whose yields were increased by 63% and 20% respectively compared with raw materials. Py-GC/MS analysis showed that Co-CS had strong decarboxylation characteristics during pyrolysis. Metal impregnation decreased the content of aromatic compounds in tar, which increased the stretching vibrations of C-H bonds in char. Ring-opening rearrangements of polycyclic aromatic hydrocarbons were promoted, which formed more -H. Nickel catalyzed the removal of CH3 and H groups and the rearrangement of C-O in volatile products, which formed more H2 and CH4. These findings provide an avenue to optimize the metal impregnation conditions to produce hydrogen via biomass pyrolysis.

Design of TiO2-based bi-functional catalyst and the catalytic mechanism of enhanced hydrazine borane hydrolysis for hydrogen production

In this study, a scheme of photocatalytic coupled metal catalytic synergistic enhancement of hydrazine borane hydrolysis is proposed, the catalytic reaction mechanism for hydrogen production from hydrazine borane hydrolysis is revealed. In addition, the effects of solvent property, external electric field conditions on the stability of N2H4BH3 molecule are also investigated systematacially. The results show that the band structure of pure TiO2 can be modulated by heterogeneous element N, C, Ni, Ru, the modification effect of co-doping with heterogeneous alloy elements (eg. NiPt@N–TiO2) is best in all doping schemes. The hydrolysis reaction of -BH3 of N2H4BH3 catalyzed by Pt metal is a stepwise dehydrogenation reaction, and the energy barrier of the reaction rate-determining of the B–N bond breakage is 50.49 kcal/mol. There are two possible cleavage reaction pathways for N2H4, which are hydrogen-producing pathway and ammonia-producing pathway, the energy barrier for the reaction rate-determining step is 67.06 kcal/mol and 82.51 kcal/mol, respectively, the hydrogen production reaction takes precedence over the ammonia production reaction. OH− solution is best among the neutral aqueous solution, rich H+, NH4+ and NaOH solution in B–H bond activation of N2H4BH3 molecule, the external electric field can promote the activation of B–H bond in hydrazine borane hydrolysis system, which is positive factor in improving the performance of hydrazine borane hydrolysis.

Theoretical study of the mechanism of hydrogen production by catalytic methane decomposition on the carbon black catalyst

Catalytic methane decomposition (CMD) is a promising chemical process for hydrogen production from natural gas with zero CO2 emissions. In the present work we perform a systematic study of CMD on the graphene edge as a model of the carbon catalyst surface. Atomistic first-principles calculations (DFT level of theory) were performed to obtain the parameters of elementary reactions including the formation of active sites, interaction of methane molecules with these active sites and regeneration of the carbon catalyst surface. Our findings show that methane pyrolysis on the carbon catalyst is a unique heterogeneous radical chain process in which active sites are migrating over the catalyst surface via gas phase radical transport. Based on quantum-chemistry calculations, detailed kinetic mechanism of CMD on the carbon catalyst was developed and verified with respect to the latest experimental data. Calculated effective activation energies and methane conversions in CMD process are in reasonable agreement with experimental data. The present investigation of the mechanism of hydrogen production by CMD process on carbon catalyst can be useful for optimization of this process taking into account degradation of the carbon catalyst.

The nature of photocatalytic hydrogen generation on silicon nanowires prepared by MAWC

Highly n-doped silicon nanowires (SiNWs) exhibit excellent hydrogen generation. Our results indicate three hydrogen generation possibilities, i.e. SiNWs oxidation, photocatalysis and the cleavage of dangling H bonds, are jointly responsible for the efficient hydrogen generation. Oxidation accounts for about 80% of total hydrogen, photocatalysis contributes less than 20% of total hydrogen, and about 0.1% of total hydrogen is from cleavage of dangling H bonds. SiNWs were oxidized in water and form SiOx (0 < X < 2) thin layer. Furthermore, the ratio of photo-generated hydrogen to photo-generated oxygen is about 2.4:1. It suggests that photocatalysis appears to be a process of water splitting. This study is significant to reveal the mechanism of hydrogen production on SiNWs prepared by Metal-Assisted Wet Chemical Etching (MAWC).

Multi-vacancy synergistic effect in a NiSe0.4S1.6/ZnO heterostructure for promoting photocatalytic hydrogen production

Defect engineering is one of the methods to improve catalytic activity of photocatalysts, but there are few reports on multi-vacancy systems. In this paper, S doping NiSe2 (NiSe0.4S1.6, NSS) was synthesized and further the NSS/xZnO heterostructures containing Ni, Se and O vacancies were constructed. The hydrogen and active oxygen ions are in situ generated at oxygen vacancy (VO) in ZnO, which greatly reduce the recombination of photocarriers, and the generated active oxygen ions and sacrificial agent anions (S2−, SO32−) involve in the regeneration of oxygen vacancy, which may be one of the reasons for the high activity and stability of the composite catalysts. The polarization electric field is formed by regulating the selenium and nickel double vacancy (VSe, VNi) generated by doping NiSe2 with S, which further improves the charge separation leading to the promotion of photocatalytic hydrogen production. The synergistic effect of the three types of vacancies and the redox properties of the composite catalyst lead to a high H2 production rate of 17.04 mmol·g−1·h−1, 54 and 76 times higher than NSS and ZnO, and a high apparent quantum yield of 15.30 % at 400 nm. The hydrogen production mechanism was explored by EPR, Mott-Schottky, VB-XPS, in suit XPS, DFT, etc. This work proves that the combination of transition metal oxides with rich oxygen defects and metal chalcogenides with metal and chalcogen di-vacancies containing local polarized electric fields is an effective strategy to design high active photocatalyts for water splitting.

Mechanism of Hydrogen Production in The Processes of Radiation Heterogeneous Splitting of Water with the Presence of Nano-Metal and Nano-MeO

Mechanism of Hydrogen Production in The Processes of Radiation Heterogeneous Splitting of Water with the Presence of Nano-Metal and Nano-MeO

Reinforced photogenerated electron convergence on graphdiyne(g-CnH2n-2) “as an active site and substrate” for enhance photocatalytic hydrogen production

Graphdiyne(GDY), as a carbon-based catalyst with tunable electronic structure, has a significant impact on the advancement of sustainable photocatalytic technology. Its tunable electronic structure can effectively regulate the activity and selectivity of photocatalytic reaction. In this paper, GDY was prepared by a new method of ball milling HEB-TMS, and CoWO4 nanoparticles were uniformly loaded on the surface of GDY to construct a Type-II heterojunction. GDY provides a dispersed and effective substrate for CoWO4, forming a closer contact interface. Based on GDY's unique electronic structure and the formation of Type-II heterojunction, GDY/CoWO4 enhances the separation of photoexcited electrons and holes, thus increasing the electron cloud density on GDY. As an electron acceptor and active site for hydrogen production, GDY promotes the proton reduction reaction. In addition, the charge transfer process of GDY/CW-15 was demonstrated by in-situ XPS and UPS, and the corresponding hydrogen production mechanism was proposed. This study provides a facile and efficient method for preparing GDY and a new idea for heterojunction photocatalyst based on GDY substrate.

Hydrogen Production Using a Nickel Catalyst Combining Redox Activity and Pendent Base Effects.

With the mounting need for clean and renewable energy, catalysts for hydrogen production based on earth abundant elements are of great interest. Herein, we describe the synthesis, characterization, and catalytic activity of two nickel complexes based on the pyridinediimine ligand that possess basic nitrogen moieties of pyridine and imidazole that could potentially serve as pendent bases to enhance catalysis. Although these ligands have previously been reported to be complexed to some metal ions, they have not been applied to nickel. The nickel complex with the pendent pyridines was found to be the most active of the two, catalyzing proton reduction electrochemically with an overpotential of 490 mV. The appearance of a wave that preceded the Ni(I/0) redox couple in the presence of protons suggests that protonation of a dissociated pyridine was likely. Further evidence of this was provided with density functional theory calculations, and a mechanism of hydrogen production is proposed. Furthermore, in a light-driven system containing Ru(bpy)32+ and ascorbic acid, TON of 1400 were obtained.

The construction of CdxZn1-xS-based photocatalysts for enhanced hydrogen generation

CdxZn1-xS (x=0~1) solid solution photocatalyst with different morphologies was synthesized by solvothermal method using ethylenediamine as solvent. The light absorption of the photocatalyst was varied by changing the morphology and electronic band structure to allow strong visible light response for hydrogen generation. The results showed that the optimum sample Cd0.5Zn0.5S showed a high hydrogen production rate of 2531.3 μmol·g-1 ·h-1 with lactic acid as sacrificial agent. Loading with NiS by solvothermal method further improves the hydrogen production performance. The photocatalytic hydrogen evolution rate of NiS/Cd0.5Zn0.5S is 4547.5 μmol·g-1 ·h-1 , which is 1.80 times that of pure Cd0.5Zn0.5S. The mechanism of hydrogen production by NiS/Cd0.5Zn0.5S is also discussed.

2023 Joseph W. Richards Fellowship – Summary Report: Toward High-throughput Electrochemical Screening of in vivo Synthesized Metalloenzymes

In recent years, bioinspired metalloenzymes have proven a viable and sustainable method for hydrogen production via the hydrogen evolution reaction (HER). By using in vivo directed evolution synthetic techniques, hydrogenase systems based on rubredoxin (Rd) scaffolds with Ni substituted metal centers have proven promising molecular catalysts. However, insight into the mechanism of hydrogen production between different mutants has proven tricky, as electrochemical characterization of the high number of mutants is slow. High-throughput electrochemistry has started to emerge at the nano and macroscale in the form of scanning electrochemical methods and by using an array of electrochemical cells. Here we utilize the array microcell method (AMCM)to electrochemically investigate each enzyme at one array.

Molecular Dynamics Investigation of the Gasification and Hydrogen Production Mechanism of Phenol in Supercritical Water

Supercritical water gasification is an efficient and clean method for converting biomass into hydrogen-rich gas. Phenol plays a crucial role as an intermediate product in biomass supercritical water gasification, and studying its reaction pathway in supercritical water is essential for understanding the chemical reaction mechanism and optimizing biomass energy conversion processes. In this paper, we investigated the conversion mechanism of phenol gasification and hydrogen production in supercritical water using a combined approach of reactive force field (ReaxFF) and density functional theory (DFT). We determined the decomposition pathways and product distribution of phenol in supercritical water. The calculation results demonstrate that in the supercritical water system, the efficiency of phenol conversion for hydrogen production is approximately 27 times higher than that of hydrogen production through gasification in the pyrolysis state. Moreover, both the carbon conversion rate and hydrogenation rate in the supercritical water system are significantly higher compared to those in the pyrolysis system. Furthermore, we found that the energy in the supercritical system is approximately half that of the pyrolysis system, favoring the ring-opening reactions of phenol and promoting hydrogen production. In contrast, the pyrolysis system produces a greater quantity of aromatic compounds, leading to tar formation and having significant implications for both the reaction process and reactor design. Additionally, we conducted comparative experiments between the supercritical water gasification process and the pyrolysis process to explore the advantages of supercritical water gasification.

Be13 cluster adsorbs water molecules splitting to produce H2 based on density functional theory

Research on the production of hydrogen from water by catalytic decomposition using metal clusters is of great significance in addressing the global energy crisis. Due to the quantum size effect, tunability, and ultra-high surface area, metal clusters exhibit many unique properties, including catalytic performance and optical properties. In this work, the lowest energy structure of Be13 cluster and intermediate states, as well as the hydrogen production mechanism of Be13 cluster and intermediate states + single water molecule were studied by DFT calculations at the PBE0-D3/DEF2TZVP level. The results show that both Be13 cluster and intermediate states release energy during water molecules adsorption and both Be13 cluster and its intermediate state + single water molecule reactions are exothermic. The electronic structures of the original and adsorbed structures were analyzed by ESP method, and their DOS plots were drawn. We investigated the chemical bonding and interactions of the initial structure, reactants and products using IRI analysis. Our results help to provide a basis for developing a more effective method for generating hydrogen from water molecules.

Self-assembly of 3D Zn0·5Cd0·5S/CoP microflower for efficient visible-light-driven photocatalytic H2 evolution

In this work, we design and fabricate a novel Zn0·5Cd0·5S/CoP composite with a 3D microflower structure by a facile hydrothermal method. Comprehensive photochemical measurements showed that the engineering of highly conductive CoP co-catalyst into Zn0·5Cd0·5S solid solution improves the visible light response capability by narrowing the forbidden band gap. At the same time, a morphology control by forming a 3D microflower structure could realize an intimate contact interface between Zn0·5Cd0·5S and CoP, which ensures that electrons from Zn0·5Cd0·5S excited by visible light (420 nm) can be effectively transferred to the highly conductive CoP for separation and migration. The systematic photocatalytic hydrogen evolution experiments illustrate a remarkable hydrogen production rate up to 72.71 mmol h−1 g−1 for Zn0·5Cd0·5S/CoP with a CoP mass fraction of 20 wt%, which is 27 times higher than that of bare Zn0·5Cd0.5S. Based on the characterization analysis results, a possible mechanism of hydrogen production by Zn0·5Cd0·5S/CoP composite catalyst is proposed.

Study on the mechanisms of hydrogen production from alkali lignin gasification in supercritical water by ReaxFF molecular dynamics simulation

Lignin is a major polymer in the black liquor of paper mill and one of the most important components of biomass. Supercritical water gasification (SCWG) technology, which is an efficient and clean method for waste lignin treatment, has a good application prospect. To improve the conversion efficiency of lignin, it is necessary to reveal the detail mechanisms of lignin gasification in supercritical water (SCW). Based on the actual molecular structure of lignin, a model of complex lignin was constructed by using Materials Studio (MS). The effects of different reaction parameters on gasification results were analyzed with the reactive force field molecular dynamics method (ReaxFF MD). The simulation results show that higher reaction temperature and lower reactant concentration lead to higher efficiency of lignin gasification in SCW, and lignin has the highest gasification efficiency at 3500 K and 15 wt%. Additionally, the decomposition pathway of lignin and the generation paths of CO2, H2 were clarified. This work will provide theoretical guidance for further research to improve the SCWG efficiency of lignin.

Photocatalytic Hydrogen Production Activity and Mechanism of New Nickel-Based Sulfur Complexes in Aqueous Solution.

The development of industry and the increase in population have caused energy shortages and environmental pollution problems. Developing clean and storable new energy is identified as a key way to solve the problems above. Hydrogen is viewed as the most potential energy carrier due to its high calorific value and pollution-free. To convert solar energy into hydrogen energy, three nickel-based catalysts, Ni(aps)(pys)2 (aps=2-amino-2-phenylacetic salicylaldehyde) (1), Ni(ads)(pys)2 (ads=aniline salicylaldehyde, pys=pyridine-2-thiolate) (2), Ni(acs)(pys)2 (acs=aniline 5-chlorosalicylaldehyde) (3), were synthesized and explored as photocatalysts for hydrogen production. A three-component photocatalytic system for hydrogen production was constructed using target complex as photocatalyst, triethanolamine (TEOA) as electron sacrificial agent and fluorescein (FL) as photosensitizer. Under the optimum conditions, about 1504 μmol of H2 can be obtained with 25 mg catalyst 2 after 3 hours of irradiation. Finally, the hydrogen-production mechanism was discussed by experimental and theoretical methods.

Construction of a Z-scheme CdIn2S4/ZnS heterojunction for the enhanced photocatalytic hydrogen evolution

In this paper, CdIn2S4/ZnS (CIS/ZnS) nanocomposites were prepared by a one-step hydrothermal method. The structures and physicochemical properties of the nanocomposites were characterized by XRD, SEM, TEM, XPS, UV-Vis, TPR, EIS, PL, and ESR. The photocatalytic activity of CdIn2S4/xZnS composites for water splitting hydrogen evolution (the molar ratio of CdIn2S4 and ZnS is 1: x) is much better than that of the pristine ZnS and CdIn2S4. The optimal catalyst CdIn2S4/12ZnS exhibits the best performance. The hydrogen production rate reaches 3743 μmol·g−1·h−1, which is about 59.1 and 14.4 times that of pure CdIn2S4 and ZnS. The reasons for the better performance of CdIn2S4/xZnS are the strong interaction between CdIn2S4 and ZnS, the formation of Z-scheme heterojunction, the more efficient charge separation, the extension light response in comparison with the single component, and the stronger redox properties. Moreover, the possible hydrogen production mechanism is proposed by the study of VB-XPS, Mott-Schottky, and EPR, which implies it is a Z-scheme photosystem. This work provides an effective method for the modification of ZnS catalysts for the application in photocatalytic hydrogen evolution.