Free Hydrogen Production Research Articles

Recent Advances in the Use of Black TiO2 for Production of Hydrogen and Other Solar Fuels.

Black TiO2 has emerged as one of the most promising photocatalysts recently discovered. The reason behind its catalytic activity is considered to be due to the presence of defects and Ti3+ species at the surface of black TiO2 nanostructures, which are crucial for its diverse applications. Moreover, disordered/crystalline surface layers and bulk regions have been identified and appear to influence the intrinsic properties of the material. Here, we present the latest studies on the use of black TiO2 for metal free hydrogen production, as well as for CO2 photoreduction and N2 photofixation. After highlighting the structure/property relations, we conclude with some critical questions and suggest further topics of research in order to better understand the underlying mechanisms of light absorption in black TiO2 , especially towards solar fuels production.

COx free hydrogen production through water-gas shift reaction in different hybrid multifunctional reactors

High-purity H2 production from the water-gas shift (WGS) reaction was assessed. Since the WGS is limited by the equilibrium, different reactor types that allow to extract one or more products from the reaction medium, namely membrane reactor (MR; for H2 separation), sorption-enhanced reactor (SER; for CO2 capture) and sorption-enhanced membrane reactor (SEMR; for simultaneous CO2 and H2 removal), were used and compared with fixed-bed traditional reactor (TR). Experimental results were obtained with commercial materials, namely WGS Cu-based catalyst and K-doped hydrotalcite for CO2 capture. Additionally, in the MR and SEMR, a self-supported Pd-Ag membrane for separating H2 selectively from the reaction zone was used.Experimental tests were performed at different temperatures and pressures, and the results obtained were compared with those predicted by theoretical simulations at the thermodynamic equilibrium. Moreover, in the case of SER, different methods for the hydrotalcite regeneration and the evaluation of its working sorption capacity under cycling conditions were also assessed. Not all sorbed CO2 can be desorbed under dry conditions (pure nitrogen purging stream); however, if steam is used during the regeneration step, all sites can be effectively regenerated, allowing to have a stable working sorption capacity. Concerning the performance of the different hybrid reactors tested, i.e. MR, SER and SEMR, it was found that all are able of overcoming the TR limitations, with performances reaching conversion above the equilibrium for the feed composition. Nonetheless, only the SER and SEMR configurations allow to obtain high-purity H2 in all reactor exiting streams under the operating conditions herein assessed.

Comparison study between Ni/TiO2 and Ni/flame synthesized TiO2 catalysts for hydrogen production using thermocatalytic decomposition of methane

Abstract: Hydrogen is considered as a fuel of future due to its environmental cleanness. Thermo Catalytic Decomposition of Methane (TCD) is one of the most advanced process, which will meet the future demand and attractive route for COx free production of hydrogen. In this study, an attempt made using flame synthesized titanium nanorods as a catalyst support for nickel based catalyst to produce hydrogen. The comparison study between Ni/TiO2 and Ni/Flame synthesized TiO2 (Ni/F-TiO2) catalysts for hydrogen production using thermocatalytic decomposition of methane. The effect of nickel weight percentage (10%, 20%, 30% and 40 wt %) and reaction temperature (650, 700, 750 and 800 °C) with Ni/TiO2 and Ni/F-TiO2 catalysts were performed for hydrogen production studies at 54sccm flowrate of methane. The maximum hydrogen production was observed with 30 wt% of Ni/TiO2 and 30 wt% of Ni/F-TiO2 as 48 and 55 vol% at 700 °C in 60min of reaction time. Before and after the reaction, catalysts were characterized by XRD, BET surface area, SEM, TEM and AAS analysis. Apart from hydrogen production, carbon nanorods were observed with a diameter and length of 5–10 nm and 0.25 μm respectively for Ni/TiO2 and for Ni/F-TiO2 catalyst, it was found to be 50–100 nm and 0.5 μm respectively.

Size structure-catalytic performance correlation of supported Ni/MCF-17 catalysts for COx-free hydrogen production.

Herein, supported Ni/MCF-17 catalysts with the size of nickel nanocrystal in the range of 1.5-8.0 nm were synthesized and employed for COx-free hydrogen production for fuel cells via the ammonia decomposition reaction. Characterized by a variety of techniques, the results show that nickel particles are in a highly dispersed state with a uniform particle size for each catalyst. Furthermore, the influence of particle size on the catalytic performance has been investigated. It was later revealed that Ni nanoparticles with different particle sizes exhibited significant differences in catalyzing the COx-free hydrogen production reaction. Moreover, the catalyst with the Ni nanoparticle size around 3.0 nm exhibited highest catalytic activity at each reaction temperature; this could be explained by the presence of high B5 active sites on the Ni-based catalyst surface.

Electrochemical Stimuli-Driven Facile Metal-Free Hydrogen Evolution from Pyrene-Porphyrin-Based Crystalline Covalent Organic Framework.

A [2 + 2] Schiff base type condensation between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAP) and 1,3,6,8-tetrakis (4-formylphenyl) pyrene (TFFPy) under solvothermal condition yields a crystalline, quasi-two-dimensional covalent organic framework (SB-PORPy-COF). The porphyrin and pyrene units are alternatively occupied in the vertex of 3D triclinic crystal having permanent microporosity with moderately high surface area (∼869 m2 g-1) and promising chemical stability. The AA stacking of the monolayers give a pyrene bridged conducting channel. SB-PORPy-COF has been exploited for metal free hydrogen production to understand the electrochemical behavior using the imine based docking site in acidic media. SB-PORPy-COF has shown the onset potential of 50 mV and the Tafel slope of 116 mV dec-1. We expect that the addendum of the imine based COF would not only enrich the structural variety but also help to understand the electrochemical behavior of these class of materials.

Neutron radiography for visualization of liquid metal processes: bubbly flow for CO2 free production of Hydrogen and solidification processes in EM field

The paper describes the results of two experimental investigations aimed to extend the abilities of a neutron radiography to visualize two-phase processes in the electromagnetically (EM) driven melt flow. In the first experiment the Argon bubbly flow in the molten Gallium – a simulation of the CO2 free production of Hydrogen process – was investigated and visualized. Abilities of EM stirring for control on the bubbles residence time in the melt were tested. The second experiment was directed to visualization of a solidification front formation under the influence of EM field. On the basis of the neutron shadow pictures the form of growing ingot, influenced by turbulent flows, was considered. In the both cases rotating permanent magnets were agitating the melt flow. The experimental results have shown that the neutron radiography can be successfully employed for obtaining the visual information about the described processes.

Carbon dioxide free production of hydrogen

The present report summarizes the theoretical modelling and experimental investigation results of the study on the direct thermal methane cracking. This work is a part of the LIMTECH-Project (Liquid Metal Technologies) funded of Helmholtz Alliance and was carried out from 2012 to 2017. The Project-part B5 “CO2-free production of hydrogen” focused on experimental testing and particularly on modelling the novel methane cracking method based on liquid metal technology. The new method uses a bubble column reactor, filled with liquid metal, where both the chemical reaction of methane decomposition and the separation of gas fraction from solid carbon occur. Such reactor system was designed and built in the liquid metal laboratory (KALLA) at KIT. The influences of liquid metal temperature distribution in reactor and feed gas flow rate on methane conversion ratio were investigated experimentally at the temperature range from 930°C to 1175 °C and methane flow rate at the reactor inlet from 50 to 200 mLn/min. In parallel with experimental investigations, a thermochemical model, giving insight in the influence of the above mentioned parameters has been developed at KIT and a CFD model was developed at LUH to get an overview about the bubble dynamics in the reaction system. The influence of different bubble sizes and shapes, multi-inlet coalescence effects as well as the potential of electromagnetic stirring have been investigated.

Rapid Production of High-Purity Hydrogen Fuel through Microwave-Promoted Deep Catalytic Dehydrogenation of Liquid Alkanes with Abundant Metals.

Hydrogen as an energy carrier promises a sustainable energy revolution. However, one of the greatest challenges for any future hydrogen economy is the necessity for large scale hydrogen production not involving concurrent CO2 production. The high intrinsic hydrogen content of liquid-range alkane hydrocarbons (including diesel) offers a potential route to CO2 -free hydrogen production through their catalytic deep dehydrogenation. We report here a means of rapidly liberating high-purity hydrogen by microwave-promoted catalytic dehydrogenation of liquid alkanes using Fe and Ni particles supported on silicon carbide. A H2 production selectivity from all evolved gases of some 98 %, is achieved with less than a fraction of a percent of adventitious CO and CO2 . The major co-product is solid, elemental carbon.

Production of COx Free Hydrogen and Nanocarbon via Methane Decomposition Over Unsupported Porous Nickel and Iron Catalysts

Methane decomposition is the most effective method to produce greenhouse gas free hydrogen and nanocarbon. In this work, unsupported nickel and iron catalysts were successfully synthesized via a facile solid state citrate fusion method and used for the non-oxidative thermocatalytic decomposition of methane. The formation of phase pure crystalline structure of NiO and Fe2O3 with high surface porosity and improved textural properties was observed by various characterization techniques. The release of huge amount of gases from the bulk of the fused sample during the annealing process could result in the porosity. The catalysts exhibited high catalytic activity and stability for methane decomposition at three different reaction temperatures of 700, 800 and 900 °C without any catalyst deactivation. The yield of hydrogen and nanocarbon increased significantly with increasing the reaction temperature. A maximum hydrogen yield of 67% was obtained for the NiO at 900 °C, with a slight deactivation with time on stream. After 180 min of time on stream, the hydrogen yield was observed to be more or less same (49 ± 2%), at all of the temperatures. The iron catalyst exhibited quite high catalytic stability, where the hydrogen yield remained more or less same. The structural characterization of spent catalysts indicated the formation of metal encapsulated carbon nanoonions and few layered graphene sheets over Ni and Fe catalysts respectively. The crystallinity of the nanocarbon was found to be increasing with increasing the reaction temperature and a high graphitization degree was observed for the nanocarbon deposited at 900 °C, over both of the unsupported catalysts.

Hydrogenated MoS2 QD-TiO2 heterojunction mediated efficient solar hydrogen production.

Herein, we report the development of a hydrogenated MoS2 QD-TiO2 (HMT) heterojunction as an efficient photocatalytic system via a one-pot hydrothermal reaction followed by hydrogenation. This synthetic strategy facilitates the formation of MoS2 QDs with an enhanced band gap and a proper heterojunction between them and TiO2, which accelerates charge transfer process. Hydrogenation leads to oxygen vacancies in TiO2, enhancing the visible light absorption capacity through narrowing its band gap, and sulfur vacancies in MoS2, which enhance the active sites for hydrogen adsorption. Due to the band gap reduction of hydrogenated TiO2 and the band gap enhancement of the MoS2 QDs, the energy states are rearranged to create a reverse movement of electrons and holes facilitated the charge transfer process which enhance life-time of photo-generated charges. The photocatalyst showed stable, efficient and exceptionally high noble metal free sunlight-induced hydrogen production with a maximum rate of 3.1 mmol g-1 h-1. The developed synthetic strategy also provides flexibility towards the shape of the MoS2, e.g. QDs/single or few layers, on TiO2 and offers the opportunity to design novel visible light active photocatalysts for different applications.

Nano size Hβ zeolite as an effective support for Ni and Ni[sbnd]Cu for COx free hydrogen production by catalytic decomposition of methane

Mono and bimetallic catalysts of Ni and Cu on Hβ zeolite supports were tested for the COx free hydrogen production by decomposition of methane. The effect of Cu addition and the support particle size were investigated. XRD analysis of the reduced samples demonstrated that for catalysts based on nano-sized Hβ zeolite particles (nano-Hβ), the Ni and Cu were only present in the form of a NiCu alloy, whereas when commercial Hβ zeolite (Hβ) was used; segregated Cu0 and Ni0 species were also observed. Addition of Cu was found to dramatically improve the H2 yield by the formation of surface NiCu alloys. The particle size of the Hβ zeolite has a pronounced effect on the Ni and NiCu dispersion, and consequently on the methane decomposition activity. The surface area of NiCu on the nano-Hβsurface was estimated by a combination of H2 pulse chemisorption and N2O titration methods. The Cu species in close proximity to Ni sites inhibited carbon deposition at the Ni sites, resulting in higher rates of H2 formation. Consistent with this finding, NiCu/nano-Hβ was the most active of the catalysts tested. The physicochemical characteristics of the commercial and nano-Hβ supported Ni and/or NiCu catalysts are rationalized by TEM, H2-TPR, XPS and Raman spectroscopy in conjunction with H2 production rates.

Non-oxidative thermocatalytic decomposition of methane into COx free hydrogen and nanocarbon over unsupported porous NiO and Fe2O3 catalysts

The non-oxidative thermal decomposition of methane is one of the most promising routes for the direct production of COx free hydrogen and nanocarbon. In this work, unsupported porous NiO and Fe2O3 catalysts were successfully synthesized by a facile precipitation method using ammonium carbonate as the precipitant and were used for the thermocatalytic decomposition of undiluted methane. The prepared catalysts were characterized for their crystalline, structural and textural properties. The pseudo spherical metal oxide nanoparticles with the size of 10–30 nm were highly inter-aggregated to provide a porous texture to the catalysts. A well packed particle arrangement was observed for the unsupported Fe2O3 catalyst whereas a loose aggregation was observed for the NiO clusters. The catalysts were found to be highly active and stable for the decomposition of methane at various reaction temperatures of 600 °C, 700 °C and 800 °C. A maximum hydrogen yield of 66% and 53% was observed for the NiO and Fe2O3 catalysts respectively for an undiluted methane feed of 150 ml/min at 800 °C. At the end of 360 min of time on stream, the hydrogen yield was measured to be 49% and 46% respectively without deactivation. Moreover, a high catalytic stability was observed for the iron catalyst due to its high carbon diffusion coefficient compared to the nickel catalyst. Bulk deposition of metal encapsulated carbon nanochunks and multilayer graphene sheets were observed over the Ni and Fe catalysts respectively. The structural, crystalline and morphological characterization of the metal dependent nanocarbon were performed by using X-ray diffraction, scanning and transmission electron microscopy, temperature programmed oxidation and Raman analysis. High oxidation stability, crystallinity and graphitization degree was observed for the metal encapsulated carbon nanochunks than the multilayer graphene sheets.

Ultra-small yellow defective TiO2 nanoparticles for co-catalyst free photocatalytic hydrogen production

Blue TiO2 (Ti3+defected TiO2) nanoparticles have been intensively investigated for photocatalytic H2 production. However, the Ti3+, with energy level ~1.0eV below the conduction band, cannot initiate visible light driven H2 production. Thus, Pt or NiOx is often used as a co-catalyst, which is economically unattractive and environmentally contaminative. In this paper, the ultra-small yellow TiO2 nanoparticles (~3nm) have been firstly synthesized without introducing any external dopants. The titanium vacancies (acceptor) and titanium interstitials (donor) that incorporated in the yellow TiO2 are evidenced by various characterization techniques, and their formation mechanism is proposed. Photocatalytic evaluations indicate that the acceptor–donor defects play key roles in the catalytic process, not only initiating, but also promoting the visible light driven H2 production. The improved activity is also evidenced by that the simulated solar light driven H2 production for the yellow TiO2 is ~3.7 fold comparing to that of the normal TiO2. A reasonable explanation is that the acceptor-donor defect associates form internal polarization for spontaneously separating photo-generated charge-carriers. The improved charge-carrier separation has been confirmed by photoluminescence spectra and photoluminescence emission decay profiles. Instead of the traditional TiO2 based photocatalysts, the acceptor–donor defect engineered photocatalyst system offers a new approach for simultaneously initiating and promoting visible light driven co-catalyst free H2 production.

Hydrogen from ammonia over cobalt incorporated silicate structured catalysts prepared using different cobalt salts

Ammonia has become an attractive source for COx free hydrogen production in order to get high activity from fuel cell applications. In the present study, cobalt incorporated silicate structured catalysts were prepared by one-pot hydrothermal synthesis procedure using cobalt acetate and cobalt acetyl acetonate, at different metal loadings and their structures and activities on ammonia decomposition reaction were compared with that of the prepared by using cobalt nitrate. While mesoporous frameworks in different sizes were observed in the structure of all the catalysts, ones prepared with cobalt acetyl acetonate had higher surface area than the others, at the same metal loading. Co3O4 crystal was the main form of cobalt species in the structure of all the catalysts after their calcination at 550 °C. All the synthesized catalysts showed activity in ammonia decomposition reaction at temperatures higher than 500 °C. Catalysts prepared by using cobalt acetate gave better activity than the catalysts prepared by using cobalt acetyl acetonate and cobalt nitrate, such as the former gave 71% ammonia conversion while the latter ones gave 31% and 52% conversion values, respectively, at a reaction temperature of 600 °C under the flow of pure ammonia with a rate of 250 ml/min.

Mesoporous silicon carbide nanofibers with in situ embedded carbon for co-catalyst free photocatalytic hydrogen production

Silicon carbide (SiC) has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombination of charge carriers. Herein, we report mesoporous SiC nanofibers with in situ embedded graphitic carbon (SiC NFs-Cx) synthesized via a one-step carbothermal reduction between electrospun carbon nanofibers and Si powders. In the absence of a noble metal co-catalyst, the hydrogen evolution efficiency of SiC NFs-Cx is significantly improved under both simulated solar light (180.2 μmol·g–1·h–1) and visible light irradiation (31.0 μmol·g–1·h–1) in high-pH solution. The efficient simultaneous separation of charge carriers plays a critical role in the high photocatalytic activity. The embedded carbon can swiftly transfer the photogenerated electrons and improve light absorption, whereas the additional hydroxyl anions (OH–) in highpH solution can accelerate the trapping of holes. Our results demonstrate that the production of SiC NFs-Cx, which contains exclusively earth-abundant elements, scaled up, and is environmentally friendly, has great potential for practical applications. This work may provide a new pathway for designing stable, lowcost, high efficiency, and co-catalyst-free photocatalysts.

COx-free hydrogen production via ammonia decomposition over molybdenum nitride-based catalysts

Co, Ni, and Fe-added Mo nitrides for ammonia decomposition facilitated the recombinative desorption of N atoms from the active components.

CO x -free hydrogen and carbon nanofibers production by methane decomposition over nickel-alumina catalysts

Nickel catalysts supported on mesoporous nanocrystalline gamma alumina with various nickel loadings were prepared and employed for thermocatalytic decomposition of methane into CO x -free hydrogen and carbon nanofibers. The prepared catalysts with different nickel contents exhibited mesoporous structure with high surface area in the range of 121.3 to 66.2m2g−1. Increasing in nickel content decreased the pore volume and increased the crystallite size. The catalytic results revealed that the nickel content and operating temperature both play important roles on the catalytic performance of the prepared catalysts. The results showed that increasing in reaction temperature increased the initial conversion of catalysts and significantly decreased the catalyst lifetime. Scanning electron microscopy (SEM) analysis of the spent catalysts evaluated at different temperatures revealed the formation of intertwined carbon filaments. The results showed that increasing in reaction temperature decreased the diameters of nanofibers and increased the formation of encapsulating carbon.

Methane decomposition over Pd promoted Ni/MgAl2O4 catalysts for the production of COx free hydrogen and multiwalled carbon nanotubes

This article reports the synthesis, characterization and catalytic performance of Pd promoted Ni/MgAl2O4 spinel catalysts for the thermal decomposition of methane into hydrogen and carbon nanotubes. The as-synthesized catalysts were characterized for their structural, textural, morphological properties. The catalytic properties of the Ni/MgAl2O4 catalyst were found to be enhanced with Pd promoter. It effectively increased the surface area of the catalyst without affecting the pore parameters and improved the fine dispersion of NiO particles on the surface of the magnesium aluminate. The reduction temperature of Ni/MgAl2O4 was found to be lowered after Pd deposition. Moreover, the Pd promoted catalyst provided high catalytic activity and stability for methane decomposition. A maximum hydrogen yield of ∼57% was obtained over the Pd catalyst at a reaction temperature of 700°C without any deactivation for 420min of time on stream. Moreover highly uniform, interwoven and thin multi-walled carbon nanotubes with high graphitization degree were deposited over the catalysts.

Progressive Loading Effect of Co over SiO2/Al2O3 Catalyst for Cox Free Hydrogen and Carbon Nanotubes Production via Catalytic Decomposition of Methane

Progressive Loading Effect of Co over SiO2/Al2O3 Catalyst for Cox Free Hydrogen and Carbon Nanotubes Production via Catalytic Decomposition of Methane

Catalytic Production of COx Free Hydrogen by Methane Decomposition over Activated Carbons

Methane decomposition over activated carbons was carried out in a fixed bed, quartz flow reactor to produce COx free hydrogen. Five types of activated carbons were used; they were derived from hardwood, rubber black, coconut shell, coal, and graphite. The effect of operating conditions like temperature (in the range of 800–900°C), gas hourly space velocity (in the range of 6–20 l/h), and impurities content were studied on decomposition. The physicochemical properties like surface area, metal, and carbon content generated from the methane decomposition for the fresh and used catalysts are tested in this work and relates to the carbon activity for production of hydrogen. A reaction order of 1 is obtained for methane decomposition over the most active one and activation energies in the range from 128 to 205 kJ mol/1. The activated carbon derived from hardwood shows a high value of sustainability factor (R0) at all of the implied temperatures.