H2 Production Reaction Research Articles

Ru-coated metal monolith catalyst prepared by novel coating method for hydrogen production via natural gas steam reforming

Ru-coated FeCrAlloy monolith catalysts were prepared by a deposition-precipitation (DP) method with different solution pHs and evaluated the catalytic activity in natural gas steam reforming (NGSR) reaction for H2 production. The characteristics of prepared monolith catalysts as to the crystallite size, surface area, pore size distribution, metal dispersion, and morphology of Ru particles were analyzed by XRD, BET, BJH, CO-chemisorption, and SEM, respectively. The solution pH had a major effect on the precipitation formation and the particle size and dispersion of Ru catalyst coated on the monolith surface. At pH 7, nano-sized Ru particles with high BET surface area (112m2/g) and metal dispersion (23.5%) were formed uniformly on the monolith surface. Among the prepared monolith catalysts, the monolith catalyst prepared at pH 7 showed the highest CH4 conversion in NGSR. Despite the less amount of Ru metal coated on the metal monolith, the monolith catalyst showed a good catalytic performance equivalent to the 2wt% Ru/Al2O3 pellet catalyst due to the high availability of the Ru active metal in NGSR. It was also confirmed that the Ru catalyst layer coated on the FeCrAlloy monolith had good adhesion via ultrasonic vibration test.

High-Throughput Screening of Catalytic H2 Production.

Hydrogenases, ferredoxins, and ferredoxin-NADP+ reductases (FNR) are redox proteins that mediate electron metabolism in vivo, and are also potential components for biological H2 production technologies. A high-throughput H2 production assay device (H2 PAD) is presented that enables simultaneous evaluation of 96 individual H2 production reactions to identify components that improve performance. Using a CCD camera and image analysis software, H2 PAD senses the chemo-optical response of Pd/WO3 thin films to the H2 produced. H2 PAD-enabled discovery of hydrogenase and FNR mutants that enhance biological H2 production is reported. From a library of 10 080 randomly mutated Clostridium pasteurianum [FeFe] hydrogenases, we found a mutant with nearly 3-fold higher H2 production specific activity. From a library of 400 semi-randomly mutated Oryza sativa FNR, the top hit enabled a 60 % increase in NADPH-driven H2 production rates. H2 PAD can also facilitate elucidation of fundamental biochemical mechanisms within these systems.

Ni nanosheet-coated monolith catalyst with high performance for hydrogen production via natural gas steam reforming

A Ni nanosheet-coated FeCrAlloy monolith catalyst was successfully prepared using a deposition-precipitation-based “Korea Institute of Energy Research” (KIER) coating method, which provides a uniform coating of highly dispersive Ni catalyst on the metal substrate. The newly developed monolith catalyst showed a higher Ni dispersion and surface area on the substrate as compared to a washcoated monolith catalyst. The Ni nanosheet-coated monolith catalyst exhibited high activity and long-lasting stability at a high space velocity of GHSV=15,000h−1 during a natural gas steam reforming reaction for H2 production. This is mainly attributed to the fact that the uniform and highly dispersed Ni nanosheet catalyst improves the availability of surface active metal sites on the metal substrate.

Electrochemical promotion of a dispersed Ni catalyst for H2 production via partial oxidation of methanol

This study reports the electrochemical promotion (EPOC) of Ni particles dispersed in a diamond-like carbon (DLC) matrix. A Ni-DLC (Ni/C molar ratio of 0.1) catalyst film was prepared on a K-βAl2O3 (K+-conductor) solid electrolyte by cathodic arc deposition (CAD). This physical vapour deposition (PVD) technique allows to decrease the metal loading used in the solid electrolyte cell and to electrochemically activate dispersed Ni particles in the methanol partial oxidation (POM) reaction by in-situ controlling the coverage of K+ ions electrochemically transferred to the catalyst surface. As compared with a pure Ni layer prepared by the same technique, the Ni-DLC catalyst film shows a higher specific activity and an improved oxidation resistance under EPOC working reaction conditions. The possibility of electrochemically activate (with a negligible energy consumption) dispersed particles of a non-noble metal catalyst (closely related to commercially catalyst formulations) is of great interest for a further commercialization step of the EPOC phenomena in H2 production reactions and in other catalytic systems.

Trilayer CdS/carbon nanofiber (CNF) mat/Pt-TiO2 composite structures for solar hydrogen production: Effects of CNF mat thickness

Solar H2 production by photocatalytic water splitting is a promising technology that permits direct H2 production from the clean and abundant resources of water and solar light. We successfully fabricated trilayer heterostructures of CdS/carbon nanofiber (CNF) mat/Pt-deposited TiO2 (Pt-TiO2) for solar H2 production. The CNF mat was prepared by electrospinning and carbonization. CdS and Pt-TiO2 were coated on the front and back of the CNF mat by doctor blading. Under visible-light irradiation on the CdS side, the addition of the Pt-TiO2 coating improved the H2 production by a factor of 3.4. This suggests that the H2 production reaction could occur on Pt-TiO2, which is not active under visible irradiation; therefore, the CNF mat could act as an efficient photogenerated electron-transfer mediator from CdS to Pt-TiO2. The H2 production rates of the trilayer CdS/CNF/Pt-TiO2 heterostructures were strongly affected by the thickness of the CNF mat and the carbonization temperatures used in production, which affect the resistance of the CNF mat between the CdS and Pt-TiO2 sides. The results clearly demonstrated that the CNF acted as an efficient electron-transfer mediator as well as a support material.

Development of a stand-alone steam methane reformer for on-site hydrogen production

A small, stationary reformer designed as a stand-alone and self-sustaining type was developed for on-site hydrogen (H2) production. We created a compact reformer to produce H2 at a rate of 1 Nm3/h using the previously reported reaction kinetics of steam methane reforming (SMR). Both catalysts for the compact reformer - i.e., 15 wt% and 20 wt% Ni/γ-Al2O3 - showed good activity, with CH4 conversion exceeding 90% at 655 °C and a contact time of 3.0 gcath/mol, which were considered critical thresholds in the development of a small, compact stationary reformer. At an H2 production rate of 1 Nm3/h, the catalyst amount was calculated to be 167.8 g and the reformer length required to charge the catalyst was 613 mm, with a diameter of 1 inch. The CH4 conversion and H2 production rates achieved with the compact reformer using the 20 wt% Ni/γ-Al2O3 catalyst at 738 °C were 97.9% and 1.22 Nm3/h, respectively. Furthermore, a heat-exchanger type reformer was developed to efficiently carry out the highly endothermic SMR reaction for on-site H2 production. This reformer comprised a tube side (in which the catalysts were charged and the SMR reaction took place by feeding the reactants) and a shell side (in which the heat for the endothermic reaction was supplied by CH4 combustion). Reforming activities were evaluated using the active 20 wt% Ni/γ-Al2O3 catalyst, depending on the reactants' gas hourly space velocity (GHSV). The H2 production rate increased as the GHSV increased. Finally, the reformer produced a CH4 conversion of 98.0% and an H2 production rate of 1.97 Nm3/h at 745 °C, as well as a high reactants' GHSV of 10,000 h−1. Therefore, the heat-exchanger type reformer proved to be an effective system for conducting the highly endothermic SMR reaction with a high reactants' GHSV to yield a high rate of H2 production.

Nonplasmonic Hot‐Electron Photocurrents from Mn‐Doped Quantum Dots in Photoelectrochemical Cells

We report the measurement of the hot-electron current in a photoelectrochemical cell constructed from a glass/ITO/Al2 O3 (ITO=indium tin oxide) electrode coated with Mn-doped quantum dots, where hot electrons with a large excess kinetic energy were produced through upconversion of the excitons into hot electron hole pairs under photoexcitation at 3 eV. In our recent study (J. Am. Chem. Soc. 2015, 137, 5549), we demonstrated the generation of hot electrons in Mn-doped II-VI semiconductor quantum dots and their usefulness in photocatalytic H2 production reaction, taking advantage of the more efficient charge transfer of hot electrons compared with band-edge electrons. Here, we show that hot electrons produced in Mn-doped CdS/ZnS quantum dots possess sufficient kinetic energy to overcome the energy barrier from a 5.4-7.5 nm thick Al2 O3 layer producing a hot-electron current in photoelectrochemical cell. This work demonstrates the possibility of harvesting hot electrons not only at the interface of the doped quantum dot surface, but also far away from it, thus taking advantage of the capability of hot electrons for long-range electron transfer across a thick energy barrier.

Incorporating nitrogen-doped graphene oxide dots with graphene oxide sheets for stable and effective hydrogen production through photocatalytic water decomposition

This study proposes incorporating nitrogen-doped graphene oxide dots (NGODs) with graphene oxide (GO) sheets to form a stable and effective NGOD:GO composite for photocatalytic H2 production through water splitting under visible light illumination. Although Pt-deposited NGOD catalysts were active in the photocatalytic H2 production reaction, they were only moderately stable. Introducing GO sheets in light-absorbing NGODs effectively mediated the transfer of photogenerated electrons from the NGODs to the GO sheets. This vectorial electron transfer, confirmed by a photoluminescence spectroscopy analysis, led to the relocation of the reaction sites from the NGODs to the GO sheets, protecting the NGODs from attack by reaction intermediates. Moreover, the GO sheets acted as an electron sink, facilitating charge separation in the NGODs. When 3wt% Pt was deposited on the developed NGOD:GO catalyst, the catalyst steadily catalyzed H2 production from a 10vol% aqueous solution of triethanolamine under visible light illumination for 96h, unlike a NGOD catalyst that exhibited an activity decay of 50% within 96h. The apparent quantum yield of H2 under 420-nm light irradiation was 16.0%, demonstrating the high activity of the NGOD:GO catalyst.

A study to develop nano-spray freeze dried Co/Ce–La catalyst for the production of hydrogen from bio-renewable feedstock

Ultra-fine Ce–Co and Cox/Ce–La (x = 4 and 10%) solid solutions (SS) were prepared for the first time by spray freezing technology, and evaluated in bio-ethanol steam reforming reaction for H2 production. The catalysts were characterized by DLS, XRD, BET and TEM, in order to reveal the structure activity relationship. It was shown that, the addition of La3+ cation to Ce–Co catalyst lead to 100% ethanol conversion at lower reaction temperature (300 °C). Hydrogen selectivity was higher on Ce–Co catalyst than on Cox/Ce–La and increase by increase Co content. Moreover, Cox/Ce–La catalysts provided highest deactivation resistant during 15 h. Characterization of spent catalysts revealed that, the addition of La as a promoter to Ce–Co catalyst preventing sintering at high temperatures. TGA analysis indicates the formation of very small amounts of amorphous carbon on Co10/Ce–La catalyst, while CNT was formed on Ce–Co which responsible for deactivation processes. Both oxygen vacancy and La2O2CO3 acted as carbon scavengers during ESR reaction over Cox/Ce–La.

Photocatalytic H<sub>2</sub> Production Using Semiconductor Nanomaterials via Water Splitting – An Overview

Heterogeneous semiconductor based photocatalytic hydrogen (H2) production by water splitting is one of the widely recognized promising sustainable technologies to deliver clean energy for future energy demands. The present review article mainly focus on the overview of principle of water splitting, different semiconductor nanomaterials used for photocatalytic water splitting in the presence of UV and solar light irradiation, role of sacrificial reagents, simultaneous degradation of pollutants and H2 production reaction, strategy for development of efficient photocatalyst for H2 production. Further the flaws associated with present photocatalytic system like recombination rate of electron–hole pairs, low visible-light response, use of hazardous irradiation sources and surface area of photocatalyst etc. has also been discussed. Recently the use of energy efficient light emitting diodes (LEDs) as an irradiation source for H2 production is highly attracted due to its unique characteristics. Recent literature on LED source based photocatalytic system for H2 production has also been summarized and highlighted. At last, the future prospects and challenges towards the designing of better photocatalytic system for H2 production have also been discussed. From the literature survey, it is concluded that construction of efficient photocatalytic system for simultaneous degradation of pollutants and H2 production under energy efficient irradiation source offer clean and simple system for solving the futuristic environmental concerns and energy crisis.

Influence of the support structure and composition of Ni–Cu-based catalysts on hydrogen production by methanol steam reforming

Cu and Ni were supported on ZrO2 by sequential impregnation method, and tested in the steam reforming of methanol (SRM) reaction for H2 production as a function of temperature. Four bimetallic catalysts were investigated, differing in ratio of nickel and copper (Cu: Ni = 1: 4 or 4: 1) and annealing temperature. The synthesized catalysts were characterized by N2 physisorption, DSC/TGA, X-ray diffraction, SEM, TEM. It was shown, that support structure has the main influence on composites activity, while the nature of a dominant metal affected on the selectivity of the resulting catalysts. The activity of catalysts decreases with increasing of materials crystallinity degree. The most active were samples coated with amorphous shell. The selectivity of copper catalysts is higher than nickel-based. Among the tested catalysts, the most active and selective catalyst was the sample Ni0.2-Cu0.8/amorphous ZrO2.

Toward Understanding Metal-Catalyzed Ethanol Reforming

Steam reforming of ethanol (SRE) is a strategic reaction for H2 production. However, despite considerable work, several aspects of the mechanism and catalytic system for this reaction are not fully understood. There have been many efforts to improve the understanding of the catalysts’ behavior during SRE, using both theoretical studies and experimental investigations based on operando characterization techniques. Even though cobalt and nickel are considered the most promising catalytically active metals for industrial SRE, acquiring further knowledge on the reaction mechanism, metal–support interactions, and catalyst deactivation (due to carbon accumulation, sintering, or metal oxidation) will enable the successful design of new and stable catalysts. In this review, we analyze the reaction pathways for metal-catalyzed SRE and discuss the available experimental and theoretical data to suggest alternatives to address three major issues: (i) the impact of particle size and metal oxidation state in the SRE pe...

Hot Electrons Generated from Doped Quantum Dots via Upconversion of Excitons to Hot Charge Carriers for Enhanced Photocatalysis.

We show that hot electrons exhibiting the enhanced photocatalytic activity in H2 production reaction can be efficiently generated in Mn-doped quantum dots via the "upconversion" of the energy of two excitons into the hot charge carriers. The sequential two-photon-induced process with the long-lived Mn excited state serving as the intermediate state is considered as the pathway generating hot electrons. H2 production rate from doped quantum dots is significantly higher than that from undoped quantum dots and also exhibited the quadratic increase with the light intensity, demonstrating the effectiveness of the hot electrons produced in doped quantum dots in photocatalytic reaction. Due to the very long lifetime of Mn excited state (∼6 ms) in the doped quantum dots, the sequential two-photon excitation requires relatively low excitation rates readily achievable with a moderately concentrated solar radiation, demonstrating their potential as an efficient source of hot electrons operating at low excitation intensities.

Preparation of efficient cadmium sulfide nanofibers for hydrogen production using ethylenediamine (NH2CH2CH2NH2) as template

The preparation of CdS was performed by the precipitation method using ethylenediamine as template and tetrahydrofuran, acetonitrile or butanol as organic solvents. The formation of CdS with hexagonal structure was observed by XRD due to the template effect. FTIR studies showed that the amount of the template linked to the surface of the CdS depends on the organic solvent used. TEM observations evidenced the formations of CdS nanofibers and the EDS analysis show the chemical composition of the surface. The photocatalytic activity of CdS nanofibers under blue light irradiation was strongly influenced by the amount of ethylenediamine template on the nanofiber surface. It was observed that when the amount of the template on the samples diminishes by the heat treatment, the photocatalytic activity is affected. The role of the ethylenediamine template in the mechanism for the H2 production reaction is discussed.

Highly Efficient Photocatalytic Hydrogen Production over PdS@CdS+ZnS(en)0.5 Photocatalyst under Visible Light Irradiation

A new photocatalyst, CdS+ZnS(en)0.5 (Cd/Zn = 6:4), was prepared by a simple mechanical mixing method and characterized by various techniques including X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of CdS+ZnS(en)0.5 was evaluated for hydrogen production from an aqueous solution under visible light. PdS-loaded CdS+ZnS(en)0.5 exhibited an efficient H2 production rate of 2600 μmol h–1 g–1, which was higher than that observed with PdS-loaded CdS and Cd0.6Zn0.4S solid solution catalysts. The apparent quantum yield at 405 nm was 23%. Furthermore, PdS@CdS+ZnS(en)0.5 showed good stability for prolonged H2 production reactions. It was proposed that enhancement of hole and electron transfer by PdS and ZnS(en)0.5 contributed to the high activity of this photocatalyst for H2 production.

Fabrication of Carbon-Platinum Interdigitated Array Electrodes and Their Application for Investigating Homogeneous Hydrogen Evolution Catalysis

Interdigitated array electrodes (IDAEs) with one carbon electrode and the other platinum electrode were constructed by electrodepositing platinum on one set of the carbon electrodes. Platinum deposition was confirmed by scanning electron microscope (SEM) and cyclic voltammetry. The width of the carbon and platinum digits is less than 2 μm and the gap between two adjacent digits is around 3 μm. The carbon-platinum IDAEs benefit from the characteristics of both carbon and platinum in that carbon can provide a wide nonreactive potential window while platinum is a good catalyst for hydrogen reactions making it useful to characterize the catalytic hydrogen production cycle of the molecular electrocatalyst [Ni(PPh2NPh2)2(CH3CN)](BF4)2 (where PPh2NPh2 is 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane). With properly set potentials, the molecular electrocatalyst was reduced at the carbon digits to initiate a homogeneous H2 production reaction while the platinum digits detect the H2 by oxidation, providing direct evidence of its production rate from the catalytic cycles.

Active Site Considerations on the Photocatalytic H2 Evolution Performance of Cu-Doped TiO2 Obtained by Different Doping Methods

A photocatalytic H2 evolution reaction was performed over copper doped TiO2. The influence of sulfate pretreatment over fresh TiO2 support and the Cu doping method has been evaluated. Wide structural and surface characterization of catalysts was carried out in order to establish a correlation between the effect of sulfuric acid treatment and the further Cu-TiO2 photocatalytic properties. Notably a different copper dispersion and oxidation state is obtained by different metal decoration methods. From the structural and surface analysis of the catalysts we have stated that the occurrence of highly disperse and reducible Cu2+ species is directly related to the photocatalytic activity for the H2 production reaction. Highly active materials have been obtained from a chemical reduction method leading to 18 mmol·h–1·g–1 for 3 mol % copper loading.

An Integrated Photoelectrochemical–Chemical Loop for Solar‐Driven Overall Splitting of Hydrogen Sulfide

AbstractAbundant and toxic hydrogen sulfide (H2S) from industry and nature has been traditionally considered a liability. However, it represents a potential resource if valuable H2 and elemental sulfur can be simultaneously extracted through a H2S splitting reaction. Herein a photochemical‐chemical loop linked by redox couples such as Fe2+/Fe3+ and I−/I3− for photoelectrochemical H2 production and H2S chemical absorption redox reactions are reported. Using functionalized Si as photoelectrodes, H2S was successfully split into elemental sulfur and H2 with high stability and selectivity under simulated solar light. This new conceptual design will not only provide a possible route for using solar energy to convert H2S into valuable resources, but also sheds light on some challenging photochemical reactions such as CH4 activation and CO2 reduction.

Generation of syngas through autothermal partial oxidation of glycerol over LaMnO3- and LaNiO3-coated monoliths

This study presents a side-by-side comparison of LaMnO3 and LaNiO3 perovskites in the autothermal partial oxidation of glycerol to syngas. Pure glycerol and glycerol/water solutions were converted to syngas under adiabatic conditions. The addition of water suppressed glycerol conversion and reaction temperature, but increased H2 selectivity with the appropriate steam-to-glycerol feed ratio. Catalytic results show that LaMnO3 is more active than LaNiO3 in autothermal partial oxidation because of its combustion-prone nature. In contrast, LaNiO3 produced higher H2 selectivity than LaMnO3 did. A comparative study of LaMnO3 and LaNiO3 in glycerol steam reforming and water-gas shift was performed as well to reveal how these H2-production reactions proceed in the oxygen-deficient regime of a catalyst bed. The outcomes indicate that LaNiO3 is more active than LaMnO3 in these two reactions, thereby enhancing H2 selectivity in a partial oxidation system. Moreover, a 24-h lifetime test of these two perovskites was conducted, showing that LaMnO3 has greater durability.

Enhanced H2 Generation of Au‐Loaded, Nitrogen‐Doped TiO2 Hierarchical Nanostructures under Visible Light

Hierarchical N‐doped TiO2 nanostructured catalysts with micro‐, meso‐, and macroporosity are synthesized by a facile self‐formation route using ammonia and titanium isopropoxide precursor. UV–vis diffuse reflectance spectra confirm the red shift and band gap narrowing due to the doping of N species in the TiO2 nanoporous catalyst. Hierarchical macroporosity with fibrous channel patterning is observed and well preserved even after calcination at 800 °C, indicating thermal stability, whereas micro‐ and mesoporosity are lost after calcination at 500 °C. The photocatalytic activity of hiearchical N doped TiO2 catalysts loaded with Au is evaluated for H2 production reaction in visible light. The enhanced photocatalytic activity is attributed to the combined synergetic effect of N doping for visible light absorption, micro‐ and mesoporosity for an increase of effective surface area and light harvestation, and hierarchical macroporous fibrous structure for multiple reflection and effective charge transfer.