H2 Production Yield Research Articles

In situ decoration of ZnS nanoparticles with Ti3C2 MXene nanosheets for efficient photocatalytic hydrogen evolution

Seeking highly-efficient and cost-effective photocatalyst remains key to boosting photocatalytic H2 evolution activity. Herein we have designed an innovative, non-heavy-metal-based hybrid photocatalyst via in-situ decoration of ZnS nanoparticles with Ti3C2 MXene nanosheets toward enhanced photocatalytic H2 production. The incorporation of Ti3C2 essentially promotes the charge transfer and extends the lifetime of photo-induced carriers, thereby resulting in an augmented H2 production yield of 502.6 μmol g−1 h−1 under optimal conditions, being almost 4-fold higher than pure ZnS (124.6 μmol g−1 h−1). Thus, this work has demonstrated ZnS/MXene photocatalytic as a promising candidate for hydrogen generation to boost the entire clean energy system and provided a new insight into further broadening the water splitting application of MXene-based materials.

Steam gasification of pyrolysis char from spent mushroom substrate

Steam gasification of char derived from spent mushroom substrate was carried out in thermobalance coupled with mass spectrometer, in the temperature range of 800–900 °C and the steam concentration from 10 to 50 vol%. Syngas production was influenced by temperature and steam concentration. The highest yield of H2 production (42.9 mol H2/kg) was achieved at temperature of 800 °C and steam concentration of 50 vol%. The composition of the generated gas was strongly influenced by the water-gas shift reaction. The grain model was used to describe the kinetics of gasification of the char and the calculated activation energy was equal to 99.0 kJ/mol. The low activation energy of the gasification process was caused by a high content of mineral compounds in the char. The obtained results indicate the potential for gasification of the spent mushroom substrate and found to be an initial and important stage in the development of the gasification process in mushroom production plants.

Simultaneous Increase of H2 and Gasoline Production by Optimizing Thermally Coupled Methanol Steam Reforming with Fischer-Tropsch Synthesis

Abstract The worldwide growing of gaseous pollutions amount has attracted a great deal of attention for development of clean energy resources like hydrogen. Recently, methanol steam reforming (MSR) has been considered as an effective method for hydrogen production compared to other fuels for reforming. Indeed, advantages of methanol such as its good accessibility and properties like its low boiling point and low probability of coke formation as well as high hydrogen to carbon ratio encourage utilizing this substance in reforming process. Therefore, in this work, MSR as an endothermic reaction has been innovatively coupled with Fischer-Tropsch (FT) exothermic synthesis in order to enhance the yield of hydrogen and gasoline production. Presence of membrane in the proposed thermally coupled membrane reactor (TCMR) promotes H2 separation as the desired product. A homogeneous one-dimensional steady- state model was considered in the present work. Differential evolution (DE) optimization technique was used to optimize feed molar flow rates and inlet temperatures in both endothermic and exothermic reaction sides with the aim of maximizing gasoline and H2 yields (in both sides). Results show 42.1 % increase in gasoline yield production and simultaneously high H2 production yield of 68.5 % in exothermic side compared with the industrial FT reactor that is considered as conventional reactor (CR). Moreover, the suggested configuration can be considered as an energy and cost effective strategy as a result of supplying required energy for endothermic section by generated heat in the exothermic side.

Thermophilic biohydrogen recovery from palm oil mill effluent

Enhancement of biological H2 production efficiency with pre-ozonation process of palm oil mill effluent (POME) prior to thermophilic dark fermentation (55 °C) was investigated. H2 fermentation experiments were conducted using varying concentrations of raw and ozonated POME. Results revealed that H2 can be produced from both raw and ozonated POME under thermophilic fermentation. Maximum H2 production yield of 77 mL.g−1CODremoved was obtained from ozonated POME, which was higher than that of 51 mL·g−1 CODremoved obtained from raw POME at the highest concentration of 35,000 mg COD.L−1. Meanwhile, the specific H2 production rate (R'max) of 1.9 and 1.5 mL·h−1·g−1 TVS were observed in raw and ozonated POME at the concentration of 25,000 mg COD.L−1, respectively. The main metabolic products during POME fermentation were acetic and butyric acids and trace amount of valeric acid. Propionic acid and ethanol have contributed, which could be reduced H2 production in all batch experiments for both POME. The highest efficiency of total and soluble COD removal of 24 and 25% was obtained from the raw POME, and those of 19 and 25% was obtained from the ozonated POME. The present study demonstrates that the POME loading was greatly influenced on the H2 production yields and rates. The comparative results showed that the ozonated POME gave higher H2 yields than the raw POME. Thus, demonstrating that the ozonation process significantly improved the POME biodegradability, which is able to enhance H2 production yields. However, the ozone pre-treatment was not improved in the specific H2 production rates.

Ozonation aided mesophilic biohydrogen production from palm oil mill effluent

Ozone pretreatment of palm oil mill effluent (POME) was employed to improve sustrate biodegradability prior to biological H2 production. The H2 production was conducted at varing pHs from 4.0 to 6.0 to examine the impact of pH on the H2 mesophilic production (37 °C). The optimal pH for H2 production was 6.0 for both raw and ozonated POME. The POME concentrations were greatly influenced the yields and rates of H2 production. At the optimal pH, the maximum H2 production yield of 182 ± 7.2 mL.g−1 COD (7.96 mmoL.g−1 COD) was achieved at the ozonated POME concentration of 30,000 mg COD.L−1. The maximum H2 production rate (Rmax) of 43.1 ± 2.5 mL.h−1 was obtained at the ozonated POME concentration of 25,000 mg COD.L−1. The highest total COD removal was 44% at of 15,000 mg COD.L−1 ozonated POME. Acetic and butyric acids were dominant products during H2 fermentation and tended to increase with the increased POME concentrations. Ozonation as a pretreatment process showed significant enhancement of the POME biodegradability , and subsequently improved the H2 production H2.

Impact of glucose concentration on productivity and yield of hydrogen production by the new isolate Clostridium beijerinckii Br21

AbstractThis paper presents a detailed analysis of the batch kinetic fermentative assays data used to evaluate how glucose concentration influences fermentative H2 production, including the non‐dissociated acid concentration threshold, with the new isolate Clostridium beijerinckii Br21. Fermentative batch assays for hydrogen (H2) production were conducted with initial glucose concentrations of 5.2, 27.2, 54.4, 97.2, or 154.4 mmol/L without pH control. The dry cell mass (X), glucose (S), and product (H2) concentrations and the pH were monitored for 60 h. Increasing initial glucose concentration raised the maximum specific H2 production rate to values as high as 1.19 mmol H2/mg X · h. However, the H2 production yield (YH2/S) decreased from 2.23 to 0.2 mmol H2/mmol glucose. The initial glucose concentration that provided the best compromise between YH2/S and H2 productivity was 37 mmol/L (6.7 g/L). The lactic acid, acetic acid, and butyric acid concentrations enhanced at higher initial glucose concentrations, leading to the largest pH decrease. Lower pH favoured non‐dissociated acids, which switched the Clostridium metabolism to solventogenesis. The threshold acid concentrations for C. beijerinckii Br21 solventogenesis were non‐dissociated butyric acid at 8 mmol/L and total non‐dissociated acetic and butyric acids at 13 mmol/L. Glucose supply and pH control in continuous or fed‐batch biorreactors could culminate in higher H2 productivity and yield by C. beijerinckii Br21.

Isolation of bacteria capable of hydrogen production in dark fermentation and intensification of anaerobic granular sludge activity

In the anaerobic biological treatment of pulp and papermaking wastewater, the gradual deposition of CaCO3 eventually leads to the inhibition of the activity of anaerobic granular sludge. In this study, a hydrogen production bacterial Raoultella DW01 was isolated from domesticated anaerobic granular sludge. The fermentation conditions were designed using central composite design, and the optimum conditions obtained by response surface analysis encompassed an initial pH 5.77, 4.13 g/L l-glutamic acid and an inoculation amount of 15%. The H2 production yield represented a 29.5% increase over the unoptimized conditions. Finally, the effect of adding DW01 on the biogas production in anaerobic granular sludge with different sludge ages was investigated. The cumulative biogas yield and the max biogas production rate increased by 27.8% and 53.5% after adding DW01 to a sludge with an age of 335 days compared with the on-intensified sludge. This paper provides a way to alleviate the CaCO3 deposition by intensifying the activity of H2 and acid-producing bacteria via improving the activity of granular sludge.

Fabrication of highly efficient and stable indirect Z-scheme assembly of AgBr/TiO2 via graphene as a solid-state electron mediator for visible light induced enhanced photocatalytic H2 production

In this study, indirect Z-schematic assembly of AgBr and TiO2 via graphene as a solid-state electron mediator was developed and investigated for photocatalytic H2 production. The AgBr/rGO/TiO2 was fabricated using facile two-step synthesis method which includes the growth of AgBr and deposition of TiO2 on graphene oxide sheets followed by partial reduction through reflux method. The photocatalysts were characterized using TEM, XRD, XPS, FTIR, nitrogen (N2) adsorption and desorption, Raman, PL and UV–Vis spectroscopy to understand morphology, structure, chemical and optical properties. Alterations in band structures, elevation of conduction band positions and reduction in band gap energies of rGO-modified AgBr/TiO2 photocatalysts were evaluated. The performance of AgBr/rGO/TiO2 exhibited 2025 ppm of H2 production, which was 7 fold higher than AgBr/TiO2 (289 ppm), 2.3 fold higher than rGO/TiO2 (885 ppm) and 13.4 fold higher than TiO2 (151 ppm). Enhanced photocatalytic activity of Z-schematic composites can be attributed to strong interfacial bonding (AgBr—rGO–TiO2), efficient transfer of electrons due to synergistic effect of AgBr and rGO as well as extended light absorption due to highly light sensitive AgBr. In addition, yield of H2 production was decreased above 5% AgBr loading and dosage of 0.10 g of photocatalyst due to incompatibility of ratio and shielding effect of particles. Moreover, with increase of temperature and concentration of hole scavenger, yield of H2 production was gradually increased which demonstrated the contribution of H2 from photoreforming of hole scavenger. Based on the experimental and characterizations results, a possible mechanism that highlighted the surface redox reactions and charge transfer pattern on AgBr/rGO/TiO2 was developed. Thus, indirect Z-scheme assembly of AgBr/rGO/TiO2 could be a promising photocatalyst for solar energy assisted H2 production.

Beyond the Theoretical Yields of Dark-Fermentative Biohydrogen.

Theoretical hydrogen (H2) yield by dark fermentative route is 12mol/mol of glucose. Biological H2 production yields of 3.8mol/mol of glucose by microbes have been reported. Transient gene inactivation in combination with adaptive laboratory evolution strategy has enabled the H2 yield to exceed the stoichiometric production values.

Assessment of the adequacy of different Mediterranean waste biomass types for fermentative hydrogen production and the particular advantage of carob (Ceratonia siliqua L.) pulp

The conversion of agro-industrial byproducts, residues and microalgae, which are representative or adapted to the Mediterranean climate, to hydrogen (H2) by C. butyricum was compared. Five biomass types were selected: brewery’s spent grain (BSG), corn cobs (CC), carob pulp (CP), Spirogyra sp. (SP) and wheat straw (WS). The biomasses were delignified and/or saccharified, except for CP which was simply submitted to aqueous extraction, to obtain fermentable solutions with 56.2–168.4 g total sugars L−1. In small-scale comparative assays, the H2 production from SP, WS, CC, BSG and CP reached 37.3, 82.6, 126.5, 175.7 and 215.8 mL (g biomass)−1, respectively. The best fermentable substrate (CP) was tested in a pH-controlled batch fermentation. The H2 production rate was 204 mL (L h)−1 and a cumulative value of 3.9 L H2 L−1 was achieved, corresponding to a H2 production yield of 70.0 mL (g biomass)−1 or 1.6 mol (mol of glucose equivalents)−1. The experimental data were used to foresight a potential energy generation of 2.4 GWh per year in Portugal, from the use of CP as substrate for H2 production.

Solar light response with noble metal-free highly active copper(II) phosphate/titanium dioxide nanoparticle/copper(II) oxide nanocomposites for photocatalytic hydrogen production

A novel Cu3(PO4)2/TiO2 nanoparticle (TNP)/CuO nanocomposite with an excellent natural solar-light-driven photocatalytic H2 production performance was synthesized using a sol-gel method. The 1%Cu3(PO4)2/TNP/CuO catalyst displayed a better photocatalytic H2 production yield (59.5 mmolg−1; natural solar light; 151 times higher than that of TNP under the optimal conditions; catalyst dosage of 0.010 g and 5% aqueous glycerol concentration) than TNP, CuO/TNP, Cu3(PO4)2/TNP, and various Cu3(PO4)2 loadings in the Cu3(PO4)2/TNP/CuO catalysts. The improved photocatalytic H2 yields could be attributed to a suppressed recombination of charge carriers, preferable visible absorption ability, crystallinity, strong interactions, and high surface areas of 1%Cu3(PO4)2/TNP/CuO, which were confirmed using X-ray diffraction, temperature programmed reduction, diffuse reflectance spectroscopy, transmission electron microscopy (TEM), high-resolution TEM, Brunauer-Emmett-Teller surface area analysis, elemental mapping, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Raman spectroscopy, photoluminescence, and photocurrent techniques. The 1%Cu3(PO4)2/TNP/CuO catalyst could also contribute to the enhanced photostability and recyclability towards the photocatalytic hydrogen production.

Determining the effect of trace elements on biohydrogen production from fruit and vegetable wastes

Trace elements are one of the important parameters for dark fermentative H2 production because they work as co-factors in H2 formation biochemistry. Lack or excess of trace element and its concentrations could be an important reason for the low yield of H2 production. In this study, the effects of 11 different trace elements (Fe, Ni, Zn, Co, Cu, Mn, Al, B, Se, Mo and W) were tested at two levels in terms of biohydrogen production from Fruit and Vegetable Wastes (FVW) with Biochemical Hydrogen Potential (BHP) Tests using Plackett-Burman statistical design. 1.1–2.8 times enhancement of biohydrogen production was determined with its addition. The most effective trace elements were found as Zn and Ni. In order to reveal the resident microbial flora, Denaturing Gradient Gel Electrophoresis (DGGE) analysis was carried out on all BHP effluent samples. Results of DGGE analysis, four microbial sequences evaluated as Clostridium sp., Clostridium baratii, Uncultured bacterium, Uncultured Streptococcus sp., and their similarity rates were 99%, 100%, 89%, 98%, respectively.

Use of Municipal Solid Waste (MSW)-Derived Hydrogen in Ecuador: Potential Applications for Urban Transportation

This paper performs an assessment of the potential energy-purposed H2 production in Ecuador from municipal solid waste (MSW). Thermochemical and electrochemical paths are considered for MSW conversion. Ecuadorian provincial MSW distribution (2016 data) provides the base information for assessing and constructing maps of the theoretical H2 production yield and its density per unit area. Additionally, the use of H2 in fuel cell-propelled urban public transportation is proposed as an end-use consumer. Results show that it is possible to fulfil urban public transportation energy demand in 91% of the country with MSW-derived H2; in fact, the three provinces that together generate 57% of the available MSW (Guayas, Pichincha, and Azuay) could satisfy their public transportation diesel fuel demand with MSW-derived hydrogen. In the case of these three provinces, H2 generation could replace by 2.57 times (on average) the local urban transportation diesel fuel demand. Finally, a possible scenario for a non-conventional H2 production path is shown, which could also represent a suitable MSW final disposal alternative with benefits to urban mobility.

Biohydrogen production from hyperthermophilic anaerobic digestion of fruit and vegetable wastes in seawater: Simplification of the culture medium of Thermotoga maritima

Biohydrogen production by the hyperthermophilic and halophilic bacterium T. maritima, using fruit and vegetable wastes as the carbon and energy sources was studied. Batch fermentation cultures showed that the use of a culture medium containing natural seawater and fruit and vegetable wastes can replace certain components (CaCl2, MgCl2, Balch's oligo-elements, yeast extract, KH2PO4 and K2HPO4) present in basal medium. However, a source of nitrogen and sulfur remained necessary for biohydrogen production. When fruit and vegetable waste collected from a wholesale market landfill was used, no decreases in total H2 production (139 mmol L−1) or H2 yield (3.46 mol mol−1) was observed.

Effect of pH on Biohydrogen Production in Green Alga Tetraspora sp. CU2551

The green alga Tetraspora sp. CU2551 has previously been identified as a hydrogen producing organism. With the promising potential in a high H2 production yield, we further studied the enhancement of the H2 production capacity by a substrate-level control to the key enzyme, Hydrogenase. This enzyme catalyzes the formation of biohydrogen gas from protons and electrons. Here, we investigated the effect of pH on the production rate which directly affected the flow of proton flux to the hydrogenase enzyme. The result revealed that pH of culture TAP medium was simply controlled by the use of HCl/NaOH solution over the pH range of 6.5 - 9.0 without any effect on the growth of algal cells. The H2 production was observed in all ranges of our focusing pH with comparable to the control condition (pH 7.0 of TAP medium). In our best condition, an increase of the H2 yield about 24% was found in cells cultivated in TAP medium adjusted the pH to 6.5 compared to the control condition. Our finding confirms the successful biohydrogen production enhancement by a substrate-level control for the key hydrogenase enzyme.

Hydrogen Production from Cyclic Chemical Looping Steam Methane Reforming over Yttrium Promoted Ni/SBA-16 Oxygen Carrier

In this work, the modification of Ni/SBA-16 oxygen carrier (OC) with yttrium promoter is investigated. The yttrium promoted Ni-based oxygen carrier was synthesized via co-impregnation method and applied in chemical looping steam methane reforming (CL-SMR) process, which is used for the production of clean energy carrier. The reaction temperature (500–750 °C), Y loading (2.5–7.4 wt. %), steam/carbon molar ratio (1–5), Ni loading (10–30 wt. %) and life time of OCs over 16 cycles at 650 °C were studied to investigate and optimize the structure of OC and process temperature with maximizing average methane conversion and hydrogen production yield. The synthesized OCs were characterized by multiples techniques. The results of X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) of reacted OCs showed that the presence of Y particles on the surface of OCs reduces the coke formation. The smaller NiO species were found for the yttrium promoted OC and therefore the distribution of Ni particles was improved. The reduction-oxidation (redox) results revealed that 25Ni-2.5Y/SBA-16 OC has the highest catalytic activity of about 99.83% average CH4 conversion and 85.34% H2 production yield at reduction temperature of 650 °C with the steam to carbon molar ratio of 2.

Enhancement of hydrogen production by optimization of pH adjustment and separation conditions following dilute acid pretreatment of lignocellulosic biomass

Biorefinery is the integration of various conversion and separation unit processes of biomass to energy, among other products. Downstream processes link these unit processes; however, these are often overlooked to affect energy yield. In this study, use of different alkaline agents and separation techniques, and order of operations, was assessed after conversion of processed sugar into hydrogen through dark fermentation. pH was adjusted to pH 6 using various basic agents; and vacuum filtration and centrifugation were performed to facilitate separation. Sugar loss of 7–40% due to the downstream processes was recorded; however, optimization of the processes ensured high volume and sugar recovery and low degradation byproduct production. Satisfactory volume recovery with high sugar and low byproduct concentrations were achieved after vacuum filtration and pH adjustment with aqueous base. H2 yield and production rate significantly increased after performing the downstream processes. Peak H2 production rate and yield were 1824 mL H2 L−1 d−1 and 1.27 mol H2 mol−1 sugar, respectively, for the optimum condition of vacuum filtration, followed by pH adjustment using 8 N Ca(OH)2.

Synthesis and characterization of cerium promoted Ni/SBA-16 oxygen carrier in cyclic chemical looping steam methane reforming

Abstract Chemical-looping steam methane reforming (CL-SMR) is based on oxidation–reduction cycles through a solid–gas reaction with an oxygen carrier (OC) for producing high purity hydrogen or synthesis gas. In this study, Ce promoted Ni-based OC was synthesized via co-impregnation method and applied in this process. The presence of CeO2 nanoparticles in the framework of nickel oxide doped SBA-16 oxygen carrier could significantly improve the uniformity and distribution of nickel oxide nanoparticles duo to the restrictional influence of the SBA-16 framework and the strong interaction of nickel and cerium. The reaction temperature (500–750 °C), Ce loading percentage (3.9–23.3 wt. %) and Ni loading percentage (10–30 wt. %) were studied in order to investigate and optimize the catalyst structure and process temperature with maximizing the average CH4 conversion and H2 production yield in this process. The synthesized oxygen carriers were characterized by X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The redox results revealed that 20Ni-11.6Ce/S16 oxygen carrier had the high catalytic activity of about 100% average CH4 conversion and 86.98% H2 production yield at reduction temperature of 700 °C.

Co-production of hydrogen and ethanol from glucose in Escherichia coli by activation of pentose-phosphate pathway through deletion of phosphoglucose isomerase (pgi) and overexpression of glucose-6-phosphate dehydrogenase (zwf) and 6-phosphogluconate dehydrogenase (gnd)

BackgroundBiologically, hydrogen (H2) can be produced through dark fermentation and photofermentation. Dark fermentation is fast in rate and simple in reactor design, but H2 production yield is unsatisfactorily low as <4 mol H2/mol glucose. To address this challenge, simultaneous production of H2 and ethanol has been suggested. Co-production of ethanol and H2 requires enhanced formation of NAD(P)H during catabolism of glucose, which can be accomplished by diversion of glycolytic flux from the Embden–Meyerhof–Parnas (EMP) pathway to the pentose-phosphate (PP) pathway in Escherichia coli. However, the disruption of pgi (phosphoglucose isomerase) for complete diversion of carbon flux to the PP pathway made E. coli unable to grow on glucose under anaerobic condition.ResultsHere, we demonstrate that, when glucose-6-phosphate dehydrogenase (Zwf) and 6-phosphogluconate dehydrogenase (Gnd), two major enzymes of the PP pathway, are homologously overexpressed, E. coli Δpgi can recover its anaerobic growth capability on glucose. Further, with additional deletions of ΔhycA, ΔhyaAB, ΔhybBC, ΔldhA, and ΔfrdAB, the recombinant Δpgi mutant could produce 1.69 mol H2 and 1.50 mol ethanol from 1 mol glucose. However, acetate was produced at 0.18 mol mol−1 glucose, indicating that some carbon is metabolized through the Entner–Doudoroff (ED) pathway. To further improve the flux via the PP pathway, heterologous zwf and gnd from Leuconostoc mesenteroides and Gluconobacter oxydans, respectively, which are less inhibited by NADPH, were overexpressed. The new recombinant produced more ethanol at 1.62 mol mol−1 glucose along with 1.74 mol H2 mol−1 glucose, which are close to the theoretically maximal yields, 1.67 mol mol−1 each for ethanol and H2. However, the attempt to delete the ED pathway in the Δpgi mutant to operate the PP pathway as the sole glycolytic route, was unsuccessful.ConclusionsBy deletion of pgi and overexpression of heterologous zwf and gnd in E. coli ΔhycA ΔhyaAB ΔhybBC ΔldhA ΔfrdAB, two important biofuels, ethanol and H2, could be successfully co-produced at high yields close to their theoretical maximums. The strains developed in this study should be applicable for the production of other biofuels and biochemicals, which requires supply of excessive reducing power under anaerobic conditions.

Improving the plasmonic efficiency of the Au nanorod-semiconductor photocatalysis toward water reduction by constructing a unique hot-dog nanostructure

A novel hot-dog (HD) structured Au NR@Cu2O NPs was designed and synthesized using Au nanorod (NR) as inner “sausage” and Cu2O as outside “bread” to improve the plasmonic efficiency of Au NR so as to enhance their performance of the photocatalysts in water photo reduction reaction. In this unique structure, the head-exposed Au NR provided plasmonic enhanced local electric field at surface of photocatalyst to improve the transfer of electrons. Compared with the traditional photocatalysts composed of bare semiconductors or the metal-semiconductor composite photocatalysts with core-shell (CS) structure, the HD Au NR@Cu2O NPs not only exhibit an extended absorption in visible light wavelength range, but also effectively reduce the recombination rate of photogenerated charge-carriers due to the exposed tips of Au NRs, thus bringing about the significant improvement in H2 production yield. Moreover, the TiO2 shell can be facilely covered on the surface of Au NR@Cu2O to form p-n junction with Cu2O shell to further enhance the efficiency of H2 evolution.