Improvement Of H2 Production Research Articles

Rational designing of TiO2-X@Cs3Bi2X9 nanocomposite for boosted hydrogen evolution

Halide perovskites are known as compounds possessing interesting properties, including visible light-induced photoactivity, however, they suffer from instability. Herein, a novel technique for reducing the decomposition rate of halide bismuth-based perovskites Cs3Bi2X9 (X=I, Br, Cl) in the aqueous environment by combining with different types of TiO2 (anatase TiO2-I, anatase/rutile TiO2-B, and rutile TiO2-C synthesized using HI, HBr, and HCl acids, respectively) has been described. The specific type of HX has a notable impact on the crystallinity, morphology, and photocatalytic abilities of TiO2-X and they constitute a reaction environment that allows perovskites to survive the synthesis of TiO2. Studies reveal that TiO2-I is the optimal support material for immobilizing perovskite nanoparticles, owing to its extensive surface area and the synergistic effect it has with Cs3Bi2I9. Adding a small amount of Cs3Bi2I9 to iodine-doped TiO2-I improved the photocatalytic performance in the aqueous environment. As a result, 24.3, 22.5, 22.0, and 13.5-fold improvement in H2 production has been realized with decreasing amounts of Cs3Bi2I9 perovskite (10, 50, 100, and 300 mg). Upon detailed characterization and analysis of photocatalytic properties, it has been suggested that when Cs3Bi2I9 nanoparticles are dispersed within the TiO2-I structure, they can establish a close connection which allows the photogenerated electrons of TiO2-I to be extracted to Cs3Bi2I9, effectively preventing the charge recombination. This study provides a feasible possibility for the photocatalytic application of perovskite-based nanocomposites in the aqueous environment.

Steps to understand the role played by the main operating conditions in the oxidative steam reforming of biomass fast pyrolysis volatiles

Biomass pyrolysis and in-line catalytic oxidative steam reforming of the volatiles (P-OSR) has been analyzed in a two-step reaction system made up of a conical spouted bed reactor (CSBR) and a fluidized bed reactor (FBR). A novel O2 multi-point injection system has been designed in order to ensure suitable O2 distribution in the FBR, and hence avoid the formation of hot spots that may lead to irreversible catalyst deactivation by metal sintering. Optimization of the main process parameters has been approached in order to maximize H2 production and overcome the high energy requirements of the endothermic reforming reaction. The study has been conducted in the following ranges of the operating conditions: Reforming temperature, 550–700 °C; space time, 5–20 gcat min gvolatiles−1; steam/biomass (S/B) ratio, 2.5–5; and equivalence ratio (ER) from 0 to 0.19. Moderate reforming temperatures (600–650 °C), a S/B value of 3 and a space time of 15 gcat min gvolatiles−1 are the optimum conditions for the process. Furthermore, when low space time values are used, O2 feeding rates into the reforming step of up to an ER value of 0.12 (corresponding to autothermal operation (ATR)) revealed a synergistic effect promoting reforming reactions. Thus, an improvement in H2 production from 6.81 wt% to 8.26 wt% was observed by changing ER from 0 to 0.12, which means H2 production increases by 21.4% compared to the conventional pyrolysis-reforming (P-SR) process. Therefore, the promising results obtained in this study prove the suitability of the continuous P-OSR strategy for H2 production from biomass and involve a step forward towards the scaling up of the process.

Maximization of Energy Recovery from Starch Processing Wastewater by Thermophilic Dark Fermentation Coupled with Microbial fuel Cell Technology

Utilization of organic wastewater for hydrogen production has dual advantages of clean energy generation and bioremediation, which is sustainable for a longer period. To maximize the energy recovery from starch rich wastewater, a two stage system comprising of thermophilic dark fermentation coupled with microbial fuel cell was employed. A single parameter optimization strategy was implemented for the operation of the batch system. The maximum cumulative hydrogen production obtained was 2.56 L L−1 with a 48% reduction in COD under the optimal conditions of 35 g L−1 initial substrate concentration (COD), temperature 60 °C, and pH 6.5. The H2 yield and H2 production rate were 6.8 mol H2/kg CODreduced and 731.3 mL L−1 h−1, respectively. The effect of the organic loading rate (OLR) on H2 production rate was studied in a continuous stirred tank reactor (CSTR). A maximum hydrogen production rate of 913 mL L−1 h−1 was observed at an OLR of 5.6 g L−1 h−1. Effluent recycle played an important role in the improvement of H2 production. A maximum H2 production rate of 1224 mL L−1 h−1 was observed at a recycle ratio of 0.6. Power density of 4.2 W m−3 was observed with MFC using the dark fermentative spent media neutralized with carbonate buffer at an optimal pH of 7. A total COD reduction of 86% was observed.

Surface modification of graphitic carbon nitride nanoparticles with B, O and S doping/carbon vacancy for efficient dehydrogenation of sodium borohydride in methanol

Herein, the surface properties of graphitic carbon nitride (GCN) with sulphur(S), boron (B) and oxygen (O) dopants were improved. The heteroatom-doped metal-free GCN exhibited both rich surface functional groups and a carbon defect structure. These metal-free catalysts were used to obtain hydrogen (H2) from the sodium borohydride (SB) methanolysis for the first time. Compared to GCN, S, B, and O doped GCN catalyst obtained showed a 2.2-fold improvement in H2 production. HGR value obtained with B, O and S doped GCN (10 mg) via SB of 2.5% was 9166 ml min −1g−1. XPS, SEM-EDX, TEM, FTIR, and XRD analyses were used for the structural properties of catalysts. The activation energy (Ea) for B, O and S doped GCN was 28.89 kJ mol−1.

Influences of specific surfactant structures on biohydrogen production from oily wastewater in batch and continuous anaerobic dark fermentation

Residual oil in palm oil mill effluent (POME) poses difficulties in its treatment chain. Non-ionic surfactants containing different hydrophobic tail structures and their optimal concentrations were evaluated for effectiveness in biohydrogen production. By adding the surfactants at their critical micelle concentration in synthetic oily wastewater, the maximal H2 yield was increased by 2.2 and 3.5 times for Triton X-100 and Tergitol 15-S-9, respectively, compared to the control. Using real POME, the supplemental Tergitol 15-S-9 resulted in a 56.4 % improvement in H2 production. For continuous digestion studies, pure POME and Tergitol 15-S-9 supplemented POME (sPOME) were fed to thermophilic anaerobic sequencing batch reactors (ASBRs) under hydraulic retention time (HRT) of 32–12.5 days. Optimally at HRT 19 days, H2 content in the biogas from sPOME-fed ASBR was noticeably higher, which gave a superior yield of 203.4 mLH2/gCODremoved (+15 %).

Potential and characteristics of bio-H2 production from brewery wastewater by a maltose-preferring butyrate-type producer: Investigation in batch and semi-continuous cultures

In the context of "Peak CO2 emissions & Carbon neutrality", H2 energy, as the green and clean energy, will make an important contribution to the carbon emission reduction and carbon neutralization. Bio-H2 production from organic wastewater achieved not only pollutants removal, but also the H2 energy recovery and carbon emission reduction. In this study, a maltose-preferring producer of Clostridium butyricum NH-02 was investigated for the potential and performance of bio-H2 production from brewery wastewater in batch and semi-continuous fermentation. Appropriate initial pH 7.0 and organic loading of 21,173mg/L chemical oxygen demand (COD) (2670mg/L reducing sugar (RS)) stimulated the batch H2 fermentation efficiency with a maximum H2 yield of 1.89mol-H2/mol-RS and cumulative H2 production of 479.3mL/L. Comparing to the batch fermentation, semi-continuous fermentation showed significant improvement in H2 productivity and yield. The maximum cumulative H2 yield of 5.21mol-H2/mol-RS and production of 254.78mL were obtained with the optimal hydraulic retention time (HRT) at 47h after a 120h fermentation. This study demonstrated the potential of H2 production from brewery wastewater with C. butyricum, and a great improvement in H2 production in semi-continuous fermentation.

Surface modification with oxygen doping of g-C3N4 nanoparticles by carbon vacancy for efficient dehydrogenation of sodium borohydride in methanol

g-C3N4, which is used in different catalytic activities, was applied to the H2 field from NaBH4 methanolysis for the first time in this study. The development of g-C3N4 is necessary to make it a viable alternative to the heterogeneous catalysts currently used in this field. The g-C3N4 used in this study contains both carbon vacancies and oxygen doping atoms. Compared to the g-C3N4 catalyst, the O doped g-C3N4 catalyst obtained showed an approximately 3.4-fold improvement in H2 production. The HGR value obtained with O doped g-C3N4 (5 mg) was 10800 ml min−1 g−1. The structural properties of the obtained catalysts were characterized by XPS, SEM-EDX, TEM, FTIR, Raman, BET and XRD analyses. These analyses showed significant changes for O doped g-C3N4. The activation energy obtained for O doped g-C3N4 was approximately 36.13 kJ mol−1.

Improvement in H2 production from Clostridium butyricum by co-culture with Sporolactobacillus vineae

Dark fermentation has emerged as a promising method for converting waste into biohydrogen, a clean and sustainable energy source. However, the interaction between biohydrogen production performance and its microbial community has not been investigated sufficiently. This study investigated the effect of S. vineae on hydrogen production using defined cultures. Co-cultures of Clostridium butyricum (C. butyricum) with Sporolactobacillus vineae (S. vineae) increased the hydrogen production from 1.57 to 1.84 mol H2/mol glucoseadded, whereas lactic acid production did not increase in comparison with single culture of C. butyricum. At all the examined co-culture conditions, C. butyricum occupied more than 90% of the microbial composition; therefore, the microbial community analysis alone could not explain the difference in hydrogen production according to S. vineae addition. PICRUSt analysis showed that co-culture with S. vineae enhanced the expression of genes relating lactate to butyrate and H2 pathway, although S. vineae did not produce butyrate. Co-cultures of Clostridium sp. and Sporolactobacillus sp. could be beneficial for H2 production from the viewpoint of acidogenic pathway regulation. This study is expected to contribute to the understanding of the synergistic mechanisms of both the strains to obtain optimal biohydrogen production.

Enhanced photocatalytic activity of hydrogen evolution through Cu incorporated ZnO nano composites

Green environment friendly and economical light responsive photocatalytic method was used to investigate the improving H2 efficiency of ZnO by Cu doping. Efficient nano composites of ZnO doped with varying percentage of copper (0.0, 0.01, 0.03 and 0.05 mol.%) were synthesized by sol-gel method to analyze H2 evolution. Cu incorporation did not change the hexagonal wurtzite structure of ZnO nanoparticles as examined by x-ray diffraction (XRD). EDX indicates no external trace found in Cu doped ZnO samples and surface area decrease by increasing Cu contents in ZnO proved by BET. Morphology of particles through scanning electron microscopy (SEM) is nearly spherical. Diffuse reflectance spectroscopy (DRS) was utilized to determine the energy band gap (Eg). Cu incorporation into ZnO decreased energy band gap from 3.19 eV to 3.00 eV. XPS shows electronic state of nanoparticles. Recombination rate of photo induced electrons and holes analyzed by photoluminescence spectroscopy (PL) decreased by increase in Cu doping percentage. Further the reduced recombination rate was examined by electrochemical impedance spectroscopy (EIS) and photocurrent density. EIS and photocurrent density are in good affiliation with photoluminescence results. Cu incorporated ZnO catalysts caused an enhancement in H2 production from 7.49 μmol g-1 to 41.55 μmol g-1. Such improvement in H2 production by Cu doped ZnO nanoparticles is due to the reduced recombination of electrons and holes during photocatalytic reaction.

Contributing factors in the improvement of cellulosic H2 production in Clostridium thermocellum/Thermoanaerobacterium co-cultures

Lignocellulosic biohydrogen is a promising renewable energy source that could be a potential alternative to the unsustainable fossil fuel-based energy. Biohydrogen production could be performed by Clostridium thermocellum that is the fastest known cellulose-degrading bacterium. Previous investigations have shown that the co-culture of C. thermocellum JN4 and a non-cellulolytic bacterium Thermoanaerobacterium thermosaccharolyticum GD17 produces more hydrogen than the C. thermocellum JN4 mono-culture, but the mechanism of this improvement is unknown. In this work, we carried out genomic and evolutionary analysis of hydrogenase-coding genes in C. thermocellum and T. thermosaccharolyticum, identifying one Ech-type [NiFe] hydrogenase complex in each species, and, respectively, five and four monomeric or multimeric [FeFe] hydrogenases in the two species. Further transcriptional analysis showed hydrogenase-coding genes in C. thermocellum are regulated by carbon sources, while hydrogenase-coding genes in T. thermosaccharolyticum are not. However, comparison between transcriptional abundance of hydrogenase-coding genes in mono- and co-cultures showed the co-culturing condition leads to transcriptional changes of hydrogenase-coding genes in T. thermosaccharolyticum but not C. thermocellum. Further metabolic analysis showed T. thermosaccharolyticum produces H2 at a rate 4-12-fold higher than C. thermocellum. These findings lead to the suggestion that the improvement of H2 production in the co-culture over mono-culture should be attributed to changes in T. thermosaccharolyticum but not C. thermocellum. Further suggestions can be made that C. thermocellum and T. thermosaccharolyticum perform highly specialized tasks in the co-culture, and optimization of the co-culture for more lignocellulosic biohydrogen production should be focused on the improvement of the non-cellulolytic bacterium.

Thermodynamic analysis of combined unit of biomass gasifier and tar steam reformer for hydrogen production and tar removal

A combined unit of biomass gasifier and tar steam reformer (CGR) was proposed in this study to achieve simultaneous tar removal and increased hydrogen production. Tar steam reforming calculations based on thermodynamic equilibrium were carried out by using Aspen Plus software. Thermodynamic analysis reveals that when selecting appropriate operating conditions, exothermic heat available from the gasifier could sufficiently supply to the heat-demanding units including feed preheaters, steam generator and reformer. The effects of gasification temperature (Tgs), reforming temperature (Tref) and steam-to-biomass ratio (S:BM) on percentages of tar removal and improvement of H2 production were investigated. It was reported that the CGR system can completely remove tar and increase H2 production (1.6 times) under thermally self-sufficient condition. The increase of H2 production is mainly via the water–gas shift reaction.

Harnessing of biohydrogen by acidogenic fermentation of Citrus limetta peelings: Effect of extraction procedure and pretreatment of biocatalyst

The extracts of Citrus limetta (sweet lime) peelings were evaluated as a fermentable substrate for hydrogen (H2) production by dark-fermentation (acidogenic) using both anaerobic mixed consortia and selectively enriched acidogenic mixed consortia. Extraction was carried by pretreating sweet lime peelings at 121 °C (1 bar pressure) at variable pH (6 and 7) and digestion time (20 and 40 min). Maximum organic matter extraction was observed at pH 7.0 (40 min). Fermentation was performed at different organic loading conditions [OL1, 1.17 kg COD/m3; OL2, 2.35 kg COD/m3; OL3, 4.69 kg COD/m3] under acidophilic microenvironment. H2 production was found to depend on the concentration of the substrate and composition. Increase in organic load showed consistent improvement in H2 production. Operation at OL3 employing selectively enriched inoculum documented higher cumulative H2 production (10.07 mmol) and H2 production rate (0.345 mmol/h) (pH 7; 40 min). Substrate degradation was also found to increase with increase in organic loading. Maximum substrate degradation (SD) was registered at pH 6 (40 min) with anaerobic culture (2.80 kg CODR/m3; ξCOD 31.82%) and at pH 7 (40 min) with selectively enriched acidogenic culture (3.20 kg CODR/m3; ξCOD 36.36%). Concentration of volatile fatty acids (VFAs) also improved with increase in organic load. Maximum VFA concentration (1098 mg/l) was observed with OL3 (pH 7; 40 min) by using selectively enriched culture.

Redirection of biochemical pathways for the enhancement of H2 production by Enterobacter cloacae

Improvement in H2 production was achieved through redirection of metabolic pathways by blocking formation of alcohol and some organic acids in Enterobacter cloacae IIT-BT 08. The wild type strain was more susceptible to allyl alcohol (7 mM) and to the combined effect of NaBr and NaBrO3 (40 mM each at pH 5.5) than were double mutants, with defects in both alcohol and organic acid formation pathways, which had higher H2 yields (3.4 mol mol−1 glucose) than the wild type strain (2.1 mol mol−1 glucose).

Hydrogen production by Rhodopseudomonas at the expense of vegetable starch, sugarcane juice and whey

Four local strains of Rhodopseudomonas sp. (BHU strains 1–4) evolved hydrogen at the expense of potato starch, sugarcane juice and whey (1% in each case) in the presence of light (2 klux), under anaerobic conditions (argon/CO2, 95/5, v/v). Among the three substrates, sugarcane juice supported the maximum level of H2 production, followed by potato starch and whey at the rates of 45, 30 and 25 μl H2 h−1 mg−1 bacterial cell dry weight, respectively. Although elevated temperature (45°C) suppressed H2 evolution by strains 1, 2 and 3, the thermotolerant strain (BHU strain 4) has shown encouraging results. Alginate-immobilized cells under an identical experimental regime, exhibited an almost one-and-a-half times improvement in H2 production in the cases of all the above substrates over their free cell counterpart. Preliminary experiments have shown the presence of amylase in all the bacterial strains and work is in progress to characterize this enzyme so that the system could be used for efficient consumption of starch-based agro- products.