Polyaniline sensitized Pt@TiO2 for visible-light-driven H2 generation

Polyaniline is a typical conducting polymer with high migration electron rate, good stability, eco-friendly properties, and high absorption coefficients for visible light. In the present study, polyaniline decorated Pt@TiO₂ for visible light-driven H₂ generation is reported for the first time. The above-mentioned nanocomposite is prepared through a simple oxidative-polymerization and characterized by infrared spectroscopy, transmission electron microscopy, X–ray diffraction, thermogravimetric analysis, and ultraviolet–visible diffuse reflectance spectra. Polyaniline modification improves the absorption of the nanocomposite in visible light region via a photosensitization effect similar to dye–sensitization but does not influence the crystal structure and size of Pt@TiO₂. The polyaniline modified Pt@TiO₂ exhibits a remarkable visible light activity (61.8 μmol h⁻¹ g⁻¹) and good stability for H₂ generation (with an average apparent quantum yield of 10.1%) with thioglycolic acid as an electron donor. This work provides new insights into using conducting polymers, including polyaniline, as a sensitizer to modify Pt@TiO₂ for visible-light hydrogen generation.     

Novel sonochemical synthesis of Zn2V2O7 nanostructures for electrochemical hydrogen storage

Although utilization of diverse classes of metal oxides as hydrogen storage materials has been reported, but there is still a major need to introduce efficient materials. Herein, mesoporous Zn₂V₂O₇ nanostructures were produced by a new sonochemical method using hydrazine, zinc nitrate, and ammonium vanadate as the starting reagents and then annealed at 700 °C. Prior to annealing, Zn₃V₃O₈ was produced in the presence of ultrasonic waves, whereas in the absence of ultrasonic waves, Zn₂(VO₄)₂ was the major product. In fact, ultrasonic waves interfered with the reaction mechanism and reduced V⁵⁺ to V⁴⁺ and V³⁺. Because of the proper composition and structure of these nanostructures, they were used for electrochemical storage of hydrogen. Storage of over 2899 mAh/g after 20 cycles by flower-like nanostructures revealed their high capability. The results also showed that morphology affects efficiency such that three-dimensional spherical nanostructures had a storage capacity of 2247 mAh/g after 20 cycles.     

Biomass gasification coupled with producer gas cleaning,bottling and HTS catalyst treatment for H2-rich gas production

The aim of the present study is to demonstrate the production of hydrogen-rich fuel gas from J. curcas residue cake. A comprehensive experimental study for the production of hydrogen rich fuel gas from J. curcas residue cake via downdraft gasification followed by high temperature water gas shift catalytic treatment has been carried out. The gasification experiments are performed at different equivalence ratios and performance of the process is reported in terms of producer gas composition & its calorific value, gas production rate and cold gas efficiency. The producer gas is cleaned of tar and particulate matters by passing it through venturi scrubber followed by sand bed filter. The clean producer gas is then compressed at 0.6 MPa and bottled into a gas cylinder. The bottled producer gas and a simulated mixture of producer gas are then subjected to high temperature shift (HTS) catalytic treatment for hydrogen enriched gas production. The effect of three different operating parameters GHSV, steam to CO ratio and reactor temperature on the product gas composition and CO conversion is reported. From the experimental study it is found that, the presence of oxygen in the bottled producer gas has affected the catalyst activity. Moreover, higher concentration of oxygen concentration in the bottled producer gas leads to the instantaneous deactivation of the HTS catalyst.     

A remarkable increase in the adsorbed H2 amount: Influence of pore size distribution on the H2 adsorption capacity of Fe-BTC

Here we show the crucial role of ultramicropores on the adsorbed H₂ amount. By synthesizing Fe-BTCs via a perturbation assisted nanofusion synthesis strategy and by the control of textural porosity via Fe:BTC ratio, BET surface area (1312 m²/g), total pore volume (1.41 cm³/g), and H₂ adsorption capacity (1.10 wt% at 7.6 bar and 298 K) were enhanced by 1.6, 3.1, and 2.6 times, respectively. The reported BET surface area, and the total pore volume are the highest of those reported for Fe-BTC, to date. The enhanced H₂ adsorption capacity of Fe-BTC-3 is attributed to the ultramicropores present in its pore structure. Presence of ultramicropores maximizes van der Waals potential, and the adsorbed H₂ amount increases. By the perturbation assisted nanofusion synthesis strategy and the control over textural porosity, an Fe-BTC that possesses a H₂ adsorption capacity higher than those of reported MOFs with higher BET surface areas has been reported.     

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO₂ catalyst doped with Ca and Ni/ZrO₂ were employed in the CO₂ methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO₂ and chemical analysis. The catalytic behavior of these catalysts in the CO₂ methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO₂, the metallic surface area did not change whereas the CO₂ consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca⁺² but also some Ni²⁺ are on the ZrO₂ surface lattice of the Ni/CaZrO₂ catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO₂ methanation rate increases. Moreover, the number of active sites of the CO₂ methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.     

Titanate quantum dots-sensitized Cu2S nanocomposites for superficial H2 production via photocatalytic water splitting

TiO₂ quantum dots-sensitized Cu₂S (Cu₂S/TiO₂) nanocomposites with varying concentration of TiO₂ QDs are synthesized via a facile two-stage hydrothermal-wet impregnation method. X-ray diffraction analysis confirms the formation of Cu₂S and TiO₂with chalcocite and anatase phases, respectively. The observed shoulder-like absorption peaks indicate the UV–visible light-driven properties of the composite. Morphological analysis reveals that the fabricated Cu₂S/TiO₂ composite consists of Cu₂S with a nano rod-like shape (average length and width of ～856 and ～213 nm, respectively) and nanosheets-like structures (average length and width of ～283 and ～289 nm, respectively), whereas the TiO₂ is formed as quantum dots with a size range of 8.2 ± 0.4 nm. Chemical state analysis shows the presence of Cu⁺, S^2?, Ni²⁺, and O^2? in the nanocomposite. The H₂ evolution rate over the optimized photocatalyst is found to be ～45.6 mmol h^?1g^?1_cat under simulated solar irradiation, which is around 5 and 2.4-fold higher than that of the pristine TiO₂ and Cu₂S, respectively. Continuous H₂ production for 30 h is achieved during time-on-stream experiments, demonstrating the excellent stability and durability of the Cu₂S/TiO₂ photocatalyst for large-scale applications.     

Steam reforming of 1-methylnaphthalene over pure CeO2 under model coke oven gas conditions containing high H2S concentrations

Tar and H₂S are obstacles to the efficient production of H₂ from unused industrial gases and biomass gasification gases. Robust catalysts against tar and H₂S are required to produce H₂ from such resources. Herein, a stable steam reforming reaction is demonstrated over pure CeO₂ under reaction conditions consisting of ~2 vol% 1-methylnaphthalene and ~1000 ppm H₂S. The presence of H₂S significantly suppressed Ni/MgO/Al₂O₃ activity and increased carbon deposition, regardless of the steam to carbon (S/C) ratio. In contrast, the promotion or suppression of CeO₂ activity in the presence of H₂S was dependent on the S/C ratio. At S/C = 1.2, H₂S deactivated the CeO₂ catalyst and increased carbon deposition. Conversely, H₂S promoted the reforming reaction and decreased carbon deposition on CeO₂ at S/C ≥ 2.0. The results of this study clarify that pure CeO₂ exhibits outstanding and stable activity for the steam reforming reaction of 1-methylnaphthalene in the presence of H₂S by controlling the S/C of the inlet gas.     

Synthesis of binary Co–Mg–O oxide system and study of its behavior in reduction/oxidation cycling

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co₃O₄) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH₃)₂ was carried out using the aqueous solution of Co(NO₃)₂ precursor. The CoO_x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H₂ flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co₃O₄ (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg_1-xCo_x)O and (Co_3-xMg_x)O₄ phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy.     

Effect of ammonia concentration on hythane (H2 and CH4) production in two-phase anaerobic digestion

Co-production of hydrogen and methane by two-phase anaerobic digestion (AD) may offer a sustainable solution for the centralized treatment of food waste (FW), while ammonia accumulation is potentially encountered. A mesophilic two-phase AD was investigated for hydrogen and methane production from FW at varying ammonia concentrations. The process achieved a hydrogen yield of 47.7 mL/g VS and a methane yield of 335 mL/g VS by optimizing the organic loading rate (OLR) and recirculation ratio. Total ammonia nitrogen (TAN) concentration of 4044 mg/L corresponded to a threshold in the hydrogen reactor, above which ammonia would initiate inhibition of hydrogenogenesis and acidogenesis. Methane yield was recovered in the methane reactor after acute inhibiting effects of TAN below 5800 mg/L, while TAN above 6200 mg/L caused chronic inhibition of methanogens. Adjusting hydraulic retention time (HRT) and recirculation ratio in hydrogen and methane reactors reduced TAN to 960 and 2105 mg/L respectively, resulting in successful recovery was achieved in the hydrogen reactor but not in the methane reactor. The two-phase AD for methane and hydrogen production can be a promising solution for ammonia accumulation in AD from FW.     

Hydrogen sulphide to hydrogen via H2S methane reformation: Thermodynamics and process scheme assessment

Hydrogen Sulphide Methane Reformation (HSMR) represents a valid alternative for the simultaneous H₂S valorisation and hydrogen production at the industrial scale, without direct CO₂ emissions. The major concerns about the process commercialization are the possible coke formation in the reaction zone and the lack of active and selective catalysts. The study of the thermodynamics is the essential preliminary step for the reaction phenomena understanding. In this work, a deep thermodynamic analysis is performed to explore the system behaviour as a function of temperature, pressure, and inlet feed composition, using the Aspen Plus RGibbs module. In this way, the optimal process operating conditions to avoid carbon lay down can be identified.Assessed the system's thermodynamics, a preliminary process scheme is developed and simulated in Aspen Plus V11.0®, considering hydrogen production and its distribution in pipeline with methane. The process performances are discussed in terms of products' purity and process energy consumptions.     

Observation of ultrasonic signal and measurement of H2 concentration from the exterior of a metal pipe

Concentration of H₂ gas in a stainless steel (SUS) pipe is measured by using ultrasound from the exterior of a pipe without making a hole. Gas concentration is calculated by the variation of ultrasound speed detected. A sound absorbing material is put on the outer surface of the SUS pipe to reduce the ultrasonic signal noise circulating through the shell of the SUS pipe. Then it is possible to measure the gas concentration by observing the airborne signal passing through the SUS pipe. Propagation of ultrasound wave in SUS pipe is also simulated by the finite-difference-time-domain method that could explain the ultrasound propagation signals in the SUS pipe.     

Simultaneous biohydrogen (H2) and bioplastic (poly-β-hydroxybutyrate-PHB) productions under dark,photo, and subsequent dark and photo fermentation utilizing various wastes

The present study is focused on bio hydrogen (H₂) and bioplastic (i.e., poly-β-hydroxybutyrate; PHB) productions utilizing various wastes under dark fermentation, photo fermentation and subsequent dark-photo fermentation. Potential bio H₂ and PHB producing microbes were enriched and isolated. The effects of substrate (rice husk hydrolysate, rice straw hydrolysate, dairy industry wastewater, and rice mill wastewater) concentration (10–100%) and pH (5.5–8.0) were examined in the batch mode under the dark and photo fermentation conditions. Using 100% rice straw hydrolysate at pH 7, the maximum bio H₂ (1.53 ± 0.04 mol H₂/mol glucose) and PHB (9.8 ± 0.14 g/L) were produced under dark fermentation condition by Bacillus cereus. In the subsequent dark-photo fermentation, the highest amounts of bio H₂ and PHB were recorded utilizing 100% rice straw hydrolysate (1.82 ± 0.01 mol H₂/mol glucose and 19.15 ± 0.25 g/L PHB) at a pH of 7.0 using Bacillus cereus (KR809374) and Rhodopseudomonas rutila. The subsequent dark-photo fermentative bio H₂ and PHB productions obtained using renewable biomass (i.e., rice husk hydrolysate and rice straw hydrolysate) can be considered with respect to the sustainable management of global energy sources and environmental issues.     

Hydrogen production using chemical looping technology: A review with emphasis on H2 yield of various oxygen carriers

Natural H₂ in useful quantities is negligible, which makes hydrogen unsuitable as an energy resource compared to other fuels. H₂ production by solar, biological, or electrical sources needs more energy than obtained by combusting it. Lower generation of pollutants and better energy efficiency makes hydrogen a potential energy carrier. Hydrogen finds potential applications in automobile and energy production. However, the cost of producing hydrogen is extremely high. Chemical-looping technology for H₂ generation has caught widespread attention in recent years. This work, presents some recent findings and provides a comprehensive overview of different chemical looping techniques such as chemical looping reforming, syngas chemical looping, coal direct chemical looping, and chemical looping hydrogen generation method for H₂ generation. The above processes are discussed in terms of the relevant chemical reactions and the associated heat of reactions to ascertain the overall endothermicity or exothermicity of the H₂ production. We have compared the H₂ yield data of different Fe/Ni, spinel and perovskites-based oxygen carriers (OC) reported in previous literature. This review is the first comprehensive study to compare the H₂ yield data of all the previously reported oxygen carriers as a function of temperature and redox cycles. In addition, the article summarizes the characteristics and reaction mechanisms of various oxygen carrier materials used for H₂ generation. Lastly, we have reviewed the application of Density Function Theory (DFT) to study the effect of various dopant addition on the efficiency of H₂ production of the oxygen carriers and discussed ASPEN simulations of different chemical looping techniques.     

Cold-start icing characteristics of proton-exchange membrane fuel cells

Understanding the icing characteristics of proton-exchange membrane fuel cells (PEMFCs) is essential for optimizing their cold-start performance. This study examined the effects of start-up temperature, current density, and microporous layer (MPL) hydrophobicity on the cold-start performance and icing characteristics of PEMFCs. Further, the cold-start icing characteristics of PEMFCs were studied by testing the PEMFC output voltage, impedance, and temperature changes at different positions of the cathode gas diffusion layer. Observation of the MPL surface after cold-start failure allowed determination of the distribution of ice formation at the catalytic layer/MPL interface. At fuel cell temperatures below 0 °C, supercooled water in the cell was more likely to undergo concentrated instantaneous freezing at higher temperatures (−4 and −5 °C), whereas the cathode tended to freeze in sequence at lower temperatures (−8 °C). In addition, a more hydrophobic MPL resulted in two successive instantaneous icing phenomena in the fuel cell and improved the cold-start performance.     

Improving inter-plant integration of syngas production technologies by the recycling of CO2 and by-product of the Fischer-Tropsch process

This paper deals with the emission reduction in synthesis-gas production by better integration and increasing the energy efficiency of a high-temperature co-electrolysis unit combined with the Fischer-Tropsch process. The investigated process utilises the by-product of Fischer-Tropsch, as an energy source and carbon dioxide as a feedstock for synthesis gas production. The proposed approach is based on adjusting process streams temperatures with the further synthesis of a new heat exchangers network and optimisation of the utility system. The potential of secondary energy resources was determined using plus/minus principles and simulation of a high-temperature co-electrolysis unit. The proposed technique maximises the economic and environmental benefits of inter-unit integration. Two scenarios were considered for sharing the high-temperature co-electrolysis and the Fischer-Tropsch process. In the first scenario, by-products from the Fischer-Tropsch process were used as fuel for a high-temperature co-electrolysis. Optimisation of secondary energy sources and the synthesis of a new heat exchanger network reduce fuel consumption by 47% and electricity by 11%. An additional environmental benefit is reflected in emission reduction by 25,145 tCO₂/y. The second scenario uses fossil fuel as a primary energy source. The new exchanger network for the high-temperature co-electrolysis was built for different energy sources. The use of natural gas resulted in total annual costs of the heat exchanger network to 1,388,034 USD/y, which is 1%, 14%, 116% less than for coal, fuel oil and LPG, respectively. The use of natural gas as a fuel has the lowest carbon footprint of 7288 tCO₂/y. On the other hand, coal as an energy source has commensurable economic indicators that produce 2 times more CO₂, which can be used as a feedstock for a high-temperature co-electrolysis. This work shows how in-depth preliminary analysis can optimise the use of primary and secondary energy resources during inter-plant integration.     

Combustion characteristics and flame stability of linear esters of palmitic acid based on OH-PLIF technology

Experimental study on combustion characteristics and method for evaluating flame stability was carried out. Methyl palmitate, ethyl palmitate, propyl palmitate, butyl palmitate, and amyl palmitate were prepared using pyridine n-butyl bisulfate ionic liquid as catalyst in a self-designed reactor to catalyze esterification reaction of palmitic acid with methanol, ethanol, propanol, butanol, and pentanol, respectively. Combustion characteristics including the flame height, flame front area, and flame speed were analyzed; and OH-PLIF time-average total signal strength by the OH-PLIF technique and cold flow properties of linear-chain alkyl esters of palmitic acid were also studied. Image diagnosis was applied to the study of flame stability, and an image segmentation method using three color feature matrices of flame corresponding to the red, green, and blue components was proposed. A color was selected as the evaluation color and the iterative method was used to obtain the optimal threshold for the area where the flame was located. Each pixel in the matrix was compared with an optimal threshold, and the flame stability was evaluated by calculating the ratio variance under continuous conditions. The method is simple in operation, accurate in repeatability, less interfered, and provides some guidance for analysis and optimization of biodiesel combustion process.     

Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Continuous H2 production during fermentation of the carbon components of lignocellulose hydrolysates: Insight into the influence of pH conditions on the conversion efficiency of individual sugars

Sugars released from lignocellulose biomass are a promising substrate for biohydrogen production. This study evaluates the effect of pH controlled between 4.0 and 7.5 on continuous dark-fermentative H₂ production from the mixture of cellobiose, xylose and arabinose. High hydrogen production rate was obtained for pH values between 6.0 and 7.0 with a maximum of 7.41 ± 0.16 L/L-d at pH 7.0. On the other hand, the highest H₂ yields of around 1.74 ± 0.02 mol/mol_consumed were obtained at pH 4.5, 5.0 and 6.0. Cellobiose was completely utilized in nearly the entire pH range, while the highest consumption of xylose and arabinose was obtained at pH 6.0 and 7.0, respectively. It shows the challenges in selecting optimum pH for fermentation of mixed sugars. Significant impact of pH conditions on the microbial structure was observed. Between pH 4.0 and 7.0 Clostridium genus dominated the consortium, while above pH 7.0 relative abundance of Bacillus genus increased significantly.     

Evaluation of performance characteristics of a novel hydrogen-fuelled free-piston engine generator

In this work, we present the experimental results obtained from hydrogen fuelled spark-ignited dual piston free-piston engine generator (FPEG) prototype operated in two-stroke and four-stroke mode. The FPEG testing was successfully conducted at 3.7 compression ratio, engine speed between 5 Hz and 11 Hz and with different equivalence ratios. The FPEG technical details, experimental set-up and operational control are explained in detail. Performance indicators show that both equivalence ratio and engine speed affect the engine operation characteristics. For every set of specified FPEG parameters, appropriate range of equivalence ratio is recommended to prevent unwanted disturbance to electric generator operation. Both two-stroke and four-stroke cycle mode were tested, and the results showed different combustion characteristics with the two thermodynamic cycles. Four-stroke cycle mode could operate with indicated thermal efficiency gain up to 13.2% compared with the two-stroke cycle.     

Transition metal/carbon nanoparticle composite catalysts as platinum substitutes for bioelectrochemical hydrogen production using microbial electrolysis cells

Various metal nanoparticle catalysts supported on Vulcan XC-72 and carbon-nanomaterial-based catalysts were fabricated and compared and assessed as substitutes of platinum in microbial electrolysis cells (MECs). The metal-nanoparticle-loaded cathodes exhibited relatively better hydrogen production and electrochemical properties than cathodes coated with carbon nanoparticles (CNPs) and carbon nanotubes (CNTs) did. Catalysts containing Pt (alone or mixed with other metals) most effectively produced hydrogen in terms of overall conversion efficiency, followed by Ni alone or combined with other metals in the order: Pt/C (80.6%) > PtNi/C (76.8%) > PtCu/C (72.6%) > Ni/C (73.0%) > Cu/C (65.8%) > CNPs (47.0%) > CNTs (38.9%) > plain carbon felt (38.7%). Further, in terms of long-term catalytic stability, Ni-based catalysts degraded to a lesser extent over time than did the Cu/C catalyst (which showed the maximum degradation). Overall, the hydrogen generation efficiency, catalyst stability, and current density of the Ni-based catalysts were almost comparable to those of Pt catalysts. Thus, Ni is an effective and inexpensive alternative to Pt catalysts for hydrogen production by MECs.