One-step facile hydrothermal synthesis of rGO-CoS2 nanocomposites for high performance HER electrocatalysts

With increasing demand for green and clean energy, the research community moves toward electrocatalytic hydrogen production. Herein, we synthesized the reduced graphene oxide decorated-cobalt disulfide (rGO-CoS₂) nanocomposites via the one-step facile hydrothermal method and investigated their excellent hydrogen evolution reaction (HER) activities. The rGO-CoS₂ nanocomposites showed an aggregated structure of spherical CoS₂ nanoparticles interconnected along with GO nanosheets. The rGO-CoS₂ nanocomposites exhibited a low overpotential of 377 mV and a small Tafel slope of 121 mV/dec. This work delivers a prospective scheme for developing the high efficient rGO-CoS₂ electrocatalysts for future green energy technology in hydrogen production.     

Advances in catalysts for hydrogen production by methanolysis of sodium borohydride

Fossil energy is a major contributor to global greenhouse gases and air pollutants, causing serious environmental and health issues. In order to develop clean new energy as a substitute, catalytic methanolysis of sodium borohydride (NaBH₄) has become a hot topic in hydrogen energy field. In this work, the latest research development of hydrogen production by NaBH₄ methanolysis is comprehensively reviewed from the perspective of different types of catalysts, furthermore, the merits and demerits of these studies are analyzed, the comparison between various catalysts is also completed from the dimensions of hydrogen generation rate, apparent activation energy as well as durability, and the technical challenges the hydrogen production process may face and the corresponding recommendations are proposed. This review can provide enlightenment for the research and application of novel catalysts for the methanolysis of NaBH₄ and the development of efficient hydrogen production technology.     

Low-carbon energy transition with the sun and forest: Solar-driven hydrogen production from biomass

There is a need to derive hydrogen from renewable sources, and the innovative stewardship of two natural resources, namely the Sun and forest, could provide a new pathway. This paper provides the first comparative analysis of solar-driven hydrogen production from environmental angles. A novel hydrogen production process proposed in this paper, named Solar-Driven Advanced Biomass Indirect-Gasification (SABI-Hydrogen), shows promise toward achieving continuous operation and scalability, the two key challenges to meet future energy needs. The calculated Global Warming Potential for 1 kg of solar-driven hydrogen production is 1.04 kg CO₂-eq/kg H₂, less than half of the current biomass gasification process which emits 2.67 kg CO₂-eq/kg H₂. Further, SABI-Hydrogen demonstrates the least-carbon intensive pathway among all current hydrogen production methods. Thus, solar-driven hydrogen production from biomass could lead to a sustainable supply, essential for a low-carbon energy transition.     

Numerical study on particle distribution characteristics of slush hydrogen in a cryogenic tank

A numerical model considering phase change and heat transfer was established by the Euler-Euler two-fluid method to investigate the storage characteristics and two-phase flow field of slush hydrogen. Numerous numerical simulations were performed to discuss the effect of particle diameter (d_p = 0.02–0.5 mm), content of solid hydrogen (α_s = 10%–50%), and heat leakage (q = 50–200W·m⁻²) on the flow field. It was found that particle deposition could occur during the storage process, and there exist moving vortices with contrary directions under specific conditions. The sedimentation characteristics and vortex size are influenced by many factors including particle size, solid hydrogen content, and heat leakage. An increase in particle size could lead to the strengthening of precipitation and the expansion of the counterclockwise vortex region on the right side of the tank. And the increase in solid hydrogen content could result in more deposition and more collisions and friction between particles. Moreover, the increase in heat leakage could increase the area of the counterclockwise vortex. Numerical results of the deposition and flow field characteristics in the storage tank could clearly show the physical law of the slush hydrogen so that the uniform distribution of slush hydrogen could be promoted for efficient storage and application.     

Simulation and exploration of cavitation process during microalgae oil extracting with ultrasonic-assisted for hydrogen production

Microalgae is promising to be used as feedstock resources for hydrogen production due to its high oil and grease contents. This promotes the development of extraction technology of microalgae oil. In this study, based on the Rayleigh-Plesset equation, the effects of temperature, pressure, ultrasonic power and frequency on the bubble motion of ethanol ultrasound cavitation are investigated. Subsequently, the effects of different process parameters on the extraction rate are studied using Schizochytrium sp. as raw material by stirring or ultrasonic-assisted extraction. And the composition of algae extraction oil is analyzed. The results show that the amplitude of cavitation bubbles increases with the increase of ultrasonic power and decrease of ultrasonic frequency. The extraction rate of algae oil reaches 93.76 ± 0.48% when the ultrasonic power is 150 W, the reaction time is 30 min, the temperature is 50 °C and the liquid-solid ratio is 10:1.     

A critical review on integrated system design of solar thermochemical water-splitting cycle for hydrogen production

The development of clean hydrogen production methods is important for large-scale hydrogen production applications. The solar thermochemical water-splitting cycle is a promising method that uses the heat provided by solar collectors for clean, efficient, and large-scale hydrogen production. This review summarizes state-of-the-art concentrated solar thermal, thermal storage, and thermochemical water-splitting cycle technologies that can be used for system integration from the perspective of integrated design. Possible schemes for combining these three technologies are also presented. The key issues of the solar copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles, which are the most-studied cycles, have been summarized from system composition, operation strategy, thermal and economic performance, and multi-scenario applications. Moreover, existing design ideas, schemes, and performances of solar thermochemical water-splitting cycles are summarized. The energy efficiency of the solar thermochemical water-splitting cycle is 15–30%. The costs of the solar Cu–Cl and S–I hydrogen production systems are 1.63–9.47 $/kg H₂ and 5.41–10.40 $/kg H₂, respectively. This work also discusses the future challenges for system integration and offers an essential reference and guidance for building a clean, efficient, and large-scale hydrogen production system.     

Enhanced biohydrogen production from corn stover hydrolyzate by pretreatment of two typical seed sludges

Five individual pretreatment methods (heat, ultrasonic, ultraviolet, acid, and base) were performed on two typical seed sludges (river sediments and anaerobic granular sludge) to evaluate their effectiveness on enriching efficient hydrogen (H₂)-producing bacteria and enhancing H₂ production using corn stover hydrolyzate. Results indicated that pretreatment processes caused more remarkable improvements for river sediments than anaerobic granular sludge. Among the five protocols, heat pretreatment reached high H₂ yield for both river sediments (4.17 mmol H₂/g utilized sugar) and anaerobic granular sludge (2.84 mmol H₂/g utilized sugar). Ultraviolet and ultrasonic pretreatments were conditionally effective for river sediments and anaerobic granular sludge, respectively. In most cases, pretreatment processes altered soluble metabolites distribution towards more acetate and less ethanol production. Microbial community analysis indicated that heat and ultrasonic pretreatments can respectively lead to significant and indistinctive change on original microbial community. Besides frequently detected Escherichia spp., Serratia spp., and Klebsiella spp., some species of Clostridium spp. and Bacillus spp. might be efficient H₂ producer responsible for better H₂-producing performances.     

Efficient solar hydrogen production by photocatalytic water splitting: From fundamental study to pilot demonstration

Photocatalytic water splitting with solar light is one of the most promising technologies for solar hydrogen production. From a systematic point of view, whether it is photocatalyst and reaction system development or the reactor-related design, the essentials could be summarized as: photon transfer limitations and mass transfer limitations (in the case of liquid phase reactions). Optimization of these two issues are therefore given special attention throughout our study. In this review, the state of the art for the research of photocatalytic hydrogen production, both outcomes and challenges in this field, were briefly reviewed. Research progress of our lab, from fundamental study of photocatalyst preparation to reactor configuration and pilot level demonstration, were introduced, showing the complete process of our effort for this technology to be economic viable in the near future. Our systematic and continuous study in this field lead to the development of a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar rector for the first time. We have demonstrated the feasibility for efficient photocatalytic hydrogen production under direct solar light. The exiting challenges and difficulties for this technology to proceed from successful laboratory photocatalysis set-up up to an industrially relevant scale are also proposed. These issues have been the object of our research and would also be the direction of our study in future.     

Supercritical water gasification of wastewater sludge for hydrogen production

The use of hydrogen as clean fuel gas in the power generation sector becomes essential to reduce the environmental issues related to conventional fuel usage. By avoiding biomass drying process, supercritical water gasification is considered the most efficient technology in hydrogen production from wastewater sludge. Wastewater sludge is difficult to disposal in its received form since it is often produced with high moisture content, contribute to numerous environmental issues and direct contact with this waste can result in health concerns. The assessment of the treatment and conversion of this material into fuel gas at condition beyond supercritical state (374°C and 22.1 MPa) is required. This paper is discussed the degradation routes of wastewater sludge in supercritical water. Furthermore, it is reviewed the influence of the main operation parameters role in the hydrogen production, which includes reaction temperature, pressure, residence time, feed concentration and catalysts. The development in reactor design and setup for maximum hydrogen production is highlighted. The technical challenges encountered during the conversion process and its solutions are also discussed. In addition, future prospective to optimal and standardization of the supercritical water gasification process is reviewed.     

Near stoichiometric reforming of biodiesel derived crude glycerol to hydrogen by photofermentation

Biodiesel manufacture produces crude glycerol as a major byproduct. At the scale estimated for future biodiesel production, extensive quantities of crude glycerol fraction will be generated, creating a large waste stream with potentially significant environmental impacts. The magnitude of projected future crude glycerol supplies suggests that its conversion to a biofuel is the only viable route to producing a product that does not cause market saturation. Previously it was shown that crude glycerol could be converted to hydrogen, a possible future clean energy carrier, by photofermentation using Rhodopseudomonas palustris through photofermentation. Here, the effects of nitrogen source and different concentrations of crude glycerol on this process were assessed. At 20 mM glycerol, 4 mM glutamate, 6.1 mol hydrogen/mole of crude glycerol were obtained under optimal conditions, a yield of 87% of the theoretical, and significantly higher than what was achieved previously.     

A complete analysis of the effects of transfer phenomenons and reaction heats on sono-hydrogen production from reacting bubbles: Impact of ambient bubble size

Several experimental and computational works have been focused on the production of hydrogen by using ultrasonic irradiation. However, the effects of the different ultrasonic conditions have been analyzed by considering a single value for the ambient bubble radius R₀ (mean value), which is not the true case as the size of active bubbles in sonicating medium is an interval rather than a sole value. In the present paper, the impacts of mass transport, heat exchange and chemical reactions heat on the sono-production of hydrogen are examined over a range of ambient bubble radii. These effects are shown for various ultrasonic frequencies of 355, 500 and 1000 kHz and under a range of acoustic amplitudes, from 1.5 to 3 atm. The numerical simulations results demonstrated that the increase of the production rate of hydrogen (around R₀ of the maximal production rate) is amortized (for all models) for the wave frequencies of 355 and 500 kHz at higher amplitude (i.e. 3 atm). On the other hand, the total production rate (around R₀ of the maximal response) is increased proportionally with the reduction of ultrasonic frequency or if the acoustic amplitude is increased. The effect of heat exchange mechanism (on H₂ and the total production rate) was found to be dominant whatever the acoustic amplitude or the wave frequency (on all the range of R₀). It has been demonstrated that at the acoustic amplitudes >1.5 atm (for f = 355 and 500 kHz) and >2 atm (for f = 1000 kHz), the impacts of chemical reactions heat and mass transport are clear compared to the normal model throughout a range of bubble sizes. The ambient bubble size (R₀) of the maximal response (maximal production rate) is shifted toward lower values when the ultrasound frequency or the acoustic amplitude is raised. In addition, it is observed that the increase in the wave frequency or the decrease in acoustic amplitude cause a narrowing in the range of active bubbles.     

Methane decomposition to pure hydrogen and carbon nano materials: State-of-the-art and future perspectives

Hydrogen is a clean fuel widely used in fuel cells, engines, rockets and many other devices. The catalytic decomposition of methane (CDM) is a CO_x-free hydrogen production technology from which carbon nano materials (CNMs) can be generated as a high value-added byproduct for electrode, membranes and sensors. Recent work has focused on developing a low cost catalyst that could work without rapid deactivation by carbon deposition. In this review, the economic and environmental evaluation of CDM are compared with coal gasification, steam reforming of methane, and methanol steam reforming in terms of productivity, CO₂ emissions, and H₂ production and cost. CDM could be a favorable technology for on-site demand-driven hydrogen production on a small or medium industrial scale. This study covers the Fe-based, Ni-based, noble metal, and carbonaceous catalysts for the CDM process. Focusing on hydrogen (or carbon) yield and production cost, Fe-based catalysts are preferable for CDM. Although Ni-based catalysts showed a much higher hydrogen yield with 0.39 mol_H2/g_cat./h than Fe-based catalysts with 0.22 mol_H2/g_cat./h, the hydrogen cost of the former was estimated to be 100-fold higher ($0.89/$0.009). Further, the CDM performance on different types of reactors are detailed, whereas the molten-metal catalyst/reactor is suggested to be a promising route to commercialize CDM. Finally, the formation mechanism, characterization, and utilization of carbon byproducts with different morphologies and structures are described and analyzed. Versus other reviews, this review shows that cheap Fe-based catalysts (10 tons H₂/1 ton iron ore) and novel molten-metal reactors (95% methane conversion) for CDM are feasible research directions for a fundamental understanding of CDM. The CNMs by CDM could be applied to the waste water purification, lubricating oils, and supercapacitors.     

Hydrogen production by Rhodopseudomonas palustris CQK 01 in a continuous photobioreactor with ultrasonic treatment

An ultrasonic treatment technique was applied to a continuous photobioreactor with Rhodopseudomonas palustris CQK 01 suspension to enhance photo-hydrogen production performance. After the start-up period, R. palustris CQK 01 suspension in the photobioreactor was intermittently agitated by ultrasonic wave with a frequency of 20 kHz and then the hydrogen production performance was evaluated. The ultrasonic agitation significantly dropped the hydrogen concentration in the suspension from 300 μmol/L to 50 μmol/L and thus increased the hydrogen production rate and hydrogen yield by nearly 2 times as compared with conventional photobioreactor. Furthermore, the effects of the ultrasonic power and time, influent substrate flow rate and concentration were investigated and discussed, respectively. The maximum hydrogen production performance of the continuous photobioreactor with ultrasonic treatment was obtained under the conditions of ultrasonic power 40 W, agitation/interval time 3/7 s, substrate concentration 75 mmol/L and substrate flow rate 40 ml/h, leading to the hydrogen production rate of 1.12 mmol/L/h and hydrogen yield of 0.23 mol-H₂/mol-glucose.     

Hydrangea like composite catalysts of ultrathin Mo2S3 nanosheets assembled on N,S-dual-doped graphitic biocarbon spheres with highly electrocatalytic activity for HER

Water electrolysis is the most clean and high-efficiency technology for production of hydrogen, an ultimate clean energy in future. Highly efficient non-noble electrocatalysts for hydrogen evolution reaction (HER) are desirable for large scale production of hydrogen by water electrolysis. Especially, exposing as many active sites as possible is a vital way to improve activities of the catalysts. Herein, a series of new hydrangea like composite catalysts of ultrathin Mo₂S₃ nanosheets assembled uprightly and interlacedly on N, S-dual-doped graphitic biocarbon spheres were facilely prepared. The unique structure endowed the catalysts highly exposed edge active sites and prominently high activities for HER. Especially, the optimized catalyst Mo₂S₃/NSCS-50 exhibited as low as 106 mV of overpotential at 10 mA/cm² (denoted as ?₁₀). The catalyst also showed low Tafel slope of 53 mV/dec, low electron transfer resistance of 34 Ω and high stability evidenced by the result that the current density only attenuated 11.7% after 10 h i-t test. The catalyst has shown broad prospect for commercial application in water electrolysis.     

Hydrogen evolution reaction in full pH range on nickel doped tungsten carbide nanocubes as efficient and durable non-precious metal electrocatalysts

Design of novel inexpensive non-precious metal electrocatalysts to replace Pt based electrocatalysts for wide pH range hydrogen evolution reaction (HER) still remains great challenges and opportunities, for globally sustainable supply of clean hydrogen. Ni doped tungsten carbide nanocubes supported on Ni foam (W_1-xNi_xC NCs/NF) synthesized via a hydrothermal-carbonization methods is reported. W_1-xNi_xC NCs/NF electrocatalysts exhibit excellent catalytic performance with overpotentials lower than 50 mV in both acidic, alkaline and neutral medium. Meanwhile, large electrochemical surface area and better conductivities of W_1-xNi_xC NCs/NF electrocatalysts are deemed in favour of its efficient catalytic properties. Moreover, the electrocatalysts show superior stability in wide pH range. It is believed that the present work provides a novel strategy for designing low-cost and efficient pH universal non-precious metal electrocatalysts for HER.     

Enhanced hydrogen production from xylose and bamboo stalk hydrolysate by overexpression of xylulokinase and xylose isomerase in Klebsiella oxytoca HP1

Biofuels production from lignocellulose hydrolysates by microbe fermentation has merited attention because of the mild reaction conditions involved and the clean nature of the process. In this work, xylulokinase (XK) and xylose isomerase (XI) were overexpressed in Klebsiella oxytoca HP1 to enhance hydrogen production by the fermentation of xylose. The recombinant strains exhibited higher enzyme activity of XI or XK compared with the wild strain. Hydrogen production from pure xylose, xylose/glucose mixtures and bamboo stalk hydrolysate was significantly enhanced with the overexpression of XI and XK in K. oxytoca HP1 in terms of total hydrogen yield (THY), hydrogen yield per mole substrate (HYPM) and hydrogen production rate (HPR). The HYPM of K. oxytoca HP1/xylB and K. oxytoca HP1/xylA reached 1.93 ± 0.05 and 2.46 ± 0.05 mol H₂/mol xylose, respectively in pure xylose, while the value for the wild strain was 1.68 ± 0.04 mol H₂/mol xylose. The xylose consumption rate (XCR) for the recombinant strain was significantly higher than that for the wild strain, particularly in the early stage of fermentation. Relative to the wild type, hydrogen yield (HY) from 1 g of preprocessed bamboo powder of HP1/xylB and HP1/xylA increased by 33.04 and 41.31%, respectively. It was concluded that overexpression of XK or XI was able to promote hydrogen production from xylose and xylose/glucose mixtures by simultaneously increasing the utilization efficiency of xylose and weakening the inhibitory effect of glucose on xylose use. In addition, the results indicated that overexpression technology was an effective way to further increase hydrogen production from lignocellulosic hydrolysates.     

Studies on evaluation of pretreatment efficiency of surfactant mediated ultrasonic pretreatment of Sargassum tennerimum (marine macroalgae) for achieving profitable biohydrogen production

Growing energy demand is inevitable in the future, due to increased commercialization and industrialization. Biohydrogen production from renewable biomass is considered as clean energy technology and, in this study, the feasibility of using Sargassum tennerimum as a renewable energy source has been attempted. Pretreatment using sonication pretreatment (ST) and surfactant Dioctyl sodium sulphosuccinate (DOSS) mediated ultrasonic pretreatment (DOSSSP) were investigated and the optimized pretreatment time and sonication power, respectively, were 30 and 200W for ST. DOSS dosage of 0.005 g/g TS was found to be optimum for DOSSSP with the corresponding maximum of 2600 mg/L and 27.36% respectively for sCOD (Soluble chemical oxygen demand) release and COD (Chemical oxygen demand) solubilization percentage. Biohydrogen assay analysis of the pretreated algal biomass was carried out and 86 mL/g COD of maximum biohydrogen production was achieved for DOSSSP pretreated sample than ST and control owing to higher COD solubilization percentage, carbohydrate and protein release. Energy analysis was performed to test the economic viability of the pretreatment process. This analysis showed that the maximum net positive energy of 0.0407 and energy ratio of 2.43 was obtained for DOSSSP revealing its economic viability. This study also reveals that macroalgae Sargassum tennerimum could be a sustainable renewable energy source for biohydrogen production as it is abundant throughout the year.     

Feasibility study for hydrogen production using hybrid solar power in Algeria

Hydrogen demand as a clean energy is one of the new energy challenges in the future. Being a very controlled technology, the water electrolysis is more efficient at high temperature level than at low one. This is because of the use of thermal energy which is less expensive than the use of electricity power to produce the hydrogen; the chemical reaction is more activated in these conditions. In this paper, the feasibility of hydrogen production at high temperature electrolyser, using a hybrid solar resource, thermal energy (parabolic trough concentrators) to produce high temperature, steam water and photovoltaic energy for electricity requirements of the HTE, is presented. The described here-after presented in this document guarantees the production of an important quantity of hydrogen at 900 °C. The production rate depends on geographic position, on climatic conditions and on sun radiation. The optimization of the process is strongly related to what preceded these three parameters. Then, we suggest the set up construction in any region allowing maximum extraction of energy based in our simulation results.     

Photo-fermentative hydrogen production performance of a newly isolated Rubrivivax gelatinosus YP03 strain with acid tolerance

Screening and excavating new photosynthetic bacteria with excellent hydrogen production performance is extremely important for improving the photo-fermentative hydrogen production. A new photosynthetic bacterium YP03 was isolated and identified to be Rubrivivax gelatinosus by morphological characterization and phylogenetic analysis. The effects of several key factors on hydrogen production performance were carried out. The results indicated that YP03 strain showed a preference for the carbon sources, and 5375 ± 398 mL/L of maximum hydrogen yield was obtained using butyrate medium. Meanwhile, YP03 strain could use several nitrogen sources to produce hydrogen, and glutamic acid was the optimum nitrogen source for hydrogen produced. Furthermore, YP03 exhibited better hydrogen production performance at initial pH 7.0, reaction temperature 33 °C and light intensity 5000 lux, and the maximum hydrogen production rate was 108.3 ± 12.4 mL/(Lh), which was relatively high compared with the previous reports by R. gelatinosus. Especially, the proper pH for hydrogen production by YP03 ranged from weak acid to neutral (6.5–7.0) and it still could produce hydrogen at pH 5.5 showing the characteristic of acid tolerance. It suggested that YP03 is a potential candidate for the integration of dark- and photo-fermentative hydrogen production. These findings contribute to our understanding of YP03 strain and provide a prospective photosynthetic bacterium for efficient hydrogen production in future research.     

Biological hydrogen production via dark fermentation: A holistic approach from lab-scale to pilot-scale

Biohydrogen is considered as fuel of future owing to its distinctive attribute for clean energy generation, waste management and high energy content. Suitable feedstock play important role for achieving high rate hydrogen production via dark fermentation process. In this regard, different organic wastes such as cane molasses, distillery effluent and starchy wastewater were examined as potential substrates for biohydrogen production by Enterobacter cloacae IIT-BT 08. Groundnut deoiled cake (GDOC) was considered as additional nutritional supplement to enhance biohydrogen yields. The maximum hydrogen yield of 12.2 mol H₂ kg⁻¹ COD_removed was obtained using cane molasses and GDOC as co-substrates. To further ensure reliability of the process, bench (50 L) and pilot scale (10000 L) bioreactors were customized and operated. The pilot scale study achieved 76.2 m³ hydrogen with a COD removal and energy conversion efficiency of 18.1 kg m⁻³ and 37.9%, respectively. This study provides an extensive strategy in moving from lab to pilot scale biohydrogen production thereby, providing further opportunity for commercial exploitation.