Maximum Hydrogen Production Rate Research Articles

Performance of a pilot-scale microbial electrolysis cell coupled with biofilm-based reactor for household wastewater treatment: simultaneous pollutant removal and hydrogen production.

The septic tank is the most commonly used decentralized wastewater treatment systems for household wastewater treatment in on-site applications. The removal rate of various pollutants is lower in different septic tank configurations. The integration of a microbial electrolysis cells (MEC) into septic tank or biofilm-based reactors can be a green and sustainable technology for household wastewater treatment and energy production. In this study, a 50-L septic tank was converted into a 50-L MEC coupled with biofilm-based reactor for simultaneous household wastewater treatment and hydrogen production. The biofilm-based reactor was integrated by an anaerobic packed-bed biofilm reactor (APBBR) and an aerobic moving bed biofilm reactor (aeMBBR). The MEC/APBBR/aeMBBR was evaluated at different organic loading rates (OLRs) by applying voltage of 0.7 and 1.0V. Result showed that the increase of OLRs from 0.2 to 0.44kg COD/m3 d did not affect organic matter removals. Nutrient and solids removal decreased with increasing OLR up to 0.44kg COD/m3 d. Global removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), ammoniacal nitrogen (NH4+), total phosphorus (TP) and total suspended solids (TSS) removal ranged from 81 to 84%, 84 to 85%, 53 to 68%, 88 to 98%, 11 to 30% and 76 to 88% respectively, was obtained in this study. The current density generated in the MEC from 0 to 0.41 A/m2 contributed to an increase in hydrogen production and pollutants removal. The maximum volumetric hydrogen production rate obtained in the MEC was 0.007 L/L.d (0.072 L/d). The integration of the MEC into biofilm-based reactors applying a voltage of 1.0V generated different bioelectrochemical nitrogen and phosphorus transformations within the MEC, allowing a simultaneous denitrification-nitrification process with phosphorus removal.

Optimization of Hydrogen Production System Performance Using Photovoltaic/Thermal-Coupled PEM

A proton exchange membrane electrolyzer can effectively utilize the electricity generated by intermittent solar power. Different methods of generating electricity may have different efficiencies and hydrogen production rates. Two coupled systems, namely, PV/T- and CPV/T-coupling PEMEC, respectively, are presented and compared in this study. A maximum power point tracking algorithm for the photovoltaic system is employed, and simulations are conducted based on the solar irradiation intensity and ambient temperature of a specific location on a particular day. The simulation results indicate that the hydrogen production is relatively high between 11:00 and 16:00, with a peak between 12:00 and 13:00. The maximum hydrogen production rate is 99.11 g/s and 29.02 g/s for the CPV/T-PEM and PV/T-PEM systems. The maximum energy efficiency of hydrogen production in CPV/T-PEM and PV/T-PEM systems is 66.7% and 70.6%. Under conditions of high solar irradiation intensity and ambient temperature, the system demonstrates higher total efficiency and greater hydrogen production. The CPV/T-PEM system achieves a maximum hydrogen production rate of 2240.41 kg/d, with a standard coal saving rate of 15.5 tons/day and a CO2 reduction rate of 38.0 tons/day. Compared to the PV/T-PEM system, the CPV/T-PEM system exhibits a higher hydrogen production rate. These findings provide valuable insights into the engineering application of photovoltaic/thermal-coupled hydrogen production technology and contribute to the advancement of this field.

Synergistic sodium alginate- and biochar-immobilized cells for enhancing fermentative hydrogen production from food waste.

An immobilized hydrogen-producing consortium investigated biohydrogen production from food waste using a combination of sodium alginate and cassava rhizome biochar. We investigated the effect of varying the biochar concentration from 0 to 3% and the size of immobilized cells from 1 to 7mm. Immobilized cells were prepared using 50% (v/v) enriched hydrogen-producing consortium, 2% (w/v) sodium alginate, and 0 to 3% (w/v) cassava rhizome biochar. The optimal conditions for achieving the highest hydrogen production in the batch fermentation reactor were identified as a biochar concentration of 2% (w/v) and an immobilized cell size of 2mm. The highest hydrogen yield, maximum hydrogen production rate, and lag time recorded were 0.69mmol H2/g-COD, 0.02mmol H2/g-COD.h, and 41.51h, respectively. This research highlights the potential of cassava biochar technology for efficient biohydrogen production from food waste, contributing to renewable energy generation and sustainable waste management.

Study of the Sodium Borohydride Hydrolysis Reaction's Performance via a Kaolin-Supported Co-Cr Bimetallic Catalyst

Hydrogen is an attractive source of energy because of its properties, which include superior quality, effectiveness, pureness, dependability, and sustainability. Technologies for producing and storing hydrogen are being developed in parallel with fuel cell development. Chemical storage of hydrogen in a metal hydride containing boron eliminates the problem of hydrogen transportation and storage. Through catalytic reactions, hydrogen stored in solid form in boron hydrides can be recovered. In this study, a nowel developed Co-Cr bimetallic catalyst supported by kaolin, a natural mineral, was synthesized to be used for hydrogen production by hydrolysis of sodium boron hydride. The structural characteristics of the produced Co-Cr@Kaolin catalyst were ascertained by EDX, FTIR, and SEM analyses. Next, the ideal conditions for the hydrolysis reaction of sodium borohydride (NaBH4) catalyzed by Co-Cr@Kaolin were examined. These included the concentration of the catalyst, the amount of support material (kaolin), the amount of catalyst, and the concentration of NaBH4. The optimal hydrolysis conditions were found to be 2.5% NaOH concentration, 40 mg of catalyst, and 2% NaBH4 concentration at 303 K. The maximum rate of hydrogen production was determined as 5007 ml g-1 min-1 under optimal conditions. After conducting hydrolysis operations at different temperatures to elucidate the reaction kinetics, it was found that the catalytic hydrolysis reaction was of the 0th order and that the reaction activation energy was 19.36 kJ mol-1. The hydrogen production rate obtained as a result of the hydrolysis reaction accompanied by a Co-Cr catalyst was determined as 3166 ml g-1 min-1. It is therefore established that supporting kaolin to Co-Cr catalyst enhances its efficacy.

Hybrid magnetic nanocomposite NiFe2O4/TiO2 for Photocatalytic dye degradation and green hydrogen (H2) generation

The present paper focuses on designing and developing nanocomposites to modify their properties to increase the ability to generate hydrogen and degrade photocatalytic dyes. A nanocomposite of nickel ferrite (NiFe2O4)/Titanium dioxide (TiO2) was formulated using the sol-gel self-ignition method. X-ray diffraction (XRD) tool was adopted to analyze the structural behavior of pure nickel ferrite (NiFe2O4), pure titanium dioxide (TiO2), and nanocomposite of NiFe2O4/TiO2. XRD pattern of NiFe2O4 and TiO2 shows a monophasic nature whereas the XRD pattern of nanocomposites shows mixed phases of NiFe2O4 and TiO2. FTIR spectra confirm the formation of NiFe2O4, TiO2, and their composites with absorption bands near 400 cm-1 and 600 cm-1, 1500 cm-1. Raman spectra unveiled the presence of five active Raman modes in the case of NiFe2O4 whereas three active Raman modes are seen in TiO2. Field emission scanning electron microscopy (FE-SEM) images exposed the dense structure with spherical cluster-like morphology in the case of NiFe2O4. Energy-dispersive X-ray spectroscopy (EDX) analysis confirms the presence of all the desired elements of NiFe2O4, TiO2, and their composites in stoichiometric proportions. BET analysis of nickel ferrite NPs suggests a large surface area of the order of 31.54 m2/gm in comparison with TiO2 (19.23 m2/gm). The optical characterization was made through the UV-visible spectroscopic technique. TiO2 shows a maximum band gap of the order of 3.02 eV while NiFe2O4 shows a low band gap of the order of 1.74 eV. A typical M-H curve with saturation magnetization of the order of 27.54 emu/gm was observed for pure NiFe2O4. No magnetic properties were observed for TiO2 as it is a semiconductor. Enhancement in magnetic properties is observed with increases in NiFe2O4 content in a composite of NiFe2O4/TiO2. The photocatalytic activities were examined by degrading Methylene Blue (MB) dye under sunlight for pure nickel ferrite (NiFe2O4), pure titanium dioxide (TiO2), and a nanocomposite of NiFe2O4/TiO2. Photocatalytic hydrogen production reactions were carried out in a methanol/water solution under visible light. Consequently, the best configuration of the photocatalyst was determined as 25% wt% NiFe2O4/ TiO2 which had shown the maximum hydrogen (H2) production rate as 146.3 μmol/g/h after 8 h owing to its reduced bandgap energy and delayed e- / h+ recombination.

Synthesis, Characterization of KNb0.99Eu0.01O3 and improved Photo-catalytic H2-Production on Ag/La2NiO4/ KNb0.99Eu0.01O3 hetero-junction

The perovskite KNb0.99Eu0.01O3 prepared by nitrate combustion is applied as a hydrogen photocathode in heterojunction with La2NiO4 under visible light. The XRD pattern confirms the formation of KNb0.99Eu0.01O3 structure with orthorhombic single phase. The SEM images present grains between 0.2 and 0.4 µm while the optical band gap (3.14 eV) is calculated from the diffuse reflectance. Under illumination, the cyclic voltammetry (CV) and the capacitance measurements in Na2SO4 electrolyte show an increased current below ∼ -0.7 V vs. Ag/AgCl and p-type behavior with a conduction band (CB = −1.95 V) cathodically positioned with respect to H2 level, thus leading to H2 photo-production. The hetero-system La2NiO4/KNb0.99Eu0.01O3 shows a much higher activity than KNb0.99Eu0.01O3 where efficient H2-photoevolution occurs with concomitant oxidation of S2O32−, as reducing agent. So, the co-junction of La2NiO4 with KNb0.99Eu0.01O3 facilitates the charge transfer and increases the reaction efficiency. At neutral pH, the H2 evolution rate for the photocatalysts KNb0.99Eu0.01O3 and La2NiO4/ KNb0.99Eu0.01O3 are 11.15 and 57 µmol g−1 min−1; respectively. Further enhancement is observed with Ag-loaded La2NiO4/KNb0.99Eu0.01O3, reaching a maximum hydrogen production rate of 67 µmol g−1 min−1, attributed to the lower overpotential introduced by Ag. These findings highlight the potential of the ternary system Ag/La2NiO /KNb0.99Eu0.01O3 as an efficient photocathode for H2 generation.

Hydrogen production from ZnCl2 salt: Application of chlor-alkali method

This experimental study investigates the efficiency of hydrogen production from an aqueous ZnCl2 solution using an electrochemical method within a chlor-alkali reactor. A laboratory-scale reactor with separate anode and cathode compartments was constructed for this purpose. The compartments are separated by a Nafion 212 membrane, which prevents the mixing of the anolyte and catholyte solutions while allowing the passage of positive ions (Zn+). Each compartment is equipped with five carbon rod electrodes. The anode chamber is fed with an aqueous ZnCl2 solution, while the cathode chamber is supplied with pure water. The experiments were conducted with a constant electrolyte transfer rate of 0.3g/s into the reactor, at three different cell voltages (5.0, 7.5, and 10.0V) and two different cell temperatures (20 °C and 45 °C). Due to the small reactor dimensions and the dilution effect caused by adding pure water to the cathode compartment which decreases electrolyte density and adversely affects the current a noticeable reduction in hydrogen gas production was observed. Furthermore, the ZnCl2 electrolyte mass flow rate did not significantly impact the current or the generation of hydrogen and chlorine gases. Consequently, no changes were made to the mass flow rate of pure water or the electrolyte. The presence of active chlorine gas was found to cause the erosion of the carbon rod electrodes in the anode chamber. As a result, the amount of chlorine gas produced in the anode chamber is significantly lower than the hydrogen gas produced in the cathode chamber. At a cell temperature of 20 °C, a mass flow rate of 0.3 g/s, and a cell voltage of 5 V with ZnCl2 aqueous solution, the minimum hydrogen production rate is 0.625 mL/min. In contrast, at a cell temperature of 45 °C, a mass flow rate of 0.3 g/s, and a cell voltage of 10 V, the maximum hydrogen production rate is 4.97 mL/min.

Novel cocatalyst MnCo2S4 based on Zn3In2S6 for enhanced photocatalytic hydrogen production and ranitidine degradation

Photocatalysis offers a sustainable method for producing hydrogen and degrading harmful substances such as ranitidine. In this research, metal-like properties of MnCo2S4 nanoparticles were synthesized using a glycerol precursor and integrated into Zn3In2S6 floral microsphere via a low-temperature hydrothermal method to function effectively as a cocatalyst. The catalyst not only exhibits excellent hydrogen production efficiency but also demonstrates outstanding performance in degrading ranitidine. Under visible light irradiation, the MnCo2S4/Zn3In2S6 composite material reached a maximum hydrogen production rate of 4471.7 µmol·g−1·h−1 within 6 h, which is 10.6 times higher than that of pure Zn3In2S6. After 24 h of reaction over 4 continuous cycles, the hydrogen evolution activity maintained 94.86 % of its initial performance. Additionally, after 60 min of visible light exposure, the composite achieved a ranitidine degradation rate of 94.7 %, significantly surpassing the performance of pure Zn3In2S6. This exceptional photocatalytic activity is attributed to the synergistic interactions between Zn3In2S6 and the conductive cocatalyst MnCo2S4, which facilitate interfacial charge transfer. A potential reaction mechanism was proposed, supported by a series of experiments and characterization techniques. The formation of a Schottky junction at the MnCo2S4/Zn3In2S6 interface enables rapid electron transfer to the MnCo2S4 nanoparticles, preventing electron backflow and thus promoting effective separation of photo-induced charge carriers. Therefore, this study introduces a novel approach for designing metal-semiconductor photocatalysts for efficient hydrogen production and ranitidine degradation.

Effect of RE-O/C catalyst on the hydrolysis kinetics and catalytic mechanism of MgH2

The reaction between MgH2 and water produces a significant amount of hydrogen gas, which is beneficial for the development of hydrogen energy in fuel cells. However, the slow hydrogen production rate and the formation of a dense Mg(OH)2 layer limit its application. In this study, MgH2 was doped with 2 wt%, 4 wt%, and 8 wt% of RE-O/C (RE-O = La2O3, CeO2, Pr6O11) catalysts through ball milling technology, and hydrolysis experiments were conducted. The hydrolysis kinetics and activation energy were analyzed using Avrami-Erofeev and Arrhenius equations for linear fitting. X-ray diffraction and scanning electron microscopy were employed to analyze the hydrolysis mechanism and the effect of the catalysts on particle surfaces. Notably, the addition of 4 wt% RE-O/C exhibited the best improvement in the hydrolysis performance of MgH2. At high temperatures, the maximum hydrogen production rates for MgH2+4La2O3/C, MgH2+4CeO2/C, and MgH2+4Pr6O11/C are 32.05, 30.92, and 29 mL·g−1·s−1, respectively, with maximum hydrogen capacities of 1996, 2140, and 2000 mL·g−1, and activation energies of 21.8, 24.8, and 21.3 kJ·mol−1, respectively. The MgH2+RE-O/C composites studied overcame the key issues of MgH2 hydrolysis, presenting a promising strategy for hydrogen production.

Ternary Fe–Ni–B particles supported on Cu(OH)2–Cu foam: A highly efficient and stable catalyst for hydrolysis of ammonia borane

Ammonia borane (NH3BH3) as a solid chemical hydrogen storage material with a high hydrogen content can be hydrolyzed under mild conditions to release hydrogen. In this work, Fe–Ni–B/Cu(OH)2–Cu foam was synthesized by combining in situ growth and electroless plating. Compared with the binary Fe–B/Cu(OH)2–Cu foam and Ni–B/Cu(OH)2–Cu foam prepared by the same method, the ternary Fe–Ni–B/Cu(OH)2–Cu foam has superior catalytic performance. The Fe–Ni–B/Cu(OH)2–Cu foam catalyst was able to achieve a maximum hydrogen production rate of 5.6 ml min−1 cm−2 at 298 K with an activation energy as low as 46.3 kJ mol−1. And more importantly, its catalytic efficiency has hardly decayed after ten cycles. These excellent properties are due to its low activation energy and the large specific surface, multi–site Cu(OH)2–Cu–foam carrier.

Synergistic approach: Photocatalytic hydrogen generation for curcumin hydrogenation

Sn1-xFexO2 (x = 0, 0.1, 0.2 & 0.3) nanomaterials were successfully synthesized by co-precipitation technique and characterized by XRD, FTIR, SEM-EDAX, TG/DSC, etc. XPS revealed the presence of Fe+3 & Sn+4 ions in the SnO2 crystal lattice. Insertion of Fe shifts the absorption of SnO2 to the visible region. These synthesized nanomaterials show efficiency for hydrogen generation and degradation of organic dyes in the presence of visible light. The water splitting was performed under different conditions. A maximum hydrogen production rate of 12.8 mmol g−1h−1 was observed for Sn0.8Fe0.2O2 with glucose as a sacrificial agent. The photogenerated H2 finds application in hydrogenation of curcumin to tetrahydrocurcumin.

An innovative electrolytic cation exchange reactor system for cleaner generation of hydrogen gas using ocean water

The study presents a novel integrated three-compartment electrochemical continuous electrodeionization reactor that was constructed in a laboratory environment. In order to extract large amounts of carbon dioxide from naturally occurring oceanwater in the form of bicarbonate and carbonate, it develops a innovative electrolytic cation exchange process. At the same time, it produces hydrogen gas for possible hydrocarbon synthesis. The study employs the Box-Behnken experimental design approach implemented through the Design Expert software to investigate and optimize the performance of electrochemical hydrogen extraction from Ocean water from an integrated reactor. The integrated electrochemical continuous-type electrodeionization reactor comprises two cation-permeable membranes that operate as boundaries between three compartments: a central compartment and electrode compartments that house the cathode and anode, each of which may reverse polarity. These membranes are made of gel polystyrene cross-linked with divinylbenzene, which has acidic properties that allow cation transport while inhibiting anions. The integrated reactor's electrode chambers are enclosed in plexiglass end plates and contain distinct Plexiglass electrode compartments. These compartments have mesh and solid steel anode and cathode electrodes, with an electrode active area of 176.71 cm2. The influence of various factors, such as voltage and electrolyte amount, on the production of hydrogen synthesis is examined. The study results demonstrate a maximum hydrogen production rate of 2.2 mg/min and a hydrogen production efficiency of 7.82%. The lab testing was carried out using experimental equipment to determine viability. The tests included 35-min runs that measured hydrogen generation under various parameters, such as applied voltage, electrolyte concentration, and pH levels. The ocean salt solutions of 0.5M, 1M, and 2M were initially prepared and evaluated for hydrogen generation. Each concentration is assessed at a voltage range of 4–15V, with matching solution pH values ranging from 2 to 7. Optimization studies were conducted to enhance the hydrogen production rate. The results indicate that hydrogen production rises proportionally with applied voltage and electrolyte concentration but falls with pH growth. Within the Design Expert software, the statistical methods for response surface analysis and optimization are utilized accordingly.

Sustainable duckweed biomass valorization for dark fermentative hydrogen production: Process evaluation under meso- and thermophilic operations

Aquatic plants are rich in biomass and contain good amounts of carbohydrates and proteins which are amenable for valorization to generate bioenergy. Duckweed is rich in proteins and carbohydrates that grow abundantly in contaminated waterbodies, which is now tested for as a substrate for biohydrogen production. Dark-fermentative hydrogen production was done by hydrothermal pretreatment of duckweed biomass under 15 lbs pressure, evaluated under three different operating temperatures that cover mesophilic (35 °C) and thermophilic conditions (50 and 55°C). The study resulted in the maximum hydrogen production rate of 0.97 mmol/day in batch culture (160 mL) from 55 °C that was found superior to 50 °C (0.84 mmol/day) and 35 °C (0.38 mmol/day) operations. From the 7 days of operation, under uncontrolled pH conditions, substrate (chemical oxygen demand, COD) utilization was 57.27 %, which is higher than in mesophilic conditions (50.67 %). Efficient hydrolysate conversion was noticed with thermophilic conditions, especially under operation at 55 °C (416 mL H2/g of biomass) than mesophilic conditions (144 mL H2/g of biomass) suggesting that duckweed can be dependable biomass for hydrogen production, and the dark-fermentation can be an appropriate solution of aquatic weed biomass management in a sustainable approach.

Embedding ZnCo2O4 quantum dots onto graphdiyne (g-CnH2n-2) nanosheets as a 0D/2D S-scheme heterojunction for highly efficient photocatalytic H2 evolution

The design of environmentally friendly and cost-effective S-scheme heterojunctions with robust interfacial interactions is pivotal for enhancing photocatalytic performance and facilitating practical application. In this work, ZnCo2O4 quantum dots (QDs)/graphdiyne (ZCOG) S-scheme heterojunction was synthesized by a simple hydrothermal method. ZnCo2O4 QDs with quantum size effect were prepared by calcination, while graphdiyne (GDY) nanosheets were synthesized by reduction-elimination reaction using CuBr as catalyst. The maximum hydrogen production rate of ZCOG reaches 2472.80 μmol g-1h−1, which is 30.75 and 10.84 times higher than that of ZnCo2O4 QDs and GDY, respectively. This significantly enhanced photocatalytic activity is attributed to the strongly coupled S-scheme heterojunction between GDY and ZnCo2O4 QDs, which accelerates the photogenerated electron transfer while effectively suppressing the recombination of photogenerated carriers. In addition, the quantum size effect of the ZnCo2O4 QDs leads to an increase in the width of the electronic forbidden band, which enhances the energy of electrons (holes) in the conduction band (valence band). The S-scheme mechanism of ZCOG was revealed by in situ XPS, UPS and TRPL spectroscopy, and the reliability of the conclusions was further verified by DFT calculations. This work provides an efficient strategy for the construction of GDY-based photocatalysts with quantum size effect.

Adjustable n→π* electronic transition by sulfonated benzene functionalized g-C3N4 for enhanced photocatalytic H2 generation

The photocatalytic efficiency of graphitic carbon nitride (g-C3N4) in hydrogen production is primarily hindered by its poor absorption of visible light, rapid recombination of electron-hole pairs, and the absence of hydroxyl radical formation. Herein, a novel g-C3N4 nanosheets functionalized with sulfonic acid groups were effectively produced through thermal polymerization of melamine and 2, 4-diamino-6-phenyl-1, 3, 5-triazine (DPT), followed by sulfonation treatment. The introduction of the phenyl group brings about alterations to the initial symmetrical arrangement of g-C3N4, leading to the disruption of certain hydrogen bonds. This, in turn, facilitates the movement of electrons from the n to π* orbitals, resulting in enhanced light absorption and improved efficiency in charge separation. Moreover, it induces modifications to the band structure and amplifies the production of hydroxyl radicals. Additionally, the introduction of sulfonic acid enhances the water affinity and the ability of dispersing graphitic carbon nitride in water. The optimized sulfonated benzene-substituted g-C3N4 (1000-BCN-SO3H) with a melamine to DPT ratio of 4:1 exhibits a maximum hydrogen production rate of 6.52 mmol·h−1·g−1 under simulated sunlight irradiation with good cycling stability, which is 3.93 times higher than that of g-C3N4 nanosheets. This research offers a promising opportunity for a novel approach in advancing carbon nitride materials for effective photocatalytic processes.

Hydrogen generation from sodium borohydride hydrolysis using a heterogeneous biocatalyst prepared with Zabrus tenebrionides Goeze 1777 (Coleoptera: Carabidae) chitin

Co–B/Chi, which is made up of highly distributed Co–B particles, was synthesized by impregnation and chemical reduction methods. Scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller adsorption and Fourier transform infrared spectroscopy analyses were used to describe the morphology and microstructure of Co–B/Chi. The synthesized catalyst showed high catalytic activity in the hydrolysis reaction of NaBH4. The unsupported Co–B samples were compared with the chitin-supported Co–B catalyst, and the result showed that higher catalytic activity and good cycling stability for NaBH4 hydrolysis were obtained with the chitin-supported catalyst. The reaction conditions were investigated to achieve high hydrogen production. The maximum rate of hydrogen production was obtained at 40 °C and 20 mg catalyst amount. At ideal conditions, the hydrolysis reaction’s activation energy was determined to be 51.65 kJ mol−1. It is indicate that Co–B/Chi is a viable low-cost catalyst for the hydrolysis of NaBH4 for hydrogen production.

Thermodynamic modelling of a combined polygeneration system with sustainability analysis for power, cooling and hydrogen production

The study presents the thermodynamic modelling of a combined polygeneration system with sustainability analysis for power, cooling and hydrogen production. The study’s objective includes producing multiple products from a single energy source from an adapted polygeneration plant and comparable cooling rate production from the condensate of one evaporator system. The system’s sustainability was also evaluated based on some considered thermodynamic parameters. The system was modelled component by component, and the thermodynamic models developed were analysed using an engineering equation solver software (EES). The results show that total energy and exergy efficiencies obtained from the operating parameters were 47.2 and 38.32%, respectively, with total cooling rate production of approximately 25 kW. The cooling rate decreases by about 3% for one one-degree rise in the dead state temperature, while for an increase in the gasifier temperature, the high-power turbine work somewhat decreases by about 5%. The maximum hydrogen production rate was about 135 kg/h obtained at 80°C of the electrolyser temperature. The system was sustainable as the exergy-based indicators showed approximately 1.66, 0.87 and 0.65 for the sustainability index, exergetic impact index and thermal exergy index, respectively. Suggestions are made for optimisation for ideal parameters that will bring the system close to ideality.

Photo-Fermentative Bacteria Used for Hydrogen Production

Photo-fermentation is an efficient hydrogen production pathway in which purple non-sulfur bacteria (PNSB) play an active role and produce hydrogen as a part of their metabolism under optimal conditions. These bacteria work under the influence of light to advance their metabolism and use various substrates, such as simple sugars and volatile fatty acids, to produce hydrogen. This article presents a comparative review of several bacterial strains that have been efficiently used to produce hydrogen by photo-fermentation under different optimized conditions, including the substrate, its concentration, type and capacity of the bioreactor, light sources and intensities, and process conditions to achieve the maximum biohydrogen production rate. The analysis showed that the Rhodopseudomonas palustris is the main bacterium used for hydrogen production, with a maximum hydrogen production rate of 3.2 mM/h using 27.8 mM of glucose in a 165 mL serum bottle and 3.23 mM/h using 50 mM of glycerol at pH 7, followed by Rhodobacter sphaeroides, which gave a hydrogen production rate as high as 8.7 mM/h, using 40 mM of lactic acid, pH 7, and 30 °C temperature in a single-walled glass bioreactor. However, it is not preferred over R. palustris due to its versatile metabolism and ability to use an alternative mode if the conditions are not carefully adjusted, which can be a problem in hydrogen production.

Dual-function macroalgae biochar: Catalyst for hydrogen production and electrocatalyst

In the current study, Enteromorpha intestinalis, a green macroalgae, has been utilized as a substrate to synthesise a new environmentally friendly and cheap dual-functional (catalyst and electrocatalyst) material. The catalyst was used for efficient hydrogen production from alcoholises sodium borohydride and as an anode catalyst for direct methanol fuel cell applications. At the catalyst synthesis stage, orthogonal arrays of Taguchi is used to find the optimum levels of independent variables for the superior catalyst performance that bears the modest kinetics. The experiments performed in accordance with the L16(45) type orthogonal array. The samples treated at relatively moderate acid, impregnation temperature, impregnation time, burning temperature and burning time showed higher catalytic activities with Exp(5) presenting the optimal catalytic activity followed by Exp(1), Exp(15), Exp(8) and Exp(12), respectively. The experimental levels of coded variables (acid molarity, impregnation temperature and time, burning temperature and time) for Exp(5) were 3 M, 50 °C, 24 h, 500 °C and 2 h., respectively. These finding suggest that providing maximum levels of each of independent variable will not provide high catalytic activity. Taking into account the binary and ternary interactions is an efficient way to determine optimal level of each parameter with regards to maximum hydrogen production rate. The morphological and structural characterization of the optimal catalyst was finally carried out with SEM- EDS, XRD and FT-IR. CV and EIS measurements were taken to determine the electrocatalytic activity of final biochar. Experimental studies revealed that the utilization of E. intestinalis-based electrocatalyst as an anode catalyst for direct fuel cell applications is promising. By employing advanced Taguchi-based experimentation, this research establishes the optimum levels of independent variables, enhancing the catalyst's performance, and highlighting a novel approach to modest kinetics improvement.

Optimization of photofermentative biohydrogen production in a mixed volatile fatty acid medium by Rhodobacter sp. MAY2: A response surface methodology (RSM) approach

Biohydrogen production through photofermentation has gained significant attention as it provides a sustainable solution for clean energy supply and addresses wastewater concerns by utilizing volatile fatty acids (VFA) which are produced in dark fermentation. In this study, response surface methodology via a Face-centered Central Composite Design (FCCD) was employed to optimize buffer solution pH, ferric citrate concentration, sodium glutamate concentration to maximize biohydrogen production by Rhodobacter sp. MAY2 with mixed VFA (acetate, propionate, butyrate) as substrates. Results showed that the concentrations of ferric citrate, sodium glutamate, and buffer solution pH positively impact the biohydrogen production of Rhodobacter sp. MAY2. The optimal conditions were shown to be 0.36 mM ferric citrate, 11 mM sodium glutamate, and buffer solution of pH 7. The predicted hydrogen production potential (HPP) at these conditions (661.1 mL/L) was within 2 % of the actual HPP (647.7 mL/L). Kinetic parameters using the modified Gompertz equation showed that the predicted values for maximum potential cumulative H2 production (P), maximum hydrogen production rate (Rm), and lag time (λ) are comparable to those reported in literature. Overall, the study highlighted the potential of a local isolate, Rhodobacter sp. MAY2, for biohydrogen production and the suitable fermentation conditions for its growth.