Modeling and statistical analysis of heat-shocked sulfate-reducers and methanogens rich consortiums for hydrogen and methane production in a bio-electrochemical cell

This study was carried to investigate the effect of thermal pre-treatment at 55 °C, 65 °C, 75 °C, and 85 °C on sulfate-reducing bacteria (SRB) and methanogens to check their potential in a Bio-electrochemical system (BES) for hydrogen and methane production. The experimental results indicate that SRB culture pre-treated at 55 °C could be used efficiently in hydrogen production up to 2.814 ± 0.091 M/M of glucose. A significant drop in methane production from Phase-I to Phase-III with an increase in pre-treatment temperature was observed. Volatile fatty acids production was found highest in Phase-III, with butyric acid in major concentration at the pre-treatment temperature range of 55 °C–65 °C in SRB-based BES. The higher hydrogen production conditions were tested with various models i.e. the Gompertz model, Richard model, and Logistic model to confirm its validity and hydrogen production prediction. Richard's model was found best fitted for cumulative hydrogen production.     

Ammonia as carbon-free substrate for hydrogen production in bioelectrochemical systems

In this study, ammonia was used as an anode substrate for cathode hydrogen generation by controlling the anode potential in two compartment bioelectrochemical systems. During batch experiments, the total quantity of electric charge increased from 129 C at 10 mM ammonia to 185 C at 20 mM ammonia, and it reached 281 C at 30 mM ammonia. Besides, the nitrogen removal efficiency reached 41%, 56% and 48% at 10, 20 and 30 mM ammonia respectively. Correspondingly, the productions of nitrogen were respectively 5.1 ml, 13.3 ml and 14.3 ml, and the productions of hydrogen were respectively 7.2 ml, 13.4 ml and 14.6 ml. However, there were no nitrogen and hydrogen production, as well as only a little electric charge of 10 C when there was no ammonia addition. The coulombic efficiency was higher than 50% during 5 days operation, which demonstrated that the bacteria growing on the anode were able to utilize most of the available ammonia for current generation. In addition, ammonia-oxidizing bacteria and ammonia-assimilating bacteria were detected by microbial community analysis of 16S rRNA genes based on high throughput sequencing, but anammox bacteria were not found at the anode biofilms, which suggested that there were two different pathways for anodic ammonia transformation.     

Hydrogen and methane production in a bio-electrochemical system assisted anaerobic baffled reactor

In this study, a new process was proposed to enhance the stability and efficiency of an anaerobic baffled reactor (ABR). The process was examined in a four equal compartments ABR with total volume of 3.46 L. The first compartment was operated for fermentative hydrogen production and the last three compartments were used as continuous singer chamber microbial electrolysis cells (MECs) for methanogenesis. The system was operated at 35 ± 1 °C and hydraulic retention time (HRT) of 24 h with influent chemical oxygen demand (COD) concentration of 3500 mg/L–4000 mg/L. The results indicated that the proportion of hydrogen in the first compartment was 20.7% and proportions of methane in the last three compartments were 98.0%, 93.6% and 70.1%, respectively. A total of 98.0% of COD removal rate was achieved as well. Hence, this new system has following advantages: hydrogen production with cleaner effluent, high COD removal rate, and net methane production for practical use.     

Performance investigation of hydrogen production from a hybrid wind-PV system

In this study, a hybrid system consisted of 10 kW wind and 1 kWp PV array is built to meet the load demand of a raise chucker partridge raising facility by renewable energy sources. The facility has an average energy consumption of about 20.33 kWh/day, with a peak demand of 2.4 kW. The solar radiation data and wind data of the region are analyzed for sizing of the renewable energy system. The performance of each alternative system is examined in terms of energy efficiency, and H₂ production capacity of the hybrid system from due to excessive electrical energy is studied. A Matlab-Simulink Software is used for analyzing the system performance. The average range of state of charge varies between 56.6% and 88.3% monthly from April to July. The amount of hydrogen production by excess electricity is 14.4 kg in the month of July, due to the high wind speed and solar radiation. Energy efficiency of the electrolyser is found to be varying between 64% and 70% percent. Energy efficiency of each hybrid system is calculated. The overall energy efficiency of wind-electrolyser system varies between 5% and 14% while the energy efficiency of PV-electrolyser system changes within a narrower range, as between 7.9% to and 8.5%, respectively.     

A comparison of hydrogen production among three photosynthetic bacterial strains

The characteristics of hydrogen production from individual and mixed volatile fatty acids (VFAs) were compared among three photosynthetic bacterial strains, Rhodopseudomonas sp., Rhodopseudomonas palustirs W004 and Rubrivivax sp. Rhodopseudomonas sp. and R. palustirs W004 could convert both butyrate and acetate into hydrogen. Rubrivivax sp. could assimilate butyrate and acetate, but could not produce hydrogen from them when individual VFA was used as substrate. The highest hydrogen amount (2191.7 mL/L culture), COD reduction efficiency (85.3%) and H₂ yield (468.3 mL H₂/g COD) were achieved by Rhodopseudomonas sp. with butyrate as carbon source. All the three strains could produce hydrogen from mixed VFAs. Rhodopseudomonas sp. and R. palustirs W004 could digest the substrates completely. Hydrogen production from mixed VFAs by Rubrivivax sp. lasted for 3.7 days and only 38.8% of COD was reduced, for high pH value of the culture harmed hydrogen production.     

Thermodynamic analysis of a photoelectrochemical hydrogen production system

The thermodynamic analysis of photoelectrochemical (PEC) hydrogen production is performed in this work for air mass 1.5 solar insolation. Because the energy required for splitting water decreases as temperature is increased, heating the system by using the long wavelength energy will increase the system efficiency.     

A novel hybrid energy system for hydrogen production and storage in a depleted oil reservoir

Renewable and carbon free energy relates to the sustainable development of human beings while hydrogen production by renewables and hydrogen underground storage ensure the stable and economic renewable energy supply. A hybrid energy system combining hydrogen production by offshore wind power with hydrogen storage in depleted oil reservoirs was constructed along with a mathematical model where the Weibull distribution, Wind turbine power function, Faraday's law, continuity equation, Darcy's law, state equation of real gas, Net Present Value (NPV) and the concept of leveling were adopted to clarify the system characteristics. For the case of a depleted oil field in the Bohai Bay, China, the annual hydrogen production, annual levelized cost of hydrogen and payback period are 2.62 × 10⁶ m³, CNY 34.6/kgH₂ and 7 years, respectively. Sensitivity analysis found that the wind speed impacted significantly on system NPV and LCOH, followed by hydrogen price and stratum pressure.     

A proposal for a novel multi-functional energy system for the production of hydrogen and power

A novel multi-functional energy system with two kinds of fuels (coal and natural gas) and two kinds of products (hydrogen and electricity) is proposed. The proposed system takes advantage of the complementary properties of coal and natural gas by integrating natural gas/steam reforming together with the combustion of coal. Coal is indirectly gasified by combustion so that the need for an air separation unit is eliminated. At the same time, a part of superior natural gas fuel, which is burnt in the reformer, is replaced with inferior coal fuel. Hence, energy utilization is improved effectively. In addition, the novel system is investigated by means of the EUD (energy-utilization diagram) methodology and then compared with the reference system, which is composed of four conventional systems. As a result, the thermal efficiency of the new system may be expected to reach 75%. Moreover, a comparison with the reference system shows that the proposed system provides a 10% energy savings. The promising result obtained here provides an attractive option for an effective utilization of coal and natural gas.     

Analysis and assessment of a continuous-type hybrid photoelectrochemical system for hydrogen production

In this study, we conceptually develop and thermodynamically analyze a new continuous-type hybrid system for hydrogen production which photoelectrochemically splits water and performs chloralkali electrolysis. The system has a potential to produce hydrogen efficiently, at low cost, and in an environmentally benign way by maximizing the utilized solar spectrum and converting the byproducts into useful industrial commodities. Furthermore, by using electrodes as electron donors to drive photochemical hydrogen production, the hybrid system minimizes potential pollutant emissions. The products of the hybrid system are hydrogen, chlorine and sodium hydroxide, all of which are desired industrial commodities. The system production yield and efficiencies are investigated based on an operation temperature range of 20 °C–80 °C. A maximum energy efficiency of 42% is achieved between the temperatures of 40 °C and 50 °C.     

A review on the catalysts used for hydrogen production from ammonia borane

Boron compounds have recently attracted attention in hydrogen production since they contain many hydrogen atoms. Among these compounds, ammonia borane, which has high hydrogen density (in weight basis), can be used to produce hydrogen through a hydrolysis reaction. However, since the ammonia borane solution is highly resistant to hydrolysis under ambient conditions, there is a need for active and stable catalysts to accelerate the reaction. In this review paper, unsupported and carbon-based supported metal catalysts used for hydrogen production through the hydrolysis of ammonia borane are presented. Noble metal catalysts (Ru, Rh, Pd, Pt and their binary and ternary alloys) and non-noble metal catalysts (Co, Ni, Fe, Cu and their binary and ternary alloys) were examined. The activation energy of reaction and turnover frequency (TOF) values were compared for these catalysts. Among the unsupported catalysts, it was concluded that the multi-metal catalyst systems (binary, ternary and quaternary) have higher catalytic activity than a single use of the same metals. In addition, the comparison showed that the supported catalysts are more resistant to catalytic cycles and suitable for long-term use. It was observed that CNT supported Rh (TOF = 706 mol H₂ mol cat⁻¹ min⁻¹) and graphene supported Ru (TOF = 600 mol H₂ mol cat⁻¹ min⁻¹) catalysts are the most active catalysts for the hydrogen generation from the ammonia borane at room temperature.     

Hydrogen production system combined with a catalytic reactor and a plasma membrane reactor from ammonia

Ammonia is a 1promising raw material for hydrogen production because it may solve several problems related to hydrogen transport and storage. Hydrogen can be effectively produced from ammonia via catalytic thermal decomposition; however, the resulting residual ammonia negatively influences the fuel cells. Therefore, a high-purity hydrogen production system comprising a catalytic decomposition reactor and a plasma membrane reactor (PMR) has been developed in this work. Most of the ammonia is converted to hydrogen and nitrogen by the catalytic reactor. After the product gas containing unreacted ammonia is introduced to the PMR, unreacted ammonia is decomposed and hydrogen is separated in the PMR. Based on these processes, hydrogen with a purity of 99.99% is obtained at the output of the PMR. Optimal operation conditions maximizing the hydrogen production flow rate were investigated. The gap length of the PMR and the gas differential pressure and applied voltage of the plasma influence the flow rate. A pure hydrogen flow rate of ∼120 L/h was achieved using the current operating conditions. The maximum energy efficiency of the developed hydrogen production system is 28.5%.     

A micro reforming system integrated with a heat-recirculating micro-combustor to produce hydrogen from ammonia

In order to evaluate the potential of reforming ammonia as a carbon-free fuel in production of hydrogen, a new configuration of a micro reforming system integrated with a micro-combustor is studied experimentally. The micro-combustor as a heat source is a simple cylinder with an annular-type shield that applies a heat-recirculation concept. A micro-reformer to convert ammonia to hydrogen is an annulus, which is effective to transfer heat from the micro-combustor. The annulus-type micro reforming system is designed to produce 1-10 W (based on lower heating value, LHV) of hydrogen using various catalysts. The feed rate of ammonia, the micro-combustor inlet velocity of fuel-air mixtures and the catalyst materials substantially affect the performance of the designed micro reforming system. Under optimized design and operating conditions, the micro reforming system using ruthenium as a catalyst produces 5.4 W (based on LHV) of hydrogen with a conversion rate of 98.0% and an overall system efficiency of 13.7%. Thus, the present configuration can be applied to practical micro reforming systems, supporting the potential of using ammonia as a clean fuel.     

Towards hydrogen production using a breathable electrode structure to directly separate gases in the water splitting reaction

A novel electrode design to directly separate the gases and improve the efficiency of the water splitting reaction is described. In this work, platinum was used as a model catalyst, deposited on porous membranes with different pore size and shape. The O₂ evolution rate was monitored at the gaseous side of these breathable electrodes. We show that the hydrophobic Goretex^® membrane electrodes provide a highly efficient removal of the gases, breathing out 92% of expected O₂ during water splitting, and thereby also largely avoiding the well known migration of oxygen to the cathode in the absence of a separator in the cell. The breathable structure is also shown to operate as a hydrogen electrode. The ability to separate the two gases, without the need for a separator, decreases gas cross-over and thereby enhances the coloumbic efficiency. Merging this approach with catalysts and photocatalysts of a variety of types e.g. non-precious metal and metal oxides will allow fabrication of cost efficient and straightforward water splitting devices.     

On-board hydrogen storage and production: An application of ammonia electrolysis

On-board hydrogen storage and production via ammonia electrolysis was evaluated to determine whether the process was feasible using galvanostatic studies between an ammonia electrolytic cell (AEC) and a breathable proton exchange membrane fuel cell (PEMFC). Hydrogen-dense liquid ammonia stored at ambient temperature and pressure is an excellent source for hydrogen storage. This hydrogen is released from ammonia through electrolysis, which theoretically consumes 95% less energy than water electrolysis; 1.55 Wh g⁻¹ H₂ is required for ammonia electrolysis and 33 Wh g⁻¹ H₂ for water electrolysis. An ammonia electrolytic cell (AEC), comprised of carbon fiber paper (CFP) electrodes supported by Ti foil and deposited with Pt-Ir, was designed and constructed for electrolyzing an alkaline ammonia solution. Hydrogen from the cathode compartment of the AEC was fed to a polymer exchange membrane fuel cell (PEMFC). In terms of electric energy, input to the AEC was less than the output from the PEMFC yielding net electrical energies as high as 9.7 ± 1.1 Wh g⁻¹ H₂ while maintaining H₂ production equivalent to consumption.     

Efficient hydrogen production using a multi-layered photobioreactor and a photosynthetic bacterium mutant with reduced pigment

A multi-layered photobioreactor (MLPR), where the light paths were formed by the localization of bacterial cells, was constructed for efficient hydrogen production. The performance was investigated under several conditions in order to clarify the effect of this reactor on hydrogen production. An analysis of the hydrogen production profile showed that the MPLR utilizes both the light that directly illuminates its surface and the light induced and diffused from its light paths for hydrogen production. It was also found that the hydrogen productivity in the MLPR was more than twice that in a plate-type reactor. When a photosynthetic bacterium mutant with reduced pigment, MTP4, was used, the maximum hydrogen production rate reached 2.0 l/m² h, which was 38% higher than that of a conventional plate-type reactor. The synergistic effect of the improvement in the reactor and the modification of the bacteria was brought about by the combination of the MLPR and MTP4, and resulted in an improvement in the hydrogen production.     

Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation

In this study, nuclear energy based hydrogen and ammonia production options ranging from thermochemical cycles to high-temperature electrolysis are comparatively evaluated by means of the life cycle assessment (LCA) tool. Ammonia is produced by extracting nitrogen from air and hydrogen from water and reacting them through nuclear energy. Since production of ammonia contributes about 1% of global greenhouse gas (GHG) emissions, new methods with reduced environmental impacts are under close investigation. The selected ammonia production systems are (i) three step nuclear Cu–Cl thermochemical cycle, (ii) four step nuclear Cu–Cl thermochemical cycle, (iii) five step nuclear Cu–Cl thermochemical cycle, (iv) nuclear energy based electrolysis, and (v) nuclear high temperature electrolysis. The electrolysis units for hydrogen production and a Haber–Bosch process for ammonia synthesis are utilized for the electrolysis-based options while hydrogen is produced thermochemically by means of the process heat available from the nuclear power plants for thermochemical based hydrogen production systems. The LCA results for the selected ammonia production methods show that the nuclear electrolysis based ammonia production method yields lower global warming and climate change impacts while the thermochemical based options yield higher abiotic depletion and acidification values.     

Cost of green hydrogen: Limitations of production from a stand-alone photovoltaic system

The aim of this work is to analyse the price of renewable hydrogen production in a stand-alone photovoltaic plant. The energy studied herein is generated in a photovoltaic plant. Two dependent parameters that directly affect the price of hydrogen are analysed in detail: the price of the electricity needed to carry out its production process, and the utilisation rate of the connected electrolyser. To this end, a photovoltaic plant is dimensioned with the help of the PVsyst simulator, by means of which the hourly generation curves are obtained. A variable power electrolyser is employed to study its performance according to these photovoltaic production curves. Furthermore, the system is studied by introducing batteries capable of storing the energy left over during the day and of supplying the electrolyser when the photovoltaic power is insufficient. The selling prices calculated in the various scenarios in terms of efficiency and electricity cost are calculated. The significance of a combined analysis of these two parameters and their real impact on the final price of hydrogen is also analysed. This article aims to analyse the price of green hydrogen produced through an isolated photovoltaic system. When the hourly production is evaluated, differences are found with respect to global production that justify the importance of the variables analysed herein, which could not be determined in any other way. The behaviour of isolated production and its effects are discussed.     

Ultra-pure hydrogen production via ammonia decomposition in a catalytic membrane reactor

In this work two alternatives are presented for increasing the purity of hydrogen produced in a membrane reactor for ammonia decomposition. It is experimentally demonstrated that either increasing the thickness of the membrane selective layer or using a small purification unit in the permeate of the membranes, ultra-pure hydrogen can be produced. Specifically, the results show that increasing the membrane thickness above 6 μm ultra-pure hydrogen can be obtained at pressures below 5 bar. A cheaper solution, however, consists in the use of an adsorption bed downstream the membrane reactor. In this way, ultra-pure hydrogen can be achieved with higher reactor pressures, lower temperatures and thinner membranes, which result in lower reactor costs. A possible process diagram is also reported showing that the regeneration of the adsorption bed can be done by exploiting the heat available in the system and thus introducing no additional heat sources.     

Influence of basic dopants on the activity of Ru/Pr6O11 for hydrogen production by ammonia decomposition

Basic oxides such as alkali metal oxides, alkaline earth metal oxides, and rare earth oxides were added to Ru/Pr₆O₁₁, and the activity of the catalysts with respect to hydrogen production by ammonia decomposition was investigated. Ru/Pr₆O₁₁ doped with alkali metal oxides, except for Li₂O, achieved higher NH₃ conversions than bare Ru/Pr₆O₁₁. Cs₂O, the most basic of the alkali metal oxides, was the most effective dopant. In contrast, other dopants with lower basicity than the alkali metal oxides achieved lower NH₃ conversions than bare Ru/Pr₆O₁₁. Changing the Cs/Ru molar ratio revealed that the best Cs/Ru ratio was 0.5–2; the reaction was effectively promoted without negative effects from coverage of the Ru surface by the Cs₂O. Varying the order of loading the Ru and Cs₂O onto Pr₆O₁₁ revealed that loading Ru onto Cs₂O/Pr₆O₁₁ was an effective way to enhance NH₃ conversion, and coverage of the Ru surface was reduced.     

Control of a grid-assisted wind-powered hydrogen production system

This paper deals with the control of a H₂ production system supplied by wind power and assisted by the grid. The system architecture consists of a pitch-controlled wind turbine coupled through a diode rectifier to an alkaline electrolyzer, which in turn is connected to the electric grid through a fully-controlled bidirectional electronic converter. A control strategy for the electronic converter is proposed to regulate the electrolyzer current at its rated value. Thus, H₂ production efficiency is optimized despite wind power and temperature variability. Control design is based on sliding mode techniques, which are particularly appropriate to control fast switching devices and exhibit strong robustness properties. Additionally, in high wind speeds, a pitch control loop is activated to limit the wind power capture below admissible values.