Evaluation of stainless steel cathodes and a bicarbonate buffer for hydrogen production in microbial electrolysis cells using a new method for measuring gas production

Microbial electrolysis cells (MECs) are often examined for hydrogen production using non-sustainable phosphate buffered solutions (PBS), although carbonate buffers have been shown to work in other bioelectrochemical systems with a platinum (Pt) catalyst. Stainless steel (SS) has been shown to be an effective catalyst for hydrogen evolution in MECs, but it has not been tested with carbonate buffers. We evaluated the combined using of SS cathodes and a bicarbonate buffer (BBS) at the applied voltages of 0.5, 0.7 and 0.9 V using a new inexpensive method for measuring gas production called the gas bag method (GBM). This method achieved an average error of only 5.0% based on adding known volumes of gas to the bag. Using the GBM, hydrogen production with SS and a BBS was 26.6 ± 1.8 mL which compared well to 26.4 ± 2.8 mL using Pt and BBS, and 26.8 ± 2.5 mL with a Pt cathode and PBS. Electrical energy efficiency was highest with a SS cathode and BBS at 159 ± 17%, compared to 126 ± 14% for the Pt cathode and BBS, and 134 ± 17% for a Pt cathode and PBS. The main disadvantage of the SS was a lower gas production rate of 1.1 ± 0.3 m³ H₂-m⁻³ d⁻¹ with BBS and 1.2 ± 0.3 m³ H₂-m⁻³ d⁻¹ with PBS, compared to 1.7 ± 0.4 m³ H₂-m⁻³ d⁻¹ with Pt and PBS. These results show that the GBM is an effective new method for measuring gas production of anaerobic gas production processes, and that SS and bicarbonate buffers can be used to effectively produce hydrogen in MECs.     

Production of hydrogen by the electrochemical reforming of glycerol–water solutions in a PEM electrolysis cell

An alternative method for producing hydrogen from renewable resources is proposed. Electrochemical reforming of glycerol solution in a proton exchange membrane (PEM) electrolysis cell is reported. The anode catalyst was composed of Pt on Ru–Ir oxide with a catalyst loading of 3 mg cm⁻² on Nafion. Part of the energy carried by the produced hydrogen is supplied by the glycerol (82%) and the remaining part of the energy originates from the electrical energy (18%) with an energy efficiency of conversion of glycerol to hydrogen of around 44%. The electrical energy consumption of this process is 1.1 kW h m⁻³ H₂. Compared to water electrolysis in the same cell, this is an electrical energy saving of 2.1 kW h N m⁻³ H₂ (a 66% reduction). Production rates are high compared with comparable sized microbial cells but low compared with conventional PEM water electrolysis cells.     

Electrohydrolysis of landfill leachate organics for hydrogen gas production and COD removal

Hydrogen gas production with simultaneous COD removal was realized by application of DC voltages (0.5-5.0 V) to landfill leachate. The rate and the yield of hydrogen gas production were investigated at different DC voltages by using aluminum electrodes and DC power supply. The highest cumulative hydrogen production (5000 mL), hydrogen yield (2400 mL H₂ g⁻¹ COD), daily hydrogen gas formation (1277 mL d⁻¹), and percent hydrogen (99%) in the gas phase were obtained with 4 V DC voltage. Energy conversion efficiency (H₂ energy/electrical energy) reached the highest level (80.6%) with 1 V DC voltage. Hydrogen gas production was mainly realized by electrohydrolysis of leachate organics due to negligible H₂ gas production in water and leachate control experiments. The highest COD removal (77%) was also obtained with 4 V DC voltage. Electrohydrolysis of landfill leachate was proven to be an effective method for hydrogen gas production with simultaneous COD removal.     

Anaerobic digestion of maize focusing on variety,harvest time and pretreatment

The methane potential of six varieties of fresh maize (whole plant) harvested at three different times and of maize silage (whole plant) in two particle size distributions was experimentally determined in batch assays. Fresh maize gave the highest methane yield/hectare at late harvest (6270 m³ CH₄ (10⁴ m²)⁻¹). The methane yield/wet weight (WW) increased from 80 (early harvest) to 137 m³ CH₄ (t WW)⁻¹ (late harvest). Maize harvested at different times, or different varieties of maize had similar specific methane production/volatile solids content (m³ CH₄ (kg VS)⁻¹). The measured yield m³ CH₄ (kg VS)⁻¹ was 84% of the theoretical methane potential. The estimated ethanol yield was between 2.5 and 3.5 t ethanol (10⁴ m²)⁻¹. The energy yield was 62 and 19–22 MWh (10⁴ m²)⁻¹ if fresh maize (whole plant) is used for methane or ethanol production respectively. Reducing the particle size of maize silage to an average size of approximately 2 mm increased the methane yield m³ CH₄ (kg VS)⁻¹ by approximately 10%.     

The effect of irradiance growing on hydrogen photoevolution and on the kinetic growth in Rhodopseudomonas palustris, strain 42OL

The relationship between hydrogen generation and the age of culture was investigated under fed-batch growth conditions. The specific growth rate (μ_e) was determined during the log phase of the growth curve and the μ_eMax was 0.02643 h⁻¹. Boltzmann's sigmoidal regression model was used to determine the specific rate of hydrogen evolution (μH): the maximum was 0.04440 h⁻¹. At low irradiance (36–75 W m⁻²), an inverse relationship was found between μH and I; after increasing the irradiance further, μH reached a plateau (0.00916 h⁻¹). The maximum reactor yield of cumulative hydrogen (4.5 l) was obtained at an irradiance of 320 W m⁻², but the highest hydrogen evolution rate (17.217 ml h⁻¹) was achieved at 500 W m⁻². The light conversion efficiency reached its maximum (6.91%) at the lowest irradiance investigated (36 W m⁻²); when the irradiance increased further, it decreased progressively down to 0.36%.     

A pilot-scale high-rate biohydrogen production system with mixed microflora

A pilot-scale high-rate dark fermentative hydrogen production plant has been established in the campus of Feng Chia University to develop biohydrogen production pilot-plant technology. This pilot-plant system is composed of two feedstock storage tanks (0.75 m³ each), a nutrient storage tank (0.75 m³), a mixing tank (0.6 m³), an agitated granular sludge bed fermentor (working volume 0.4 m³), a gas-liquid-solid separator (0.4 m³) and a control panel. The seed mixed microflora was obtained from a lab-scale agitated granular sludge bed bioreactor. This pilot-scale fermentor was operated for 67 days at 35 °C, an organic loading rate (OLR) of 40-240 kg COD/m³/d, and the influent sucrose concentration of 20 and 40 kg COD/m³. Both biogas and hydrogen production rates increased with increasing OLR. However, the biomass concentration (volatile suspended solids, VSS) only increased with an increasing OLR at an OLR range of 40-120 kg COD/m³/d, whereas it decreased when OLR was too high (i.e., 240 kg COD/m³/d). The biogas consisted mainly of H₂ and CO₂ with a H₂ content range of 23.2-37.8%. At an OLR of 240 kg COD/m³/d, the hydrogen content in biogas reached its maximum value of 37% with a hydrogen production rate (HPR) of 15.59 m³/m³/d and a hydrogen yield of 1.04 mol H₂/mol sucrose. This HPR value is much higher than 5.26 m³/m³/d (fermented molasses substrate) and 1.56 m³/m³/d (glucose substrate) reported by other pilot-scale systems. Moreover, HPR was also greatly affected by pH. At an optimal pH of 5.5, the bacterial community became simple, while the efficient hydrogen producer Clostridium pasteurianum was dominant. The factors of energy output compared with the energy input (E_f) ranged from 13.65 to 28.68 on biohydrogen, which is higher than the E_f value on corn ethanol, biodiesel and sugarcane ethanol but in the similar range of cellulosic ethanol.     

A study on H2S permeability of CsHSO4 membranes

The gas permeability of H₂S gas at 150 °C through ultra-thin cesium hydrogen sulfate (CsHSO₄) membranes has been investigated. Gas chromatography–mass spectrometry analyses indicate that CsHSO₄ membrane is impermeable to H₂S gas under test conditions. The apparent micropore diameter of the membrane averaged between 9.5 and 11.5 Å with a maximum permeance of 0.09 Barrer (6.75 × 10⁻¹⁹ m² s⁻¹ Pa⁻¹). Atomic force microscope and X-ray diffraction analyses show respectively that the surface morphology and crystal structure of the membranes are preserved, with no adverse effect from prolonged exposure to H₂S gas. Electrochemical impedance spectroscopy analysis confirm over a 30% decrease in membrane resistance via an 80% reduction in membrane thickness.     

Hydrogen gas production from olive mill wastewater by electrohydrolysis with simultaneous COD removal

Diluted olive mill wastewater (OMW) was subjected to direct current (DC) voltages (0.5-4.0 V) for hydrogen gas production with simultaneous chemical oxygen demand (COD) removal by electrohydrolysis. The highest cumulative hydrogen production (3020 ml) and hydrogen yield (2500 ml H₂ g⁻¹ COD) were obtained with 3 V DC voltage while the highest current intensity (80 mA), percent hydrogen (95%) in the gas phase, hydrogen gas formation rate (614 ml d⁻¹), percent COD removal (44%) and energy conversion efficiency (95%) were realized with 2 V. Hydrogen gas production by electrolysis of water was negligible for all voltages. COD removal from OMW with no DC voltage application was usually lower than that obtained with DC power application. Hydrogen gas production by electrohydrolysis of OMW was proven to be a fast and effective method with simultaneous COD removal.     

Photovoltaic-thermal collectors for night radiative cooling of buildings

A new photovoltaic-thermal (PVT) system has been developed to produce electricity and cooling energy. Experimental studies of uncovered PVT collectors were carried out in Stuttgart to validate a simulation model, which calculates the night radiative heat exchange with the sky. Larger PVT frameless modules with 2.8 m² surface area were then implemented in a residential zero energy building and tested under climatic conditions of Madrid. Measured cooling power levels were between 60 and 65 W m⁻², when the PVT collector was used to cool a warm storage tank and 40-45 W m⁻², when the energy was directly used to cool a ceiling. The ratio of cooling energy to electrical energy required for pumping water through the PVT collector at night was excellent with values between 17 and 30. The simulated summer cooling energy production per square meter of PVT collector in the Madrid/Spain climatic conditions is 51 kWh m⁻² a⁻¹. In addition to the thermal cooling gain, 205 kWh m⁻² a⁻¹ of AC electricity is produced under Spanish conditions. A comparative analysis for the hot humid climate of Shanghai gave comparable results with 55 kWh m⁻² a⁻¹ total cooling energy production, mainly usable for heat rejection of a compression chiller and a lower electricity production of 142 kWh m⁻² a⁻¹.     

Investigation of the combined effects of acetate and photobioreactor illuminated fraction in the induction of anoxia for hydrogen production by Chlamydomonas reinhardtii

In the context of hydrogen production by microalgae, the growth of Chlamydomonas reinhardtii was characterized under autotrophic and mixotrophic conditions in a fully controlled photobioreactor (PBR). The combined effect of light transfer conditions, as represented by the illuminated fraction γ, with acetate consumption was observed upon establishment of anoxia. Anoxia was reached in batch cultures when γ was close to 1 (almost fully illuminated culture) in mixotrophic conditions while a value of γ ≈ 0.46 in autotrophic conditions was not sufficient. Based on these results, continuous hydrogen production was established in a cylindrical PBR operated in luminostat with constant illumination and in mixotrophic conditions. Maximum hydrogen gas production was equal to 1.4 ± 0.1 ml_H2 l⁻¹ h⁻¹ for photon flux density of 110 μmol m⁻² s⁻¹ and reactor illuminated fraction of γ = 0.5. Carbon mass balance was realized, emphasizing the necessity to work in strictly autotrophic conditions for hydrogen production with no concomitant CO₂ release.     

Microstructural analysis of a solid oxide fuel cell anode using focused ion beam techniques coupled with electrochemical simulation

Porous composite electrodes play a critical role in determining the performance and durability of solid oxide fuel cells, which are now emerging as a high efficiency, low emission energy conversion technology for a wide range of applications.In this paper we present work to combine experimental electrochemical and microstructural characterisation with electrochemical simulation to characterise a porous solid oxide fuel cell anode. Using a standard, electrolyte supported, screen printed Ni-YSZ anode, electrochemical impedance spectroscopy has been conducted in a symmetrical cell configuration. The electrode microstructure has been characterised using FIB tomography and the resulting microstructure has been used as the basis for electrochemical simulation. The outputs from this simulation have in turn been compared to the results of the electrochemical experiments.A sample of an SOFC anode of 6.68 μm × 5.04 μm × 1.50 μm in size was imaged in three dimensions using FIB tomography and the total triple phase boundary density was found to be 13 μm⁻². The extracted length-specific exchange current for hydrogen oxidation (97% H₂, 3% H₂O) at a Ni-YSZ anode was found to be 0.94 × 10⁻¹⁰, 2.14 × 10⁻¹⁰, and 12.2 × 10⁻¹⁰ A μm⁻¹ at 800, 900 and 1000 °C, respectively, consistent with equivalent literature data for length-specific exchange currents for hydrogen at geometrically defined nickel electrodes on YSZ electrolytes.     

Proton transport, water uptake and hydrogen permeability of nanoporous hematite ceramic membranes

For the first time, mesoporous acid-free hematite ceramic membranes have been studied as proton conductors. The xerogels after calcination at 300 °C for 1 h were mesoporous, as is mentioned above, with a BET surface area of 130 ± 2 m² g⁻¹, an average pore diameter of 3.8 nm and a pore volume of 0.149 ± 0.001 cc g⁻¹. A sigmoidal dependence of the conductivity and the water uptake with the RH at a constant temperature was observed. The conductivity of the ceramic membranes increased linearly with temperature for all relative humidities studied. The highest value of proton conductivity was found to be 2.76 × 10⁻³ S cm⁻¹ at 90 °C and 81% RH. According to the activation energy values, proton migration in this kind of materials could be dominated by the Grotthuss mechanism in the whole range of RH. The low cost and high hydrophilicity of these ceramic membranes make them potential substitutes for perfluorosulfonic polymeric membranes in proton exchange membrane (PEMFCs). In addition, since hydrogen permeability values are in the range of 10⁻⁹ to 10⁻¹⁰ mol cm⁻¹ s Pa, in order to fabricate oxide-based PEMs that are capable of keeping streams of H₂ and O₂ from mixing, a separation layer with pore sizes <2 nm whose pores are filled with water will be needed.     

Changes in hydrogen storage properties of carbon nano-horns submitted to thermal oxidation

The effect of thermal oxidation on the hydrogen storage properties of carbon nano-horns was investigated by gravimetric and electrochemical methods. The pristine nano-horn sample was oxidised at 673 K in air for different periods (15, 30 and 60 min) and the resulting materials were characterised. The N₂ adsorption experiments reveal a marked increase in the surface area, from 267 m² g⁻¹, for the pristine sample, up to 1360 m² g⁻¹ for the sample oxidised for the 60 min period, and a reduction in the average pore diameter. The gravimetric investigation, conducted at low temperature (77 K) showed an increase in the hydrogen storage, from 0.75 wt% for the pristine sample up to 2.60 wt% for the oxidised material. Reproducible and stable hydrogen storage was found for all the samples examined apart from the sample oxidised for 60 min. For the latter, a decrease in the amount of hydrogen stored between the first and second cycles was found. Electrochemical loading of hydrogen in the samples was performed at room temperature (298 K) in alkaline solution by the galvanostatic charge/discharge technique. The results obtained here however show a much lower hydrogen storage level by the samples as compared to the gas storage method, with a maximum value of 0.124 wt% H₂ and with very little dependence on the thermal oxidation treatment.     

Simple and fast fabrication of polymer template-Ru composite as a catalyst for hydrogen generation from alkaline NaBH4 solution

Polymer template-Ru composite (Ru/IR-120) catalyst was prepared using a simple and fast method for generating hydrogen from an aqueous alkaline NaBH₄ solution. The hydrogen generation rate was determined as a function of solution temperature, NaBH₄ concentration, and NaOH (a base-stabilizer) concentration. The maximum hydrogen generation rate reached 132 ml min⁻¹ g⁻¹ catalyst at 298 K, using a Ru/IR-120 catalyst that contained only 1 wt.% Ru. The catalyst exhibits a quick response and good durability during the hydrolysis of alkaline NaBH₄ solution. The activation energy for the hydrogen generation reaction was determined to be 49.72 kJ mol⁻¹.     

Comparisons of the hydrogen-rich syngas compositions from wet rice husk slurry steam reforming reactions using different catalysts

Rice husk slurry is pumped into a packed reactor and the products from the steam reforming reactions using different catalysts are studied. The steam/biomass weight ratio of such a system is between 3.47 and 5.25. The solids, liquid and gaseous products are a mass fraction of 2.8-4.1%, a mass fraction of 92.4-93.0% and a mass fraction of 3.5-4.7%, respectively. The hydrogen concentration in the gaseous product is approximate a volume fraction of 41% using the Al₂O₃ catalyst of a CuO mass fraction of 13%, a volume fraction of 38% using the Al₂O₃ catalyst of a Ni mass fraction of 13%, a volume fraction of 31% using the Al₂O₃ catalyst of a ZnO mass fraction of 13%, and a volume fraction of 20% using the Al₂O₃ catalyst at the reactor temperature of 800 °C. In the reactor temperature range studied (350-800 °C), the hydrogen concentration in the product stream increases monotonically with the increasing of the reactor temperature and the steam/carbon molar ratio. The value of dry gas LHV is between 9.4 MJ m⁻³ and 12 MJ m⁻³ at the reaction temperature of 600-800 °C. Considering the simple catalyst used in current study, the syngas of a hydrogen volume fraction of approximate 40% is obtained by pumping the biomass slurry to carry out the catalytic steam reforming reaction.     

Automotive hydrogen storage system using cryo-adsorption on activated carbon

An integrated model of a sorbent-based cryogenic compressed hydrogen system is used to assess the prospect of meeting the near-term targets of 36 kg-H₂/m³ volumetric and 4.5 wt% gravimetric capacity for hydrogen-fueled vehicles. The model includes the thermodynamics of H₂ sorption, heat transfer during adsorption and desorption, sorption dynamics, energetics of cryogenic tank cooling, and containment of H₂ in geodesically wound carbon fiber tanks. The results from the model show that recoverable hydrogen, rather than excess or absolute adsorption, is a determining measure of whether a sorbent is a good candidate material for on-board storage of H₂. A temperature swing is needed to recover >80% of the sorption capacity of the superactivated carbon sorbent at 100 K and 100 bar as the tank is depressurized to 3–8 bar. The storage pressure at which the system needs to operate in order to approach the system capacity targets has been determined and compared with the breakeven pressure above which the storage tank is more compact if H₂ is stored only as a cryo-compressed gas. The amount of liquid N₂ needed to cool the hydrogen dispensed to the vehicle to 100 K and to remove the heat of adsorption during refueling has been estimated. The electrical energy needed to produce the requisite liquid N₂ by air liquefaction is compared with the electrical energy needed to liquefy the same amount of H₂ at a central plant. The alternate option of adiabatically refueling the sorbent tank with liquid H₂ has been evaluated to determine the relationship between the storage temperature and the sustainable temperature swing. Finally, simulations have been run to estimate the increase in specific surface area and bulk density of medium needed to satisfy the system capacity targets with H₂ storage at 100 bar.     

Bio-hydrogen production from acid hydrolyzed wheat starch by photo-fermentation using different Rhodobacter sp

Hydrogen gas production from sugar solution derived from acid hydrolysis of ground wheat starch by photo-fermentation was investigated. Three different pure strains of Rhodobacter sphaeroides (RV, NRLL and DSZM) were used in batch experiments to select the most suitable strain. The ground wheat was hydrolyzed in acid solution at pH = 3 and 90 °C in an autoclave for 15 min. The resulting sugar solution was used for hydrogen production by photo-fermentation after neutralization and nutrient addition. R. sphaeroides RV resulted in the highest cumulative hydrogen gas formation (178 ml), hydrogen yield (1.23 mol H₂ mol⁻¹ glucose) and specific hydrogen production rate (46 ml H₂ g⁻¹ biomass h⁻¹) at 5 g l⁻¹ initial total sugar concentration among the other pure cultures. Effects of initial sugar concentration on photo-fermentation performance were investigated by varying sugar concentration between 2.2 and 13 g l⁻¹ using the pure culture of R. sphaeroides RV. Cumulative hydrogen volume increased from 30 to 232 ml when total sugar concentration was increased from 2.2 to 8.5 g l⁻¹. Further increases in initial sugar concentration resulted in decreases in cumulative hydrogen formation. The highest hydrogen formation rate (3.69 ml h⁻¹) and yield (1.23 mol H₂ mol⁻¹ glucose) were obtained at a sugar concentration of 5 g l⁻¹.     

Synthesis and hydrogen permeation of Ni-Ba(Zr0.1Ce0.7Y0.2)O3−δ metal-ceramic asymmetric membranes

Ni-Ba(Zr_0.1Ce_0.7Y_0.2)O_3−δ (BZCY) metal-ceramic asymmetric membranes consisted of Ni-BZCY top membrane and porous substrate were successfully prepared and developed as hydrogen permeation membrane for the first time via a method to combine co-pressing technique and two-step sintering process. The uniform fine NiO-BZCY composite powders as the precursor of top membranes were co-synthesized through the citrate-nitrate combustion route (co-synthesis method), which was the key to fabricating Ni-BZCY thin membrane. The homogeneity and phase structure of two phases in powders were characterized using element-map technique and X-ray diffraction analysis, respectively. The fluxes through a metal-ceramic membrane of about 30-μm-thickness were measured as a function of temperature under different feed gas hydrogen partial pressures. The results indicated the asymmetric membrane displayed high hydrogen permeation flux and using 80%H₂/N₂ (with 3% of H₂O) as feed gas and dry high purity argon as sweep gas, a maximum flux of 2.4 × 10⁻⁷ mol cm⁻² s⁻¹ was achieved at 900 °C, exhibiting the predominance of asymmetric structures.     

Modeling the performance of the anaerobic phased solids digester system for biogas energy production

A process model was developed to predict the mass and energy balance for a full-scale (115 t d⁻¹) high-solids anaerobic digester using research data from lab and pilot scale (1-3000 kg d⁻¹ wet waste) systems. Costs and revenues were estimated in consultation with industry partners and the 20-year project cash flow, net present worth (NPW), simple payback, internal rate of return, and revenue requirements were calculated. The NPW was used to compare scenarios in order to determine the financial viability of using a generator for heat and electricity or a pressure swing adsorption unit for converting biogas to compressed natural gas (CNG).The full-scale digester consisted of five 786 m³ reactors (one biogasification reactor and four hydrolysis reactors) treating a 50:50 mix (volatile solids basis) of food and green waste, of which 17% became biogas, 32% residual solids, and 51% wastewater. The NPW of the projects were similar whether producing electricity or CNG, as long as the parasitic energy demand was satisfied with the biogas produced. When producing electricity only, the power output was 1.2 MW, 7% of which was consumed parasitically. When producing CNG, the system produced 2 hm³ y⁻¹ natural gas after converting 22% of the biogas to heat and electricity which supplied the parasitic energy demand. The digester system was financially viable whether producing electricity or CNG for discount rates of up to 13% y⁻¹ without considering debt (all capital was considered equity), heat sales, feed-in tariffs or tax credits.