Highest Hydrogen Production Research Articles

Influence of Cocatalysts (Ni, Co, and Cu) and Synthesis Method on the Photocatalytic Activity of Exfoliated Graphitic Carbon Nitride for Hydrogen Production.

Exfoliated graphitic carbon nitride (ex-g-CN) was synthesized and loaded with non-noble metals (Ni, Cu, and Co). The synthesized catalysts were tested for hydrogen production using a 300-W Xe lamp equipped with a 395 nm cutoff filter. A noncommercial double-walled quartz-glass reactor irradiated from the side was used with a 1 g/L catalyst in 20 mL of a 10 vol% triethanolamine aqueous solution. For preliminary screening, the metal-loaded ex-g-CN was synthesized using the incipient wetness impregnation method. The highest hydrogen production was observed on the Ni-loaded ex-g-CN, which was selected to assess the impact of the synthesis method on hydrogen production. Ni-loaded ex-g-CN was synthesized using different synthesis methods: incipient wetness impregnation, colloidal deposition, and precipitation deposition. The catalysts were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption using the Brunauer-Emmett-Teller method, and transmission electron microscopy. The Ni-loaded ex-g-CN synthesized using the colloidal method performed best with a hydrogen production rate of 43.6 µmol h-1 g-1. By contrast, the catalysts synthesized using the impregnation and precipitation methods were less active, with 28.2 and 10.1 µmol h-1 g-1, respectively. The hydrogen production performance of the suspended catalyst (440 µmol m-2 g-1) showed to be superior to that of the corresponding immobilized catalyst (236 µmol m-2 g-1).

Scalable membrane-less microbial electrolysis cell with multiple compact electrode assemblies for high performance hydrogen production

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) is a promising method for sustainable energy production and decarbonization of energy systems. However, the application of MECs is limited by the electrochemical performance, scalability, and the cost associated with expensive materials. In this study, a scalable MEC (500 mL) with novel compact electrode assemblies and high electrode surface area to volume ratio (160 m2/m3) was designed and constructed. The use of membranes, precious metal catalyst, and current collectors with high costs was avoided. A high current density at the steady state of 49.5 ± 5.3 A/m2 was achieved using acetate as the substrate with phosphate buffer under the applied voltage of 1.01 V. The corresponding volumetric current density was 3948 ± 422 A/m3. The compact electrode assembly design limited methane production rate to 3.9 ± 0.2 L/L/D, while achieving a hydrogen production rate of 33.7 ± 1.7 L/L/D. With the suppression of microbial hydrogen consumption, the hydrogen production rate was 39.8 ± 1.9 L/L/D, higher by almost one order of magnitude than those of MECs with scaling up attempts. The compact electrode configuration reduced internal resistance to 88.5 ± 4.4 Ω cm2. The energy efficiency based on input electricity was 146 ± 7 % to 189 ± 9 % within the applied voltage range of 0.71 to 1.05 V. The results in this study demonstrated successful scaling up of high performance small MECs and offered a new possible approach of scaling up MECs by stacking high-performance subunits, with no trade-offs on electrochemical performance.

Bi4TaO8Cl as a New Class of Layered Perovskite Oxyhalide Materials for Piezopotential Driven Efficient Seawater Splitting.

Piezocatalytic water splitting is an emerging approach to generate "green hydrogen" that can address several drawbacks of photocatalytic and electrocatalytic approaches. However, existing piezocatalysts are few and with minimal structural flexibility for engineering properties. Moreover, the scope of utilizing unprocessed water is yet unknown and may widely differ from competing techniques due to the constantly varying nature of surface potential. Herein, we present Bi4TaO8Cl as a representative of a class of layered perovskite oxyhalide piezocatalysts with high hydrogen production efficiency and exciting tailorable features including the layer number, multiple cation-anion combination options, etc. In the absence of any cocatalyst and scavenger, an ultrahigh production rate is achievable (1.5 mmol g-1 h-1), along with simultaneous generation of value-added H2O2. The production rate using seawater is somewhat less yet appreciably superior to photocatalytic H2 production by most oxides as well as piezocatalysts and has been illustrated using a double-layer model for further development.

H2 production by cellulose photoreforming with TiO2-Cu photocatalysts bearing different Cu species

TiO2-Cu photocatalysts (1 wt% Cu) containing different copper species have been prepared and used for the generation of hydrogen by photoreforming of cellulose (the major component of biomass) in water at room temperature using UV light. A positive effect of copper has been clearly observed, and the analysis of the role of the Cu species present shows that a mixture of Cu(I) and Cu(II) favors the process. Among the TiO2-Cu photocatalysts, the one prepared by a simple impregnation method and not heat-treated, which shows small and well dispersed copper species particles, gives the highest hydrogen production.

Facile integration of core–shell catalyst and Pd-Ag membrane for hydrogen production from low-temperature dry reforming of methane

Dry reforming of methane (DRM) is an important way of conversion of CH4 and CO2, two greenhouse gases, for the production of hydrogen. In this study, a catalytic membrane reactor combining an ultra-thin Pd-Ag alloy membrane with a coke-resistant Ni-SiO2@CeO2 core–shell catalyst was developed for high yield hydrogen production from DRM. The performance of membrane in the presence of gases such as CO, CO2 and CH4 was evaluated, and very little reduction in H2 flux (∼2.5 %) was observed in the presence of these gases at the relevant reaction conditions. The catalyst was tested for DRM reaction in both fixed bed reactor (FBR) and catalytic membrane reactor (CMR) to evaluate its performance at different reaction conditions. In a catalytic membrane reactor, the removal of hydrogen resulted in 1.5 times higher methane conversion compared to the calculated conversion at thermodynamic equilibrium at the used reaction conditions when hydrogen is not removed from the reaction mixture. Around 70 % of the produced H2 was recovered from the reaction stream, by virtue of the high H2 flux through the ultra-thin Pd-Ag membrane. Further, the competing reverse water gas shift reaction, that consumes the produced H2, was drastically suppressed by using membrane reactor. The suppression of reverse water gas shift reaction (RWGS) in CMR was confirmed by analyzing downstream gases using gas chromatography mass spectrometer, the result showed significantly lower H2O content for CMR than FBR. Thus, the coupling of ultra-thin membrane with a core shell catalyst synergistically improved the performance of the dry reforming of methane.

Interfacial construction and lattice distortion-triggered bifunctionality of Mn-NiS/Mn-Ni3S4 for H2 production

• Mn-NiS/Mn-Ni 3 S 4 composite catalysts were successfully synthesized by using Ni(OH) 2 as the precursor with Mn doping and sulfurization at low temperature. • The successful doping of Mn atoms induced lattice distortion, vacancy defects, changed the electronic structure and microscopic morphology of NiS x . • The alkaline electrolytic cell consisting of double Mn-NiS x electrode achieved a cell voltage of only 1.52 V at a current density of 10 mA/cm 2 . The hydrogen is described as a clean and sustainable alternative to fossil fuels in numerous energy systems. Hydrolysis is an important method for high purity, high volume hydrogen production. In order to accelerate the kinetics of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, it is essential to explore efficient catalysts. In this paper, the nanoscale self-supported Mn-NiS/Mn-Ni 3 S 4 composite catalysts was assembled on nickel foam. Benefiting from the lattice distortion and vacancy defects caused by the doping of Mn elements, the catalysts exposed an increasing number of electrochemical surfaces and effective active sites, showing impressive electrochemical performance with a HER overpotential of only 94.2 mV at 10 mA/cm 2 and an OER overpotential of only 253 mV to drive 50 mA/cm 2 . Applying as the bifunctional catalysts, the Mn-NiS/Mn-Ni 3 S 4 couple only achieved a low voltage of only 1.52 V to drive 10 mA/cm 2 . This paper provides new ideas and references for the rational design of high-performance sulfide catalysts with non-precious metal composites.

Self-supporting sandwich-structured Co–Pt–Co/CC electrocatalysts for high effective hydrogen production by electrolysis of water in alkaline solution

Trace precious metal modifying inexpensive transition metal catalyst is an effective method to optimize the activity, stability and cost of hydrogen evolution catalysts. In this feature work, self-supporting sandwich structured Co–Pt–Co/CC sheets were assembled on a carbon cloth (CC) by a simple electrodeposition/chemical displacement alternate growth method. Surprisingly, only 2.1 wt % Pt sandwich layer greatly improved the electrochemical activity of Co–Pt–Co/CC, which delivered a current density of 10 mA cm −2 at an overpotential as low as 46 mV. Importantly, its overpotential is almost 6 times lower than that of Co/CC, and is comparable to that of Pt–Co/CC. After well-tuning the sandwich layer, the optimized Co–Pt–Co/CC exhibited a higher current density and better long-term durability compared with Pt–Co/CC and Co/CC, which can be attributed to the unique tissue-structure and electronic structure optimization of the Co–Pt–Co/CC by the Pt sandwich layer.

Remarkable photoelectrochemical activity of titanium dioxide nanorod arrays sensitized with transition metal sulfide nanoparticles for solar hydrogen production

The synthesis of a cost-effective and efficient catalyst is vital for accelerating the rate of photoelectrochemical hydrogen production. Here, titanium dioxide nanorods sensitized by nickel sulfide, cadmium sulfide, and zinc sulfide nanoparticles (ZnS/CdS/NiS@TiO2) were developed as a photoanode material via a hydrothermal process followed by the successive ionic layer adsorption and reaction. The morphological analysis of ZnS/CdS/NiS@TiO2 revealed the nanorods (TiO2) phase in which NiS, CdS, and ZnS nanoparticles are distributed homogeneously. The photoelectrochemical performance analysis of ZnS/CdS/NiS@TiO2 furnished a maximum photocurrent density of 6.1 mA/cm2, which is 7.6 times higher than that of pure TiO2 (0.8 mA/cm2). Additionally, the sensitized TiO2 nanorod arrays as a photoanode show high photoelectrochemical hydrogen production of 491.52 μmol/cm2, which is 4.9 times higher than that of pristine TiO2 (99.61 μmol/cm2) over 6 h under simulated solar irradiation. These results suggested the potential for the synthesis and usage of novel hybrids of TiO2 nanorods decorated with transition metal chalcogenides for efficient photoelectrochemical hydrogen production.

Sr, Mg co-doped LaGaO3-δ supported Fe2O3 improved the water gas shift reaction with chemical looping

Fe2O3 is prospective for the chemical looping redox cycles but must contain a significant amount of inert supports to ensure high stability. The traditional inert supports (Al2O3, MgAl2O4, etc.) have a dilution effect on Fe2O3, which results in a compromised reactivity. In this work, we propose several Sr, Mg co-doped LaGaO3-δ to support Fe2O3 for chemical looping water splitting and investigated the synergy for the enhanced performance. Mechanistic study manifests that doping Sr increases the amount of oxygen vacancies, promoting the oxygen release and uptake during the redox reaction. Doping Mg mitigated the interaction between Fe2O3 and the supports, leading to much enhanced stability. Therefore, Fe2O3/La0.6Sr0.4Mg0.4Ga0.6O3-δ shows both high hydrogen yield (9.75 mmol.g−1) and peak hydrogen production rate (3.7 mmol.g−1.min−1). The performance shows only a slight decrease even after 100 cycles. The observed results can also inspire the selection and development of advanced supports to improve both the reactivity and stability of oxygen carriers.

Energy and exergy analyses of an integrated membrane reactor and CO2 capture system to generate decarbonized hydrogen

At present, most of the world hydrogen production comes from the steam reforming of natural gas, carried out in conventional reactors, which show some disadvantages such as thermodynamic equilibrium limitation, harsh operating conditions, and are responsible for huge CO2 emission in the atmosphere. To overcome these disadvantages and meet the pressing requests of the hydrogen energy decarbonisation, the interest in membrane reactors, able to provide both hydrogen generation and separation in the same unit and at milder conditions, is increasing. Indeed, in these devices, the produced hydrogen in the reaction side is removed for permeation through a membrane continuously, and it is collected as a decarbonized stream in the permeate side, meanwhile overcoming the thermodynamic equilibrium limitation of the conventional reactors, and contributing to the intensification of the process and to the CO2 capture and storage. In this study, firstly, a one-dimensional model of a membrane reactor is developed and validated. The changes in the molar flow rates of each species and the temperature through the membrane reactor length are investigated. Furthermore, the effects of some operating parameters (the operating temperature, the steam-to-carbon ratio, and the inlet pressure on the reaction side of the membrane reactor) on the system performance (methane conversion, hydrogen yield, CO2 yield, and thermal efficiency based on lower heating value) are examined. Successively, the membrane reactor model is integrated into a system-level model, taking into account further a CO2 capture unit and the plant components (compressor, boiler, burner, pump, blower, and two mixers) in order to analyze theoretically the potentiality of this integrated membrane reactor based system to generate decarbonized hydrogen (high grade hydrogen production combined to the full CO2 capture to avoid its release in the environment). The novelty of this work deals with the application for the first time of a system-level modeling is based on the principles of electrochemistry and thermodynamics to develop a detailed energy and exergy analysis, calculating further the rate of exergy destruction of each component of the proposed membrane reactor based integrated system. At the baseline simulation conditions (773 K, 9 bar, and S/C = 3/1), thermal efficiency (based on lower heating value), methane conversion of the system, hydrogen yield, CO2 yield are equal to 51 %, 67 %, 22 %, and 66 %, respectively. Furthemore, the exergy destructions distribution is 49 % for the burner, 36 % for the boiler, 14 % for the membrane reactor, and 1 % others.

Parameter study for dimensioning of a PV optimized hydrogen supply plant

Green hydrogen produced from intermittent renewable energy sources is a key component on the way to a carbon neutral planet. In order to achieve the most sustainable, efficient and cost-effective solutions, it is necessary to match the dimensioning of the renewable energy source, the capacity of the hydrogen production and the size of the hydrogen storage to the hydrogen demand of the application.For optimized dimensioning of a PV powered hydrogen production system, fulfilling a specific hydrogen demand, a detailed plant simulation model has been developed. In this study the model was used to conduct a parameter study to optimize a plant that should serve 5 hydrogen fuel cell buses with a daily hydrogen demand of 90 kg overall with photovoltaics (PV) as renewable energy source. Furthermore, the influence of the parameters PV system size, electrolyser capacity and hydrogen storage size on the hydrogen production costs and other key indicators is investigated. The plant primarily uses the PV produced energy but can also use grid energy for production.The results show that the most cost-efficient design primarily depends on the grid electricity price that is available to supplement the PV system if necessary. Higher grid electricity prices make it economically sensible to invest into higher hydrogen production and storage capacity. For a grid electricity price of 200 €/MWh the most cost-efficient design was found to be a plant with a 2000 kWp PV system, an electrolyser with 360 kW capacity and a hydrogen storage of 575 kg.

Accelerated pyro-catalytic hydrogen production enabled by plasmonic local heating of Au on pyroelectric BaTiO3 nanoparticles

The greatest challenge that limits the application of pyro-catalytic materials is the lack of highly frequent thermal cycling due to the enormous heat capacity of ambient environment, resulting in low pyro-catalytic efficiency. Here, we introduce localized plasmonic heat sources to rapidly yet efficiently heat up pyro-catalytic material itself without wasting energy to raise the surrounding temperature, triggering a significantly expedited pyro-catalytic reaction and enabling multiple pyro-catalytic cycling per unit time. In our work, plasmonic metal/pyro-catalyst composite is fabricated by in situ grown gold nanoparticles on three-dimensional structured coral-like BaTiO3 nanoparticles, which achieves a high hydrogen production rate of 133.1 ± 4.4 μmol·g−1·h−1 under pulsed laser irradiation. We also use theoretical analysis to study the effect of plasmonic local heating on pyro-catalysis. The synergy between plasmonic local heating and pyro-catalysis will bring new opportunities in pyro-catalysis for pollutant treatment, clean energy production, and biological applications.

Screening of Nickel and Platinum Catalysts for Glycerol Conversion to Gas Products in Hydrothermal Media

The production of low-carbon gaseous fuels from biomass has the potential to reduce greenhouse gas emissions and promote energy sustainability, stability and affordability around the world. Glycerol, a large-volume by-product of biodiesel production, is a potential feedstock for the production of low-carbon energy vectors. In this present work, an aqueous solution of pure glycerol was reacted under hydrothermal conditions using a total of 10 types of heterogeneous catalysts to evaluate its conversion to gas products (hydrogen, methane, CO, CO2 and C2–C4 hydrocarbon gases). Two bimetallic Ni-Fe and Ni-Cu catalysts, three Pt-based catalysts and physical mixtures of the five catalysts were tested. The reactions were carried out in a batch reactor for 1 h reaction time, using a 9:1 mass ratio of water/glycerol (10 wt%) and the reaction temperatures ranged between 250–350 °C using and without using 1 g of catalyst. The effects of the catalysts and reaction conditions on the conversion of glycerol in terms of carbon and hydrogen gasification efficiencies, selectivity and yields of components in the gas products were investigated. CO2 remained the most dominant gas product in all experiments. The results indicated that increasing the reaction temperature favoured gas formation and both carbon and hydrogen gasification efficiencies. The combination of Ni-Cu and Pt/C catalysts was the most selective catalyst for gas formation at 350 °C, giving carbon gasification efficiency of 95.6 wt%. Individually, the catalyst with the highest hydrogen production was Pt/C and the highest propane yield was obtained with the Ni-Cu bimetallic catalyst. Some catalysts showed good structural stability in hydrothermal media but need improvements towards better yields of desired fuel gases.

Characterizing Effect of Porous Transport Layers on Electrolyzer Performance Using Neutron Imaging

Demand for high purity hydrogen production using renewable energy sources is growing to meet the clean energy demands. Polymer electrolyte membrane water electrolyzer (PEMWE) is one of the viable options for H2 production, but its high capital cost and operational expenditures increase the cost of H2. Improving the interface between the catalyst layer (CL) and the porous transport layer (PTL) is critical to increasing the efficiency of PEMWEs and thereby lowering the cost of H2. Increased contact between the CL and PTL improves catalyst utilization, and the optimal structure of the PTL reduces the mass transport issues related to O2 bubble removal.(1-3) Improved understanding of the PTL microstructure is necessary to improve the performance and efficiency of the PEMWE.This work presents a systematic study to elucidate the effect of PTL properties (morphology, thickness, and porosity) and their impact on PEMWE performance under different operating conditions. Polarization curves with different anode PTL (felt, sinter and pore graded hierarchical PTL) are presented in Figure 1a. The separation of mass transport resistance and the contract resistance for the different PTLs will be elucidated to show the impact of water management and interfacial contact. Mass transport in an operating electrolyzer is also studied by estimating the water content using neutron imaging. Figure 1b shows water thickness across a membrane electrode assembly (MEA) with a pore graded hierarchical PTL in anode at different current densities. Water content across the MEA with different PTL is also studied. The cells with these PTLs were evaluated in operando using micro x-ray computed tomography (CT) and x-ray radiography. The x-ray techniques revealed oxygen distribution within the PTLs on the pore-scale at varied current densities, complementing neutron imaging water thickness studies and providing micro-scale insight into transport. Acknowledgment This research is supported by the U.S. Department of Energy (DOE) Hydrogen and Fuel Cell Technologies Office, through the H2NEW consortium. References J. K. Lee, C. Lee, K. F. Fahy, B. Zhao, J. M. LaManna, E. Baltic, D. L. Jacobson, D. S. Hussey and A. Bazylak, Cell Reports Physical Science, 1, 100147 (2020).T. Schuler, J. M. Ciccone, B. Krentscher, F. Marone, C. Peter, T. J. Schmidt and F. N. Büchi, Advanced Energy Materials, 10, 1903216 (2020).P. Lettenmeier, S. Kolb, F. Burggraf, A. S. Gago and K. A. Friedrich, Journal of Power Sources, 311, 153 (2016). Figure 1

Simulation and design of an energy accumulator around the hydrogen energy vector

This work demonstrates the study of the numerical modelling and a design of a compact energy generator based on green hydrogen. This generator aims allowing the energy storage, electricity, cold and heat productions as well as a supply the energy for the production of the sanitary hot water. The generator is considered to be powered by 30 solar cells panels and will mainly consist of a Proton Exchange Membrane (PEM) electrolyzer compiled with a Metal Hydride (MH) tank, a PEM fuel cell, and a system of heat exchangers sized to recover the heat from the electrolyzer, PEM fuel cell and MH tank. Furthermore, the generator will contain an adsorber to manage air conditioning (cooling and heating) and a production of the sanitary hot water. A converter block is included in the generator, in particular, a Buck-booster to raise the voltage of the solar panels and the DC-AC converter for the electricity consumption in the household. The desorption of the hydrogen contained in the tank MH will take place using the heating resistance. In overall, the designed generator is foreseen to have a dimension of 1800 × 1000 × 500 mm and its role is to allow integration of the hydrogen energy for the tertiary and residential sectors. As such it is a suitable choice of components for the cost reduction and high yield hydrogen production, storage, and consumption.

Catalytic activites of a biomaterial (sumac) catalyst in sodium borohyride methanolysis reactions

Biomass waste (sumac) in particular, is an excellent starting point for preparing carbon materials since it is abundant, inexpensive, environmentally beneficial, and renewable. Therefore, the aim of the present study is defatted sumac (DS)- hydrochloric acid (HCl)- cobalt (Co) (DS-HCl-Co) catalyst (it will be used as a catalyst for the first time) in the presence of low activation energy and high hydrogen production rate (HPR). The effect of different parameters such as amount of catalyst, concentration of NaBH4 and temperature on HPR value obtained as a result of NaBH4 methanolysis in the presence of DS-HCl-Co catalyst have been investigated. The synthesized catalysts are named DS-HCl (pure) and DS-HCl-Co (supported). While the HPR value (mL*gcat−1 *min−1) obtained as a result of the hydrolysis experiments carried out is 3516.16 for the DS-HCl catalyst, it is 8298.5 for the DS-HCl-Co catalyst. Thus, it should be noted that the HPR value increases approximately 2.36 times in the presence of support material. Our other motivation in the current study is to have low activation energy, which is an important factor that increases catalytic activity. Using the Arrhenius equation, the activation energy for the DS-HCl-Co catalyst is calculated as 31.67 kJ/mol and this value is lower than some reported values ​​when compared to the literature.As a result, it can be said that the DS-HCl-Co catalyst is a unique, inexpensive, and ideal catalyst with high activity values ​​for hydrogen production from alkali hydrides.

Underground hydrogen storage in a naturally fractured gas reservoir: The role of fracture

As hydrogen provides a high heating value with the least environmental impact, it can be considered as an energy carrier pioneer in following the global zero-carbon policies. Then, since storing hydrogen in large quantities can also be a valuable technique for alleviating energy shortages due to energy consumption fluctuations, underground hydrogen storage (UHS) is being explored further in today's world. To the best of our knowledge, the role of fracture on underground hydrogen storage performance has not comprehensively been evaluated. For the first time, in this study, the effects of fracture on hydrogen storage and production were investigated in a naturally fractured gas reservoir in the Middle East using a numerical simulation. Then, to determine whether the fracture was able to accelerate hydrogen production, UHS was evaluated under various conditions, including the fracture system, condensate presence, Initial hydrogen injection stage, cushion gas type, hydrogen storage commence time and different injection/production cycle duration. The results of this study proves that although a huge amount of hydrogen is invaded into the matrix during hydrogen injection, the fracture accelerates hydrogen production, resulting in higher hydrogen recovery and purity, which indicates fractures are suitable media for hydrogen storage. However, it should be noted that the purity of hydrogen produced from naturally fractured reservoirs (NFR) decreases more rapidly than a conventional one during a single cycle due to the higher mixing of gases in the fracture. In the case of the initial stage of hydrogen injection, fractures are not found to be attractive as storage media. Therefore, it is necessary to analyze the fracture effects as a storage media under various situations and stages. In addition, alternative gas injection revealed that nitrogen injection into cushion gas resulted in the highest hydrogen production in the entire porous media, whereas methane injection led to the highest hydrogen recovery in the fracture media. Also, the rapid injection/production cycle duration improved hydrogen recovery, indicating that the required time for high hydrogen invasion into the matrix is not provided during hydrogen injection.

Experimental study on non-isothermal oxidative characteristics and kinetics of methane in accelerating rate calorimetry tests

The non-isothermal oxidative characteristics and kinetics of natural gas have important effects on performance of gas reservoir combustion, which directly determines temperature distribution, playing a significant role in hydrogen generation boundary. In this paper, the non-isothermal oxidation of methane, as main component of natural gas, is in depth analysis, which is rarely studied. At first, the non-isothermal oxidative characteristics at different pressure, oxygen/methane ratio, and debris were investigated by accelerating rate calorimetry (ARC). Afterwards, the non-isothermal oxidation kinetic parameters were analyzed and calculated. The difference of onset self-exothermic, ignition temperature, and kinetics parameters under different conditions were extraordinarily emphasized, aiming achieving successful and stable gas reservoir combustion for high efficiency hydrogen production. The results indicated that there is no even self-exothermic phenomenon at depleted reservoir condition (7.1–9.8 MPa and 100–150 °C), and the minimum starting self-exothermic temperature ignition temperature of methane oxidation are 220.6 °C and 312.7 °C. The pressure did not have effect on oxidation temperature in methane oxidation while did in catalytic oxidation. It was observed that rock debris has catalytic effect on methane oxidation suggested by obviously lower onset self-exothermic temperature detected and significantly smaller activation energy calculated in oxidation process of methane with debris. Moreover, the oxidation reaction rate of methane with debris is lower than that of methane, assisting more methane undergoes a more thorough HTO reaction conducive to combustion and decreasing the possibility of explosion in the injection air ignition process. According to the results obtained by ARC tests, we suggested that the near-wellhole places of gas reservoirs should be better heated over 313 °C for successfully achieving stable combustion. Some new knowledge got from this study is conducive to achieve rapid and stable combustion, thus achieving high-efficiency hydrogen generation.

Potato waste as feedstock to produce biohydrogen and organic acids: A comparison of acid and alkaline pretreatments using response surface methodology

The effects of physicochemical pre-treatment were evaluated on hydrogen (H2) production and organic acids from hydrolyzed potato peel. Central composite design (CCD) and response surface methodology (RSM) were used to evaluate the effects of different substrate concentrations on a wet basis (38.8–81.2 g.L−1) and hydrolyser ratios (6M NaOH and 30% HCl: 1.6–4.4% v.v−1; and H2SO4: 2.2–7.8% v.v−1). The experiments were conducted in batch reactors at 37 °C, using a heat-treated microbial consortium. The maximum H2 production potential (P), lag phase (λ), and maximum H2 production rate (Rm) were evaluated for untreated and pre-treated potato peel waste. H2 production was positively influenced under hydrolyzed substrate concentrations ≥75 g.L−1 in the three CCDs performed. Only the increase in the H2SO4 proportions (≥5% v.v−1) had a negative influence on H2 production. Increasing the 30% HCl and 6M NaOH proportions did not significantly influence the cumulative H2 production. The highest hydrogen production was obtained after alkaline pre-treatment by dark fermentation (P: 762.09 mL H2.L−1; λ: 14.56 h; Rm: 38.39 mL H2.L−1.h−1). Based on the CCD and RSM, the highest H2 production (1060.10 mL H2.L−1) was observed with 81.2 g.L−1 hydrolyzed potato peel with 3.0% v.v−1 of 6M NaOH. The highest yield liquid metabolites were acetic (513.70 mg. g−1 COD) and butyric acids (491.90 mg. g−1 COD).

Mo-activated VC as effective cocatalyst for an enhanced photocatalytic hydrogen evolution activity of CdS

Seeking an efficient and stable cocatalyst is of importance for semiconductor-based photocatalytic water splitting to produce hydrogen. In this sense, Mo-activation of VC for better cocatalytic properties was proposed for the first time, aiming to attain improved hydrogen generation of CdS. Our novel, yet facile physical preparation method permits intimate coupling of Mo-activated VC cocatalyst to CdS (through electrostatic attraction force), thereby promises drastic activity enhancement for hydrogen generation. Results indicate the best VC-activating competency of Mo against other transition metals (Co, Fe, Ni, Zn and Cu), which induces highest H2 productivity of CdS after modifying with Mo-activated VC. Under optimum setting, CdS/Mo(0.38)-VC(5 wt%) manifested highest photocatalytic hydrogen production rate of 2267 μmol h−1 g−1, associated to 300 % and 440 % improvement as compared to that of CdS/VC(5 wt%) and pure CdS, respectively. Such activity also outperformed those that yielded by MoSx- or noble metals(Pt, Au or Ag)-co-catalyzed CdS, attributed to the promoted interfacial charges transfer and lowered overpotential of CdS/Mo(0.38)-VC(5 wt%) in hydrogen generation. Correspondingly, high apparent hydrogen production quantum efficiency of 4.3 % was also recorded by the same photocatalyst at 420 nm. In term of stability test, CdS/Mo(0.38)-VC(5 wt%) manifested excellent longevity in 24 h continuous photoreaction and fair recyclability over five consecutive photoreaction cycles. This work provides a new insight to cocatalysts design and synthesis, thereby realizing economic alternatives to precious metal (Pt, Au, Ag) in solar-derived H2 production.