Designing future hydrogen infrastructure: Insights from analysis at different spatial scales

This paper critically reviews the growing literature optimising hydrogen infrastructure. We examine studies across spatial scales: national scale studies using energy system models; regional scale studies optimising spatially disaggregated hydrogen infrastructure; and local scale studies optimising the siting of filling stations. For the latter two types of study, we critically assess the assumptions made around hydrogen demand, a key exogenous input into these studies. We identify knowledge gaps and issues that have not been sufficiently addressed in the literature, and we suggest areas for further work.     

Inhibitory effect of ethanol,acetic acid,propionic acid and butyric acid on fermentative hydrogen production

The inhibitory effect of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate. The experimental results showed that, at 35 °C and initial pH 7.0, during the fermentative hydrogen production, the substrate degradation efficiency, hydrogen production potential, hydrogen yield and hydrogen production rate all trended to decrease with increasing added ethanol, acetic acid, propionic acid and butyric acid concentration from 0 to 300 mmol/L. The inhibitory effect of added ethanol on fermentative hydrogen production was smaller than those of added acetic acid, propionic acid and butyric acid. The modified Han–Levenspiel model could describe the inhibitory effects of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production rate in this study successfully. The modified Logistic model could describe the progress of cumulative hydrogen production.     

Kinetic modelling of the first step of Mn2O3/MnO thermochemical cycle for solar hydrogen production

This work reports the kinetic study of the first step of the Mn₂O₃/MnO thermochemical cycle for hydrogen production by water splitting. The reaction kinetics of Mn (III) oxide thermal reduction has been evaluated using dynamic thermogravimetric analysis at constant heating rate under nitrogen flow. This way the reaction rate can be described as a function of temperature and different kinetic models were fitted to the experimental data obtained from thermogravimetric experiments. A good fitting can be observed for each experiment, although a significant disparity in the values estimated for the Arrhenius parameters has been found (activation energies and pre-exponential factors). Unique values for the kinetic parameters have been calculated by application of a multivariate non-linear regression method for the simultaneous fitting of data from all the experiments carried out at different heating ramps. However, also in this case the values of the Arrhenius parameters are significantly different depending on the chosen kinetic equation. Optimal kinetic parameters have been finally calculated through the estimation of activation energy values by model-free isoconversional methods and using a rigorous multivariate nonlinear regression for the calculation of the model-dependant pre-exponential factors.     

Catalytic performance and kinetic modeling of ethylene glycol steam reforming over surfactant-modified Pd–Ni/KIT-6

In the current study, steam reforming of ethylene glycol as a well-known bio-oxygenate, was carried out over 2%Pd–10%Ni/KIT-6 catalyst in a fixed-bed reactor. 2%Pd–10%Ni/KIT-6 was synthesized via surfactant-assisted impregnation method, whose physicochemical properties were determined by XRD, XRF, BET, FE-SEM, EDX-dot mapping, TEM, H₂-TPR, NH₃-TPD and TGA analyses. The performance of the synthesized catalyst was investigated at temperatures from 623 to 773 K and at 10 wt% of ethylene glycol in water. Furthermore, the W_cat/F_EG0 ratio varied between 100.08 and 202.22 (g h mol^?1). At T = 773 K and W_cat/F_EG0 = 202.22, ethylene glycol conversion and H₂ yield were 99.8% and 71.36%, respectively. Also, a stability test of 2%Pd–10%Ni/KIT-6 was conducted for 28 h. No significant change was shown in the catalytic activity. Some different models were used to describe the kinetic behavior. The power-law model indicated that the reaction order changed with temperature. The kinetic data were interpreted by the Langmuir-Hinshelwood models, in which the surface reaction between the adsorbed reactants was considered as a rate-determining step. The activation energy for the Langmuir-Hinshelwood and power-law models were 28.03 and 33.07 kJ mol^?1, respectively. This synthesized nanocatalyst as the first Pd–Ni/zeolite in SREG through well-known kinetics and mechanism, is superior in high stability, excellent EG conversion, good yield and selectivity to H₂ and less production of toxic products.     

Synthesis by reactive ball milling and cycling properties of MgH2–TiH2 nanocomposites: Kinetics and isotopic effects

MgH₂, MgH₂–TiH₂ nanocomposites and their deuterated analogues have been obtained by reactive ball milling and their kinetic and cycling hydrogenation properties have been analysed by isotope measurements and high-pressure differential scanning calorimetry (HP-DSC). Kinetics of material synthesis depends on both Ti-content and the isotopic nature of the gas. For pure Mg, the synthesis is controlled by isotope diffusion in Mg and therefore MgH₂ forms faster than MgD₂. For the MgH₂–TiH₂ nanocomposites, the synthesis is controlled by the efficiency of milling. Kinetics of reversible hydrogen/deuterium sorption in nanocomposites have been studied at 548 K. The rate limiting step is isotope diffusion for absorption and Mg/MgH₂ interface displacement for desorption. HP-DSC measurements demonstrate that the TiH₂ phase acts as a gateway for hydrogen sorption even in presence of MgO and provides abundant nucleation sites for Mg and MgH₂ phases. The 0.7MgH₂–0.3TiH₂ nanocomposite exhibits steady hydrogen storage capacity after 100 cycles of absorption–desorption.     

OH*-chemiluminescence during autoignition of hydrogen with air in a pressurised turbulent flow reactor

Autoignition of hydrogen in air was studied in a turbulent flow reactor using OH*-chemiluminescence. High-speed imaging was used to visualise the formation of autoignition kernels in the flow, and to analyse the conditions under which temporary stabilisation of the flame kernels occurred. The experiments were carried out at temperatures of 800–850 K, pressures of 0.8–1.2 MPa and an equivalence ratio of φ = 0.25. Measurements of the autoignition delays yielded values in the range of τ = 210–447 ms. The autoignition delay results indicated that, over the range of conditions studied, ignition delays reduced with decreasing pressure. This observation contradicted homogeneous gas-phase kinetic calculations, which predicted an increase in autoignition delay with decreasing pressure. If the kinetic model was altered to include surface reactions at the reactor walls, the calculations could be qualitatively reconciled with the experimental data, suggesting that wall reactions had a significant influence on autoignition delays.     

The evaluation of Ni–Co/Al2O3 via olive pomace pyrolysis to generate hydrogen-rich gas: Experimental and kinetic study

The aim of this study is to evaluate olive pomace (OP) as a fuel potential and to examine the effect of Ni–Co/Al₂O₃ catalyst on the pyrolysis of OP by experimental and thermogravimetric analysis (TGA). Pyrolysis studies and kinetic studies were performed in a fixed-bed reactor and a TG analyzer, respectively. The kinetic study was compared with the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and their thermodynamic properties were determined. The average activation energy of the OP and OP-20% catalyst was found to be 142.59 and 132.83 kJ/mol, respectively. In addition, the H₂ yield increased from 1.76 mol H₂/kg biomass to 6.08 mol H₂/kg biomass in the presence of 20 wt% catalyst. Based on the results obtained, the pyrolysis of OP can be considered as a suitable alternative for biofuel production.     

Isolation of anoxygenic photosynthetic bacteria from Songkhla Lake for use in a two-staged biohydrogen production process from palm oil mill effluent

We are developing a process to produce biohydrogen from palm oil mill effluent. Part of this process will involve photohydrogen production from volatile fatty acids under low light conditions. We sought to isolate suitable bacteria for this purpose from Songkhla Lake in Southern Thailand. Enrichment for phototrophic bacteria from 34 samples was conducted providing acetate as a major carbon source and applying culturing conditions of anaerobic-low light (3000 lux) at 30 °C. Among the independent isolates from these enrichments 19 evolved hydrogen with productivities between 4 and 326 ml l⁻¹ d⁻¹. Isolate TN1 was the most efficient producer at a rate of 1.85 mol H₂ mol acetate⁻¹ with a light conversion efficiency of 1.07%. The maximum hydrogen production rate for TN1 was determined to be 43 ml l⁻¹ h⁻¹. Environmentally desirable features of photohydrogen production by TN1 included the absence of pH change in the cultures and no detectable residual CO₂.     

Modelling the mitigation of hydrogen deflagrations in a vented cylindrical rig with water fog and nitrogen dilution

Nitrogen dilution and very fine water mist fogs have both been suggested as possible methods of mitigating the overpressure rise, should a hydrogen deflagration in a vented enclosure occur. A numerical CFD gas explosion code (FLACS) has been used to simulate the pressure-time curves and the rate of pressure rise generated following the ignition of different hydrogen–oxygen–nitrogen mixtures in a small scale vented cylindrical explosion rig. This has allowed the potential mitigating effect of nitrogen dilution (reduced oxygen) and very fine water fog, used both alone and in combination, to be explored and permitted their direct comparison with corresponding experimental test data.     

Possibility of hydrogen production during cheese whey fermentation process by different strains of psychrophilic bacteria

The aim of this study was to determine the possibility of applying psychrophilic bacteria for hydrogen production in whey biofermentation process. Experiments were conducted in 500-mL anaerobic respirometers at a temperature of 20 °C. The initial organic load of fermentation tanks reached 10 g COD/L. Depending on the experimental variant, analyses were carried out for psychrophilic bacteria isolated from underground water and from demersal lake water that represented Gammaproteobacteria class – Rahnella aquatilis (9 strains) and Firmicutes phylum: Carnobacterium maltaromaticum, Trichococcus collinsii and Clostridium algidixylanolyticum. The effectiveness of biogas production was diversified and strain-specific, ranging from 126.48 to 4737.72 mL/g bacterial biomass. The highest concentration of H₂ in biogas, ranging from 65.15% to 69.12% and effectiveness of H₂ production from 1587.47 to 3087.57 mL/g bacterial biomass, were determined for R. aquatilis strains isolated from the demersal lake water. The lowest H₂ concentration in the gaseous metabolites, i.e. 15.46% to 20.70%, was noted for bacteria of the phylum Firmicutes.     

Kinetic analysis of the chemical effects of hydrogen addition on dimethyl ether flames

The chemical effects of hydrogen addition on premixed laminar low-pressure dimethyl ether flames were studied by kinetic analysis. The chemical effects of hydrogen addition on flame structures and mole fractions of major species, intermediate species and free radicals have been distinguished clearly from the dilution and thermal effects. The results show that the chemical effects of hydrogen addition cause the DME profile to move toward the upstream side and can suppress the production of acetylene and ethylene. The production of formaldehyde is promoted by the chemical effects of hydrogen addition but the dilution and thermal effects are more dominant which decrease the mole fraction of formaldehyde so that the overall effects make formaldehyde mole fraction decrease. The dominant effects of hydrogen addition on H, OH and O radicals are the chemical effects that make mole fractions of these radicals increase.     

Detailed and reduced chemistry for methanol ignition

Simplified chemical-kinetic mechanisms are sought that can provide agreement with measured shock-tube autoignition times and counterflow critical ignition conditions for methanol (CH₃OH) oxidation. Existing detailed chemistry over-predicts measured counterflow ignition temperatures by 100 K or more. It was found that the elementary step CH₃OH + HO₂ → CH₂OH + H₂O₂ most strongly affects the predictions. Increasing the pre-factor in the Arrhenius expression for the rate of this step from different available literature values by a factor ranging from 2 to 13, namely to 8 × 10¹³ cm³/(mol s), within existing uncertainty, produces agreement of predictions with experiment. Using this revised rate, unimportant steps are deleted from the San Diego mechanism to obtain a set of 26 irreversible elementary steps (augmented to 27 by including fuel dissociation to CH₃ + OH for high-temperature shock-tube conditions) that predict ignition nearly as well as the detailed mechanism. In this mechanism, the intermediate species CH₂OH, CH₃O, HCO, H, O, and OH accurately obey steady states, while the intermediates CH₂O, HO₂, H₂O₂, CO, and H₂ do not. The result is a six-step overall reduced mechanism that describes ignition well at the lower temperatures. At higher temperatures, the aforementioned fuel decomposition becomes important, increasing the six-step mechanism to a seven-step mechanism. Expressions for the reaction rates, branching ratios, and steady-state species concentrations in the six-step reduced mechanism are given to facilitate future methanol ignition computations. Higher alcohols, which are less dependent on HO₂ attack in ignition, are indicated to nevertheless possibly benefit from an increase of the rate of the corresponding step.     

Numerical modeling of hydrogen absorption measurements in Ni-catalyzed Mg

Magnesium has been deeply studied as a possible hydrogen storage material for both, mobile and static applications. In this work, hydrogen absorption in Ni-catalyzed magnesium was measured in a wide range of pressure (500 kPa–5000 kPa) and temperature (498 K–573 K). Using this information, a model for the absorption kinetics and thermal behavior of the hydrogen storage system was proposed. This model could be used in the design of Ni-catalyzed magnesium storage tanks and other applications. It considers the independent contribution of three variables: temperature, pressure and reacted fraction to estimate the hydrogen absorption rate. An activation energy for the process was estimated and the value obtained (92 kJ/mol) was concordant with previous values reported in the literature.