Russian Federation

The liquid organic hydrogen carriers (LOHC) are aromatic molecules which can be considered as an attractive option for the storage and transport of hydrogen. A considerable amount of hydrogen up to 7–8% wt. can be loaded and unloaded with a reversible chemical reaction. Substituted quinolines and pyridines are available from petroleum coal processing and wood preservation or they can be synthesized from aniline. Quinolines and pyridines can be considered as potential LOHC systems provided they have favorable thermodynamic properties which were the focus of this current study. The absolute vapor pressures of methyl-quinolines were measured using the transpiration method. The standard molar enthalpies of vaporization of alkyl-substituted quinolines and pyridines were derived from the vapor pressure temperature dependencies. Thermodynamic data on vaporization and formation enthalpies available in the literature were collected evaluated and combined with our own experimental results. The theoretical standard molar gas-phase enthalpies of formation of quinolines and pyridines calculated using the quantum-chemical G4 methods agreed well with the evaluated experimental data. Reliable standard molar enthalpies of formation in the liquid phase were derived by combining high-level quantum chemistry values of gas-phase enthalpies of formation with experimentally determined enthalpies of vaporization. The liquid-phase hydrogenation/dehydrogenation reaction enthalpies of alkyl-substituted pyridines and quinolines were calculated and compared with the data for other potential liquid organic hydrogen carriers. The comparatively low enthalpies of reaction make these heteroaromatics a seminal LOHC system.

Polymer electrolyte membrane (PEM) water electrolysis has demonstrated its potentialities in terms of cell efficiency (energy consumption ≈ 4.0-4.2 kW/Nm3 H2) and gas purity (> 99.99% H2). Current research activities are aimed at increasing operating pressure up to several hundred bars for direct storage of hydrogen in pressurized vessels. Compared to atmospheric pressure electrolysis high-pressure operation yields additional problems especially with regard to safety considerations. In particular the rate of gases (H2 and O2) cross-permeation across the membrane and their water solubility both increase with pressure. As a result gas purity is affected in both anodic and cathodic circuits and this can lead to the formation of explosive gas mixtures. To prevent such risks two different solutions reported in this communication have been investigated. First the chemical modification of the solid polymer electrolyte in order to reduce cross-permeation phenomena. Second the use of catalytic H2/O2 recombiners to maintain H2 levels in O2 and O2 levels in H2 at values compatible with safety requirements.

Today it is not known – neither qualitatively not quantitatively - how large the impact can be of the promoters on sensitivity to hydrogen-air detonation in hypothetical accidents at hydrogen-containing installations transport or storage facilities. Report goal is to estimate theoretically an effect of hydrogen-peroxide (as representative promoter) on sensitivity to detonation of the stoichiometric hydrogen-oxygen gas mixtures. The classical H₂-O2-Ar (2:1:7) gas mixture was chosen as reference system with the well established and unambiguously interpreted experimental data. In kinetic simulations it was found that the ignition delay time is sensitive to H₂O₂addition for small initial H₂O₂concentrations and is nearly constant for the large ones. Parametric reactive CFD studies of two dimensional cellular structure of 2H₂-O₂-7Ar-H₂O₂ detonations with variable hydrogen peroxide concentration (up to 10 vol.%) were also performed. Two un-expected results were obtained. First result: detonation cell size is practically independent upon variation of initial hydrogen peroxide concentration. For practical applications it means that presence of hydrogen-peroxide did not change drastically sensitivity of the stoichiometric hydrogen-oxygen gas mixtures. These theoretical speculations require an experimental verification. Second result: for large enough initial H₂O₂concentrations (> 1 vol.% at least) a new element of cellular structure of steady detonation wave was revealed. It is a system of multiple secondary longitudinal shock waves (SLSW) which propagates in the direction opposite to that of the leading shock wave. Detailed mechanism of SLSW formation is proposed.

Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and nonuniform mixture compositions was performed by the group of partners within the EC funded project “Hydrogen Safety as an Energy Carrier” (HySafe). Several experiments were conducted previously by Whitehouse et al. in a 10.7 m3 vertically oriented (5.7-m high) cylindrical facility with different hydrogen-air mixture compositions. Two particular experiments were selected for simulation and comparison as a Standard Benchmark Exercise (SBEP) problem: combustion of uniform 12.8% (vol.) hydrogen-air mixture and combustion of non-uniform hydrogen-air mixture with average 12.6% (vol.) hydrogen concentration across the vessel (vertical stratification 27% vol. hydrogen at the top of the vessel 2.5% vol. hydrogen at the bottom of the vessel); both mixtures were ignited at the top of the vessel. The paper presents modelling approaches used by the partners comparison of simulation results against the experiment data and conclusions regarding the non-uniform mixture combustion modelling in real-life applications.

The report deals with the investigation of non-stationary combustion of hydrogen-air mixtures extremely relevant to the issues of safety. Considered are the conditions of its formation and development in the tubes in the conic element and in the spherical 12-m diameter chamber. The report shows that at the formation of non-stationary combustion in the conic element in its top the pressure can develop exceeding 1000 atmospheres. It is also shown that in large closed volumes non-stationary combustion can develop from a small energy source in contrast to detonation for whose stimulation in large volumes significant power influences are required. Simultaneously in the volume a pressure can be formed by far exceeding the Chapman-Jouguet pressure in the front of stationary detonation.

This paper has experimentally proved that hydrogen accumulates in large quantities in metal-ceramic and pocket electrodes of alkaline batteries during their operation. Hydrogen accumulates in the electrodes in an atomic form. After the release of hydrogen from the electrodes a powerful exothermic reaction of atomic hydrogen recombination with a large energy release occurs. This exothermic reaction is the cause of thermal runaway in alkaline batteries. For the KSL-15 battery the gravimetric capacity of sintered nickel matrix of the oxide-nickel electrode as hydrogen storage is 20.2 wt% and cadmium electrode is 11.5 wt%. The stored energy density in the metal-ceramic matrix of the oxide-nickel electrode of the battery KSL-15 is 44 kJ/g and in the cadmium electrode it is 25 kJ/g. The similar values for the KPL-14 battery are as follows. The gravimetric capacity of the active substance of the pocket oxide-nickel electrode as a hydrogen storage is 22 wt% and the cadmium electrode is 16.9 wt%. The density of the stored energy in the active substance oxide-nickel electrode is 48 kJ/g and in the active substance of the cadmium electrode it is 36.8 kJ/g. The obtained results of the accumulation of hydrogen energy in the electrodes by the electrochemical method are three times higher than any previously obtained results using the traditional thermochemical method.

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean complex-chemistry hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed to perform a priori assessment of predictive capabilities of the flamelet approach for evaluating mean species concentrations. For this purpose dependencies of mole fractions and rates of production of various species on a combustion progress variable c obtained from the laminar flame are averaged adopting either the actual Probability Density Function (PDF) P (c)  extracted from the DNS data or a common presumed β-function PDF. On the one hand the results quantitatively validate the flamelet approach for the mean mole fractions of all species including radicals but only if the actual PDF P (c) is adopted. The use of the β-function PDF yields substantially worse results for the radicals’ concentrations. These findings put modeling the PDF P (c) on the forefront of the research agenda. On the other hand the mean rate of product creation and turbulent burning velocity are poorly predicted even adopting the actual PDF. These results imply that in order to evaluate the mean species concentrations the flamelet approach could be coupled with another model that predicts the mean rate and turbulent burning velocity better. Accordingly the flamelet approach could be implemented as post-processing of numerical data yielded by that model. Based on the aforementioned findings and implications a new approach to building a presumed PDF is developed. The key features of the approach consist in (i) adopting a re-normalized flamelet PDF for intermediate values of c and (ii) directly using the mean rate of product creation to calibrate the presumed PDF. Capabilities of the newly developed PDF for predicting mean species concentrations are quantitively validated for all species including radicals.

Ultra-lean hydrogen-air combustion is characterized by two phenomena: the difference in upward and downward flame propagation concentration limits and the incomplete combustion. The clear answers on the  two  basic  questions  are  still  absent:  What  is  a  reason  and what  is  a  mechanism  for  their manifestation? Problem statement and the principal research topics of the Flame Ball to Deflagration Transition (FBDT) phenomenon in gaseous hydrogen-air mixtures are presented. The non-empirical concept of the fundamental concentration limits discriminates two basic low-speed laminar combustion patterns - self-propagating locally planar deflagration fronts and drifting locally spherical flame balls. To understand - at what critical conditions and how the baric deflagrations are transforming into iso- baric  flame  balls? - the  photographic  studies  of   the  quasi-2-dim  flames  freely  propagating  outward radially  via  thin  horizontal  channel   were  performed. For  gradual  increase  of  initial  hydrogen concentration from 3 to 12 vol.% the three representative morphological types of combustion (star-like dendrite-like  and   quasi-homogeneous)  and  two  characteristic  processes  of  reaction  front  bifurcation were revealed. Key elements of the FBDT mechanism both for 2-dim and 3-dim combustion are the following. Locally  spherical  ""leading  centres""  (drifting  flame  balls) are  the  ""elementary  building blocks"" of all ultra-lean flames. System of the drifting flame balls is formed due to primary bifurcation of the pre-flame kernel just after ignition. Subsequent mutual dynamics and overall morphology of the ultra-lean flames are governed by competitive non-local interactions of the individual drifting flame balls and their secondary/tertiary/etc. bifurcations defined by initial stoichiometry."

Hydrogen embrittlement has been intensively studied in the past. However its governing mechanism is still under debate. Particularly the details of the formation of specific cleavage-like or quasi-cleavage fracture surfaces related to hydrogen embrittled steels are unclear yet. Recently it has been found that the fracture surface of the hydrogen charged and tensile tested low-carbon steel exhibits quasi-cleavage facets having specific smoothly curved surface which is completely different from common flat cleavage facets. In the present contribution we endeavor to shed light on the origin of such facets. For this purpose the notched flat specimens of the commercial low carbon steel were tensile tested using ex- and in-situ hydrogen charging. It is found that in the ex-situ hydrogen charged specimens the cracks originate primarily inside the specimen bulk and expand radially form the origin to the specimen surface. This process results in formation of “fisheyes” – the round-shape areas with the surface composed of curved quasi-cleavage facets. In contrast during tensile testing with in-situ hydrogen charging the cracks initiate from the surface and propagate to the bulk. This process results in the formation of the completely brittle fracture surface with the quasi-cleavage morphology - the same as that in fisheyes. The examination of the side surface of the in-situ hydrogen charged specimens revealed the straight and S-shaped sharp cracks which path is visually independent of the microstructure and crystallography but is strongly affected by the local stress fields. Nano-voids are readily found at the tips of these cracks. It is concluded that the growth of such cracks occurs by the nano-void coalescence mechanism and is responsible for the formation of fisheyes and smoothly curved quasi-cleavage facets in hydrogen charged low-carbon steel.

Hydrogen accumulation and distribution in pipeline steel under conditions of enhanced corrosion has been studied. The XRD analysis optical spectrometry and uniaxial tension tests reveal that the corrosion environment affects the parameters of the inner and outer surface of the steel pipeline as well as the steel pipeline bulk. The steel surface becomes saturated with hydrogen released as a reaction product during insignificant methane dissociation. Measurements of the adsorbed hydrogen concentration throughout the steel pipe bulk were carried out. The pendulum impact testing of Charpy specimens was performed at room temperature in compliance with national standards. The mechanical properties of the steel specimens were found to be considerably lower and analogous to the properties values caused by hydrogen embrittlement.