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Project titleDevelopment of the scientific and technical groundings of autonomously controlled hydrogen generation for fuel cells by the oxidation of alloys-based energy carriers in aqueous media

AffiliationJoint Institute for High Temperatures of the Russian Academy of Sciences,

KeywordsHydrogen generation, heat and mass transfer, kinetics of heterogenuous reactions, oxidation of alloys in aqueous media

Annotation
At present, most of the leading countries pay high attention to the development of hydrogen technologies. In Russian Federation, there is also a growing trend of the creation and deployment of hydrogen-based power plants as well as designing solutions for ecological hydrogen production. For special applications, power supply systems based on fuel cells are currently considered as an alternative to accumulator batteries because of their higher specific energy capacity and better performance at sub-zero temperatures. The said systems are becoming increasingly widespread in the transport industry; they are used to equip drones and robotic platforms and represent a perfect solution for emergency and decentralized heat and power supply. For today, a number of methods are known for a large-scale production of ‘low-carbon’, ‘medium-carbon’ and ‘high-carbon’ hydrogen, and a strategy is formed for the transition to the production of ‘carbon-free’ hydrogen via electrolysis with power supplied from renewable energy sources or atomic stations. However, the problems of safe storage and transportation of this highly explosive gas are still unsettled. Building and maintenance of the proper infrastructure as well as ensuring its safety are associated with tremendous efforts and costs. Therefore, special solutions are required to distribute the largest amount (about 90%) of the hydrogen fuel immediately upon its production. The present project is aimed on the designing of a system for controlled hydrogen generation by the oxidation of energy carriers based on aluminum and magnesium alloys in water and aqueous salt solutions for hydrogen supply to fuel cells. The major advantage of such a concept is hydrogen production on demand and in-situ that eliminates any hydrogen storage and transportation troubles. Another important advantage constitutes in the implementation of aluminum – the most common metal (and the second most common element) in the earth’s crust, available in enormous quantities. Taking into account recent projects on the aluminum industry modernization, such as ALLOW (production of ‘low-carbon’ aluminum using ‘carbon-free’ energy sources, mainly hydroelectric power), ELYSIS (melting of aluminum using ‘carbon-free’ – or ‘inert’ – electrodes, that involves evolution of oxygen instead of carbon dioxide), and research activity of the Laboratory of the Fundamental Investigations of Aluminum Production Problems (MSU, Department of Physical Chemistry) focused on the ‘inert cathodes’ engineering, a transition to the production of ‘carbon-free’ aluminum can be expected in the nearest future. The reaction products from aluminum oxidation (boehmite, bayerite) are safe for the environment and can be implemented as raw material in the aluminum production cycle. The novelty of the present solution is that a prototype of a hydrogen source providing hydrogen generation with autonomously pressure-regulated hydrogen yield will be created, for which the experimental and numerical studies of the heat and mass transfer processes will be performed. The experiemental study of the heat transfer from the surface of the reacting samples to the near-surface two-phase layer and study of their oxidation kinetics in different aqueous media will be another novel result of the project.

Expected results
The expected results of the present project include the following: - data from the experimental investigation of the oxidation kinetics for the samples manufactured of 3004/3104, 5182, D16, V95 and PAM-1 aluminum- and magnesium-based alloys with addition of other metals (Fe, Ni, Sn, Pb, Cu, Zn, Bi, Co, Ga) in aqueous media (pure water and NaCl, KCl, LiCl, CaCl2, ZnCl2, MgCl2, NiCl2, CoCl2, SnCl2, SnCl4, CuCl2, AlCl3 aqueous solutions) at a temperature range from 0 to 90 °C; - results from the analyses of the solid reaction products characteristics (phase composition, microstructure); - results from the experimental study on the heat transfer from the alloy sample in form of a thin plate to the near-surface gas-liquied layer (aqueous solution and floating hydrogen bubbles) for the selected alloy and solution compositions; - prototype of a hydrogen generator for studying heat and mass transfer processes, with the options of pressure, temperature and level measuring, thermocouples and energy carrier sample altitude positioning, providing hydrogen outflow in a continuous form or in form of discrete portions, hydrogen evolution autonomously controlled by the pressure in the system; - results from the numerical and experimental investigations of the heat and mass transfer processes during the operation cycle of the hydrogen generator prototype; - model for the simulation of the heat and mass transfer processes in the hydrogen generator prototype, tested/improved using the abovementioned results; - results from the analysis of the impurity profile for the hydrogen produced in the hydrogen generator prototype. The results of this project will be published in top-rated journals (from Scopus and Web of Science databases) and represented at the thematic conferences. The proposed project has great significance for the development of new research fields in our laboratory, as the project participants will gain valuable experience in the following areas: - experimental study of heat and mass transfer processes in chemical reaction systems; - numerical simulation of heat and mass transfer processes in chemical reaction systems; - creation and testing the operation of a compact device for controlled hydrogen generation and analysis of the impurity profile of the hydrogen produced.

Annotation of the results obtained in 2023
In 2023, research activities under the project included the manufacture of the compacted samples (tablets) of a composite powder elaborated via ball milling of the D16 aluminum alloy scrap together with 10 wt.% ‘PMS-1’ copper powder by means of a cold pressing and spark plasma sintering methods. For the monolithic samples their physical and chemical properties (density, heat capacity, thermal conductivity, microstructure, and elemental and phase compositions) were determined. Under three temperature regimes (60, 70 и 80 °C), for the samples reacting with aluminum chloride solution (21 wt.%), their hydrogen generation performance (hydrogen yield and reaction rate) were obtained; and the physical properties (density, heat capacity, thermal conductivity, and kinematic viscosity) of the solution were measured as well. Within the hydrogen yield range from 3 to 93%, the resulting kinetic curves were approximated by the ‘contracting volume’ equation (for one-dimensional case of flattened cylinders with all its surfaces excepting the top edge insulated). From that approximation, the reaction rate constants were derived which were, in their turn, used for obtaining the activation energy and collision frequency factor — the parameters of the Arrhenius equation that determines the reaction rate constant dependence on temperature. The data from analyses and measurements were used for the numerical simulation of the heat and mass transfer processes. For the temperature regimes specified above, the calculations of the temporal evolution of the sample and solution temperatures and heat transfer coefficients were performed by two methods. A first was based on the parametric identification of the heat transfer coefficient for the sample-solution system and determination of the global minimum of the root mean square residual functional for the predicted temperature and the corresponding readings of the thermocouple. Another method constituted in the successive execution of solving the ‘direct’ heat exchange problem that included the determination of the solutions for two heat balance equations in the dynamic mode and the calculation of the heat transfer coefficient from the free convection Nusselt number using the corresponding dimensionless equation. The data processing for the 70 and 80 °C temperature regimes provided a good compliance between the experimental data and simulation results (the temperature difference for the thermocouple hot joint was 0.05–0.1 °C), and the stationary heat transfer coefficients fell within the range of 500–2000 W/(m2×K), that was observed in some previous studies on the heat transfer to the two phase media in bubble columns. In the case of 60 °C, a larger discrepancy in the heat transfer coefficient values and relatively big temperature error of 0.6 °C was obtained. Those deviations could be reduced by the increase in the convection heat transfer surface (for a larger sample), and implementation of less ‘noisy’ temperature transducers (shielded thermocouples or resistance temperature detectors). The measurements of the impurities in the hydrogen sample obtained at 80 °C evidenced a relatively high chlorine content (~0,02 vol.%), that could have deteriorating effect on the catalyst of fuel cells with proton exchange membranes. The reduction in the chlorine content could be provided by means of reducing salt concentration in the solution and the process temperature , as well as by effective condensing of the moisture entrained by the hydrogen flow. An option work included the manufacture of hydrogen generating powder samples of the waste of a high-pure (99.9%) aluminum alloy and 10 wt.% silver powder ‘POS-3’ and their further testing in the saline solutions of aluminum chloride, calcium chloride and sodium chloride. In order to increase particle size reduction, an additive of 20 wt.% anhydrous LiCl and 1 wt.% gallium. The experimental and analyses results proved that, despite an intensive purging of the starting materials with argon prior to ball milling, and implementation of toluene as a process control agent, a significant fraction of aluminum was oxidized with residual air directly during the ball milling process, thus yielding only 80–85% of the expected hydrogen amount. If a successful solution of this problem is found, the elaborated material could be considered as promising for the manufacture of compacted samples.

Publications

1. Olesya A. Buryakovskaya, Mikhail S. Vlaskin, Aleksey V. Butyrin Metal Scrap to Hydrogen: Manufacture of Hydroreactive Solid Shapes via Combination of Ball Milling, Cold Pressing, and Spark Plasma Sintering Nanomaterials, Том 13, выпуск 24, стр. 3118 (year - 2023) https://doi.org/10.3390/nano13243118

Annotation of the results obtained in 2022
In 2022, research activities under the project included experimental investigation of hydrogen production kinetics from the oxidation of aluminum (D16 alloy) and magnesium (ML5 and ML10) scrap materials activated by high energy ball milling without additives and together with different activating substances: copper powders, Wood's alloy, KCl salt and their mixture, and Devarda's alloy, in different aqueous salt solutions. The selested powder material (D16 alloy activated with 10wt.% PMS-1 copper powder) was used to manufacture a bulk sample by cold pressing. The said samples were used to produce thin plates for further experiments. It was established that the activation parameters (ball milling mode and duration, milling ball sizes, composition and content of activator) had great importance for the hydroreactive properties of the composite materials, their microstructure and phase composition. A facility for the investigation on heat transfer was improved: its reactor unit was equipped with the elements of plastic and corundum stable to corrosion, ultrathin thermocouples (50 micrometers in thickness) of copper and constantan were manufactured in order to be arranged within a thin two-phase layer of hydrogen bubbles and solution adjacent to a hydroreactive sample's surface. At the facility, heat transfer processes were investigated for the pressed thin plates (mentioned above) and selected solution (AlCl3, 2 M). The specific reaction constant and heat transfer coefficient values were obtained. The prototype of a hydrogen generator for the investigations of heat and mass transfer processes was equipped with the measuring instruments and prepared for the following part of the project.

Publications

1. Olesya A. Buryakovskaya, Musi Zh. Suleimanov, Mikhail S. Vlaskin, Vinod Kumar, Grayr N. Ambaryan Aluminum Scrap to Hydrogen: Complex Effects of Oxidation Medium, Ball Milling Parameters, and Copper Additive Dispersity Metals, 2023, 13(2), 185 (year - 2023) https://doi.org/10.3390/met13020185