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This work aims at developing an innovative solution for storing renewable energies, so-called “Smart Energy Hub” (SEH) developed by Sylfen, based on reversible Solid Oxide Cell (rSOC) technology. It is able to operate either in electrolysis (SOEC) mode storing excess electricity to produce hydrogen, or when energy needs exceed local production, in SOFC (solid oxide fuel cell) mode producing electricity (and heat) from hydrogen or any other hydrogenated fuel. Particularly this paper focuses on stack development and optimization, partly performed through the REFLEX project supported by European commission funding. To achieve the project’s objectives, in terms of efficiency and increase of system power density, as well as multi-stack operation, optimizing CEA stack is necessary to upgrade a stack originally designed for SOEC research purposes, to a stack reversibly operated, but also integrated as a part of module. This paper presents results of stack optimisations and integration of cells developed within the REFLEX project. First, a reduction in cell thickness of ~20 % led to adapting the stack manufacturing process parameters. Some tests, here presented, demonstrate that the stack performances were not affected by this change. Then, significant effort was devoted to air distribution at the Single Repeat Unit (SRU) scale to minimize pressure drop, undesirable for both global system efficiency and mechanical resistance of stack sealing. At the SRU scale, air path adjustment reduced the pressure drop by a factor 2; at stack scale, the performances obtained in i-V curves demonstrated reactants distributions were unchanged. Optimized cells (so called G2) developed in the frame of REFLEX project were then integrated in a short stack (5 cells vs. 25 full size) to be compared to short stack comprising regular cells produced by Elcogen. Both stacks were tested in terms of durability over more than 1000 hours at 700°C. A first period of about 800 h of operation was conducted alternating from SOFC to SOEC mode by steps of ≈100 h. During this first part, the stack was supplied by 50/50 H2O/H2 at total flow rate of 12.0 NmL/min/cm² on fuel side and air (clean and dry) on oxygen side. Stack performances were checked at each change of operating mode through i-V curves recorded at 800, 750 and 700°C. For the reference cell, durability tests were operated galvanostatic at 0.36 A/cm² in fuel cell mode and -0.51 A/cm² in electrolysis mode. The fuel utilization (FU) was respectively 42% in SOFC, and Steam Conversion (SC) 59% in SOEC. For the optimized cell, tests were carried out at 0.35 A/cm² (FU=41%), and -0.58 A/cm² (SC=67%). A second stage of more than 250h of operation consisted to alternate daily from SOEC to SOFC by cycles of respectively 8h and 16h. Finally, degradation was evaluated and despite the increase in SOEC current density during G2 cell testing, degradation rate was very similar for both cells in SOEC as well as in SOFC mode. A full size (25-cells) stack made of G2 cells was manufactured integrating the fluidic optimizations but also manifold and an electrical insulation necessary to operate stacks serially connected electrically within the REFLEX modules produced by Sylfen. The change of scale was validated by obtaining similar i-V curves recorded for 5-cells and 25-cells stacks. REFLEX Smart Energy Hub will be operated in ENVIPARK Torino using three modules comprising of four stacks each. Stack production has to be as uniform as possible and consequently, manufacturing process has to be optimized. Dispersion in performance, that results of cell production and stack manufacturing process is checked at final stage by i-V curves recording before delivery. Uniformity in production (in terms of tightness, reactant distribution and so initial electrochemical performance) is found to be satisfactory, the dispersion of median cell stack voltage over the stack production is less than the voltage dispersion observed between the whole cells at stack level. For near future needs in rSOC system, an increase of stack power density is required to both reduce the CAPEX and increase system energy efficiency. In that frame cells produced by Elcogen has an active cell area that was extended from 100 to 196 cm² and tested at stack levels of 5 and 25 cells, respectively. Enlarged stack performances are measured via i-V curves and compared to reference 100 cm² cells stacks. As difference in median cell voltage is less than 10 mV up to a current density of -1.25 V/cm² (80% SC), this paper shows that, from a mechanical and fluidic point of view, the enlarged cell were successfully integrated in full-scale stack. Figure 1

Deliverable 4.3, Technical report on developed recovery technologies for LSC cathode materials. Prepared by Politecnico di Torino with inputs from Elcogen.

During the XIII INSTM Congress,Advanced Materials and Green Processes for a Sustainable Society(23-26 January 2022), this poster wasnominated in the category "Materials and Technologies for H2economy"andreceived the first award among all the categories, obtaining recognition by the international scientific community specialised in materials studies. (Dr. Sofia Saffirio, Politecnico di Torino)

This work aims at developing an innovative renewable energy storage solution, based on reversible Solid Oxide Cell (rSOC) technology. That is to say, one system optimized to operate either in electrolysis mode (SOEC) to store excess electricity to produce H2, or in fuel cell mode (SOFC) when energy needs exceed local production, to produce electricity and heat again from H2 or any other fuel locally available. Firstly, work focused on optimization of the different layers constituting the single SOC cell to reach high initial performance applying state-of-the-art materials as previously reported [1]. Secondly, the initially highest performing cells were selected for long-term reversible SOFC/SOEC single cell tests. Thirdly, these cells were integrated in a stack design optimized for reversible operation at high degrees of H2 and H2O utilization. The long-term single cell tests showed significant degradation in galvanostatic test periods during electrolysis but not in fuel cell mode prior to starting the reversible test operation while the degradation diminished during the subsequent rSOC operation of the cells operating at 700 C, +0.6 and -1.2 A/cm2 in SOFC and SOEC modes respectively, at fuel utilization (FU) up to 80% in both modes. Electrochemical impedance spectroscopy analyses and post-mortem SEM investigations of tested single cells reveal that the fuel electrodes degraded significantly during the long-term single cell tests. Furthermore, long-term stack tests were conducted on 5-cell stacks, integrating both reference cells and optimised cells. The long-term stack tests were conducted applying different switches between SOFC and SOEC modes. Initially long duration tests (100h each mode) were performed in a mixture of 50% H2O and 50% H2 to see the effect of the polarisation only. The alternating cycle SOEC/SOFC was repeated over a 1800 h testing period. Then stack switched daily from SOEC mode (8h in 90% H2O and 10% H2 @ 0.84 A/cm2 FU 54%) to SOFC (16 h in 100% H2 @ 0.26A/cm2@ FU 60%) for full cycles over a testing period of 500 h. Stack tests were operated in reversible mode for up to several thousands of hours and results on the stack performance and lifetime will be presented.

Elcogen is one of the leading European manufacturers of solid oxide cell (SOC) technology. Elcogen products are unique combination of best in class performance and low-cost product structure. The unit cell and stack products are designed for low temperature operation enabling major cost reductions in the system level. Elcogen’s operations are located in the Nordic-Baltic technology cluster of Finland and Estonia. This article summarizes the recent activities and development trends of Elcogen. Elcogen is currently focused in ramping up its unit cell and stack production with the increased customer needs. The short-term goal is to set-up of a demonstration manufacturing plant for the unit cells and stacks with annual capacity of 50 MW. To facilitate the goals Elcogen has signed EUR 12 million loan facility with The European Investment Bank (EIB). The loan is the first in the Baltic countries to get support under the InnovFin – EU-finance for innovators programme, which is financed from the EU’s Horizon 2020 research and innovation programme. Specifically, the financing falls under InnovFin’s Energy Demonstration Projects (EDP) facility. Elcogen is continuously developing its products for higher performance, longer lifetime, lower costs, increased quality and expanded applications. As an example, Elcogen has been testing its stack efficiency and lifetime for methane-based gas applications. The maximum efficiency has exceeded 75 % efficiency. The degradation rate in 23 000 hours test has been 15 mOhm.cm2/1000h.

The works presented here aim at developing an innovative renewable energies storage solution, so-called “Smart Energy Hub” (SEH), based on reversible Solid Oxide Cell (rSOC) technology. This systemis able to operate either in electrolysis (SOEC) or in fuel cell (SOFC) mode in order to store excess electricity to produce hydrogen, or when energy needs exceed local production, to produce electricity (and heat) again, from hydrogen or any other hydrocarbon fuel locally available. To be more efficient, the rSOC system is completed with an electrochemical storage solution allowing fast response to the electrical energy needs. In the frame of the REFLEX project, a SEH, made of 3 modules of 4 rSOC stacks, able to produce 16 Nm3/h in SOEC mode and up to 15 kWe in SOFC mode will be installed for an in-field demonstration in a technological park. Here the system will provide electricity and heat to the headquarters and maximize the auto-consumption of local renewable energies mixture. The rSOC system will be coupled to a Battery Energy Storage System (BESS), based on 8 lithium ion battery modules serially connected, able to store 50 kWh. Innovative work was done on each component to maximize, since this first try, the overall efficiency of the system prepared for field operation. Both cells and stacks have been optimised to increase performance (+20%) in both SOFC and SOEC modes, and their behaviour in rSOC operation have been characterized at different conditions. To increase the power density forward, enlarged cells have also been developed. The cell active area was near doubled passing from 100 cm² for reference cell to 196 cm². Concurrently, stack sectional dimension increased of about 40% only. This extension was validated up to stack level by performance testing of the enlarged stack. Voltage evolution, as current density increases, is very comparable for both stacks (reference and with enlarged cells). Voltage scattering is, also, quite similar. Steam starvation effect appears at the same level of steam conversion slightly higher than 80%, which shows that even for enlarged cells appropriate fluidic distribution was obtained. Large power modulations have been validated at stack level in three modes: SOEC, SOFC in H2 and SOFC in CH4, with ranges 58-100%, 23-100% and 13-100% respectively. To increase overall system efficiency by minimizing the energy losses in the balance of plant (BoP) components, specific reversible power electronics have been developed and an efficiency as high as 96% has been obtained, associated with a wide operation window (see figure). High performance heat exchangers and a steam generator able to generate stable steam flows have also been selected. Modelling activities have been performed to support the system design and to find the operating conditions in which the system to be built should/could be operated to ensure achieving maximum efficiency, while still operating the system in safe and lifetime-optimal conditions. The benefit of a recycling loop has been evaluated. Furthermore, techno-economic simulations have been carried out to evaluate market driven requirements on system sizing and costs to be competitive with other storage solutions. The article provides the results associated to these activities. Figure 1

Testing is a necessary step in the manufacturing process of Solid Oxide Fuel Cells (SOFC) to assess the performance of the produced cells before on-field deployment. In this work, the implementation of Electrochemical Impedance Spectroscopy (EIS) and subsequent data elaboration via Equivalent Circuit Modelling (ECM) is evaluated as a viable experimental framework for characterization and Quality Control (QC) of cells or cell batches, complemented to standard polarization-based methods. By performing a statistical analysis of the ECM parameters (representative of each physico-chemical process) the cell and batch operational parameters can be determined and compared. The validity of the proposed methodology is assessed using a wide experimental dataset of a significant number of SOFC samples (20 cells from 3 batches – two of which identical and the third with an intentional modification in the manufacturing process in order to validate the proposed methodology) tested in identical conditions. Results show that the impedance-based method provide detailed information in terms of impedance breakdown (anode gas diffusion process resulting the main criticality), as well as confirming the preliminary results obtained from the polarization approach (Batch#2 showing the lowest total performance and highest uniformity). Highly reproducible intra-batch distributions of the ECM parameters encourage the applicability of such methodology for QC purposes, even with few data collected only in Open Circuit Voltage (OCV) conditions. A relevant deviation of charge transfer and diffusion resistances in Batch#3 respect to other batches is observed (not visible from the polarization curves), which is reconducted to the modified anode functional layer, opening potential applications of the proposed methodology to assess the impact of targeted modifications of manufacturing methods on specific cell electrochemical performances.

A set of long-term tests (t ≥ 1000 h) have been carried out in fuel cell and electrolysis modes on typical Ni-YSZ//YSZ//LSCF-CGO cells. The degradation rates were found to be higher in electrolysis than in fuel cell operation. Post-test analyses have revealed that Sr diffusion and formation of SrZrO3 at YSZ/CGO interface occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode. As a consequence, LSCF destabilization is found to be not involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. An in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF demixing mechanism. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in LSCF material (while the fuel cell condition results in an increase in the concentration of oxygen vacancies). It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation is detailed.

Ceramic high-temperature fuel cells and electrolysers are efficient energy conversion systems for electrical power generation and hydrogen production. Their core components are constituted by a stack of electroactive Solid Oxide Cells (SOCs) in which the electrochemical reactions take place. Thanks to their flexibility, the same stack can be alternatively operated in both fuel cell and electrolysis modes. However, the insufficient durability of SOCs still constitutes a major limitation for the technology. The present study addresses this issue and aims to bring some new insights on the effect of the Solid Oxide Fuel Cell (SOFC) versus Solid Oxide Electrolysis Cell (SOEC) operating modes on degradation of a typical Ni-YSZ//YSZ//CGO//LSCF-CGO cell. The electrochemical degradations are generally attributed to several underlying phenomena such as electrode microstructural evolution, material chemical decomposition or electroactive sites poisoning by contaminants. Among them, it is generally considered that Ni agglomeration in the Ni-YSZ cermet and Lanthanum Strontium Cobalt Ferrite (LSCF) material destabilization are two prevalent mechanisms involved in the cell performance deterioration. Therefore, these two mechanisms have been specifically investigated by a coupled approach of long-term testing in both SOFC and SOEC modes (1000 ≤ t (h) ≤9000) and post-test characterizations. The experimental results have then been analyzed in the frame of an in-house multi-scale model with the purpose to interpret them and to quantify the effect of material ageing on cell performances. The extent of Ni agglomeration has been characterized by three-dimensional electrode reconstructions obtained by X-ray nano-holotomography at European Synchrotron Radiation Facility (ESRF) (on the new Nano-Imaging beamline ID16A-NI). The new set-up and protocol enable the reconstructions of valuable 3D volumes (Fig. 1) with a large field of view (~50 µm) along with a high spatial resolution (~50 nm). The electrode morphological properties, which have been measured on the 3D volumes, have revealed a substantial Ni coarsening over time at 850°C and 750°C, whereas no Ni depletion was detected at the electrolyte interface. The increase of the Ni particle size is found to induce a decrease in both (i) the density of Triple Phase Boundary (TPBs) lines and (ii) the interfacial surface area between Ni and gas. Moreover, it was found that the Ni/YSZ interfacial surface area does not evolve during the experiments. This statement indicates that the ceramic backbone in the cermet prevents a massive Ni agglomeration at the SOFC/SOEC operating temperature. The compilation of all experimental data have allowed fitting the parameters of a physically-based law for Ni coarsening that was introduced in the modelling framework. The simulations have revealed that Ni agglomeration explains around 20-25% of the electrochemical degradation at 850°C after 1000 hrs of operation. However, the electrode microstructural evolution is found not to be affected by the cell polarizations. Therefore, the mechanism cannot explain the higher degradation rates recorded in electrolysis mode compared to the fuel cell ones. To explain the impact of the operating modes (SOFC or SOEC) on the degradation rates, several post-test analyses (i.e. Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray µfluorescence and µdiffraction techniques) have been employed to investigate the phase reactivity in the region of the CGO barrier layer. The characterizations have revealed that Sr diffusion across the barrier layer and formation of SrZrO3 secondary phase occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode (Fig. 2). As a consequence, LSCF destabilization is found not to be involved in the degradation of cell performances during fuel cell operation while it could explain the highest degradation rates recorded in electrolysis mode. The post-test analyses have also revealed a diffusion and an accumulation of Co in the region of the barrier layer which is concomitant with the formation of SrZrO3. The formation of these Co-rich segregates in contact with SrZrO3 grains have been identified as cobalt-ferrite type compound. The in-house multi-scale model has been used to interpret the role of the cell operating mode on the LSCF destabilization mechanism. The cell polarization curves and the local quantities within the O2 electrode have been computed in both fuel cell and electrolysis modes. The simulations have shown that the electrolysis operation leads to a strong depletion of oxygen vacancies in the LSCF material. It has been proposed that the depletion in oxygen vacancies under electrolysis polarization could drive the Sr release from the structure, and in turn, could explain the experimental results. Based on this proposition, a possible mechanism for the LSCF destabilization and SrZrO3 formation has been detailed. Figure 1

Elcogen is one of the leading European manufacturers of solid oxide cell (SOC) technology. Elcogen products are unique combination of best in class performance and low-cost product structure. The unit cell and stack products are designed for low temperature operation enabling major cost reductions in the system level. Elcogen's operations are located in the Nordic-Baltic technology cluster of Finland and Estonia. This article summarizes the recent activities and development trends of Elcogen.

Solid oxide cells are among the best candidates for viable energy conversion and storage solutions. Their capability to operate reversibly as electrolyser (‘SOEC mode’) or as fuel cell (‘SOFC mode’), provides an opportunity to balance out electricity needs. Yet, reversible operation requires an optimized cell and stack design to withstand alternating conditions. In this study, more than ten different cells have been produced and their initial performance evaluated. For selected cells, durability tests were conducted and showed that primarily the oxygen electrode contributes to performance losses in SOFC mode whereas the fuel electrode is mainly affected under SOEC mode conditions. The stack design was optimized in order to withstand the envisaged operating conditions. An optimization of internal pressure drop (reduced by a factor of 2) and sealing resistances towards higher pressure has been achieved while maintaining the electrochemical performance.

International audience; Herein are reported the first results and the discussion about the oxidation of the highly stable aqueous solution of sodium dodecahydro-closo-dodecaborate Na2B12H12, a potential anodic fuel for energy conversion devices (fuel cells). The anion B12H12− is indeed chemically stable: it has an excellent stability over 3 weeks in both alkaline and acidic media; and heterogeneous hydrolysis does not take place as evidenced by differential electrochemical mass spectrometry (DEMS) measurements (using a gold electrode). According to the cyclic voltammetry experiments, the B12H122− anion can be oxidized over bulk electrodes made of platinum, gold or silver, the oxidation taking place at low potential values with platinum and high potential values with gold and silver electrodes. The overall reaction is complex and generates various products, which were analyzed over 1000 cycles of voltammetry in the range −1.05 and 0.6V vs. SCE. These products are mainly composed of B7- and B11-based polyboranes, which is indicative of a partial oxidative degradation of B12H12−. To sum up, the present article demonstrates the potential of the aqueous solution of sodium dodecahydro-closo-dodecaborate Na2B12H12 as anodic fuel, but it also stresses on the necessity of further works especially focusing on multimetallic electrodes (electrocatalysts) that could quantitatively and completely valorize this fuel.

In the present work, the behavior of hydrazine borane N 2 H 4 BH 3 in the presence of alkali/alkaline-earth hydrides is investigated. ( i ) Hydrazine borane N 2 H 4 BH 3 is readily destabilized by an alkali hydride MH (M=Li, Na, K). The electronic properties of M drive the reactivity of MH 1 towards N 2 H 4 BH 3 . KH is the most reactive (at 25 °C, Δ r H = −70.25 kJ mol −1 ) while K is the least electronegative and the biggest element. Hydrazinidoboranes MN 2 H 3 BH 3 form. ( ii ) Hydrazine borane N 2 H 4 BH 3 is destabilized by MH x ( x = 2, 3; M=Mg, Ca, Al). In comparison to pristine N 2 H 4 BH 3 , better dehydrogenation properties are found: MgH 2 has a catalytic effect; CaH 2 strongly destabilizes N 2 H 4 BH 3 ; and, unstable AlH 3 is able to destabilize N 2 H 4 BH 3 under heating. Though the synthesis of hydrazinidoboranes M(N 2 H 3 BH 3 ) x is difficult, the mixtures MH x –N 2 H 4 BH 3 leads to composites. The most efficient composite is CaH 2 –N 2 H 4 BH 3 . The aforementioned hydrazinidoboranes and composites may have potential as solid-state hydrogen storage materials. This is discussed herein.

Theoretically, sodium octahydrotriborate NaB3H8, solved in alkaline aqueous solution, is a potential boron-based liquid anodic fuel of direct liquid fuel cell, since the B3H8− anion could be oxidized (B3H8− + 20OH− → 3BO2− + 14H2O + 18e−) in a reaction ideally involving 18 electrons. Hence, we focus on this material. We firstly synthesize NaB3H8 and fully characterize it (NMR, FTIR, Raman, XRD, TGA, DSC), then study its stability in protic solutions by NMR, and lastly investigate its oxidation with the help of electrochemical techniques. The diffusion coefficient for the B3H8− anion is calculated (3.7·10−5 cm2 s−1) in order to assess the coulombic efficiency for the oxidation on platinum and gold electrodes. It is found effective numbers of electrons of 5.2 and 10.1 (out of a theoretical total of 18 electrons) respectively. Neither platinum nor gold smooth surfaces enable the complete oxidation of B3H8−, which is explained mainly by the occurrence of heterogeneous hydrolysis (i.e. hydrogen evolution), but also by the difficulty to break the B–B bonds (difficult to oxidize) present in the B3H8− anion. Yet, these first results confirm that the B3H8− anion has a potential as anodic fuel, provided the proper electrocatalyst is isolated: this is discussed herein.

The title compound, N2H4(BH3)2, is prepared from a mixture of freshly ground [N2H5][HSO4] and NaBH4 in THF (Ar-filled glovebox, round-bottom flask, 40 °C, 42—90 h, 87% yield).

International audience; Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during dehydrogenation) but can be used for the synthesis of derivatives with improved dehydrogenation properties. In liquid-state chemical hydrogen storage, it can be studied for room-temperature dehydrogenation, but this requires the development of an active and selective metal-based catalyst. HBB is a thus a candidate for chemical hydrogen storage.

National audience