• Energy Research

AbstractHigh temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. If coupled to a CO2‐free electricity and a low cost heat source, this process is liable to a high efficiency. High levels of performance and durability, in association with cost‐effective stack and system components are the key points. To reach such goals, a low‐weight stack has been designed, keeping the advantages of the high performing and robust stack previously validated in terms of performance, durability, and cyclability [1], but aiming at reducing the cost by the use of thin interconnects. This low‐weight stack has demonstrated at the scale of a 3‐cell stack a good performance of –1.0 A cm–2 at 1.3 V at 800 °C. Before performing the durability test, preliminary studies at the cell level have been carried out to highlight the effect of two major operating parameters that are the current density and the steam conversion (SC) ratio, those studies being carried out at one temperature, 800 °C. Based on these results, optimized operating parameters have been defined to perform the durability test on the stack, that is –0.5 A cm–2 and a SC ratio of 25%. Degradation rates around 3–4% 1,000 h–1 have been measured. The thermal cyclability of this stack has also been demonstrated with one thermal cycle. Therefore it can be concluded that these results make HTSE technology getting closer to the objectives of performance, durability, thermal cyclability, and cost.

Abstract This work aims at investigating through a modeling approach the difference in thermal and electrochemical responses between high temperature H 2 O electrolysis and H 2 O+CO 2 co-electrolysis in solid oxide cells. The study has been conducted by considering a typical planar stack configuration with cathode supported cells. The influence of the local temperature on the polarization curve is discussed. Operating maps are simulated for both electrolysis modes depending on cell voltage and inlet gas flow rate, covering a complete range of gas conversion rates. The optimum domains of operating conditions combining high performances and reasonable temperature elevations are identified. In overall, higher performances are found in steam electrolysis. Indeed, the co-electrolysis process is found to be strongly limited by mass transport through the thick cathode. However, co-electrolysis exhibits an easier thermal management. Finally, the composition of the syngas produced by co-electrolysis is found to be highly flexible through adjustments of the operating parameters.

AbstractHigh Temperature Steam Electrolysis (HTSE) is one of the most promising ways for hydrogen production. If coupled to a CO2-free electricity and low cost heat sources, this process is liable to a high efficiency.The present study describes recent promising results obtained in terms of performance and durability in stack environment, thanks to the use of protective coatings on one hand, and of advanced cells on the other hand.As for Solid Oxide Fuel Cells, it has been demonstrated that the integration of protective coatings was mandatory to decrease the degradation rate in HTSE stacks, and that with optimized coatings, (CoMn)3O4 in the present case, the same durability as the one of the single cell tested in a ceramic housing could be reached. The type of cell was also shown to play a major role on the degradation rate. With advanced cells, degradations below 2%/kh could be reached. The higher is the current density, the higher is the degradation rate, with a mostly reversible effect. These degradation rates are close to the objectives, even if a bit higher than in SOFC mode.Finally a low-weight stack has been designed, targeting high performance and durability while reducing the cost by the use of thin interconnects. An electrochemical performance similar to the previous stack design has been obtained for a 3-cell stack (-1 A/cm2 at 1.3V at 800°C), with degradation rates below 3%/1000h in the testing conditions.The thermal cyclability of stacks has been demonstrated, from 800°C to 20°C, as well as electrical load cycling. The results showed that the HTSE stacks considered in the present study can cycle very rapidly, and that the cycles considered do not induce any degradation. Therefore it can be concluded that these results makes HTSE technology getting closer to the objectives of performance, durability, thermal and electrical cyclability and cost, and that HTSE is a candidate to produce hydrogen as a mean to store renewable intermittent energies.