Analysing the performance of MCECs over a wide range of operating temperatures

Hydrogen production through water electrolysis has gained significant attention in the past years as a means of tackling the problem of the imbalance between the intermittent rate of electricity production from renewable sources and the continuous electricity demand from end users. Recently, much of the effort has been shifted toward the electrolysis of steam rather than water, for example in solid oxide cells, which operate at temperatures around 800°C. In this manner, part of the energy required for the conversion to hydrogen is provided as heat rather than electricity. At the same time, the high temperature levels require the use of highly resistant materials, which increase the overall cost of the process. An interesting alternative is represented by molten carbonate electrolysis cells (MCECs), operating at temperatures well below 700°C. In the present work, a molten carbonate cell was operated in a lower temperature range (490-550°C) by changing the composition of the electrolyte mixture. The data obtained, along with experimental results at higher temperature (570-650°C) available in the literature, was analyzed using a 0D model accounting for Ohmic and activation overpotentials to determine the correlation between current and potential. It was found that, while the dependence of Ohmic losses on temperatures is discontinuous when cell operation is switched from the lower to the higher temperature range, activation losses vary with continuity. This result provides important insight on the performance of MCECs that can serve as a basis for future studies.