Assessment of Pressure Effects on High Temperature Steam Electrolysis Based on Solid Oxide Technology
In this context, experimental and modelling approaches have been adopted in order to understand the basic underlying mechanisms of pressurized electrolysis operation. In this frame, SOEC performance tests were realized under pressure in the range of 1 to 10 bars on two types of single commercial cells. They were based on conventional materials and differentiated by their microstructure. Concerning the set-up, the test platform requirements were achieved by developing an innovative mechanical design associated to a specific steam management. Moreover, a previously proposed electrochemical model of solid oxide electrolysis cell was adapted to take into account the pressure effects. The model allows computing all the most important operation parameters such as local current densities, local molar fraction, overpotentials and also the cell microstructural parameters .
According to the complete I-V curves from 0 to -1.3 A/cm2 at 800°C with high steam conversion, it has been observed that OCVs respect the Nernst relation under pressure while the limit current appears at higher current values. This work shows that the hydrogen production can be increased thanks to a 10 bars operation at the autothermal voltage. Moreover, these trends have been analyzed with the model. The impact of pressure on the electrochemical performances is much more important in the range of 1 to 5 bars than above. In our experimental conditions, the diffusion improvement in the porous cathode alone can explain this behavior. Finally, the impact of each microstructural parameter on the cell performances with pressure is discussed.
The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) Fuel Cells and Hydrogen Joint Undertaking (FCH-JU-2013-1) under grant agreement 621173.
 J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser : impact of the operating conditions on hydrogen production, 2011, Journal of Power Sources, 196, 2080-2093.