Supplementary information files for "A transient simulation study of a reversible solid oxide hydrogen planar cell (rSOC): optimising switching strategy between fuel cell and electrolyser modes"

Supplementary files for "A transient simulation study of a reversible solid oxide hydrogen planar cell (rSOC): optimising switching strategy between fuel cell and electrolyser modes"Reversible solid oxide cells (rSOCs) require frequent mode-switching between fuel cell (FC) and electrolysis cell (EC) modes to accommodate the intermittency of renewable energy and the fluctuation of electrical loads. To investigate and optimise the transient behaviour during mode-switching, a 2D transient multiphysics model of an anodesupported planar rSOC cell was developed, incorporating reversible electrochemistry, charge transport, and coupled momentum/mass/heat transport. The model investigates the dual influence of voltage switch and fuel/steam (F/S) ratio on mode switching. The study revealed that higher hydrogen fractions in FC-to-EC transitions and higher steam fractions in EC-to-FC transitions induce larger current overshoots and longer relaxation times. Rapid voltage switching exacerbates overshoot due to insufficient time for species redistribution, while oxygen diffusion emerges as a key limiting factor for switching speed. Coordinated adjustment of gas composition along with voltage switching reduces or eliminates overshoot, with exponential voltage transitions producing smoother and faster responses than linear switching. These findings provide valuable insights for improving rSOC performance, efficiency, and longevity under dynamic operating conditions. The proposed control approaches serve as guidance for developing advanced strategies to integrate rSOC systems effectively with intermittent renewable energy sources.© The Author(s), CC BY 4.0