Comparison of gas phase transport effects between fuel cell and electrolysis cell modes of a 100 cm2 class molten carbonate cell

Abstract

• Gas phase transport effects are compared between electrolysis and fuel cell modes with 100 cm 2 class cells. • Symmetric overpotential behaviours are obtained between electrolysis and fuel cell modes. • Severe gas phase mass transfer resistance exists in the hydrogen electrode of electrolysis cell. • Negligible gas phase resistance is observed in the oxygen electrode of electrolysis cell. The gas-phase mass transfer effects of 100 cm 2 class molten carbonate cells (MCCs) were investigated in both the fuel cell and electrolysis modes using steady-state polarization (SSP) and inert-gas step addition (ISA) methods. The SSP results showed symmetric and linear behaviours between fuel cell (FC) and electrolysis cell (EC) modes without showing activation polarization in both modes. The ISA results showed that the hydrogen electrode (HE) has significant gas-phase mass transfer resistance in both modes, and the overpotential shift pattern of HE by the flow rate change is symmetric in both modes. On the contrary, a small gas-phase mass transfer inducing overpotential was observed at the OE in the FC mode compared to the HE, while there was no gas-phase mass transfer-induced overpotential in the EC mode. Therefore, the EC mode of MCCs comprises mainly gas-phase mass transfer controlling processes at HE and negligible at OE. In addition, it can be inferred that reversible operation in both modes is possible, and the reaction mechanisms are symmetrical between FC and EC modes.