A unified theory explaining the effect of interconnect on the optimization of structural parameters in protonic ceramic electrolysis cells for hydrogen production

Protonic ceramic electrolysis cells (PCECs) can efficiently convert renewable electricity into hydrogen, but optimization of their structural parameters has been studied less extensively than oxygen-ion conducting ceramic cells. Moreover, optimization results from button cells cannot be directly extrapolated to planar stacks due to interconnect effect. This study systematically investigates the influence of interconnect on the optimization of steam electrode structural parameters—thickness, porosity, and particle radius—and their effects on PCECs performance. Since interconnect mainly affect concentration loss and contact resistance—with the latter being independent of electrode's structural parameters—optimal parameter values shift systematically to mitigate concentration loss. For instance, as the rib width increases from 0.8 mm to 1.2 mm, the optimal porosity increases from 0.4 to 0.5. This is because a larger porosity helps alleviate the concentration loss induced by wider ribs. In addition, among the parameters studied, electrode thickness has the most pronounced effect on performance. At 600 °C and 1.3 V, increasing the thickness from 40 μm to 160 μm results in a 21.3 % rise in proton current density—from 455 mA cm⁻² to 552 mA cm⁻². This improvement is attributed to the expansion of the electrochemically active zones facilitated by the high proton conductivity of BaCo_0.4Fe_0.4Zr_0.1Y_0.1O₃ (BCFZY). In contrast, other structural parameters result in relatively minor variations in current density, on the order of approximately 20 mA cm⁻². In summary, this work provides practical guidance for the structural design of high-performance PCECs stacks.