Understanding the polymer binder effect on the microstructure and performance of micro-tubular solid oxide fuel cells with continuously graded pores fabricated by the phase inversion method

Micro-tubular solid oxide fuel cells (MT-SOFCs) have recently attracted great attentions because of their great thermal shock resistance, fast start-up capability, and increased volumetric power density compared with the planar SOFCs and conventional tubular SOFCs. In this work, three representative MT-SOFCs with different anode microstructures are fabricated by varying the polymer binders used in the phase inversion slurry. A superior anode substrate with graded pore distribution is obtained, moreover, the dense skin layer close to the inner surface is effectively eliminated when the polyethersulfone (PESf)/polyethylenimine (PEI) blend material instead of PESf material or PEI material is utilized as the polymer binder. Meanwhile, no secondary impurity phase is detected in the anode supports prepared by these three polymer binders, indicating the good adaptability of these polymer binders. Additionally, three single cells are assembled based on these anode supports, and a maximum power density of 630 mW∙cm⁻² is obtained for the cell fabricated by the PESf/PEI blend polymer binder at 750 °C, which is strongly higher than 201 and 330 mW∙cm⁻² for PEI polymer binder and PESf polymer binder at the same temperature, respectively. Moreover, the electrode polarization resistance is largely decreased from 2.53 to 0.662 Ωcm² by changing the polymer binder from PEI polymer binder to PESf/PEI blend polymer binder. The fitting results obtained based on the polarization model reveal that the greatly improved electrochemical performance can be explained by the accelerated gas transportation in the anode. Our findings demonstrate that the PESf/PEI blend material is a promising polymer binder candidate for MT-SOFC fabrication through the phase inversion method.